Antioxidant activity of Maillard reaction products derived from stingray (Himantura signifier) non-protein nitrogenous fraction and sugar model systems

•Antioxidant activity of the MRPs from stingray NPN-sugar was evaluated.•Antioxidant activity of stingray NPN can be improved by Maillard reaction.•Stingray NPN-sugar MPRs can be applied as a potential antioxidant in food products.

This study aimed to evaluate the antioxidant activity of the Maillard reaction products (MRPs) derived from stingray non-protein nitrogenous (NPN) fraction and sugar (glucose, galactose and fructose) model systems. MRPs were prepared by heating the solution containing NPN (2 g nitrogen/100 ml) and sugar (2 g/100 ml) in 0.05 M sodium hydrogen carbonate buffer, pH 12 for 120 min at 100 °C. Reducing power and capacity to scavenge hydrogen peroxide (H2O2), hydroxyl radical (OH), 2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) radical (ABTS+) and 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) of all MRPs were greater than those of original NPN solution (P < 0.05). The MRPs derived from NPN-fructose tended to have the highest reducing capacity and free radical scavenging ability. However, the ferrous (Fe2+) chelating activity of all MRPs was lower than the original NPN solution (P < 0.05). Therefore, reducing power and scavenging activity toward free radicals and reactive oxygen species of NPN from stingray muscle can be improved significantly by reacting NPN with sugar particularly fructose via the Maillard reaction. However, the Maillard reaction seemed to show a negative impact on the Fe2+ chelating activity of stingray NPN.