Centre for Nutrition
http://hdl.handle.net/2263/5854
2024-03-29T13:09:58ZAntioxidant content and activity of selected African leafy green vegetables in the gastrointestinal tract (GIT) : determination using simulated GIT digestion
http://hdl.handle.net/2263/68041
Antioxidant content and activity of selected African leafy green vegetables in the gastrointestinal tract (GIT) : determination using simulated GIT digestion
Introduction
The incidence of non-communicable disease such as cancer, diabetes, and cardio vascular disease (CVD) is increasing. Major contributing factors are diets that are poor in minerals, vitamins and antioxidants. Leafy green vegetables (LGV) are an important source of these nutrients. In addition, indigenous LGV are drought resistant, robust and easy to cultivate than more exotic LGV such as spinach and cabbage. Little is known about the effects of cooking and digestion on the polyphenol, flavonoid and ß-carotene content of African LGV as well as the associated antioxidant activity. The aims of this study are firstly to evaluate the effect of pH, the digestive enzymes and the phase of digestion on the polyphenols, flavonoids and β-carotene content and associated antioxidant activity of LGVs, spinach, pumpkin, cowpea, amaranth and jute mallow. Then to determine whether following digestion the antioxidant properties of the African LGVs is better than spinach which is commercially and widely cultivated.
Spinach, pumpkin, cowpea, amaranth and jute mallow leaves were cooked for 30 minutes, the water was discarded and the remaining solid cooked LGV which is usually consumed was subjected to two methods of digestion. The first referred to as gastrointestinal model of digestion (GI) of digestion consisted only of the stomach and intestinal phase of digestion, while the second model which was more complex included the oral, stomach and intestinal (OGI) phases of digestion. Raw, cooked, pH adjusted and digested samples at each phase of digestion were collected. For each sample the total polyphenol content (TPC), the total flavonoid content (TFC) was determined with the Folin-Ciocalteu method and aluminum chloride methods respectively. The ß-carotene content was determined with HPLC. Antioxidant activity was determined with the Trolox equivalent antioxidant capacity (TEAC), the 1, 1-diphenyl–2-picrylhydrazyl (DPPH) and the oxygen radical absorbency capacity (ORAC) assays.
Cooking decreased significantly the TPC, TFC, TEAC and DPPH of spinach, pumpkin and cowpea, while the ß-carotene content of these LGV remained unchanged. For amaranth and jute mallow, cooking increased the TFC, ß-carotene and DPPH values, while their TPC and TEAC remained unchanged. All the LGVs decreased their antioxidant activity when measured by ORAC assay, except for jute mallow which was unchanged. During digestion, the pH controls had varying effects with different assays, as it did not change the TPC of spinach, pumpkin and cowpeas, but decreased that of amaranth while the TPC of jute mallow was higher. Overall, the gastric and intestinal digestion increased the antioxidant activity of all the LGVs as measured by the ORAC assay. TPC and TEAC increased significantly for spinach, pumpkin and cowpea, while their TFC remained unchanged and antioxidant activity measured with the DPPH assay was lower. For the amaranth and jute mallow the TFC was decreased, DPPH increased, while TEAC was unchanged. Except for pumpkin the ß-carotene content was reduced following digestion. In general, the effect of pH was minimal while digestive breakdown of the LGV matrix resulted in a significant release of molecules with antioxidant activity.
In the OGI model of digestion, the oral phase of digestion contributed significantly to the levels of polyphenols and flavonoids released from the matrix. The effect on ß-carotene content was variable. Antioxidant activity for all LGV was increased (TEAC assay), variable (DPPH assay) and reduced (ORAC) assay. When considering the effect determined by the ORAC assay which is considered to be the physiologically the most relevant assay, using models that only simulate gastric and intestinal digestion may over estimate antioxidant activity.
Compared to spinach the antioxidant properties of the LGVs, although in some instances statistically different, were similar to spinach. In conclusion, LGVs evaluated in this study retained to various degrees the antioxidant activity following digestion. The biggest contributing factor to these antioxidant properties was not pH but the ability of the digestive enzymes to break down the food matrix resulting the release of antioxidant molecules. Based on the findings of this study are that African LGV are an ideal source of bioactive molecules that can prevent diseases of the GIT and if bio- available can effectively reduce the risk of diabetes, cancer and CVD.
Dissertation (MSc)--University of Pretoria, 2018.
2018-01-01T00:00:00ZAntioxidant properties and cellular protective effects of selected African green leafy vegetables
http://hdl.handle.net/2263/25198
Antioxidant properties and cellular protective effects of selected African green leafy vegetables
Phenolic compounds in African green leafy vegetables (GLVs) may have a significant impact on human health. However, there is little information on the phenolic composition, antioxidant properties, as well as biological and cellular protective effects of these vegetables. The effects of boiling and extraction solvent on these compounds and on their antioxidant properties are also unknown. Phenolic content, antioxidant activity and cellular protective effects of four African GLVs in comparison with spinach, an exotic GLV, was determined. African GLVs had appreciable levels of total phenolics and antioxidant activity and in higher quantities compared to spinach. Boiling decreased the antioxidant content and activity of these vegetables and 75% acetone was more effective in extracting antioxidants from the GLVs compared to water. GLVs with high levels of phenolics also contained higher levels of antioxidant activity, suggesting that phenolics are likely to have contributed to radical scavenging activity of these vegetable extracts, even though the degree of scavenging varied in each extract of the vegetable species. The flavonoid compositions of raw and boiled African GLVs and spinach were determined using high-performance liquid chromatography. Epicatechin and rutin were the most dominant flavonoids found in both water and 75% acetone extracts. Among water extracts, pumpkin contained higher concentrations of detected flavonoids, while among the acetone extracts, cowpea exhibited higher concentrations. The effect of boiling was dependent on the type of vegetable and the specific flavonoids. There were no major differences observed between the type of flavonoids detected in extracts of African GLVs and those in spinach. However, similar to the results of total phenolics and antioxidant activity, the 75% acetone extracts of African GLVs also exhibited higher amounts of flavonoids than spinach. The protective effects of GLVs against oxidative haemolysis were dependent on the type of vegetable species. Boiling had variable effects depending on the species. The highest level of protection of erythrocytes against oxidative damage was offered by amaranth extracts, while extracts of raw jute mallow contributed to the damage of erythrocytes. The highest antioxidant protection activity against oxidative damage in plasmid DNA was offered by extracts of jute mallow and lowest by spinach.<p. For the cell viability assays, GLVs were evaluated to determine their cytotoxicity levels and functional role in oxidative damage. The results of the long-term cell viability (i.e. MTT, NR and CV) assays indicated no cytotoxicity, while the short-term cell viability (i.e. DCF) assay indicated that all extracts of raw GLVs were significantly (p < 0.05) cytotoxic to SC-1 fibroblast and human adenocarcinoma colon cancer (Caco-2) cells than extracts of cooked samples, and the levels of toxicity in the extracts of spinach was higher than in African GLVs. These results indicate that there was an initial cytotoxic effect as extracts of raw GLVs were added to the cells. However, after about 72 h, the cells recovered from the initial shock and started proliferating as usual. In the presence of peroxyl radicals, extracts of African GLVs exhibited higher protective effects against oxidative damage in both types of cell cultures than extracts of spinach. These results indicate that these protective effects could be attributed to the presence of phenolics and antioxidant properties of these extracts. Although boiling reduced the antioxidant content and activity of African GLVs, the levels remained higher than in spinach. Boiling also decreased the cytotoxicity and cell damage caused by extracts of raw GLVs samples. African GLVs are consumed after boiling, and therefore the observed cytotoxicities might not be experienced in practical terms. African GLVs have therefore a potential to reduce the risk and development of diseases associated with oxidative stress in communities that consume these vegetables.
Thesis (PhD)--University of Pretoria, 2012.
2012-06-07T00:00:00ZEffects of reducing phytate content in sorghum through genetic modification and fermentation on in vitro iron availability in whole grain porridges
http://hdl.handle.net/2263/20315
Effects of reducing phytate content in sorghum through genetic modification and fermentation on in vitro iron availability in whole grain porridges
Kruger, Johanita; Taylor, J.R.N. (John Reginald Nuttall); Oelofse, Andre
Improved iron availability from sorghum porridges will benefit many malnourished communities in rural
Africa, where there is a high prevalence of iron deficiency. This research compared the efficacy of reducing
sorghum phytate content by genetic modification (GM) and natural lactic acid fermentation on
in vitro iron availability in porridges. GM low phytate, non-tannin (38% phytate reduction) and tannin
(36% phytate reduction) sorghums and their null controls were processed into thick unfermented and fermented
porridges. The inhibitory effect of the tannins seemed to prevent any increase in in vitro iron
availability, regardless of the level of phytate reduction. Only the additive effect of GM in combination
with fermentation in reducing the phytate content appeared to cause a substantial increase in in vitro
iron availability in the GM fermented porridge (30%) made from the non-tannin line, compared to the
GM unfermented porridge (8.9%) or the fermented porridge (17.6%) of the control sorghum. This could
be of nutritional significance.
2012-03-01T00:00:00ZSelenium concentration of maize grain in South Africa and possible factors influencing the concentration
http://hdl.handle.net/2263/19835
Selenium concentration of maize grain in South Africa and possible factors influencing the concentration
Courtman, C.; Van Ryssen, J.B.J.; Oelofse, Andre
A total of 896 maize grain samples were obtained from all the maize silos throughout South Africa (231 silos) and analysed for selenium (Se) content. This information was used to compile a regional distribution map of the Se content of maize grain in South Africa. Of the samples analysed, 94% contained below 50 μg selenium/kg DM and can thus be classified as deficient from an animal and human nutritional point of view. Maize grain in South Africa is therefore a poor source of Se for animals and humans. The geographical distribution of Se values of maize grain is consistent with that of previous studies on the Se status of herbivores in South Africa, suggesting that plants growing in most of the maize-producing areas of the country contain low concentrations of Se. However, these findings contradict those of the soil Se status in the country as reported by the Agricultural Research Council’s Institute for Soil, Water and Climate, which states that the eastern part of the maize-producing areas of the country tends to have adequate to high soil Se levels and the western areas to have low levels. These contradictory results can be explained to a large extent by the varying soil pH throughout the country. Soil pH plays a primary role in the availability of selenium to plants. Although the eastern parts of the country tend to have high Se concentration in the soil, it is not available to the maize plant owing to a low soil pH, while in the western parts of the country, where soil pH may be suitable for Se uptake by plants, there seems to be an inadequate concentration of available Se in the soil.
2012-01-01T00:00:00Z