Enhancing the molecular weight dependent antioxidant and antidiabetic activities of zein hydrolysates via thermal and ultrasonic pretreatments and enzyme specific hydrolysis

In this study, zein was treated with thermal (90 °C, 10 min) and ultrasound pretreatments at varying power levels (100, 200, 400 W) and durations (5, 10, 20 min), followed by hydrolysis using three distinct proteases (Alcalase, papain, pepsin). The hydrolysate was subsequently fractionated using sequential ultrafiltration membranes with molecular weight cutoffs of 30 and 10 kDa. The resulting hydrolysate and its corresponding fractions were evaluated for their antioxidant activity and inhibitory effects against α-glucosidase and α-amylase enzymes. The thermally pretreated sample hydrolyzed with Alcalase demonstrated the highest degree of hydrolysis (16.62 %). In contrast, the hydrolysates generated using papain showed the lowest hydrolysis efficiency. In addition, the thermally pretreated sample hydrolyzed with Alcalase exhibited the highest DPPH (∼78 µmol Trolox/g sample) and ABTS (∼195 µmol Trolox/g sample) radical scavenging activity, as well as the greatest iron ion chelating ability (∼35 µmol EDTA/g sample). The results showed that ultrafiltration and the production of peptides with low molecular weights (<10 kDa) enhanced antioxidant properties. The α-amylase inhibition results indicated that the inhibitory properties increased with higher peptide molecular weight. The thermally pretreated sample with a molecular weight 10-30 kDa exhibited the highest inhibitory activity (∼40 %). Similarly, the ultrasound pretreated hydrolysate (200 W, 10 min) of the same molecular weight range demonstrated notable α-glucosidase inhibition (∼30 %). Hence, thermal and ultrasound pretreatments enhanced the efficiency of zein hydrolysis, promoting the production of antioxidant and α-glucosidase inhibitory peptides that can be utilized in both the food and pharmaceutical industries.