Effects of pH on headspace volatiles and properties of Maillard reaction products derived from enzymatically hydrolyzed quinoa protein-xylose model system

The enzymatically hydrolyzed quinoa protein (E-HQP) was used as a main precursor of a wide range of thermal process flavours. Identification of the volatile compounds generated from the reaction of E-HQP-xylose model mixture at different initial pH values (5, 6, 7, 8 and 9) was performed using a solid phase microextraction GC MS technique. The content of free amino acids, colour intensity and radical scavenging activity of the Maillard reaction products (MRPs) formed at each pH were determined. The results revealed a great influence of the pH values on chemical composition and odour profile of the generated volatiles. The studies showed that low pH favoured formation of furans, furanones and cyclopentanones. In contrast, the pyrazines comprised the highest yield of the total volatiles at pH 9. A positive correlation was found between increasing the pH values and browning intensity of MRPs. The antioxidant activity of MRPs and total content of free amino groups showed a gradual decrease by increasing the pH. A correlation was found between the antioxidant activity of MRPs and the volatile compounds generated at each pH. Principle component analysis clearly elucidated a distinct separation among the investigated E-HQP-xylose model mixtures based on the volatile compounds generated at different pH.