Property analysis of resistant wheat amylose and amylopectin with wheat gliadin

Abstract: Starch is the reserve carbohydrate in the plant kingdom. There is about 65 - 70% starch, 11 - 13% protein and some other components in wheat. Resistant starch (RS) has been investigated mainly with regard to colonic effects, glycemic index, cholesterol lowering capability, and losing weight effect. The daily intake of a certain amount of resistant starch is particularly important to human health. Retrogradation is the process of starch recrystallization which is one of the most important methods for the preparation of RS. Gliadin, accounting for 40%-50% of wheat gluten, promotes the retrogradation of wheat starch while glutelin retards it. The objective of this research is to study the effects of external gliadin in gluten on deferent kinds of wheat starch after purified by lipase and protease, which is a part of a large research program aimed at gaining an enhanced molecular understanding of the transformations occurring during the processing and storage of starch materials. Gliadin was isolated from wheat flour and its effect on retrogradation of wheat starch was investigated by visible absorbance (starch-iodine), IR, XRD, DSC respectively. The results showed that gliadin probably interacted with starch during the process of gelation and retrogradation, resulting in enhance of starch retrogradation. The IR spectra indicated that the addition of gliadin to wheat starch led to the reduction of hydrogen bonds between amylose. Addition of gliadin in crystal of retrograded wheat starch caused presence of two new lattice planes. The DSC results indicated that the hydrogen bond of amylose and gliadin was formed in the retrogradation progress. The polycrystal structure and the double helix reign were coexisting. The hydroxyl group of C-6 with less steric hindrance can form six-membered ring with carboxyl and acylamino group of prolines and glutamine by hydrogen bond respectively. Starch could combine with gliadin by hydrogen bond to form double helix during retrogradation, which resulted in the promotion of short term retrogradation of wheat starch. Gliadin and starch formed double helix in the interface of themselves that inhibit the enzymolysis of starch. This kind of hydrogen bonding might be an inhibitor for α-amylase. The gliadin would not promote the retrogradation of starch anymore when all of the amino acid formed hydrogen bond with starch. In a word, this study has provided some distinct insights into the understanding of the effects of gliadin on the retrogradation of wheat starch. .