Effect Of Ethanol Addition On The Bitterness Of Wheat Gluten Hydrolysates And The Yield Of Glutamine Peptides

Wheat gluten as a good resource of dietary protein is produced worldwide in enormous quantities.Enzymatic hydrolosis is used to hydrolyze wheat gluten to obtain functional bioactive peptides and to extend its application field.But meanwhile,bitter peptides are also obtained during enzymatic hydrolosis and result in bitter taste,which has been limited its application in food industries.This work investigated the impact of ethanol on the wheat gluten hydrolysates hydrolyzed by Alcalase and compound protease respectively,and explore the release of glutamine peptides with the presence of ethanol.Firstly,wheat gluten was hydrolyzed by Alcalase in the distilled water with the addition of ethanol 0%,5%,10% and 15% and the changes of hydrolysates were investigated.At the same DH the presence of ethanol decreased the bitterness value of hydrolysates.The proportion of relative molecular weight less than 1 000 of hydrolysates was also decreased with addition of ethanol and was negatively correlated with the concentration of ethanol.At the DH of 10%,ultrafiltration separation results for hydrolysates showed that the proportion of relative molecular weight less than 1 000 owned the highest bitterness value and the value was negatively correlated with the concentration of ethanol.Amino acid content results for different components showed that with the addition of ethanol,the content of hydrophobic amino acids(Pro,Ile,Phe and Leu)of relative molecular weight was between 1 000 and 3 000 and less than 1 000 hydrolysates both decreased.Free amino acid content results showed that with the same DH the content of free hydrophobic amino acids(Pro,Ile,Phe and Leu)increased at the presence of ethanol.With the increasing of ethanol concentration,hydrophobic value of hydrolysates and the content of alpha helix,beta folding and beta angle of Alcalase in ethanol solution both decreased.Secondly,wheat gluten was hydrolyzed by three kinds of enzymes Alcalase,Neutral protease and Flavourzyme and two kinds of enzymes Alcalase and NPU in the distilled water with the addition of ethanol 0%,5%,10% and 15%,to figure out the effect of ethanol on the hydrolysates.The results showed that the DH of hydrolysates was decreased with the addition of ethanol.Less bitterness value hydrolysates was obtained with the addition of ethanol and the value was negatively correlated with the concentration of ethanol.The content of protein(MW<1 000)significant(p<0.05)decreased in ethanol groups and the value was also negatively correlated with the concentration of ethanol.Meanwhile the acid soluble proteins was decreased with the increasing of ethanol concentration at the same hydrolysis time,5% concentration of ethanol had less effect on the enzyme activity than 10% and 15% concentration of ethanol.The bitterness value of the hydrolysates hydrolyzed by Alcalase and NPU was also decreased with the increasing of ethanol concentration at the same hydrolysis time.Furthermore,the content of hydrolysates(MW<1 000)and the content of acid soluble proteins decreased in ethanol groups.Finally,the effect of ethanol on the release of glutamine peptides was studied.The results showed that at the same DH the content of glutamine peptides in ethanol groups were increased in hydrolysates hydrolyzed by Alcalase.At the same hydrolysis time,the content of glutamine peptides showed decreasing tendency in hydrolysates hydrolyzed by combination of different enzymes.