Integrated evaluation of protease selection and drying method for oyster protein hydrolysates: Physicochemical, antioxidant, and umami-related characteristics

This study evaluated the effects of protease selection and subsequent drying on the production of oyster protein hydrolysate powder, with emphasis on physicochemical properties, antioxidant activity, and chemically inferred umami-related characteristics. Oyster homogenates were hydrolyzed with bromelain, papain, and neutral protease at 0.1–1.0% (w/w) under the same processing conditions. The selected hydrolysate was then converted into powder by freeze-drying or hot-air drying. Among the tested enzymes, neutral protease showed the most favorable hydrolytic performance under the selected mass-based screening conditions (pH 6.5, 50 °C), as indicated by the highest degree of hydrolysis and free amino group content, greater protein breakdown, and the lowest DPPH IC 50 values. Neutral protease hydrolysis markedly increased total free amino acid content, especially glutamic acid, and significantly increased the equivalent umami concentration. Although IMP and AMP contents decreased after hydrolysis, the chemically inferred umami-related potential increased, mainly because of the marked increase in umami amino acids. Drying method significantly affected powder quality, with freeze-drying producing powders with lower water activity, higher free amino group content, lighter color, lower malondialdehyde content, and stronger DPPH radical-scavenging activity than hot-air drying. These results suggest that, under the tested processing conditions, neutral protease hydrolysis followed by freeze-drying is a promising processing strategy for producing oyster protein hydrolysate powder with favorable quality attributes while retaining hydrolysis-derived antioxidant and umami-related characteristics.