Optimized preparation, characterization, and antioxidant activity of chitooligosaccharide–glycine Maillard reaction products

In this study, chitooligosaccharide (COS) and glycine (Gly) were selected to prepare Maillard reaction products, which were designated COS–Gly–MRPs. Changes in the FTIR and fluorescence spectra confirmed the formation of the COS–Gly–MRPs. Using ferric reducing antioxidant power (FRAP) as a response, the optimal reaction conditions, i.e., a time of 107 min, temperature of 121 °C, pH of 6.0, and nCOS:nGly = 2.5:1, were obtained by one-variable-at-a-time method and by response surface methodology. The resulting COS–Gly–MRPs exhibited much stronger antioxidant activity than their substrates. The FRAP of COS–Gly–MRPs was 32.14 mmol Fe2+/L, and the radical scavenging activity of COS–Gly–MRPs reached 78.6, 89.0, 92.3, and 86.0% for ABTS, superoxide, DPPH, and hydroxyl radicals, respectively. After 7 days of storage, COS–Gly–MRPs-treated fruit juices showed higher antioxidant capacity than those treated with a mixture of COS and Gly.