Theses and dissertations (Applied Sciences)
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Item Production process improvement and characterization of starch nanocrystals(2023-05) Nzama, Nkosingiphile Lucky; Amonsou, Eric OscarStarch nanocrystals (SNCs) are promising biomaterials for novel applications in foods, cosmetics, and medicine. In general, acid hydrolysis below the gelatinization temperature of starch is the most common method used for nanocrystals production. Major drawbacks associated with this method are the extended hydrolysis time required (up to 5 days) and the low yield (4–15%) of SNCs. Different methods, including physical and enzymatic pretreatments of starch prior to acid hydrolysis, have been investigated. Among these methods, enzymatic hydrolysis can be regarded as a promising and green strategy for the creation of pores in starch to enhance acid diffusion into the inner regions during SNCs fabrication. Debranching enzymes such as pullulanase are gaining attention in the food industry due to their ability to modify the starch structure and properties through selective hydrolysis of the branched chain of α-1,6-glycosidic bonds. However, pullulanase has not yet been applied as a pretreatment method aiming at starch nanocrystal preparation. Therefore, the pretreatment of starch granules with pullulanase and β-amylase (i.e., to hydrolyze the linear α-1,4-linkages) concurrently could be a novel technique to modify starch surfaces for faster production of SNCs and improved yield. To improve the efficiency of starch nanocrystals production and properties, pullulanase (15 U/g starch) was used alone or together with β-amylase (50 and 100 U/g starch) to modify the starch before acid hydrolysis. The compound enzyme system of pullulanase:β-amylase (15 : 50 U/g starch) had the most pronounced effect on starch morphology compared to a single enzyme system by creating a dense and more porous structure on starch surfaces as evidenced by microscopy images, a high degree of oil absorption and extent of hydrolysis data. Nanocrystals were produced after 3 days with modified starches instead of 5 days. The yield of SNC was approx. 25 wt.%, which is 3 times greater than that of the conventional SNC preparation method. SNC derived from the modified starches were small in size (less than 50 nm) and appeared mostly as platelet and isolated round particle aggregates. Nanocrystals from modified starches showed the A-type crystalline structure similar to the native starch, but with a significant increase in the degree of crystallinity (from 32.85% to 45.28%.), and the short-range molecular order during the early stage of acid hydrolysis. Starch hydrolysis using compound enzymes consisting of pullulanase and βamylase hydrolysis seems to be the most effective and green to produce SNC in a shorter time and with increased yield and enhanced properties. SNCs were incorporated in different concentrations (0, 5, 10, 15, and 20 wt.% starch) together with stearic acid to improve cassava starch-based nanocomposite film properties using a solution casting method. The addition of SNCs from 5 to 15% in combined with stearic acid into starchbased nanocomposite films presented better water resistance, water vapor permeability, and tensile strength than native cassava starch film. Conversely, beyond 15% SNC content, nanocrystals seem to aggregate which impaired the tensile strength of the nanocomposite films. The surfaces of the nanocomposite films were relatively smooth and homogenous after the addition of nanocrystals at up to 15 wt.% concentration compared to native starch film as demonstrated by the atomic force microscopy (AFM). Furthermore, the opaqueness of the nanocomposite films progressively increased with the SNC content, which might be beneficial in the packaging of foods that are easily degraded when exposed to light and high moisture. XRD analysis revealed sharp peaks at approximately 2θ of 13.5° and 20.3°, which are characteristics of typical V-type crystalline pattern in starch films prepared with added steric acid. This further indicates the formation of amyloselipid complexes in films. The inclusion of SNC in films also enhanced their thermal stability. Therefore, the combined effect of SNC at different concentrations and stearic acid into cassava starch-based films was a successful approach to further improve the mechanical reinforcement and barrier properties of nanocomposite films.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 Influence of growth locations on physicochemical properties of starch and flour from amadumbe (Colocasia esculenta) genotypes(2017) Mawoyo, Bruce; Amonsou, Eric Oscar; Gerrano, Abe S.Amadumbe commonly, known as taro is a traditionally underutilised tuber crop in Southern Africa. Nutritionally, amadumbe corms contain appreciable levels of carbohydrate mainly in the form of starch which is resistant to digestion. It also contains mucilage, a soluble fibre, which is good for the human digestive health. Thus, amadumbe starch and mucilage can be used as functional ingredients in food formulations. The aim of this research was to investigate the effects of genotypes and growth location on the physicochemical properties of amadumbe flour and starch. Eighteen (18) amadumbe genotypes grown in Roodeplaat, Gauteng and Umbumbulu, Kwazulu-Natal, South Africa, were studied. Roodeplaat received a lower annual average rainfall (514 mm) and high environmental temperature (24oC) compared to Umbumbulu (828 mm, 19oC) during the cropping season. Specifically, the influence of growth location and genotypes on the chemical composition (proximate composition and mineral contents) as well as the functional properties of amadumbe flours were investigated. Furthermore, starch was extracted and its physicochemical and functional properties were also studied. The carbohydrate contents (73-81%) of amadumbe flours were substantially high and varied with growth location. Mucilage contents (6-9%) were very low across genotypes in both locations. Water absorption and oil absorption capacities positively correlated to carbohydrates and mucilage in the flour irrespective of growth locations. Swelling power and solubility index was influenced by the amylose content of the flour. Genotype and growth location significantly affected the pasting properties of amadumbe flour. The pasting temperature was very high (approx. 90oC) across genotypes in both locations, while peak viscosity differed significantly (54-242 RVU) for genotypes grown in different environments. The amylose contents (0-14.4%) of amadumbe starches were low and varied significantly with growth location and among genotypes. Three genotypes, G2, G20, and G21 grown in Roodeplaat lacked amylose. Amadumbe starches showed reflective peaks at 2θ=15o and doublet at 17o, 18o and 24o typical of A-type starches. Amadumbe genotypes had small sized (1-5 µm) and polygonal starch granules. Functional properties including water absorption, swelling power, gelatinisation temperature and peak viscosity significantly positively correlated with amylose content. These findings further suggest that water availability could have a major effect on starch synthesis as the two locations received a different amount of rainfall during the growing season. Findings from this study are important for future improvement programmes and selection of appropriate genotypes for industrial production or food application of amadumbe flour and starch.Item Characterization and application of bambara groundnut starch-lipid complexes(2017) Oyeyinka, Samson Adeoye; Amonsou, Eric Oscar; Singh, SurenBambara groundnut (Vigna subterranea) is an indigenous underutilised leguminous crop to Africa. It is a good source of protein and carbohydrate including starch. Bambara groundnut is a traditional crop grown mainly for subsistence in Southern Africa. Bambara groundnut has the advantage of being drought tolerant and can thrive in hot temperatures and poor soil conditions. Therefore, it has great potential as an alternative crop to soya bean and peanuts for cultivation and utilisation. Bambara groundnut starch can potentially be used for various industrial applications. However, native starches are not suitable for most industrial applications, hence the need for modification. Bambara groundnut starch has been previously modified using physical and chemical modification methods. Natural alternatives such as the use of lipids are being sought to modify starches due to the associated risk with chemically modified starch. In this research, Bambara groundnut starch was modified with lipids to improve functional properties, utilisation and application. Specifically, the physicochemical properties of native Bambara groundnut starch obtained from five Bambara groundnut genotypes and three landraces (maroon, brown and cream) were determined. Bambara groundnut starch was modified with lipids (palmitic acid, stearic acid, oleic acid, linoleic acid and lysophosphatidylcholine) and the physicochemical properties of the modified starch were investigated. Further, the influence of high-pressure homogenization on complexation of Bambara groundnut starch with lipids was assessed in comparison with maize and potato starches. Lastly, an application of modified Bambara groundnut starch in biofilm production was also studied. Bambara groundnut landraces generally showed higher amylose contents (approx. 33%) than the genotypes (approx. 28%). Differences were observed in the crystalline patterns of these starches. Bambara groundnut genotypes exhibited the C-type-crystallinity, while the landraces showed the unusual A-type pattern. In terms of functionality, landrace starches showed better swelling than the genotypes. Subsequent studies on modification used maroon Bambara groundnut starch since the amylose content was higher than other landraces and there was a consistent supply of the grains during the period of the study. Generally, Bambara groundnut starch showed higher complexing ability with all the lipids than maize and potato reference samples. These differences in complexing ability among the starches could be due to the variation in amylose contents (Bambara groundnut starch: 31.5%, maize: 22.5% and potato: 24.6%). Fatty acids complexed better with Bambara groundnut starch than lysophosphatidylcholine, which could be due to the structural differences in comparison with the lysophosphatidylcholine molecule. The number of fatty acid in the glycerol backbone and the additional steric hindrance of the polar phosphatidic acid group in the lysophosphatidylcholine may have reduced its complexing ability. Among the fatty acids, palmitic acid complexed better than stearic and the unsaturated fatty acids, possibly due to its short chain length compared to other fatty acids. Bambara groundnut starch showed reduced peak and setback viscosities in the presence of stearic acid, linoleic acid and lysophosphatidylcholine, suggesting the formation of V-amylose complex. Bambara groundnut starch pasted with lipids displayed reduced gelling ability compared to their unmodified counterparts. XRD studies of freeze-dried paste revealed peaks at 2Ѳ = 7.4, 12.9 and 19.9o confirming the formation V-amylose complexes in Bambara groundnut starch. Modification of Bambara groundnut starch with lipids resulted in reduced digestibility. High-pressure homogenization significantly increased the complexing ability of Bambara groundnut starch with lipids. Homogenized Bambara groundnut starch-lipid complexes generally exhibited higher complex index than their unhomogenized counterparts. The higher complexing ability could be attributed to the effect of high-pressure which may have enhanced greater dispersion of lipids in the starch-water system. X-ray diffraction studies also revealed the formation of higher complexes as shown by high intensities at peaks (2Ѳ= 7.4, 12.9 and 19.9o) corresponding to V-amylose complexes. Bambara groundnut starch-lipid complexes displayed significantly higher melting temperatures (95.74-103.82oC) compared to native uncomplexed starch (77.32oC). Homogenized Bambara groundnut starch complexes were non-gelling while the unhomogenized types produced weak gels, with G′ ˃ G″ in the range of 0.1- 10 Hz. Complexation of Bambara groundnut starch with lipids using high-pressure homogenization may be employed in the production of modified starch with non-gelling properties and higher thermal stability suitable for certain industrial application, such as fat replacers in mayonnaise, frozen foods and desserts for a better mouth feel. The physicochemical and mechanical properties of biofilm prepared from Bambara groundnut starch modified with stearic acid at varying concentrations of 0, 2, 4, 6, 7 or 10% were further studied. By SEM, Bambara groundnut starch films containing stearic acid (˃ 2%) showed a progressively rough surface compared to those with 2% stearic acid and the control. The addition of 2% stearic acid to Bambara groundnut starch film reduced water vapour permeability by approximately 17%. However, mechanical properties of starch films were generally negatively affected by stearic acid. Bambara groundnut starch film may be modified with 2% stearic acid for improved water vapour permeability and thermal stability with minimal effect on tensile strength.