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. / Centre for Nutrition / PhD / Unrestricted

Thesis(M.Sc.(Agriculture Horticulture)) -- University of Limpopo, 2019 / Innovative methods of preserving the quality of traditionally processed green leafy vegetables are underway in Africa. Improvement of processing and preservation methods of leafy vegetables is another way of overcoming perishability restrictions and guaranteeing continued quality food supply in rural areas. The objectives of this study were: to determine the effect of time-based oven-drying on (1) mineral composition, (2) proximate composition and (3) microbial profiling of cowpea (Vigna unguiculata). Separate experiments were conducted for raw and cooked cowpea leaves with four treatments, viz 0 (sun dried), 24, 48 and 72 hours of oven-drying, arranged in a randomised complete block design with 5 replications. In raw cowpea leaves, relative to control (sun-drying), oven-drying period 48hrs, significantly decreased Potassium (K), Manganese (Mn), and Sodium (Na) content in raw cowpea leaves by 6, 9 and 13%, respectively. Similarly, oven-drying period 72hrs significantly decreased Ca, Fe, Mg, Zn, P and S by 5, 11, 16, 18 and 57%, respectively. In cooked cowpea leaves, relative to control (sun-drying), oven-drying period 24hrs significantly increased Na by 18%. Similarly 48hrs oven-drying periods increased Fe and K by 6 and 8%, respectively. Similarly, oven-drying period 72hrs significantly increased Ca, Mg and Mn by 8, 8 and 3%, respectively. In contrast, oven-drying period 72hrs significantly reduced Zn, P and S by 16, 10 and 39%, respectively. Relative to control (sun-drying), oven-drying period 24hrs significantly increased fat by 46% in raw cowpea leaves, however oven-drying period 72hrs significantly decreased protein, moisture, ash, fibre and carbohydrate by 10, 29, 18, 0.5, and 7% respectively. In contrast, relative to control (sun-drying), 72hrs increased energy by 3%. In cooked cowpea leaves, relative to control (sun-drying), ovendrying period 24hrs significantly increased energy by 1%. In contrast, relative to control (sun-drying) 72hrs oven-drying period decreased energy by 1%. Similarly, oven-drying 72hrs significantly decreased protein, moisture, ash, fat, fibre and carbohydrate by 8, 14, 13, 19, 0.4 and 10% respectively. Relative to control (sun-drying), oven-drying periods 24hrs significantly increased Staphylococcus spp. in raw cowpea leaves by 6%, respectively. Relative to control (sun-drying) 72hrs oven-drying period significantly decreased Shigella spp. by 92%, respectively. In cooked leaves, relative to control (sundrying), 72hrs drying periods decreased both Shigella spp. and Staphylococcus spp. by 99 and 21%, respectively. Total coliforms unit of Salmonella spp, Escherichia coli, Pseudomonas spp, and Bacillus cereus were absent and/or at an undetectable level according to the Tempo Biomerieux system results. In conclusion, cooked leaves retained most essential mineral elements as compared to raw when subjected to 72hrs of ovendrying as there was an improvement in the concentration of Ca, Fe, K, Mg, Mn and Na. However, in both raw and cooked cowpea leaves proximate composition was negatively affected as there was a decrease in protein content. Oven-drying period of 24 hours can be used to minimize the loss of protein. Cooked cowpea leaves subjected to 72hrs of oven-drying had least total coliforms for both Shigella spp and Staphylococcus spp, therefore have potential to serve as an alternative to sun-drying to reduce microorganism causing spoilage in leafy vegetables. Drying raw cowpea leaves under oven-drying periods less than 72 hours should be avoided as it reduces the mineral concentration and increase microbial count of microorganisms responsible for spoilage / National Research Foundation (NRF)

Concern regarding the decline in the knowledge and use of indigenous green vegetables exists in many southern African regions including Swaziland. Reasons for this are, amongst others, attributed to a lack of inter-generational knowledge transfer, the influence of westernisation and changing food values and attitudes, as people nowadays regard indigenous green leafy vegetables as a low status food. It is imperative that knowledge of these foods be documented before it is lost to future generation. Indigenous green leafy vegetables have long been considered healthier options than the many recently introduced western-orientated foods, which are closely linked to chronic lifestyle diseases. The aim of this study was to determine, describe and compare the knowledge of indigenous green leafy vegetables among two generations of rural Swazi women from the Eluyengweni community, and how it manifests in their food practices. Studies on indigenous green leafy vegetables in Swaziland are limited. This study will fill the knowledge gap in this field. The human ecological perspective was adopted as theoretical perspective and an explorative mixed method approach was followed. Qualitative data was collected through focus group discussions with younger (25-45 years) and older (over 45 years) women. Face-to-face structured interviews provided quantitative data on the knowledge the women had of indigenous green leafy vegetables, including their procurement, preparation, preservation and consumption patterns. The convenience sample comprised 102 respondents. Observation was done concurrently during both phases of data collection and photographs accompanied comprehensive field notes. It transpired that the availability of indigenous green leafy vegetables had declined in the community and those that were available were not easily accessible as they were located on the outskirts of the community. In spite of changes in the physical and natural environment, some indigenous green leafy vegetable species are still available in summer. It is clear that the older women, in comparison to their younger counterparts, had more knowledge of indigenous green leafy vegetables in terms of identifying them, where they are found and how they are used. Familiar and available indigenous green leafy vegetables such as imbuya (Amaranthus), chuchuza (Bidens pilosa) were preferred, and consumed fairly regularly. Although indigenous green leafy vegetables were still part of the food practices in this community, their consumption among the younger generation had declined. However, due to factors related to modernisation, economic influences and technological advancement the majority of both the younger and older participants seem to have become dependent on, and often include, western-orientated food in their food consumption patterns. Based on the results, recommendations are made to capture and preserve the knowledge of indigenous green leafy vegetables in this community and to revive interest in these vegetables and promote their consumption. / Daar is 'n besorgdheid oor die afname in kennis in die gebruik van inheemse groen blaargroentes in baie streke in Suider Afrika, insluitend Swaziland. Redes wat hiervoor aangevoer word, is onder andere, die gebrekkige oordrag van kennis van een geslag na die volgende, die invloed van verwestering asook 'n verandering in waardes en houdings aangesien mense inheemse groen blaargroentes deesdae as 'n lae status voedsel beskou. Daarom is dit noodsaaklik dat kennis oor hierdie voedsel gedokumenteer word voordat dit verlore gaan vir die nageslag. Inheemse groen blaargroentes word gesonder geag in vergelyking met Westers-georienteerde voedsel, wat op hul beurt nou geassosieer word met kroniese lewenstyl siektes. Die doel van hierdie studie was om die kennis van inheemse groen blaargroentes van twee geslagte landelike Swazi vroue van die Eluyengweni gemeenskap te bepaal, beskryf en te vergelyk asook hoe dit manifesteer in hul voedselpraktyke. Studies oor inheemse groen blaargroentes in Swaziland is beperk en hierdie studie dra by om die leemte in kennis in hierdie studieveld te vul. Die menslike ekologiese perspektief is a teoretiese perspektief gebruik en 'n verkennende gemengde metodologie is as navorsingsbenadering gevolg. Kwalitatiewe data is deur middle van fokusgroep gesprekke met beide die jonger (25-45 jaar) en ouer (ouer as 45 jaar) vroue ingesamel. Met behulp van gestruktureerde individuele onderhoude is kwantitatiewe data oor die kennis van inheemse groen blaargroentes ingesamel wat die verkryging, voorbereiding, preservering en verbruikspatrone van hierdie groentes ingesluit het. 'n Geriefssteekproef van 102 respondente het aan die studie deelgeneem. Waarnemings is gedurende beide fases van die data insameling uitgevoer en fotos en volledige veldnotas is ingesluit. Dit is duidelik dat die beskikbaarheid van inheemse groen blaargroentes in hierdie gemeenskap afgeneem het, en dit wat beskikbaar was, was nie maklik toeganklik nie, omdat dit aan die buitewyke van die gemeenskap gelëe was. Ten spyte van die verandering in die fisiese en natuurlike omgewing is sommige inheemse groen blaargroentes steeds beskikbaar gedurende die somer. Dit is duidelik dat die ouer vroue, in vergelyking met die die jonger vroue oor meer kennis van inheemse groen blaargroentes beskik het met betrekking tot die identifisering, waar hulle groei en hoe om hulle te gebruik. Bekende en beskikbare inheemse groen blaargroentes soos gewone misbredie (Amaranthus) en knapsakkerwel (Bidens pilosa) was voorkeur groente en is redelik gereeld gebruik. Alhoewel inheemse groen blaargroentes steeds deel vorm van die voedselpraktyke in hierdie gemeenskap, het die gebruik daarvan deur die jonger geslag afgeneem. As gevolg van faktore soos modernisering, die ekonomie en tegnologiese vooruitgang het die meerderheid van beide die jonger en ouer geslag afhanklik geword van westers-georienteerde voedsel en dit dikwels in hulle eetpatrone ingesluit. Die resultate van hierdie studie het bygedra dat aanbevelings oor die vaslegging en bewaring van die kennis oor inheemse groen blaargroentes in hierdie gemeenskap gemaak kon word, asook om 'n oplewing in die belangstelling in die gebruik daarvan te bevorder. / Dissertation (MConsumer Science)--University of Pretoria, 2017. / Consumer Science / MConsumer Science / Unrestricted