Effects of Amino Acids on Structures, Morphologies and Heat-induced Phase Transformation of Starches
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Abstract:
In this work, corn starch was used as model material and the effects of amino acids on its morphology structure and phase transformations were systematically studied with a combination of traditional characterization techniques and molecular dynamics simulation. The results showed that the pH values were significantly changed from 7.13 to 3.27 and 9.72 by addition of acid glutamic acid and alkaline lysine, respectively. The amorphous areas of starch granules were damaged when treated by the strong acidic or alkaline condition of non-neutral amino acid solutions, which resulted in the rougher granule appearance and an increased in relatively crystalline content. In the blending system of amino acid/starch, the hydrogen bond interactions between starch molecules and amino acid molecules were gradually enhanced with an increased content of amino acid. The gelatinization of starch was inhibited by three amino acids at different contents. The peak gelatinization temperature of starch was increased by 3.71 ℃, 6.00 ℃ and 5.58 ℃ by 10% glycine, lysine and glutamate, respectively. Moreover, molecular dynamics simulation showed that the number of water molecules interacting with starch molecules through hydrogen bonding was reduced by amino acid molecules via affecting the distribution of water molecules around starch molecules, which induced a more stable structure of starch and further inhibited starch swelling and gelatinization.
