Controlled enzymatic hydrolysis for improved exploitation of the antioxidant potential of wheat gluten

Abstract

The aim of the study was to find the optimal operational and process parameters for the enzymatic hydrolysis of wheat gluten in a batch stirred bioreactor regarding both degree of hydrolysis and antioxidant capacity of the obtained hydrolysates. It appeared that impeller geometry and agitation speed influenced the mass transfer resulting in enhanced gluten hydrolysis. The highest initial reaction rate (0.83 0.02 min(-1)) and degree of hydrolysis (30.47%) were achieved with the pitched four-bladed impeller and agitation speed of 350-450 rpm, conditions which provided proper balance between requirements for adequate mass/heat transfer and low shear stress. The impact of other process conditions including gluten concentration, temperature, pH and enzyme gluten (E/S) ratio on the enzymatic reaction was investigated by applying a Box-Behnken experimental design from the viewpoint of the degree of hydrolysis (DH) and antioxidant activity. Three models obtained allowed calculation of the hydrolysis degree, and both 2,2-diphenyl-1-picrylhydrazyl (DPPH) and ABTS (2,2'-azino-bis (3-ethylbenzothiazoline-6-sulpfonic acid) radical scavenging activity from a given set of reaction conditions with good predictability. The statistical analysis showed that each variable had a significant effect on degree of hydrolysis and the antioxidant capacity of both tested systems. Hydrolysis up to around DH 15% improved DPPH radical scavenging activity, while excessive hydrolysis worsened it. The ABTS activity of the hydrolysates was not associated with the DPPH activity nor with the DH, revealing that it was not possible to fulfill all desirable quality requirements (maximum degree of hydrolysis and protein yield, maximum DPPH and ABTS scavenging activities) by using the Same reaction conditions. Overall, the study might contribute to approve wheat gluten, a by-product of wheat starch industry, as an accessible and cheap source of bioactive compounds for the development of novel nutraceuticals, cosmetics and drugs.