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Theses and dissertations (Applied Sciences)

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    The prebiotic effects of amadumbe (Colocasia Esculenta) and okra (Abelmoschus esculentus) mucilage
    (2023) Gajadhar, Sharmista; Amonsou, Eric Oscar; Mchunu, Nokuthula Peace
    Prebiotics have been shown to aid in the improvement and maintenance of human health through positive manipulation of gut microbiota. Diet-induced changes in gut microbial diversity has been recognized as a factor which contributes to the rising epidemics of chronic illnesses in both developed and developing countries. Traditional crops, amadumbe (Colocasia esculenta) and okra (Abelmoschus esculentus (L.) Moench) offer nutritional security to many communities in South Africa. These crops are rich in mucilage and are presumed prebiotics. Structural composition and functional properties of polysaccharides like mucilage are suggested to influence their fermentability by gut microbiota and potential health effects. The purpose of this study was to investigate the prebiotic effects of amadumbe and okra mucilages for potential application as dietary supplements. Mucilage was extracted from amadumbe and okra by cold water extraction. Purified mucilage was obtained by Sevag method, lipid removal and thereafter dialyzed. The composition and structure of crude and purified mucilage were analyzed using Fourier transform infrared spectroscopy (FT-IR), size exclusion chromatography (SEC) and high pressure liquid chromatography (HPLC). Functional properties including water and oil holding capacity, swelling and solubility were determined. The prebiotic potential of amadumbe and okra mucilage was carried out by in- vitro fermentation using human faecal sample. Glucose was the common monosaccharide present in both amadumbe and okra mucilage. Monosaccharides present in amadumbe mucilage were arabinose, mannose and xylose, while galactose, ribose and rhamnose were the main monosaccharides present in okra mucilage. The presence of β-glucan was found to be higher 0.20 g/100 g in amadumbe mucilage than in okra mucilage 0.07 g/100 g. The resistant starch content in amadumbe mucilage was higher 4 g/100 g than in okra mucilage 0.7 g/100 g. Asparagine, proline, glutamine, and threonine were the most common amino acids found in both amadumbe and okra mucilage samples. Purified amadumbe and okra mucilage displayed the same characteristic peaks as crude amadumbe and okra mucilage in the FT-IR spectrum but at a lower intensity suggesting that purification contributed to a more stable and uniform structure. The FT-IR spectrum indicated the presence of uronic acid and hydroxyl groups which confirm the existence of carbohydrate in both amadumbe and okra mucilage. The molecular weight of crude amadumbe and okra mucilages ranged between 219 and 224 kDa while molecular weight of purified amadumbe and okra mucilage ranged between 220 and 244 kDa. The purification process was seen to improve functional properties such as the water holding capacity, swelling and solubility of mucilages. In comparison to okra mucilage, crude and purified amadumbe mucilage showed low water holding capacity 5 and 9 g/100 g and high percentage solubility 61 and 73%. Amadumbe mucilage had a slightly higher oil holding capacity 11 g/100 g in comparison to okra mucilage 10 g/100 g. During in-vitro fermentation, inulin (positive control) rapidly decreased the pH of the fermentation medium from 7.0 to 6.5, in comparison to amadumbe (7.0 to 6.7) and okra (7.0 to 6.8) mucilage. At the end of fermentation inulin had maximum gas production of 233.19 mL, followed by amadumbe mucilage 158.98 mL and okra mucilage 113.98 mL. These results suggest inulin is more easily fermented by microbes compared to amadumbe and okra mucilage. Gut microbiota analysis at phylum level showed that amadumbe mucilage stimulated the proliferation of Actinobacteria and reduced the presence of Firmicutes in comparison to okra mucilage. At species level, okra mucilage promoted the growth of Bacteroidaceae bacteroidetes, Bacteroides ovatus and Bacteroides uniformis. These species are known to assist in protection of the gut and are capable of providing nutrients to other microbial species. This suggest that amadumbe and okra mucilages are fermented differently by gut microbiota possibly due to differences in their structure and composition. This study concluded that amadumbe and okra mucilages has potential to be utilized as an emerging prebiotic in food applications or as supplements.
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    The effects of laccase and xanthan gum on the quality of glutten-free amadumbe bread
    (2018) Seke, Faith; Kudanga, Tukayi; Amonsou, Eric Oscar
    Celiac disease (CD) is an auto-immune disorder that is triggered by the consumption of gluten in predisposed individuals. The only remedy that has been proposed thus far is total exclusion of gluten from the diet. This may be the most difficult task to most celiac disease patients for most of the convenient and widely consumed baked products such as bread are prepared using ingredients that contain gluten. The replacement of gluten in the baking industry comes with some implications on the overall quality of the baked products, especially bread. It has been observed that gluten-free baked products currently on the market are of poor texture, less volume, not visually appealing and have a bad taste. Hence, the need for polymeric substances that can mimic gluten properties, yielding baked products with similar characteristics as the gluten-containing counterparts. Various crops such as rice, sorghum, sweet potato and cassava have been used and additives such as hydrocolloids, protein-based ingredients, emulsifiers and enzymes included to improve gluten-free bread quality. The use of carbohydrate-rich tubers and protein-rich legumes as gluten-free ingredients shows great potential in the food industry. Amadumbe (Colocasia esculenta) is a carbohydrate rich tuber which is highly underutilized in South Africa and contains vast amounts of mucilage, a hydrocolloid which can be of great help to improve dough rheology. Hydrocolloids have been reported in literature to have the ability of improving dough water holding capacity and improving dough viscosity hence facilitating gas retention and impacting on the overall quality of the baked product. However, despite the presence of mucilage, amadumbe is very low in protein and it is difficult to produce bread with properties that resemble gluten-containing bread. Hence the need for protein supplementation which may also potentially facilitate protein cross-linking during bread making. Legume proteins from crops such as soy bean and bambara groundnuts contain abundant quantities of lysine, tyrosine and cysteine which could potentially be manipulated through the use of enzymes such as laccase in order to initiate the formation of a network similar to gluten. The project investigated the effect of laccase and xanthan gum (a hydrocolloid) on the quality of gluten-free bread supplemented with bambara groundnut flour and soy protein isolate as protein sources. Flour blends were prepared using a ratio of 70:30 (amadumbe flour: bambara groundnut flour) and 88:12 (amadumbe flour: soy protein isolate) based on a targeted protein content of 16 g/100 g and the quality properties were determined. Colour analysis showed that amadumbe flour had a higher L* value compared to the other flours and the blends, showing that amadumbe can be used in applications where food colour contributes to food perceptions. However, when bambara groundnut flour and soy protein isolate were added the L* value decreased. The nutritional profile of the individual flours and the blends showed that amadumbe flour protein content was improved with the addition of bambara groundnut flour and soy protein isolate in the above-mentioned ratios. The protein content of amadumbe increased from 2.36 g/100 g to 15.87 g when bambara groundnut flour was added and to 16.10 g/100 g when soy protein isolate was added, values that were close to the targeted protein content. Incorporating bambara groundnut flour and soy protein isolate in amadumbe flour resulted in improved water absorption capacity, foam capacity and stability as well as emulsion capacity and stability of the amadumbe flour. However, there was no significant difference in oil absorption capacity between amadumbe flour and the blends. The blends were then used to formulate different bread samples incorporating the enzyme laccase (25 nkat/g flour) and a hydrocolloid, xanthan gum (1%). Laccase-mediated treatment of gluten-free amadumbe dough resulted in a 30% decrease in the free sulfhydryl groups and a 40% decrease in phenolic content indicating that crosslinking had occurred. Laccase action resulted in a 64% increase in bread specific volume and a 32% decrease in bread crumb hardness. Sensory analysis showed that laccase-treated bread samples were more acceptable compared to the non-treated bread samples in terms of appearance, texture, aroma and taste. The acceptability index varied between 46% and 86.2%. This study showed that there is great potential of laccase in gluten-free bread making. The addition of 1% xanthan gum to amadumbe dough supplemented with bambara groundnut flour and soy protein isolate resulted in gluten-free amadumbe bread with improved crumb texture and specific volume, and decreased the rate of moisture loss. Sensory analysis also revealed that gluten-free amadumbe bread with added xanthan gum was more acceptable compared to the bread samples without xanthan gum. The acceptability index of the bread samples ranged between 40% and 85%. The resulting bread with xanthan gum showed that hydrocolloids such as xanthan gum can be successfully used in the development of gluten-free baked products. Overall, this study has shown that the incorporation of laccase and xanthan gum to gluten-free amadumbe bread results in bread with improved and acceptable bread properties.
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    Characterization and application of amadumbe starch nanocrystals in biocomposite films
    (2017) Mukurumbira, Agnes R.; Amonsou, Eric Oscar; Mellem, John Jason
    Amadumbe (Colocasia Esculenta) commonly known as Taro is an underutilized tuber crop that produces underground corms. It is a promising tropical tuber grown in various parts of the world including South Africa, where it is regarded as a traditional food. It is a significant subsistence crop, mostly cultivated in rural areas and by small scale farmers. Amadumbe is adapted to growing in warm and moist conditions. The tubers are characterised by a high moisture content and consequently high post-harvest losses. The losses can be minimized through the utilization of various preservation techniques such as flour and starch production. Amadumbe corms may contain up to 70-80% starch. The starch granules are characterised by a small size and relatively low amylose content. The combination of high starch content, low amylose and small starch granules thus make amadumbe a potentially good candidate for nanocrystal production. In this study two amadumbe varieties were utilized to extract starch. Amadumbe starch nanocrystals (SNC) were produced using an optimized hydrolysis method. The physicochemical properties (morphology, crystallinity, thermal properties) of the resulting SNC were investigated. The SNC were then applied as fillers in three different matrices namely, amadumbe starch, potato starch and soy protein. The influence of the SNC at varying concentrations (2.5, 5 and 10%) on the physicochemical properties of bio-composite films was examined. Amadumbe starch produced a substantially high yield (25%) of SNCs. The nanocrystals appeared as aggregated as well as individual particles. The individual nanocrystals exhibited a square-like platelet morphology with sizes ranging from 50-100 nm. FTIR revealed high peak intensities corresponding to O-H stretch, C-H stretch and H2O bending vibrations for SNCs compared to their native starch counterparts. Both the native starch and SNC exhibited the A–type crystalline pattern. However, amadumbe SNCs showed a higher degree of crystallinity possibly due to the removal of the armorphous material during acid hydrolysis to produce SNCs. Amadumbe SNC showed slightly reduced melting temperatures compared to their native starches. The SNC presented similar thermal decomposition properties as compared to their native starches. In general, the inclusion of SNCs significantly decreased water vapour permeability (WVP) of composite films whilst thermal stability and tensile strength were increased. The degree of improvement in the physicochemical properties of the films varied with the type of matrix as well as the concentration of the nanocrystals. It generally seemed that the enhancement of the physicochemical properties of starch matrices occurred at a lower SNC concentration in comparison to that of soy protein films. Amadumbe SNC can indeed potentially be used as a filler to improve the properties of biodegradable starch and protein films