Huang, Ying2025-08-182025https://hdl.handle.net/2097/45250Waxy sorghum contains essentially only amylopectin in its endosperm starch and has unique properties that could be potentially used as value-added food ingredients and increase its value compared with normal sorghum. Currently, waxy maize starch is the preferred base starch, which is further chemically modified to produce food thickeners. However, clean label is an emerging global trend in packaged foods, and waxy sorghum flours and starches have the potential to be directly used as effective thickeners in food applications. In this study, a comprehensive investigation was conducted to evaluate the potential of waxy sorghum starches and flours as food thickeners by examining their structural and functional properties in comparison to waxy maize starch. The objectives of the first part of the study were to develop an efficient process for isolating starch from decorticated and whole waxy sorghum grains using alkaline protease, and to compare the properties of starches isolated by enzymatic with that of starches isolated from traditional wet milling methods. To evaluate the efficiency and effectiveness of the isolation process, key parameters such as starch recovery, yield, residual protein, ash, damaged starch content, color, as well as pasting and thermal properties were determined. Starch recovery showed no statistically significant differences among the three methods, and all isolated starches exhibited desired purity regardless of the method employed. However, enzymatic treatment methods not only produced starches with lower residual protein (0.18-0.22%) but also resulted in significantly greater peak (1992-2023 cP), breakdown (1123-1172 cP), and setback viscosities (275-355 cP) in comparison to the wet milling. The starches isolated by wet milling and enzymatic treatment of decorticated sorghum exhibited similar onset and peak gelatinization temperatures, while both methods produced starches with better color quality (higher L*, lower b*) compared to the enzymatic treatment of whole sorghum. Overall, the enzymatic treatment of decorticated sorghum could be used as an effective method for starch isolation at the laboratory scale, with promising potential for application in industrial-scale processes. The objectives of the second part of the study were to identify waxy sorghum starches and flours with greater thickening power and cold storage stability, determine the relationship between pasting properties and morphology of waxy starch during cooking, understand how the retrogradation properties are affected by chain-length distribution, and investigate correlations between the starch content, starch structural features, and functional properties of waxy sorghum starches and flours. Waxy sorghum starches exhibited a greater degree of granule swelling and significantly higher pasting viscosities compared to waxy maize starch. Starches with lower retrogradation tendency contained a higher proportion of chains with DP 6-11 and a lower proportion of chains with DP 12-24. The peak, setback, and final viscosities of waxy sorghum flours were significantly positively correlated with the corresponding viscosities of their starches (peak: r = 0.606*; setback: r = 0.635*; final: r = 0.656*, p < 0.05). The total starch content was only found to be significantly correlated with setback (r=0.694*) and final viscosities (r=0.682*). In contrast, grain hardness exhibited a significant negative correlation with the peak (r =-0.785*) and breakdown (r =-0.780**, p<0.01) viscosities of waxy sorghum flours. The third part of the study was conducted to investigate the impact of protein matrix on pasting properties of waxy sorghum flours. The objectives were to obtain waxy sorghum flours with different protein levels using enzymatic treatment or solvent extraction methods and to investigate how the protein matrix affects the pasting properties after cooking by using a confocal laser scanning microscope (CLSM). Protease treatment was an effective way to hydrolyze and remove part of the protein and obtain flours with reduced protein contents. Unmodified waxy sorghum flours with a higher protein content exhibited lower pasting peak viscosity due to the protein matrix inhibiting starch swelling by forming a physical network around starch granules and restricting the swelling of starch granules during pasting. The hydrolysis of the protein matrix resulted in increased peak pasting viscosities by disrupting the protein network that restricted the swelling of starch granules. These findings show the critical role of the proteins in modulating the functional properties of waxy sorghum flours, providing valuable insights for optimizing their use in food applications, such as effective thickeners and gluten-free products.en-USWaxy sorghumStarch isolationIodine stainingPasting propertiesChain-length distributionProtein matrixThesis