Influence of ultrasound during wheat gluten hydrolysis on the antioxidant activities of the resulting hydrolysate

Summary Wheat gluten was hydrolysed by Alcalase 2.4L under ultrasound. Different antioxidant assays in vitro , such as ferrous ion‐chelating activity, reducing power, inhibition of linoleic acid emulsion peroxidation and 2,2′‐azinobis (3‐ethylbenzothiazoline‐6‐sulphonic acid) diammonium salt (ABTS) radical scavenging activity, were employed to evaluate the antioxidant activities of the wheat gluten hydrolysate (WGH) obtained. It was found that WGHL (WGH which was obtained by low frequency (LF) ultrasound) exhibited the strongest antioxidant activities, with an EC 50 value of 0.513 mg mL −1 for ferrous iron‐chelating activity, as well as a high and dose‐dependent reducing power. In the linoleic acid system, a longer induction time indicated a significant decrease of lipid peroxidation. In addition, WGH also exhibited notable ABTS radical scavenging activity. A good correlation was observed between antioxidant activities and the amount of WGH, but a poor correlation was observed between antioxidant activities and degree of hydrolysis. The molecular weight distribution of WGH was affected by ultrasonic frequency and WGHL had the highest proportion of peptide fractions of molecular weight 3000–500 Da. All the results showed that the WGH treated by ultrasound had strong antioxidant activities and low molecular weight.