Faculty of Applied Sciences
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Item Characterization and application of amadumbe starch nanocrystals in biocomposite films(2017) Mukurumbira, Agnes R.; Amonsou, Eric Oscar; Mellem, John JasonAmadumbe (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 filmsItem Enhanced production of inulinase from Xanthomonas campestris pv. phaseoli(2010) Naidoo, Kameshnee; Singh, Suren; Permaul, KugenXanthomonas campestris pv phaseoli produced an extracellular endoinulinase on various carbon sources. The highest inulinase production of 9.24 ± 0.03 IU ml¯¹by X. campestris pv. phaseoli was attained using an optimized medium comprising of 3% sucrose and 2.5% tryptone. Inulinase production in X. campestris pv. phaseoli was further enhanced through ethylmethanesulfonate mutagenesis. The resulting mutant, X. campestris pv. phaseoli KM 24 demonstrated enhanced inulinase production of 22.09 ± 0.03 IU ml¯¹after 24 h, which was 2.4 – fold higher than that of the wild type. Inulinase production by this mutant was scaled up in a 5 L fermenter yielding a final activity of 21.87 ± 0.03 IU ml¯¹with an inulinase/invertase (I/S) ratio of 2.6 after 18 h. Maximum volumetric (21 865 IU 1¯¹ h¯¹) and specific (119 025 IU g¯¹ h¯¹) productivities of inulinase were attained in a fermenter after 18h growth. Inulin hydrolysis by the crude inulinase and subsequent detection of mono- and oligosaccharides indicated the presence of an endoinulinase. The extracellular endoinulinase from the mutant KM 24 was purified to homogeneity by gel filtration chromatography and had a specific activity of 174.74U/mg. the optimum pH and temperature of the purified enzyme were found to be 6.0 and 50°C, respectively. The enzyme was stable up to 60°C, retaining over 60% activity for 30 min, but activity rapidly declined at temperatures above 60°C. The pure inulinase enzyme was also found to be stable between pH 6-9. The Lineweaver-Burk plots showed that the apparent Km and Vmax values of the inulinase for inulin were 1.15 mg/ml and 15µM/min, respectively. The Kcat value was found to be 0.145 min¯¹ with an enzyme catalytic efficiency of 0.126 mg¯¹.ml.min¯¹.This mutant demonstrated good potential for large scale production of inulinase and fructooligosaccharides.