Physicochemical Properties of Wheat Gluten Hydrolysates Produced by Different Proteases

Abstract

Hydrolysis of proteins has been widely used to produce ingredients with functional characteristics (foaming, solubility, emulsifying, etc.) as well as various physiological activities (antioxidant, antimicrobial, anti-inflammatory, anti-hypertensive activities, etc.). Enzymatic hydrolysis has been applied to various foods of animal and plant sources. Wheat gluten, which is produced while separating starch from wheat, is relatively inexpensive. The objective of the study was to evaluate the changes in chemical characteristics and antioxidant properties of wheat gluten hydrolysates (WGH) and utilize the WGH as an ingredient in a beverage system. Single (2, 6, 12 and 24 h) and sequential enzymatic hydrolyses (8, 10 and 12 h) were conducted to produce WGH using commercial proteases (Alcalase, Flavourzyme, Protamex and Neutrase). Wheat gluten was suspended in distilled water (20%, w/w) and hydrolyzed with the enzyme to wheat gluten ratio of 1:100 (w/w) at 50˚C in a water bath. Yields of all the produced WGH were over 50%. Degree of hydrolysis (DH) of the WGH significantly increased with hydrolysis time (p<0.05). DH of the WGH produced by Flavourzyme was the highest, independent of hydrolysis time, while that of the WGH by Neutrase was the lowest. Sequential enzymatic hydrolysis remarkably decreased the fraction with more than 10 kDa and increased the fraction with less than 500 Da compared with the single enzymatic hydrolysis. Contents and compositions of free amino acids in the WGH were significantly affected by the enzyme types and hydrolysis conditions including the number of treated enzymes and sequences of the treated enzymes. DPPH radical scavenging activity of the WGH significantly increased with hydrolysis time (p<0.05). On the other hand, ABTS radical scavenging activity of the WGH was rarely affected by the enzyme types and hydrolysis conditions. The WGH produced by Protamex showed lower turbidity, better thermal stability and higher solubility, suggesting they may be suitable for beverage development.