Mechanisms underlying the effect of gluten and its hydrolysates on in vitro enzymatic digestibility of wheat starch

Abstract Understanding the interactions between protein, starch and digestive enzymes is important to reveal the mechanisms of starch digestibility affected by protein. In this study, the effect of gluten or its hydrolysates on wheat starch digestibility was investigated. The first order rate coefficient (k) and hydrolysis percentage at 120 min were decreased by the addition of gluten and its hydrolysates, with a greater decrease observed for gluten hydrolyzed for 1 h (GH-1). The k value was decreased by 82.4% with the addition of 20% GH-1. The activity of α-amylase was inhibited by gluten and its hydrolysates, with the greater inhibition percentages observed for GH-1 (approximately 87%). Binding kinetics of α-amylase and gluten or its hydrolysates by surface plasmon resonance showed that GH-1 bound α-amylase more rapidly and tightly than gluten or other hydrolysates. Fourier-Transform Infrared analysis of gelatinized starch-gluten/hydrolysate samples showed that starch interacted with gluten or its hydrolysates through hydrogen bonding, with the stronger interaction observed between starch and GH-1. From the present study, we concluded that both the binding of α-amylase with gluten/hydrolysates and the interaction between starch and gluten/hydrolysates inhibited the digestibility of starch.