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Millet Starches: Structural Characteristics and Glycemic Attributes

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Title: Millet Starches: Structural Characteristics and Glycemic Attributes
Author: Annor, George Amponsah
Department: Department of Food Science
Program: Food Science
Advisor: Koushik, SeetharamanMassimo, Marcone
Abstract: The hypoglycemic property of millet can be exploited in developed countries for the management of type II diabetes and its complications. Understanding the attributes that confer this hypoglycemic property in millet is important in maintaining its low glycemic index following processing. This study investigated the physical and molecular characteristics of starches from pearl, proso, foxtail and finger millets, grown in Ontario, Canada, as well the effects of starch-protein-lipid interaction on millet starch hydrolysis rates and glycemic index. Proso and foxtail millet starches had similar starch characteristics but were different from finger and pearl millet starches, which were also similar. The former had more of short amylose chains with short chain segments between branch points in their branched amylose. Finger millet amylopectin crystals, melted over the widest temperature range (10.2°C), compared to pearl, foxtail and proso millet starches. The unit and internal chain profiles of the millet amylopectins showed significant (P < 0.05) differences between the starches, with values of 17.9–18.1 and 11.9–12.3 calculated for average chain length (CL) and external chain length (ECL) respectively. Millet amylopectin could be structurally classified as type 2, based on the classification of amylopectins (Bertoft et al 2008). Removal of proteins, lipids or both significantly (P < 0.05) increased enzymatic starch hydrolysis rates and glycemic index of the millet starches, with starch-lipid interaction having more effect than starch-protein interactions. The complimentary effects of lipids and proteins on reducing starch hydrolysis rates was also observed. Millet starches complexed with palmitic, oleic, linoleic and elaidic acids to different extent. The complexing index (CI) of fatty acids with millet starches increased with increasing degree of unsaturation. Reductions in starch hydrolysis rates of the starch-fatty acid complexes depended on the amounts of the fatty acids added. Oleic acid was very effective in reducing millet starch hydrolysis rates while linoleic acid-complexed starches were much less resistant to hydrolysis. Cis oleic acid was more effective in reducing glycemic index than its trans configuration. This study showed that millet starch structural characteristics and starch-protein-lipid interactions are part of the reason why millet have low glycemic and insulinemic response.
URI: http://hdl.handle.net/10214/7715
Date: 2013-12
Rights: Attribution-NoDerivs 2.5 Canada
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Attribution-NoDerivs 2.5 Canada Except where otherwise noted, this item's license is described as Attribution-NoDerivs 2.5 Canada