Screening of different wheat protease hydrolysates inhibiting retrogradation of corn starch

Abstract: Retrogradation is the molecular interaction that occurs between glucan molecules in gelatinized starch during cooling. It profoundly affects quality, acceptability, and shelf-life of starch-containing foods. Corn starch is cheap and is widely used in foods such as instant noodles, sausages, pastries, etc. But the quality of these foods in hardness, digestion, compatibility, etc, becomes deteriorated during storage due to starch retrogradation. Wheat gluten is a kind of nutritious, high quality, and inexpensive plant-based protein. It is often suggested that gluten has an anti-firming effect in bread, but the reason for this is not clear. There are four kinds of proteins in wheat flour: albumin, globulin, glutenin, and gliadin. In order to find the peptides with the ability of hindering corn starch retrogradation, these proteins were hydrolyzed by acid, neutral, and alkali proteases. The effects of these peptides in hydrolysate of globulin, glutenin, and gliadin on the retrogradation of corn starch were carried out in this paper. The results showed that the peptides from hydrolysis of glutenin by acid protease strongly inhibited retrogradation of corn starch, lowering the retrogradation rate of corn starch from 14.0% to 8.0%. Other hydrolysis promoted the retrogradation of corn starch, in which the largest increase in the retrogradation rate of corn starch was the peptides from the hydrolysis of gliadin by alkaline protease, enhancing the corn starch retrogradation rate from 14.0% to 19.5%. The possible mechanism in enhancing or inhibiting the retrogradation of corn starch was analyzed by IR and nuclear magnetic resonance. The increase in the corn starch retrogradation rate was caused by peptides with hydroxyls in hydrolysate of gliadin that formed glycosidic bonds with hydroxyls on corn starch. These glycosidic bonds were resistant to hydrolysis of starch by α-amylase. The factor that reduced the corn starch retrogradation rate was the presence of hydrophilic peptides in hydrolysate of glutenin that had the ability of forming a double helix with corn starch. This double helix was in favor of gel formation. The gel system hindered the formation and growth of a crystal nucleus of retrograded corn starch, thus reducing the retrogadation rate of corn starch. Sulfdryl groups were absent in the hydrolysate of these proteins, inferring that those groups might only exist in the spatial structure of these proteins. A further study of these peptides on the retrogradation of corn starch should be carried out on the aspect of interaction of peptides and starches in three-dimensional space. The findings in the paper provide a new way to control retrogradation of corn starch.