Iron bioavailability, nutritional and health-promoting properties of extruded sorghum porridge fortified with Baobab fruit, moringa leaves and Bambara groundnut

Abstract

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.