The Contribution of Melanoidins to Soy Sauce Antioxidant Activities and Their Structure Characteristics

Melanoidins, generated during the Maillard reaction in soy sauce fermentation, have potential health benefits due to its excellent bioactivity. This study aimed to investigate the antioxidant contributions and structural characteristics of melanoidins in soy sauce. Five molecular weight fractions (1–3 kDa, 3–10 kDa, 10–30 kDa, 30–50 kDa, and >50 kDa) were isolated and their composition was analyzed. Results showed that soy sauce melanoidins mainly comprised proteins, sugars, and phenolic compounds. Antioxidant activities of the melanoidins were influenced by their molecular weights and structures. The >50 kDa melanoidins fraction contributed the most to the overall antioxidant activities of soy sauce. The total contributions of melanoidins to the antioxidant activities of soy sauce ranged from 34.21% to 75.03%. Spectroscopic analyses indicated that the antioxidant activities were positively correlated with the presence of conjugated structures and active functional groups (i.e., C=C, C=O, N-H, O-H) in melanoidins. This study provides new insights into the health-promoting properties of soy sauce melanoidins and offers theoretical support for the development of soy sauce as a functional food.