Unravelling the Factors that Influence Starch Chain Realignment and Interactions Within the Amorphous and Crystalline Domains of Waxy Normal and High Amylose Starches of Different Botanical Origins on Annealing

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Native starches do not have properties that make them ideally suited for applications in food products. Consequently, these starches are modified chemically to improve their stability to high temperature processing, shear, and repeated freezing and thawing. There is considerable interest in providing starches that are physically modified because no chemical reagents are used, and the physically modified starch can be used in any type of food application. Annealing (ANN) is a physical modification technique that is carried out by heating and holding starch granules in excess water (>65% w/w) for a specified length of time at a temperature close to the onset temperature of gelatinization. ANN has been shown to increase crystalline stability resulting in changes to starch properties. However, the mechanism by which these changes are achieved in starches of different amylose content is poorly understood. Against this background, the proposed research aims to understand the structural changes that occur within the amorphous and crystalline regions of the above starches subjected to ANN under similar conditions. Short term objectives: 1) To determine the influence of the internal organization of amylopectin chains (the main crystalline component of starch) on ANN induced structural changes within the crystalline lamellae, 2) To explore the structural changes that occur within the amorphous regions (amylose and some amylopectin branch points are present in these regions) on ANN, 3) To determine the contribution of amorphous regions to changes within the crystalline regions on ANN, 4) To understand the influence of ANN on starch properties. Long term objectives: 1) To create novel starches with improved physicochemical properties by selectively hydrolysing amorphous regions followed by ANN and by dual modification techniques in which ANN is combined with other physical and/or chemical modification techniques, and 2) To determine whether ANN in the presence of other plasticizers (glycerol, propylene glycol, sorbitol) are able to modify starch structure to the same extent as water. Novelty - The proposed research is original, innovative and will add new knowledge to the mechanism of ANN with respect to the structural changes at all levels of granule organization in starches varying widely in amylose content. It will also explain how changes to starch structure on ANN impacts the rate and extent of enzyme hydrolysis, reactivity towards reagents used in chemical modification, lipid complexing ability and crystalline stability. Significance - The knowledge gained from this study would enable food processors to tailor the structure of under-utilized cereal, pulse and tuber starches by using different ANN protocols to a level met by chemical modification.