Influence of pH on the formation and radical scavenging activity of volatile compounds produced by heating glucose with histidine/tyrosine

Abstract

In this study, the effect of pH on the volatile generation over reaction time as well as the DPPH radical scavenging activity of volatile MRPs was investigated in the Maillard reaction of glucose (Glc) with tyrosine (Tyr) and histidine (His). Factor analysis showed clearly that volatiles generated in 5-h open system were of similar composition to those in 0.5-h close system regardless of pH level and amino acid, implying higher pressure in close system could accelerate the volatile formation in Maillard reaction. Besides, all volatiles showed increasing tendency over reaction time under different pH levels with the exception of pyrones which decreased with the extension of reaction time at pH = 7 and pH = 9. Furans, phenols and 2-acetylpyrrole that were favored under acidic condition showed larger increase at pH = 5 over reaction time, while other volatiles except pyrones, furans, phenols and 2-acetylpyrrole, which were favored under neutral and alkaline conditions, showed greater increase at pH = 7 and pH = 9 over reaction time. The measurement of DPPH radical scavenging activity of dichloromethane extract obtained from Maillard reaction mixture revealed that volatile MRPs from Glc–Tyr system showed stronger antioxidant activity under alkaline condition, while volatile MRPs from Glc–His system showed greater antioxidant activity under acidic condition.