Enzymatic hydrolysates from tuna backbone and the subsequent Maillard reaction with different ketohexoses

Enzymatic hydrolysates from tuna backbone were prepared, and the subsequent Maillard reaction with rare sugars (d-psicose, d-sorbose and d-tagatose) was investigated. The hydrolysates were found to contain a large number of short peptides under 1000 Da and were good sources of essential amino acids. In assays of free radical scavenging activity and reducing power, the Maillard reaction products from rare sugars, especially d-tagatose, performed better than that from d-fructose. After heating at 55 degrees C for 48 h, the scavenging capacity of the hydrolysates for 1,1-diphenyl-2-picryl-hydrazyl radicals improved by 8.9- and 16-fold in the presence of d-fructose and d-tagatose. Hence, hydrolysates with high nutrient contents could be prepared from fish by-products via proteolysis, and the Maillard reaction of rare sugars may greatly promote the antioxidant activity of the hydrolysates.