Theses and Dissertations (Food Science)

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Cooking quality and nutritional properties of extruded maize pasta with orange-fleshed sweet potato
(University of Pretoria, 2019-11) Emmambux, Mohammad Naushad; Duodu, Kwaku Gyebi; roseotemabaah@gmail.com; Baah, Rose Otema
Vitamin A deficiency is prevalent in sub-Saharan Africa and is considered a serious problem of public health significance. The use of bio-fortified staple foods is an intervention strategy to address vitamin A deficiency and one example is orange-fleshed sweet potato (OFSP) cultivar with increased beta-carotene content. Replacing white-fleshed potato cultivars with orange-fleshed sweet potato can improve the vitamin A status of school-aged children. Taking this information into consideration, the diversification of diet through inclusion of orange-fleshed sweet potato could be a useful approach for alleviating vitamin A deficiency. This presents an opportunity whereby white maize flour can be composited with orange flesh sweet potato flour to produce gluten-free pasta with enhanced β-carotene content. This product will also be suitable for celiac patients and other consumers who want to abstain from gluten due to some health related issues, and contribute to the RDA requirements for vitamin A for various groups. This study therefore investigates the effect of extrusion processing on cooking quality, β-carotene content and antioxidant properties of gluten free maize – orange-fleshed sweet potato pasta. Maize and orange-fleshed sweet potato composite (100:0, 80:20, 70:30, 50:50 w/w) flours were extruded into pasta using a twin-screw extruder. Raw flours and raw pasta samples were analysed for proximate composition, β-carotene content and in-vitro radical scavenging properties. Cooked pasta samples were analysed for cooking quality (cooking time, cooking loss and water absorption capacity), textural properties (firmness, stickiness and fracturability), in-vitro starch digestibility and in-vitro protein digestibility. Raw and cooked pasta samples were analysed for thermal properties. Gluten free commercial pasta made from corn and rice was used as a reference. Increase in addition of OFSP flour increased the cooking loss and decreased cooking time and water absorption capacity of pasta. There was an increase in insoluble and soluble dietary fibre as the proportion of OFSP flour in the composite decreased. The fibre content in the OFSP flour caused a loosening of the compact structure of the pasta disrupting the compact protein-starch matrix resulting in higher cooking loss and sticky pasta. This also led to lower hydration of starch as well as protein hydration resulting in lower water absorption capacity. However, compared to the commercial pasta which was conventionally made, extruded pasta samples showed indistinct starch granules as observed with scanning electron microscopy (SEM) indicating higher amount of disrupted starch thereby leading to faster absorption of water during cooking resulting in lower optimum cooking time. Extruded pasta samples exhibited lower in-vitro protein digestibility as compared to the commercial pasta that was conventionally made. Higher temperature used during extrusion cooking leads to the disruption of protein structures by unfolding, re-organization and polymerization through the formation of disulphide bonds. Disulphide bonds can result in reduction in protein solubility resulting in lower in-vitro protein digestibility. Extruded pasta samples showed lower in-vitro starch digestibility. Differential scanning calorimetry showed that amylose-lipid complexes were formed which reduced starch digestibility. Increasing proportion of OFSP in the composites increased β-carotene content and antioxidant properties of both raw flour and pasta samples. After extrusion, β-carotene content of pasta samples decreased but antioxidant properties increased. The high temperature and shear rate conditions used during extrusion processing may have caused losses of β-carotene through cis-trans isomerization, fragmentation and oxidative decomposition. The possible formation of Maillard reaction and caramelization products with reducing properties as a result of extrusion could have contributed to the observed increased antioxidant properties of the pasta samples. In conclusion, addition of 20 % OFSP to maize flour produces pasta by extrusion that have similar characteristics in terms of its good cooking quality and textural properties to the commercial pasta and 100 % maize pasta as evidenced by low cooking time, less cooking loss, less stickiness and more firmness and required greatest amount of force to break. The cooking quality of extruded pasta seems to be related to the microstructure and dietary fibre seems to play an important role in contributing to negative cooking qualities. The addition of OFSP flour in cereal-based pasta could potentially meet an appreciable amount of the recommended daily amount of vitamin A for various groups and exerting good antioxidant properties.
Sensory, rheology, tribology and shelflife of reduced fat mayonnaise-type emulsions formulated with lipid-modified maize starch as fat replacer
(University of Pretoria, 2019-11) Emmambux, Mohammad Naushad; De Kock, Henrietta Letitia; ampjoyce@gmail.com; Agyei-Amponsah, Joyce
The increasing rate of obesity and its related diseases (cancers, heart disease and diabetes) has become a global health issue. Dietary fat is highlighted as one of the critical risk factors contributing to this problem. Reduction of the fat content of popular food products, in an attempt to reduce fat intake without compromising the desirable sensory properties provided by fat, is challenging. This study characterised two lipid-modified maize starches (maize starch modified with 1.5 % stearic acid and maize starch modified with 2 % monoglyceride) produced by incorporating food-friendly lipids into maize starch through wet-heat processing. Sunflower oil was substituted with these complexes in the production of reduced-fat mayonnaise-type emulsions, at 0 % (control), 50 %, 80 % and 98 % oil replacement, with qualities similar to that of full-fat mayonnaise. The effect of the substitution on the rheological, lubricating, descriptive sensory profile (panel, n =10), consumer acceptance (consumers, n = 207), and accelerated shelf-life (40 °C with 24 h UV illumination) of the reduced-fat mayonnaise-type emulsions was determined. The lipid-modified starches were non-gelling, glossy, smooth, creamy, easy-to-swallow and had good lubricating properties. These attributes could be ascribed to the formation of amylose-lipid complexes during the modification process of maize starch with stearic acid and monoglyceride. The formation of amylose-lipid complexes prevented further aggregation of amylose double helixes from forming crystalline structures and made amylose less available for junction zone formation and molecular entanglement, resulting in non-gelling starches. The lower friction coefficient values recorded for the starch-lipid complexes could be due to the nanoparticle sizes (2.4–6.7 nm) of the amylose-lipid complexes. The nanoparticle nature of the amylose-lipid complexes possibly increased the volume to surface area ratio of the complexes making them more available to act as a layer of lubricant. Lower friction coefficient implies increased lubricating effect, which enhances the sensory perception of fat-related attributes, thus influencing the perceived smoothness, creaminess, and easy-to-swallow nature of the starch-lipid complexes. All the reduced-fat mayonnaise-type emulsions were smooth, melting, and easy-to-swallow and the starch/monoglyceride emulsions had a higher thickness, creaminess and mouth-coating. The higher thickness and mouth-coating can be attributed to the availability of uncomplexed amylose, which is more abundant in the starch/monoglyceride fat-replacer than in starch/stearic acid one, to form junction zones and molecular entanglements. The amylose-lipid complexes present in the fat replacers provided the emulsions with a non-gelling highly viscous matrix that stabilised the residual oil droplets in the reduced-fat mayonnaise-type emulsions. All the reduced-fat mayonnaise-type emulsions showed good lubrication with starch/monoglyceride emulsions showing more sensitivity to coalescence and gave rise to lower friction than starch/stearic acid emulsions. The lipid-modified starches did not effectively retard the rate of lipid oxidation in the reduced-fat mayonnaise-type emulsions at accelerated storage. Hence the oil droplets could easily interact with the aqueous phase pro-oxidants, thus increasing the rate of oxidation. The possible increase rate of oxidation could also be due to the presence of liberated iron ions, Fe2+, from the egg yolk present as a stabiliser in the aqueous phase at the lower pH (< 4). At 50 % probability of consumer acceptance, the reduced-fat mayonnaise-type emulsion containing 80 % starch/monoglyceride was the most acceptable and had a predicted accelerated shelf-life beyond the 35 storage days. The study has demonstrated the effective use of the two novel fat replacers to replace up to 80 % sunflower oil in the production of reduced-fat mayonnaise-type emulsions without compromising the desirable in-mouth textural properties of smoothness, creaminess, melting and mouth-coating. These fat replacers can be produced on a large scale and used as ingredients in commercial applications to improve the in-mouth textural properties of reduced-fat foods.
Growth and neurodevelopmental outcomes of children with in utero growth restriction due to placental insufficiency and modification by maternal HIV status
(University of Pretoria, 2024-07) Hoffman, Marinel; Feucht, Ute; mothusi.nyofane@tuks.co.za; Nyofane, Mothusi
Background: South Africa is burdened with a high prevalence of HIV infection in pregnant women (30.0%). Nevertheless, access to antiretroviral therapy (ART) has greatly increased, leading to an expanding population of HIV-exposed-uninfected children (CHEU). Adverse birth outcomes, including intrauterine growth restriction (IUGR), have been documented in women living with HIV, even when on ART. Child HIV exposure, anaemia and IUGR due to placental insufficiency carry significant risks to early child growth and neurodevelopment. This study determined and compared growth and neurodevelopmental outcomes, micronutrient intakes, and anaemia in CHEU compared to a control group of HIV-unexposed-uninfected children (CHUU) stratified by history of placental insufficiency. Methods: An abnormal umbilical artery resistance index (UmA-RI) on pregnancy Doppler ultrasound was used to detect placental insufficiency as a proxy for IUGR. The cross-sectional study investigated 271 mother-child pairs at 18-months postnatal, grouped into four subgroups: CHUU with normal UmA-RI (CHUU/N-RI; control group), CHEU with normal UmA-RI (CHEU/N-RI; single exposure), CHUU with abnormal UmA-RI (CHUU/AbN-RI; single exposure) and CHEU with abnormal UmA-RI (CHEU/AbN-RI; double exposure). Pregnancy and birth information was available. World Health Organisation standard procedures were followed to collect anthropometric data and compute z-scores. International Guide for Monitoring Child Development (GMCD) was used for developmental screening, and Bayley Scale of Infant and Toddler Development III (Bayley-III) was used to test for cognitive, language and motor development. Premature births were corrected for gestational age. Previously used questionnaires and quantified 24-hour dietary recall were used to collect sociodemographic variables and dietary intake. FoodFinder™ 3.0 was used for meal analysis, quantifying dietary intake of iron, zinc, and iodine. Both maternal and children's haemoglobin concentrations were tested using HemoCue® Hb 201+. Comparisons were performed using independent t-test and Mann-Whitney U test. Spearman’s correlation and regression models were used to determine associations. Results: Lower length-for-age z-scores (LAZ) were observed in CHEU than CHUU ( 0.71±1.23 vs 0.05±1.32; p=0.004), and children who had abnormal UmA-RI than normal counterparts ( 0.68±1.53 vs 0.14±1.29; p<0.001). CHEU/AbN-RI had the lowest LAZ compared to CHUU/N-RI ( 1.3±1.3 vs 0.03±1.30; p<0.001). The prevalence of stunting (LAZ < 2) was higher in CHEU/AbN-RI (40.0%) and CHEU/N-RI (16.0%) than in CHUU/N-RI (4.8%); p<0.001 and p=0.016, respectively. GMCD screening indicated a concern for delay in gross motor development among 21.4% of CHEU/AbN-RI. Bayley-III test demonstrated lower mean cognitive scores in CHEU/AbN-RI compared to CHUU/N-RI: 93.9±12.9 vs 100.0±10.6; p=0.045, with 21.4% of CHEU/AbN-RI having mild delay in cognitive development. Further, zinc intake and weight-for-age z-scores were positively associated with language (r=0.10; p=0.042) and motor (r=0.10; p=0.028) development, respectively. Above one-third of children were mildly anaemic: CHUU/N-RI: 44.4%, CHEU/N-RI: 44.7%, CHUU/AbN-RI: 40.0% and CHEU/AbN-RI: 33.3%. In the CHEU group, maternal haemoglobin concentrations were associated with child haemoglobin concentrations: β=0.19, 95% confidence interval (CI) (0.02,0.36); p=0.028. There was no evidence to suggest an association between maternal or child haemoglobin concentration and child neurodevelopment. On further analysis cognitive development was positively associated with LAZ: β=3.34, 95%CI (1.13,5.54), P=0.004 in the CHEU group. Conclusion: Maternal HIV exposure and placental insufficiency are risk factors for stunting and cognitive deficits, both independently and compounded. CHEU and children who had IUGR are a high-risk population in need of identification and appropriate interventions within child health and nutrition-sensitive programmes. Childhood anaemia remains a paramount public health concern.
Mafura seed oil : improvement in oxidative stability
(University of Pretoria, 2016-04) Duodu, Kwaku Gyebi; Uamusse, A.A.; Chemane, Lúcia Narcésia Guilhermina
Trichilia emetica seeds are processed for their oil by rural communities in the South of Mozambique. Traditionally, the oil is extracted by boiling the seed pulp in an aqueous medium for 5 h and recovering the clear yellow oil. The extended heating period and the use of water for oil extraction may reduce the oil quality. Mafura oil was extracted using a laboratory method that mimics the traditional method. Acid value (titrimetry), iodine value (Wijs method), saponification value (titrimetry) and fatty acid composition (gas chromatography) were determined in comparison with sunflower and olive oils. Oxidative stability (OS), (peroxide and anisidine values) of mafura oil stored at (65oC) over a 14 day period was also determined in comparison with sunflower and olive oils. The effect of refining, solvent extraction (hexane and ethanol) and the effect of incorporation of freeze dried crude phenolic extract (CPE) from red condensed tannin sorghum bran (at 1000 and 2000 ppm) compared with tertiary-butylhydroquinone (TBHQ) (200 ppm) on OS of mafura oil during storage was determined. Whole grain, bran and CPE were analysed for total phenolic content (TPC), (Folin-Ciocalteu assay) and antioxidant activity, (ABTS radical scavenging). Phenolic composition of the CPE was determined using High Performance Liquid Chromatographic. Traditionally extracted crude mafura oil (CMFO) had the highest acidity. Crude and refined mafura oils had the lowest iodine values and the highest saponification values compared with sunflower oil and the olive oils. CMFO was rich in palmitic acid, sunflower oil in linoleic acid and the olive oils were rich in oleic acid. CMFO was the least stable during storage as shown by high anisidine values. Solvent extraction (but not refining) improved the OS of CMFO. Mafura oil treated with CPE was more oxidatively stable than the control and this seemed to be dose-dependent. CPE at 2000 ppm was less effective in inhibiting the formation of primary oxidation products than TBHQ, however, it was as effective in reducing secondary oxidation. The CPE had higher TPC and antioxidant activity than whole grain and sorghum bran. The CPE contained phenolic acids and high levels of (+)-catechin and (-)-epicatechin. The ability of the CPE to improve the OS may be related to the action of the phenolic compounds as primary antioxidants in scavenging free radicals. This study shows that the traditional method of mafura oil extraction decreases its OS due to extensive heating in an aqueous medium. The CPE may potentially be used as a natural antioxidant to prevent oxidation of mafura oil due to the antioxidant properties of the phenolic compounds present in the sorghum bran.
Physico-chemical quality assessment of honey from different floral and geographical origin
(University of Pretoria, 2024-02-13) Schonfeldt, H.C. (Hettie Carina); Pretorius, Beulah; Tersiadb@dalrrd.gov.za; de Beer, Tersia
Honey is a natural product made by bees from the nectar of flowers, the secretions of living plants and excretions of plant-sucking insects. The ever-increasing demand for natural honey amplifying the risk of fraud, affecting the livelihood of communities negatively. From a legislative point of view, the South African government is currently concerned about labelling, which might be false, misleading or deceptive. Hence, food authenticity and traceability have become important issues in food testing. The Agricultural Product Standards (APS) Act, 1990 (Act No 119 of 1990), Regulation No R. 835 of 25 August 2000 was used to evaluate the quality of honey on the South African market. Food safety monitoring is the mechanism which is used to evaluate the quality of food products on a continuously basis. Furthermore, to support the food safety status of honey production and supply, effective national food control systems are essential.
Growth, feeding practices, and haemoglobin levels in 6 to 12 month-old infants exposed and unexposed to maternal HIV status in a peri-urban area in Gauteng province, South Africa
(University of Pretoria, 2024-02) Hoffman, Marinel; Legodi, Heather; Ute, Feucht; phumudzo.mamphwe@up.ac.za; Tshiambara, Phumudzo
Introduction:Undernutrition is a significant public health issue, primarily caused by inappropriate feeding practices that negatively impact infant growth and development. In Sub-Saharan Africa, South Africa has the highest prevalence of human immunodeficiency virus (HIV). Antiretroviral therapy (ART) programmes reduce the infection rate, but leave infants exposed to maternal HIV infection but uninfected (HEU), and more than one million HEU infants are born annually. HEU infants are at a higher risk of mortality and morbidity than HIV-unexposed-uninfected (HUU) infants, leading to poor growth and increased risk of stunting, underweight and anaemia. Limited information exist on the growth, feeding practices and haemoglobin levels of 6-12 months old infants. Aim: To compare the growth, feeding practices, and haemoglobin levels of HEU and HUU infants aged 6–12-months, and determine the relationship between growth, feeding practices and haemoglobin levels in these infants, stratified by maternal HIV status. Methods: This cross-sectional study with repeated measurements was embedded in the Siyakhula Study, where data collection started in October 2018 until August 2023. Infants’ anthropometric measurements (weight, length, head circumference and mid-upper-arm circumference), feeding practices (complementary- and breastfeeding, food frequently consumed, and dietary intake), and haemoglobin level (a marker for anaemia) were collected using calibrated scales, structured questionnaires and the HemoCue® device by trained research assistants using a local language. Hand expressed breastmilk was analysed for the nutrient composition of copper, iron, manganese, selenium, and zinc using the inductively coupled plasma mass spectroscopy method. Results: The study included 181 infants (86 HEU; 95 HUU), with 58% males. High percentages of low birth weight was found in HEU than HUU infants (22% vs. 13%; p<0.001). Length-for-age Z-scores (LAZ) (p<0.05), weight-for-age Z-scores (WAZ) (p<0.05), and mid-upper-arm circumference-for-age Z-scores (MUACAZ) (p<0.05) were lower in HEU versus HUU infants at 6 and 9 months. Lower weight-for-length Z-scores (WLZ) (−0.2±1.2 vs. 0.2±1.2; p=0.020) was observed at 12 months in HEU infants. The HEU and HUU infants were introduced to complementary foods too early, and lower breastfeeding rates were found in HEU than HUU infants at 9 (36% vs. 57%; p=0.013) and 12 months (25% vs. 48%; p=0.005). Only 11% of HEU and 6% of HUU achieved a minimum dietary-diverse diet and flesh foods consumption was significantly higher in HEU (24%) than HUU (11%) at 12 months. Dietary fat intakes were low in HEU and HUU infants, with iron, calcium, and vitamin A intakes higher in HEU than HUU infants at 12 months. Haemoglobin levels and anaemia was similar in HEU and HUU infants but more percentages of anaemia were found in HEU than HUU infants at 6 (27% vs. 18%) and 9 months (33% vs. 29%). Haemoglobin levels positively correlated with WAZ (p=0.039), LAZ (p=0.007), and MUACAZ (p=0.039) at 9 months, and at 12 months WAZ (p=0.018) and WLZ (p=0.041) in HEU infants. Conclusion: The HEU infants had suboptimal growth and inappropriate feeding practices including lower breastfeeding rates than HUU infants. The HEU infants had higher dietary intakes, dietary diversity, and flesh consumption than HUU infants. Infant growth and feeding habits are impacted by maternal HIV infection but better infant feeding counselling and implementation need to be prioritized for all South African mothers, irrespective of the HIV status.
Drying kinetics, nutritional and functional characterisation of flours produced from edible insects from East Africa
(University of Pretoria, 2023) Duodu, Kwaku Gyebi; Emmambux, Mohammad Naushad; yisa.njowe@gmail.com; Yisa Njowe, Kieran Bong
The growing global awareness of edible insects as a nutritious food that can be used to contribute in the fight against protein energy malnutrition has met many barriers. These barriers include sustainable processing techniques especially in rural areas where most wild edible insects are collected and the disgust factor which shrinks the consumer market as most consumers are turned-off eating meals having visible whole edible insects. This disgust factor could be circumvented by producing dry insect-based food ingredients that can be included in familiar food as it masked the appearance of the whole edible insect. It is therefore important to understand the drying behaviour, nutritional and functional properties of these edible insect flour to successfully guide their suitability as food ingredients into familiar foods without greatly altering the food’s sensory properties. This study evaluated the effect of sustainable solar dying methods (sun drying, solar cabinet drying, blanching before sun drying or solar cabinet drying) on the drying behaviour of African field cricket; the effect of these sustainable drying methods compared to conventional drying methods (freeze drying and oven drying at 40°C) on the nutritional properties of edible long horn grasshoppers, African field crickets and saturniid caterpillar; and the effect of the sustainable and conventional drying methods on the functional properties of flours produced from defatted edible grasshopper, cricket and caterpillar compared to commercially available soy and whey protein ingredients as a novel protein-rich food ingredients in familiar foods. The decrease in moisture content of African field cricket over time was best described by the empirical quartic polynomial model (fourth order polynomial) for all four sustainable drying methods with a high coefficient of determination (R2 = 0.979 – 0.996), least sum of squared errors (SSE = 0.0046 – 0.0141) and the least reduced chi square (ꭓ2 = 0.0007 – 0.0046). Solar cabinet drying was a faster drying method compared to direct sun drying and blanching before drying greatly reduced the drying time for each drying method. The blanched cricket dried the fastest in the solar cabinet (10 hours), followed by the fresh cricket in the solar cabinet (12 hours), and the fresh cricket placed directly in sunlight recorded the longest drying time (32 hours). This was evident by the calculated moisture diffusivity (Deff) with the highest value (2.0  10-10 m2/s) recorded when crickets were blanched and solar cabinet dried and the least (5.2  10-11 m2/s) when crickets were only sun dried. Blanching may have increased the permeability of the cricket matrix to water and the higher peak drying temperature inside the solar cabinet (approximately 58°C) than the surrounding (45°C) may have enabled the water molecules to quickly attain activation energy and start moving from the cricket core to its surface, followed by evaporation. These results suggest blanching before solar cabinet drying could be a preferential pre-processing method for edible crickets in rural settings where energy and expensive drying equipment are lacking. There were no changes in proximate composition, available lysine, and protein digestibility of whole edible grasshopper, cricket and saturniid caterpillar that were dried using the six different drying methods. Protein Digestibility Corrected Amino Acid Score (PDCAAS) was lower in boiled dried cricket and caterpillar than the other dried forms. Boiled and dried insects had lowest proportions of linoleate and α-linolenate. Despite these losses in boiled dried insects, the essential amino acid indices (EAAI) (0.8 - 0.97) and lipid quality indices (Atherogenicity Index (AI): 0.47 – 0.83 and Thrombogenicity Index (TI): 0.36 – 1.93) of differently dried insects were within desirable limits of greater than 0.7 (EAAI) and less than 2 (AI and TI) for human nutrition. The differently dried edible insects were ground and defatted to produce edible insect protein-rich flours. The nitrogen solubility indices (NSI) for all boiled solar dried grasshopper, cricket, and caterpillar protein concentrates decreased by 35.2, 63.8 and 32.4% respectively while the water solubility indices (WSI) decreased by 37.1, 35.5 and 22.9% respectively compared to the other dried forms of grasshopper, cricket and caterpillars. The water absorption capacity (WAC) (1.7 – 2.97%), oil absorption capacity (OAC) (1.2 – 1.51%), foam stability (FS) (67 – 77.9%), foam capacity (FC) (32 – 49%), emulsion stability (ES) (65 – 78%), emulsion capacity (EC) (81 – 97%) of the insect protein concentrates were not affected by drying methods but varied with insect species. Dried insect protein concentrates had lower foaming and emulsion capacities compared to commercial soy (FC: 55.9%, EC: 94.3%) and whey (FC: 52.9 – 55.6% EC: 93.7 – 96.3%) protein ingredients but exhibited higher foam stability (43.2 – 52.8%) and good emulsion stability (83.4 – 93.0%). The presence of chitin in the defatted flour could have masked the effect the drying method have on the protein functional properties. However, the functional properties of the defatted insect flours suggest that they are not suitable for liquid food products because of its low NSI and WSI but could be suitable for semi solid to solid food products. Therefore, sun drying and solar cabinet drying on their own or with prior boiling could be cost-effective and affordable alternatives to freeze drying and oven drying for preserving edible insects and producing dry edible insect ingredients. These dried insect ingredients could be good candidates for solid and semi-solid food products and the manufacture of texturised proteins.
Techno-functional properties, dough rheology and bread quality of flours from infrared and microwave heat-treated bambara groundnuts grains
(University of Pretoria, 2023) Emmambux, Mohammad Naushad; peter.mukwevho@up.ac.za; Mukwevho, Peter
This work was undertaken to investigate the effects of heat treatment (130 °C surface temperature) of pre-conditioned (20 or 53% moisture) Bambara groundnut (Vigna subterranea) seeds using infrared, microwave energy alone and in combination on the techno-functional properties of their flours, and the effects of these flours on dough rheology. Heat treatment caused starch pre-gelatinisation and denaturation of protein in resulting flours, which significantly increased with moisture level and treatment time (0,5 and 10 minutes). Endothermic peak by DSC decreased with increased treatment time for all heat treatments in flours from 53% moisture level seeds. Pasting temperature of Bambara groundnut flours significantly (P<0.05) increased with heat-treatment times (0,5 and 10 minutes), but final paste viscosities decreased. The low viscosity can be explained by unavailability of starch to form a viscous paste due to surrounding protein matrix around the starch granules. Proteins have been proposed as the major biomolecules responsible to coat starch and make it unavailable to paste, thus, a low paste viscosity. In the second research chapter, proteins were removed by trypsin and the flours were analysed. CLSM did not show a protein signal after the trypsin treatment. The removal of Bambara groundnut proteins significantly (P<0.05) increased the flour paste viscosities. During infrared, microwave and combination heat treatment of Bambara groundnut seed, there was disulphide bonding and polymerisation of Bambara groundnut protein indicated by an increase in higher molecular weight band intensity from SDS-PAGE. FTIR showed a reduction in the α-helix and an increase in β-sheet for all the heat treatment methods indicating changes in the Bambara groundnut protein secondary structures. Molecular changes of Bambara groundnut protein caused by heat treatment play a major role in low paste viscosities of resulting flours from heat-treated Bambara groundnut seeds. And lastly, flours from heat treated Bambara groundnut seeds were composited to wheat (15 and 30% Bambara groundnut flour addition) and their effects on dough rheology and bread making properties were investigated. Mixolab, Alveograph and the creep and recovery test were used to investigate dough rheological properties of wheat-Bambara groundnut composite dough. There was an increase in flour water absorption from the mixolab (P>0.001) with addition of Bambara groundnut flours from heat treated seeds when compared with the addition of flours from untreated Bambara groundnut seeds. Bambara groundnut flour negatively affected viscoelastic behaviour and increase the energy required to inflate the dough (W) while dough elastic compliance (J1) was reduced. The addition of Bambara groundnut flour to wheat flour results had negative effects on dough viscoelastic properties which subsequently affected bread properties. Addition of heat-treated flour provided bread with softer crumb and high specific volume when compared with untreated flours. Compositing wheat flour with resulting flours from heat treated Bambara groundnut seeds may be useful in the production of composite bread with softer crumb structure. In conclusion, infrared and microwave heat treated Bambara groundnut grain changed the molecular structure of the protein by increase in β-sheet and disulphide bond formation; and pregelatinized the starch. The protein thus became hydrophobic and coated the starch to reduce pasting viscosity. This change also increased dough water absorption and produce softer bread when compositing with wheat flour.
Iron bioavailability, nutritional and health-promoting properties of extruded sorghum porridge fortified with Baobab fruit, moringa leaves and Bambara groundnut
(University of Pretoria, 2023) Duodu, Kwaku Gyebi; Taylor, J.R.N. (John Reginald Nuttall); Emmambux, Mohammad Naushad; john.lubaale1@gmail.com; Lubaale, John
Iron deficiency, protein energy malnutrition (PEM) and the rise in diet-related non-communicable diseases (NCDs) are major public health concerns in developing countries. Food-to-food fortification (FtFF) is an emerging strategy that can be used to manage malnutrition. Moringa leaf powder (MLF) (rich in iron) and baobab fruit pulp (BFP) (rich in mineral bioaccessibility enhancers, such as ascorbic and citric acids), can be used in FtFF of starchy foods like sorghum to help reduce iron deficiency. They are also rich in bioactive polyphenols, which have been shown to have health-promoting properties in terms of offering protection against NCDs. Compositing cereals with legumes such as Bambara groundnut can improve the protein quality of cereal-based foods and thus help to address PEM. Extrusion cooking is used to produce convenient food products such as instant porridges, which are popular, particularly among urban communities in sub-Saharan Africa. It has been shown to reduce antinutrients in foodstuffs, thus improving the bioavailability of nutrients. There is, therefore, an opportunity to use FtFF and extrusion cooking technology to enhance nutritional quality (micro- and macronutrients) and health-promoting properties of sorghum-based foods. This research investigates the impact of FtFF (with BFP, MLP, and Bambara groundnut) and extrusion cooking on the iron bioaccessibility, health-promoting properties and macronutrient (protein and starch) quality of sorghum-based porridge. Formulations of non-tannin sorghum-based flours (sorghum alone or composited with Bambara groundnut flour) were prepared by FtFF with BFP and MLP (either alone or in combination). Flours were cooked into porridges by conventional cooking or instantized using extrusion cooking at a feed moisture level of 3 L/h, barrel temperature zone profile of 60/70/80/140/140ºC and a screw speed of 250 rpm. The iron bioaccessibility (measured as in vitro dialyzability and ferritin formation by Caco-2 cells) of the plain sorghum-based porridges FtFF with BFP and MLP, phytate content, and total phenolic content (TPC) (Folin-Ciocalteu method were determined. Antioxidant properties of the porridges were determined using [(2,2-azinobis-(3-ethyl-benzothiazoline-6-sulphonic acid) (ABTS) and nitric oxide (NO) radical scavenging and oxygen radical absorbance capacity (ORAC)], while phenolic profiles of the foodstuffs used for fortification and the porridges were determined using liquid chromatography-mass spectrometry. Cellular antioxidant protection in human carcinoma (Caco-2) cells using the dichlorofluorescein diacetate (DCFH-DA) assay, NO scavenging activity in RAW264.7 macrophages, inhibition of advanced glycation end products (AGEs) and prevention and treatment of lipid droplet accumulation in 3T3-L1 cells were determined. The FtF-fortified composite (with Bambara groundnut) porridges were analysed for functional properties (water absorption and solubility index, nitrogen solubility index and flow properties), in-vitro starch digestibility (IVSD), soluble and insoluble dietary fibre content and in-vitro protein digestibility (IVPD). Sorgum-based porridges fortified with BFP had higher iron bioaccessibility (in vitro iron dialysability) compared with porridges fortified with MLP. This indicates that the type of plant foodstuff used for FtFF had an effect on the resultant iron bioaccessibility. BFP had high levels of organic acids (citric and organic acids) that are well-known mineral bioaccessibility enhancers and could account for the enhanced iron bioaccessibility of porridges fortified with BFP. MLP was high in mineral bioaccessibility inhibitors (polyphenols, calcium and phytate). Polyphenols and phytate could form insoluble complexes with iron, and stable, insoluble complexes could be formed between iron, phytate and calcium, which reduces bioaccessible iron. Extrusion-cooked instant sorghum-based porridges had increased ferritin formation by Caco-2 cells compared to conventionally wet-cooked porridges, which indicates an enhancing effect of extrusion cooking on iron bioaccessibility. This could be due to the ability of extrusion cooking to reduce the contents of antinutrients such as phytate (probably by dephosphorylation) and polyphenols (probably by degradation). Instant sorghum porridges fortified with BFP produced higher ferritin formation in Caco-2 cells than porridges where MLP was used for FtFF. This was a further indication of the importance of the role of the type of plant foodstuff used for FtFF in mineral bioaccessibility. FtFF of wholegrain sorghum-based porridges with BFP and MLP enhanced health-promoting properties of sorghum-based porridges in terms of radical scavenging activity (ABTS and ORAC) (protection against oxidative stress), cellular nitric oxide (NO) inhibition (anti-inflammatory properties) and inhibition of advanced glycation end products (AGEs) formation (antidiabetic properties). The observed enhanced health-promoting properties could be related to the enhanced levels of various bioactive phenolics (phenolic acids and their esters, flavonoids and flavonoid glycosides) in the sorghum-based porridges after FtFF. Phenolic extracts from the sorghum-based porridges showed protection against AAPH radical-induced oxidation in Caco-2 cells, an indication of their potential ability to protect against radical-induced oxidative stress. Extracts from all the sorghum-based porridges reduced in vitro chemical formation of NO, an indication of their potential to contribute to alleviating radical-induced inflammation. FtFF significantly improved the inhibition of cellular NO production in RAW264.7 macrophages, possibly due to the enhancement of the phenolic profile of sorghum-based porridges following FtFF with baobab and moringa. Extrusion-cooked instant porridges exhibited decreased inhibition of NO formation in RAW264.7 macrophages, possibly due to their reduced phenolic content as a result of the extrusion cooking process. Extracts from all the sorghum-based porridges showed prevention and treatment of accumulated adipocytes in 3T3-L1 cells, indicating their potential application in managing obesity. The porridges exhibited antidiabetic properties by reducing the formation of AGEs. The FtFF porridges, in particular, significantly reduced the formation of AGEs, possibly due to the increase in phenolic content and higher antioxidant activity following FtFF with BFP and MLP. Sorghum-Bambara groundnut composite (SBC) porridges FtF-fortified with BFP and MLP showed a marked reduction in starch digestibility {decreased rapidly digestible starch (RDS) increased slowly digestible starch (SDS) and resistant starch (RS)} and estimated glycaemic index (GI) compared to the unfortified composite. The high levels of anti-nutritional compounds - polyphenolics, phytate, and soluble and insoluble dietary fibre (SDF and IDF) in the fortificants (BFP and MLP) could account for the reduced starch hydrolysis. Dietary fibre could entrap starch molecules and reduce their accessibility to digestive enzymes, while polyphenols could form indigestible complexes with starch and could also bind enzymes responsible for the digestion of starch. Extrusion-cooked instant SBC porridges had higher RS, RDS, and protein digestibility (IVPD) with lower SDS in comparison with conventionally cooked porridges. The dextrinisation of starch and reduction in anti-nutritional compounds (that bind both starch and proteins) because of the high temperature, shear and pressure conditions during extrusion cooking could make the starch and protein molecules more susceptible to enzymatic hydrolysis and lead to increased RDS, IVPD, and lower SDS. Extrusion-cooked SBC porridges had higher SDF and lower IDF compared to conventionally wet-cooked porridges, possibly due to the hydrolysis of glycosidic bonds in IDF during extrusion cooking, solubilising it into SDF. This increase in SDF could account for the increase in RS and SDS as the gelatinised and disrupted starch molecules could be entrapped in the SDF, making them less accessible for enzymatic hydrolysis (resistant starch type 1). Retrogradation of starch in the extruded porridges during storage could also produce enzyme-resistant starch (resistant starch type III). A third possible occurrence during extrusion is the formation of amylose-lipid complexes resistant to enzymatic hydrolysis (resistant starch type V). The high RS content of these instant sorghum-based porridges suggests they could be useful in managing type 2 diabetes. Extrusion-cooked SBC porridges had lower pasting viscosities, probably due to the dextrinisation of starch (the primary biopolymer responsible for pasting) during the high temperature, shear and pressure conditions of extrusion cooking. This provides a shear-thinning porridge, which could increase nutrient intake for infants who have difficulty orally processing thick foods and thus preventing the prevalence of PEM. In conclusion, extrusion cooking can be used to produce instant porridges from FtF-fortified and composited non-tannin sorghum with improved bioaccessibility of iron, protein and starch digestibility and health-promoting properties. Thus, extrusion cooking and FtFF of non-tannin sorghum can be employed as strategies to improve the nutritional and health status of at-risk communities.
Food patterns in relation to weight status and body composition of female adolescents in Tshwane
(University of Pretoria, 2022) Pretorius, Adeline; White, Zelda; ntsepasematete@gmail.com; Matete, Ntsepase P.
Introduction: In South Africa there is a high prevalence of overweight/ obesity among adolescence, which in turn indicates an increased risk of non-communicable diseases (NCDs) in adulthood (DoH, 2016, WHO, 2018). Obesity/overweight is linked to a diet high in saturated fat foods (e.g. fast foods), snacks and/or sugar added foods and beverages (Popkin et al., 2012, Romieu et al., 2017). Aims: This cross-sectional study aimed to determine the relationship between food patterns, and weight status (BMI-for-age) and body composition (BC), respectively, of female adolescents (N=91) aged 13 – 19 years attending two private schools in the City of Tshwane. Methods: Convenience sampling was used to recruit participants. Weight and height were measured with the Seca mBCA 514 and stadiometer 274, respectively, and used to calculate the body mass index (BMI). World Health Organization reference standards were used to obtain BMI-for-age z-score. Bioelectrical impedance analysis with the Seca mBCA 514 was used to obtain frequency outputs for the calculation of fat mass (FM) and fat free mass (FFM). The rapid eating assessment for patients (REAP) questionnaire was used to assess food patterns and obtain a diet quality score, in total and per food group. The Spearman correlation test was performed to determine the relationship between REAP scores and: FM, FFM, fat mass index (FMI), fat free mass index (FFMI) and BMI-for-age z-score, respectively. Results: The mean BMI-for-age z-score was 0.62 (0.37; 0.87), FM was 23.50kg (21.77; 26.32), FFM was 39.03 kg (38.07; 39.98), FMI was 8.95 kg/m2 (8.26; 10.03), FFMI was 14.79 kg/m2 and total REAP score was 52.95 (51.62; 54.27). A total of 29.2% was overweight and 8.99% obese. A moderate, statistically significant correlation was found in the overweight category between the REAP score for whole grains/starch consumption and FFM (r=0.51, p=0.01) and FFMI (r=0.47, p=0.02), respectively, and between high sodium consumption and FM (r=0.42, p=0.04). A weak, negative, yet statistically significant correlation was found between the dairy consumption and FFM (r= -0.30, p=0.04) of the black African subgroup. Lastly, a moderate, negative, yet statistically significant correlation was found between the dairy consumption and FFM (r=-0.40, p=0.05) of the overweight category. Conclusion: The present findings indicate that participants have a poor-quality diet including a high consumption of fats and oils, sugar, sodium and high fat meat, and a low consumption of fruits and vegetables and whole grains. The BMI-for-age z-scores, FM and FMI indicate that a high percentage of participants were overweight with an increased risk of developing NCDs later in life. The correlation analysis could not be used to draw a meaningful conclusion about the relationship between dietary intake and BMI-for-age z-score, FM, FMI, FFM and FFMI. Future research may need to include a more detailed analysis of dietary intake
Sensory properties and consumer acceptance of orange-fleshed sweet potato bread : the effect of food neophobia
(University of Pretoria, 2022) De Kock, Henrietta Letitia; annelizesteyn99@gmail.com; Steyn, Annelize
A considerable effort is placed on developing food products for food-insecure environments. Vitamin A deficiency is a problem that is plaguing the nutrition security of many consumers in Sub-Saharan Africa. Nutrition security requires the intake of a wide range of foods which provides all the essential needed nutrients. Vitamin A is essential for immune function, eye and vision health and skeletal growth. To address this problem bread that is high in β-carotene (a precursor of vitamin A) was developed by partially replacing part of the wheat flour and water in a standard formulation with orange-fleshed sweet potato (OFSP) puree. In this dissertation, the term OFSP bread will be used to refer to this wheat and OFSP composite bread. Many new food products such as this one fail in the market. One of the reasons why new food products fail is due to consumers’ fear of the novelty e.g. sensory properties that are different to what the consumers are used to. Food neophobia is the term that is used to describe “the reluctance to eat or the avoidance of unfamiliar foods” (Pliner and Hobden, 1992). Understanding consumers’ food neophobic attitudes can assist in the development of products that meet the consumers’ needs. Food neophobia is generally measured using the Food Neophobia Scale (FNS) developed by Pliner and Hobden (1992). In this study, sensory properties of the OFSP bread had to be determined. In addition, the effect of food neophobia on consumer acceptance of the OFSP bread This study investigated whether research participants’ food neophobia scores could serve as a predictor for (1) the likelihood of choosing unfamiliar foods and (2) expected liking of the sensory properties of unfamiliar products including OFSP bread. The project consisted of two phases. Phase 1: an online survey to determine the effect of food neophobia (measured with an adapted FNS) on participants’ consisting of liking/expected liking of a selection of familiar and unfamiliar foods and the likelihood of choosing the options. Phase 2: This phase consisted of physico (L *, a * and b * colour values, instrumental texture and image analysis) and descriptive sensory (with trained sensory panel) characterisation of the different bread types. In addition consumer evaluation of standard familiar wheat bread and the bread containing the unfamiliar ingredient (OFSP) was conducted. As expected, the food neophobic score of participants did affect whether they expected to like or dislike and were likely to choose and unfamiliar food item. The results showed that individuals with higher food neophobia scores were expected to dislike and were more reluctant to choose unfamiliar food items than low neophobic individuals. The food neophobia score of participants can therefore serve as a predictor of their willingness to try unfamiliar foods. However, contrary to expectations consumers with high food neophobia did not rate the liking of the sensory properties of the unfamiliar OFSP bread lower than consumers with low food neophobia scores. Food neophobia did not play a significant role in whether the OFSP bread was liked or disliked. The finding can be explained as follows: the sensory properties of the OFSP bread, except for the colour, were as acceptable as the wheat bread to the consumers that participated in the research probably because the OFSP bread had very similar sensory properties to the wheat bread. This research concludes that food neophobia is indeed a reliable predictor of the potential of consumers to accept novel food products. However, the extent of the novelty of the sensory properties of a new product is an important factor in the neophobic effect. The OFSP bread can be introduced into the market with a low risk of rejection of the sensory properties even by individuals with high food neophobia tendencies. Regular consumption of OFSP bread has the potential to reduce vitamin A deficiency among affected individuals and communities. Further research is required to determine if food neophobic individuals will choose a labelled and branded OFSP bread option within a real market situation where novel and familiar wheat bread options are offered side by side. More research on other food product options to address vitamin A deficiency using OFSP or other applications.
Lactic acid bacteria from traditionally fermented African food affect the diarrhoeagenic potential of enteroaggregative Escherichia coli
(University of Pretoria, 2022-09) Buys, E.M. (Elna Maria); wakselorm@gmail.com; Agbemavor, Wisdom Selorm Kofi
Probiotic bacteria undergo specialised activities, including aggregation, cell surface hydrophobicity, adhesion to epithelial cells, and production of certain antimicrobial substances against pathogens. These activities enable them to exert their beneficial effects on their host. Selected lactic acid bacteria (LAB) and enteroaggregative E. coli (EAEC) previously isolated from traditionally fermented West-African cereal, ogi and unpasteurised fresh milk, respectively, were obtained studied for their abilities to aggregate and adhere to hydrocarbons. The LAB was further evaluated for their abilities to inhibit the EAEC. The LAB (Lactobacillus plantarum FS2 and Pediococcus pentosaceus D39) and EAEC demonstrated satisfactory cell surface properties and aggregation abilities with their EAEC counterparts. However, their auto-aggregation and co-aggregation were strain specific. Also, their adhesion to hydrocarbons and the exclusion of EAEC by LAB depended on the two bacteria involved and their incubation time. Neither LAB nor EAEC shows a correlation between auto-aggregation and adhesion, a requirement for colonisation and infection of the gastrointestinal tract. Likewise, there was no correlation between auto-aggregation and adhesion to Caco-2 cells and between hydrophobicity and auto-aggregation abilities for the two combatting bacteria. Therefore, the two LAB from traditionally fermented West African cereal, ogi, demonstrated promising properties worth considering for further applications in fermented functional foods and food products to improve human health.
Characterisation, health-promoting properties and food applications of anthocyanin-rich pigments of flowers from the Geraniaceae and Lamiaceae plant families
(University of Pretoria, 2022-04-18) Duodu, Kwaku Gyebi; Stafford, Gary I.; Fisher, Hennie; anton.venter@up.ac.za; Venter, Anton
Colour is an important characteristic of food and plays a significant role in enhancing the visual appeal of food products. The colourants mostly used in the food industry are synthetic azo-dyes due to their brightness and stability. However, scientific evidence has shown that these compounds may pose adverse health effects. This has created a demand for more natural food colourants by consumers who have become more health conscious. Plant species from the Geraniaceae (Pelargonium) and Lamiaceae (Salvia (sage) and Plectranthus (spurflower)) families produce flowers with a range of different colours. The flowers are non-toxic and could be a source of novel stable pigments for potential application as natural colourants in foods with added health benefits. Plant species from the Geraniaceae (Pelargonium grandiflorum Willd., P. × hortorum L.H. Bailey and Pelargonium zonale (L.) L’Hér.) and Lamiaceae (Salvia aurea × dolomitica, Salvia dolomitica Codd and Plectranthus zuluensis T. Cooke) families were used in this research. The petals of their flowers were collected, air-dried at 30ºC for 24 hours and ground into a powder. Pigmented extracts were prepared by extracting the flower powder with formic acid-acidified water for 24 hours. The pigmented flower extracts were evaluated for total phenolic content (Folin-Ciocalteu assay), anthocyanin and phenolic profiles and concentrations of phenolic compounds (Ultra Performance Liquid Chromatography-Quadropole Time-of-Flight Mass Spectrometry). Degradation kinetics experiments were conducted to determine the thermal and oxidative stability of the pigmented flower extracts. Health-promoting properties of the pigmented flower vi | P a g e extracts were determined using chemical radical scavenging assays (2,2-diphenyl-1-picrylhydrazyl [DPPH] radical scavenging, oxygen radical absorption capacity [ORAC] and nitric oxide [NO] radical scavenging), cellular assays (Caco-2 cellular antioxidant activity, NO radical scavenging in RAW 264.7 macrophages and anti-adipogenic activity in 3T3-L1 adipocytes) and anti-glycation activity (Advanced Glycation End Products assay). The pigmented flower extracts were applied as natural colourants in yogurt, fondant and gelatine candies while the flower petal powder was applied directly as colourant in yogurt. The food products with the natural colourants were evaluated for their colour stability (chromaticity analysis) during storage. Anthocyanins in the Geraniaceae pigments were mainly 3,5-diglucoside of delphinidin, petunidin, pelargonidin, peonidin and malvidin and acetyl-acylated malvidin, delphinidin and petunidin. Anthocyanins in the Lamiaceae pigments were rutinosides of pelargonidin, glucosides of petunidin, pelargonidin and p-coumaric acid- and malonyl-acylated delphinidin and malvidin. Geraniaceae pigments also contained rutinosides of kaempferol and quercetin, quercetin-3-O-glucoside (isoquercetin), luteolin-7-O-glucoside and hydrolysable tannins (β-glucogallin, penta and tetra-galloyl glucose). Lamiaceae pigments contained naringin and hesperidin. The only phenolic acid in the Geraniaceae pigments was p-coumaric acid and the Lamiaceae pigments contained rosmarinic acid and its derivatives such as sagerinic acid and salvianolic acid B. Lamiaceae pigments were more thermally and oxidatively stable (lower degradation rate constants and longer half-life) than Geraniaceae pigments. The greater stability of the Lamiaceae pigments could be due to hydrophobic intramolecular self-association interactions of their aromatic acylated anthocyanins in combination with stabilising interactions of these aromatic acylated anthocyanins with rosmarinic acid and its derivatives. The pigmented flower extracts from the Geraniaceae had higher total phenolic content and DPPH radical scavenging activity than the Lamiaceae. All pigmented flower extracts exhibited Caco-2 cellullar antioxidant activity (reduction of oxidative stress), inhibition of LPS-induced NO production in RAW 267.4 macrophage cells (anti-inflammatory effects) and ability to reduce lipid accumulation in 3T3-L1 adipocytes after 14 days treatment (anti-obesity effects). Despite their lower total phenolic content and DPPH radical scavenging activity, Lamiaceae pigments showed similar Caco-2 cellular antioxidant activity and inhibition of NO production in RAW 267.4 macrophages to Geraniaceae pigments. This may be related to the observed vii | P a g e greater thermal and oxidative stability of the Lamiaceae pigments. P. grandiflorum and P. × hortorum pigmented flower extracts showed significant anti-glycation activity (anti-diabetic effects) which was notably similar to that of the anti-diabetic drug aminoguanidine. The pigmented flower extracts were successfully applied as natural colourants in yogurt (low pH food), fondant (sugar-based food system) and gelatine (protein-based food system) in comparison with the commercial E163 anthocyanin colourant. The colour of the food products was stable over a 15-day storage period with only some indications of slight decreases in redness and total colour. Compared to the commercial E163 colourant which only gave a purple colour, the pigmented flower extracts imparted a greater range of colours to the food products (red, purple, pink and orange) and in different shades of intensity and brightness. The application of the powdered flower samples directly into yogurt as colourant led to development of brown colouration in the yogurt possibly due to residual activity of browning enzymes in the flowers. This indicates that direct incorporation of the powdered flower samples as colourants in foods may not always be desirable. This research shows the potential of flowers from the Geraniaceae and Lamiaceae plant families for application as novel natural food colourants. It represents important innovations in natural food colourants and provides novelty in terms of the stability of the pigments, the variety of colours they confer to food systems and their health-promoting properties. The findings of this study open up new opportunities for production of natural colourants for application in the food industry and also meets consumer demands.
Bioaccessibility of phenolic compounds and related antioxidant and health promoting properties of soured sorghum porridges
(University of Pretoria, 2022-06-06) Duodu, Kwaku Gyebi; Kayitesi, Eugenie; nomfundodlamini59@gmail.com; Dlamini, Nomfumdo
The percentage of deaths due to non-communicable diseases (NCDs) such as diabetes, cancer, obesity and heart disease has been growing steadily in South Africa. Rapid urbanization and increased demand for convenience foods have driven changes in dietary choices towards those based on highly refined grains which has led to an increase in susceptibility to oxidative stress and NCDs among consumers. This brings into focus the importance of sorghum which is a cereal crop consumed in many parts of Africa and is well known as an important source of bioactive phenolic compounds with the potential to protect against diet-related NCDs. Phenolic compounds in sorghum occur mainly in bound forms which limits their extractability, bioaccessibility and subsequently their ability to exert health-promoting effects. Processing methods such as souring could release phenolics in sorghum from their bound forms and therefore enhance their bioaccessibility. This research studied the effect of souring using spontaneous fermentation and citric acid acidification on the bioaccessibility of phenolic compounds and related antioxidant and health promoting properties of sorghum porridges. Two type I non-tannin sorghums (red and white phenotype) were used. Soured sorghum porridges were prepared using spontaneous fermentation and exogenous acidification with citric acid. For determination of bioaccessibility of phenolic compounds, supernatants were obtained from sorghum porridges digested using a static simulated in vitro gastrointestinal digestion procedure. Total phenolic content (TPC) using the Folin-Ciocalteu assay, phenolic composition using Ultra Performance Liquid Chromatography-Quadrupole Time-of-Flight Mass Spectrometry (UPLC-QToF-MS), esterase enzyme activity, ABTS and DPPH radical scavenging activity, Oxygen Radical Absorbance Capacity (ORAC), Nitric Oxide (NO) inhibition, Caco-2 cellular antioxidant activity as well as the capacity to protect against plasmid DNA oxidative damage were evaluated for the sorghum flours, porridges and supernatants of digested porridges. Phenolic compounds identified in the two sorghums were phenolic acids and flavonoids. The major phenolic acids class present were the hydroxycinammic acids. Flavonoids identified were flavanones (the major identified flavonoid class), flavonols, flavan-3-ols and flavones. Red sorghum flour, porridges and supernatants contained higher levels of total phenolic compounds compared to that for white sorghum. Souring through spontaneus fermentation led to an increase in TPC and radical scavenging activity against ABTS, DPPH and ORAC values for the sorghum flours and resultant porridges. This increase was attributed to the acidic conditions imposed by the fermentation process combined with the action of esterase enzymes which facilitate ester bond hydrolysis and the release of bound phenolic compounds. Fermented red sorghum slurry exhibited higher esterase enzyme activity compared to that for white sorghum. On the other hand, acidification with citric acid had no effect on the TPC but produced more bioaccessible phenolic compounds compared to souring through fermentation. This souring method also enhanced the antioxidant activity in all the samples except for ABTS radical scavenging. Although souring had no significant effect on NO inhibition, red sorghum flours, porridges and supernatants of digested porridges had significantly higher NO inhibition capacity than those from white sorghum. Simulated in vitro gastrointestinal digestion also enhanced the TPC and the radical scavenging properties of the porridges. This was attributed to the action of the enzymes used during the in vitro digestion process such as amylase, pepsin, pancreatin leading to breakdown of the food structure and enhanced extractability of phenolic compounds. The flours, porridges and supernatants from both sorghum types exerted Caco-2 cellular antioxidant activity and protected the DNA from AAPH-induced oxidative damage. This is an indicator of the potential health promoting properties of the soured sorghum porridges by offering protection against diet-related NCDs. This research has shown that souring, either through spontaneous fermentation or through exogenous acidification with citric acid can enhance the bioaccessibility of phenolic compounds and antioxidant properties of sorghum porridges. These soured sorghum porridges can therefore play a vital role in contributing towards efforts to combat and reduce the current rising trends of the occurrence and mortality from diet- and oxidative stress-related NCDs in Africa.
Pasting properties of teff, maize, and potato starches with added microcrystalline cellulose and cellulose nanofiber
(University of Pretoria, 2022) Emmambux, Mohammad Naushad; kawumareagan.sa@gmail.com; Kawuma, Reagan
An increase in health concerns from consumers towards the use of synthetic chemicals in starchy food formulation has led to a significant preference for “clean” label starches. Hydrocolloids are organically-sourced food additives. This study utilized microcrystalline cellulose (MCC) and cellulose nanofiber (CNF), a group of cellulose-derivative hydrocolloids that have not yet been extensively in starch modification to investigate the effect of CNF (a nano-polymer) and MCC (a micro-polymer) on the pasting properties of teff, maize, and potato starches. Starch suspensions with MCC and CNF at different concentrations (0%, 0.2%, 0.5%, 2% and 5% w/w) underwent short and extended pasting cycles for 30 and 120 minutes respectively. MCC and CNF significantly increased the peak and final viscosities of the starch pastes. Hydrocolloids when added to a water-rich continuous phase form viscous networks via hydrogen bonding that increase the overall viscosity of the starch hydrocolloid system. However, a decrease in the starch gel strength was observed with an increase in MCC and CNF concentration. Hydrocolloid and leached amylose interactions limit junction zone formation which results in the formation of weaker gels. Overall, starches treated with CNF had higher paste viscosities and lower gel strength than those with MCC. This results from the nanostructure of CNF which gives it a high surface area and hydrodynamic volume to form more associations. Modified starch produced by the addition of MCC and CNF to starch is a possible “clean” replacement for chemically modified starches in the food industry because of their increased viscosity and non-gelling properties
Antioxidant and antimicrobial activity of Carica papaya extracts in minimally processed fresh produce
(University of Pretoria, 2022) Mehlomakulu, Nwabisa; Kayitesi, Eugenie; Duodu, Kwaku Gyebi; lilianruthkafuko@gmail.com; Kafuko, Lilian
Food (especially fruit derived) waste has a detrimental influence on the environment and food security of a country. As the world’s population continues to rise, the challenge becomes feeding more people nutrient dense meals and preventing wastage of what we already produce. Fresh produce is important for a healthy diet, however, challenges arise around retaining their freshness and quality during processing and distribution. A lot of produce gets wasted along the supply chain and so technologies that help in retaining the quality are needed. The conversion of by-products obtained during processing to high end food additives is one way of reducing fresh produce waste. Papaya (Carica papaya L.) is one such produce whose by-products are underutilised. Based on the nutritional quality of the edible part, there was potential in utilising the papaya peel in the study. There is not much that has been reported on papaya with regards to utilization of its by-products as preservatives within the food industry. Therefore, the antioxidant and antimicrobial properties of C. papaya peel crude extracts were studied in this work. The bioactive compounds in the peel crude extracts were also identified. The ability of the crude extracts to inhibit more common foodborne pathogens was investigated. Furthermore, the crude extracts were also tested as anti-browning agents using apples and potatoes as model systems. Using the agar well diffusion technique, the antibacterial activity of the peel crude extracts against bacteria (Listeria monocytogenes and Escherichia coli) was examined. The crude extracts were active against both L. monocytogenes and E. coli. Because of the difference in cell wall structure between the two bacteria (the former is a gram positive bacterium and the latter is a gram negative bacterium), antimicrobial activity was more pronounced in L. monocytogenes than in E. coli. The crude extracts were also stored at 4°C and 10°C for 5 days and thereafter their activity tested against the two bacterial species. The results showed that the crude extracts generally retained their antimicrobial properties even after exposure to the low temperatures for the 5 day period. The antimicrobial activity of the crude extracts was found to be due to presence of bioactive compounds. The bioactive component profiles of the peel crude extracts were investigated using a high-resolution ultra-performance liquid chromatography system with diode array detection, quadrupole time-of-flight and mass spectrometer (UPLC-DAD-QTOF-MS). Metabolites such as citric acid, ascorbic acid, gluconic acid, malic acid, ρ-coumaric acid, ferulic acid, caffeic acid glucoside, vanillic acid, sinapic acid, rutin, quercetin-3-O- rhamnosyl rutinoside, Isorhamnetin-3-O- dirhamnosyl glucoside and benzyl glucosinolate were identified. Phenolic compounds were found to be the most predominant in the crude extracts. Overall, the bioactive compounds identified within the crude extracts were organic acids, phenolic acids, flavonols and a glucosinolate. The Folin-Ciocalteu (F-C) technique, the aluminium chloride test and the ferric reducing antioxidant power (FRAP) assay were used to measure the total phenolic (TPC), total flavonoid content (TFC), and metal chelating activity of the crude extracts, respectively. The TPC, TFC and FRAP in the crude extracts were 6865 ± 153 mg GAE/g dw, 3638 ± 252 mg QE/g dw and 7968 ± 38 mM TE/g dw, respectively. The crude extracts therefore showed antioxidant activity. The presence of the enzymes chymopapain and papain in the crude extracts was determined using SDS-PAGE (Sodium dodecyl-sulphate polyacrylamide gel electrophoresis). This was done to test for toxicity of the crude extracts. Additionally, the BCA (Bicinchoninic acid) assay was used to determine the overall protein concentration in the crude extracts. There were low concentrations of proteins observed in the crude extracts. Ultimately, the absence of enzymes chymopapain and papain in the crude extracts gave evidence that the extracts were not toxic. To determine the crude extracts’ ability to inhibit enzymatic browning, potato and apple pieces were immersed in treatments containing the extracts and these were compared with other standard and control treatments. Browning was measured as change in colour using a CR-400 Chromameter where Lab values were obtained and used to calculate the overall colour change (ΔE) and the browning index (BI). Browning was also measured through visual assessment where browning scores (BS) for the apples and potatoes were recorded. The crude extracts inhibited enzymatic browning but were less effective than the standard treatment where the apples and potatoes had been immersed in a solution containing sodium metabisulphite, citric and ascorbic acids. The ability of these crude extracts to inhibit browning is supported by the presence of antioxidants and their ability to slow down the enzymatic browning process. The outcomes and findings of this research open further avenues and opportunities for the increased utilisation of C. papaya peels which is are derived from the consumption of papaya.
Nutritional, antioxidant and microbiological properties of finger millet-based beverages as influenced by starch source during lactic acid fermentation
(University of Pretoria, 2021) Duodu, Kwaku Gyebi; Buys, E.M. (Elna Maria); Schonfeldt, H.C. (Hettie Carina); lunganianyathi@gmail.com; Nyathi, Lungani A.
In Sub-Saharan Africa (SSA), where nutrient malnutrition is of concern, finger millet contributes substantially to the dietary protein and mineral intake of many communities. The quality of finger millet protein is, however, poor due to deficiency of essential amino acids like lysine and reduced digestibility due to complexation with antinutrients such as phytate which can also reduce mineral bioaccessibility. Despite the nutritional challenges, finger millet is rich in bioactive phenolic compounds which are gaining increased research focus due to the potential health benefits they can offer in terms of protection against diet-related non-communicable diseases (NCDs). Various fermented beverage products are consumed in SSA, where the fermentation process involves inclusion of an exogenous source of starch. Crucially, the fermentation process can modify the microbial population, nutrients, and bioactive compounds. This presents an opportunity for the improvement of cereal-based diets to leverage their nutritional and health benefits fully. In this study, the influence of starch source- maize and rice- on protein quality, mineral bioaccessibility, phenolic content, and antioxidant and microbiological properties of fermented finger millet-based beverages was determined. Finger millet slurries were prepared by spontaneous fermentation with or without addition of exogenous starch from maize or rice, whilst beverages were prepared by cooking finger millet slurries. Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) and 16S ribosomal ribonucleic acid (16S rRNA) amplicon sequencing were used to assess microbial diversity of slurries, whilst in vitro dialysability, in vitro protein digestibility (IVPD), and reactive (available) lysine assays were done on slurries and/or beverages to determine iron and zinc bioaccessibilities, and protein quality, respectively. Phenolics were extracted from slurries and beverages using acidified methanol [1% (v/v) conc. HCl in methanol] and the total phenolic content [TPC, Folin-Ciocalteu (F-C) method] and antioxidant properties of extracts against 2,2´-azinobis [3 ethylbenzothiazoline-6-sulphonic acid] (ABTS) diammonium salt were determined. MALDI-TOF MS revealed the dominance of Weissella confusa, Enterococcus casseliflavus, E. hermanniensis, Lactobacillus acidipiscis, L. salivarius, L. lactis, L. fructivorans, and L. lactis ssp. tructae at the end of finger millet fermentations. 16S rRNA sequencing revealed the dominance of Weissella at the end of fermentation followed by the genera Enterococcus and Lactococcus only in the formulation with added maize starch. Overall, there were no differences in microbial diversity and relative abundance within the fermentation groups. Starch source did not affect IVPD and reactive lysine content of beverages. Lactic acid fermentation improved IVPD with fermented and cooked samples showing higher IVPD than unfermented and cooked samples. This accentuates the role of fermentation in alleviating the negative effects of cooking on protein quality. The improvement in IVPD was attributed to pre-digestion of storage proteins and release of bound proteins at low pH which enhanced their availability to pepsin attack. Iron and zinc bioaccessibility were improved by the addition of exogenous starch. The improvement was attributed to complexation of starch hydroxyl groups to mineral ions whose release during digestion enhanced mineral bioaccessibility in vitro. Although fermentation reduced the phytate content of the samples, no improvement was observed in bioaccessible iron, however, zinc bioaccessibility was improved relative to unfermented samples. The reduction in phytate content was attributed to dephosphorylation of phytate by endogenous phytases activated at low pH. The reduction in iron bioaccessibility can be due to iron chelation by non-phytate organic compounds such as phenolic compounds. The addition of starch improved TPC and Antioxidant Activity (AA) of finger millet-based beverages. The increase was attributed to improved fermentation efficiency and better mobilisation of hydrolytic enzymes, which presumably helped release of bound phenolics. Although cooking did not affect TPC, AA was reduced. The decrease in AA suggested the presence of heat unstable antioxidants whose destruction during heat processing led to a decrease in AA of beverages. Lactic acid fermentation, with or without added exogenous starch, shows the potential to improve zinc bioaccessibility, protein quality (IVPD), and antioxidant properties of finger-millet beverages. Soured finger millet-based foods can potentially be used to reduce mineral and protein malnutrition, and oxidative stress-related NCDs in SSA.
Nutritional and health benefits of heat - moisture treated maize starch and maize meal with stearic acid
(University of Pretoria, 2022) Emmambux, Mohammad Naushad; Hamaker, Bruce; nakanite@gmail.com; Asare, Isaac Kwabena
ABSTRACT Nutritional and health benefits of hydrothermally treated maize starch and maize meal with stearic acid By Isaac Kwabena Asare Supervisor: Prof M.N Emmambux Co-Supervisor Prof Bruce R. Hamaker Diet-related non-communicable disease such as obesity and type – 2 diabetes is increasing especially in the Sub-Sahara African region, and this is related to the increased consumption of processed foods and the decline of high fibre foods. In Sub-Saharan Africa, maize meal stiff pap or soft porridge is a staple food, and it is presumed to be rapidly digestible and estimated as high glycaemic index food. Resistant starch is considered as dietary fibre and can also lower the glycaemic index of starchy foods. This study investigates the formation of resistant starch from maize through the use of heat moisture treatment alone, stearic acid addition alone and their combination on both maize starch and maize meal on upper gastro-intestinal tract (GIT) in vitro digestibility as well as the in vitro faecal fermentation to simulate the lower GIT. Stearic acid was added to both maize starch and maize meal at 1.5 % (w/w) alone, maize starch and maize meal were also treated with heat-moisture treatment at the moisture of 20 % at 110 ℃ for 16 h, and the combination of both stearic acid and heat – moisture treatment was done, as well as their control. Addition of stearic acid moderately changed the peak, breakdown and final viscosities of the paste compared to untreated maize starch and maize meal. The lower peak viscosity was attributed to the coating of the granule surface by the stearic acid to reduce the intake of water that prevents swelling. Stearic acid treatment pastes were non-gelling resulting from complex formation which prevents the development of junction zones among starch molecules which is an integral part of gel formation. Heat moisture treatment without stearic acid more significantly reduced peak, breakdown and final viscosities and produced a stronger gel than the untreated maize starch and maize meal. The strong gel can be attributed to increased cross-linking between the starch polymer v chains to form more junction zones. Also, addition of stearic acid followed by heat moisture treatment similarly reduced the peak, breakdown and final viscosities compared to untreated maize starch and maize meal. XRD and DSC of unpasted maize starch and maize meal with added stearic acid alone, heat moisture treatment alone and their combination increased gelatinization temperatures and crystallinity compared to the control. Following of pasting of maize starch and maize meal, there was the formation of amylose – lipid complex of type I and IIa and IIb with a corresponding increase in the degree of crystallinity. There was a decrease in the in vitro starch digestibility and lower estimated glycaemic index with addition of stearic acid alone, heat moisture treatment alone and in combination treatments for both maize starch and maize meal. This reduced digestibility is attributed to an increase in crystallinity due to formation of resistant starch as amylose-lipid complexes. In vitro faecal fermentation of both maize starch and maize meal with added stearic acid, heat moisture treatment alone, and the combination saw increased production of short-chain fatty acids with the corresponding rise in gases and a decrease in the pH. Although fructooligosaccharides produced higher concentrations of the short-chain fatty acid, the combination treatment was seen having significantly higher concentrations in terms of the indigestible residue compared to its control. With regards to individual short-chain fatty acids produced, acetate and butyrate were in higher concentrations compared to propionate. DNA sequencing showed that the production of short-chain fatty acids was of these modified and unmodified starches was associated with certain of the microbes in the colon. Firmicutes was the dominate phylum followed by Bacteroidetes and then Actinobacteria. Comparably high butyrate levels were associated with Firmicutes, as it contains the major butyrogenic bacteria. In conclusion, the results from this study demonstrated that modification of both maize starch and maize meal by HMT with added stearic acid produced resistant starch containing amylose-lipid complexes that has the potential to reduce estimated glycaemic index and to act as a potential prebiotic. The combination treatment produced a high amount of short-chain fatty acids, which has beneficial effects associated with diet-related non-communicable diseases like obesity and type-2 diabetes.
The application of dehydration technologies on drying kinetics and physicochemical properties of orange-fleshed sweet potato
(University of Pretoria, 2021) Emmambux, Mohammad Naushad; Mehlomakulu, Nwabisa; u12176941@tuks.co.za; Kgonothi, Daddy
Orange-fleshed sweet potato is a highly researched crop due to its nutritional content and more specifically, its high β-carotene content. Most developing countries around the world have adopted the use of orange-fleshed sweet potato as one of the staple food. The short growth period (3-6 months), low agronomical input, and dual-purpose use are properties to combat food security issues in most sub-Saharan African countries. The β-carotene compound is also a precursor for vitamin A, which is one of the most crucial nutrients, especially in children aged between 0-6 years, and pregnant women. African countries (Sub-Saharan region) are known to have a prevalence of vitamin A deficiency. There are challenges when it comes to the storage of fresh plant-based food such as orange-fleshed sweet potato, which is highly perishable and therefore has a short shelf life. Alternative processing methods such as drying and milling into flour can help to extend the shelf life of the orange-fleshed sweet potato. Traditional drying methods such as sun drying, solar drying and oven drying have been used for over decades. However, these methods generally destroy heat-sensitive compounds such as the critical β-carotene content, mainly due to exposure of the orange-fleshed sweet potato to oxygen, sunlight and high temperature for longer periods. The exposure of β-carotene to the mentioned factors can result in isomerization and auto-oxidation of β-carotene, which reduce the vitamin A content, thereby producing a product with poor nutritional content. The current study seeks to explore novel drying technology, such as freeze-drying, microwave and infrared drying methods. Orange-fleshed sweet potato (Bellevue and Orleans cultivar) was dried by application of oven (40°C, 4 hours, air velocity 5.2 m/s), microwave (80 W, 1 hour, air temperature of 40°C, air velocity 4.5 m /s), infrared (250 W, 2 hours, air temperature of 40°C, air velocity 4.5 m/s), microwave-infrared (80 W + 250 W, 45 minutes, air temperature 40°C, air velocity 4.5 m/s) and freeze-drying (-45°C, 100KPa, 5 days) technologies, and milled into flour. The drying kinetics were analysed by different models. The produced flour was analysed for physicochemical properties and nutritional composition. The analysed functional properties include water absorption capacity, swelling capacity, solubility index, bulking density, pasting properties and thermal properties. Proximate composition was also evaluated including total dietary fibre and β-carotene content of the flours. The oven-drying method was the slowest, due to a slow drying rate. The latter is due to the moisture transfer mechanism, as low temperatures are used during drying. The moisture transfer is by capillary diffusion which is a slow moisture transfer mechanism. Oven drying took about 4 hours to dehydrate the sweet potato slices to solid content of less than 13%. Infrared drying was the second slowest drying method, while microwave took only 1 hour to completely dry the sweet potato slices. The electromagnetic radiation by microwave and infrared cause a rapid structural collapse, releasing water from cytoplasm and vacuole, thus increasing cell membrane water permeability, which makes it easy for water to be transported out of the plant cell. The drying rate of the microwave-infrared drying method was the fastest (45 minutes). The coefficient of diffusion from the models also showed that the microwave-infrared combination had the highest diffusion rate, as compared to other drying methods which showed a lower coefficient of diffusion. The Page model was the most suitable for the oven drying method, Lewis model for infrared drying, while Henderson and Pabis for infrared and Logarithmic for microwave-infrared combined method. The pasting and thermal properties of the flours were not significantly affected by the different drying methods. However, infrared and microwave-infrared dried flours have indicated a higher final viscosity when compared to other drying methods. The freeze-dried flour showed a higher enthalpy value (4.29 J/g), as compared to other drying methods. Microwave-infrared drying methods, infrared, and microwave had a higher solubility index, while the oven and freeze-drying methods showed a lower solubility index. The freeze-dried flours exhibited the lowest bulk density as compared to other drying methods. Microwave-infrared combined drying methods revealed a higher retention of β-carotene (85.06-90.14%) and this seem to be mainly due to the fast drying rate of the combined drying methods. The microwave also had a higher retention of β-carotene, followed by infrared, while oven and freeze-drying method showed a lower retention of β-carotene as a result of longer drying periods, exposure to oxidative and destructive conditions, which can cause the degradation of β-carotene (high drying temperature, endogenous enzymes, and oxidative agents). The study suggest that a combination of microwave-infrared or microwave alone are energy efficient alternatives to produce dried orange fleshed sweet potato flour, with minimal reduction in β-carotene and change in functional properties
Extended shelf life milk processing : effect of cleaning-in-place (CIP) on the survival of bacillus subtilis
(University of Pretoria, 2021) Buys, Elna Maria; nanamhlaado93@gmail.com; Adonis, Nanamhla
Bacillus subtilis vegetative cells have been found to remain in dairy processing equipment such as filler nozzles and heat exchangers even after cleaning processes such as Cleaning in Place (CIP). The cells form biofilms on the stainless steel and continue to grow and spread, detach, and move to other processing areas and equipment further down the processing line, leading to cross- contamination and ultimately accelerated spoilage of Extended Shelf Life (ESL) milk during storage post-processing at refrigeration temperatures. The objective of this study was to determine the effect of simulated CIP on the physiological state of B. subtilis cells, their attachment and subsequent growth in understanding the effectiveness of CIP and subsequent survival of B. subtilis vegetative cells. Three B. subtilis strains previously isolated from packaged ESL milk and ESL milk stored at 4 and 7 °C were subjected to a simulated CIP procedure with cells then subjected to flow cytometry and scanning electron microscopy. Enzymatic analysis was performed to vi determine the capability of the vegetative cells to produce proteolytic and lipolytic enzymes and the subsequent effect of these enzymes on the quality and shelf life of ESL milk. Flow cytometry results showed that approximately 98% of B. subtilis cells were physiologically dead after simulated CIP treatment, with 0.1% remaining viable. SEM revealed that the cells could reattach to stainless steel after simulated CIP treatment, and some cell multiplication was evidenced. The enzyme assays showed that all the B. subtilis strain cells continued to produce proteolytic enzymes after treatment, and only one strain could produce lipolytic enzymes. Over the 28 days of storage at 7 and 10 °C, the cells could grow in the milk. The results showed that simulated CIP treatment did not influence cell reattachment with bacterial growth evident 28 days at 7 and 10 °C after the treatment, accelerating the deterioration of the ESL milk. The industry must identify easier non- evasive methodologies of identifying biofilm formation and develop new food processing equipment coated surfaces that discourage the attachment of bacterial cells and spores.

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