Mechanism of protein component addition on digestive properties of starch in fermented barley

Previous studies have found that removing protein from fermented barley flour promotes starch hydrolysis. In this paper, we investigate how the addition of fermented barley proteins to fermented starch affects starch digestive properties and explore the underlying mechanisms. The results show that the starch-protein complex (with a mass ratio of 1:0.35) forms larger protein aggregates during the co-gelatinization of starch and protein, which limits the swelling of starch and thus inhibits starch digestion. Analysis of the peak positions in the infrared spectrograms revealed that the absorption peaks of the starch-protein complexes shifted from 3313.65 cm⁻¹ to 3302.49 cm⁻¹. The addition of sodium dodecyl sulfate (SDS) to some extent lowered the storage modulus (G′) and loss modulus (G″) of the mixed system. The proteins confer a stronger resistance to enzymatic hydrolysis on the starch through the formation of hydrogen bonds and participation in hydrophobic interactions. The protein inhibits the activity of α-amylase, with inhibition as high as 77.32% at a protein concentration of 80 mg/mL and a semi-inhibitory concentration of 35.22 mg/mL. Thus, the addition of protein attenuates starch digestion. These findings elucidate the mechanism of protein effects on starch digestion properties during fermented barley digestion and provide a theoretical basis for the subsequent preparation of low-glycemic starch foods.