Impact of aging on physicochemical properties of dried abalone and immunomodulatory activities of its simulated <em>in vitro</em> digestion products

During the long aging process of dried abalone not only are distinctive color, flavor, and texture developed, but the immunomodulatory potential of its protein-derived components may also be altered. Therefore, the physicochemical properties of dried abalone aged for 0, 3, 5, and 10 years were investigated, and the immunomodulatory activity of their mimic digestion products (MDP) were evaluated. The results demonstrated that during the aging process, a gradual decrease was observed in both lightness (<em>L*</em>) and whiteness (<em>W*</em>) values of dried abalone. Concurrently, the A₂₉₄ and A₄₂₀ values were increased from 0.53 to 0.93 and from 0.08 to 0.17, respectively, accompanied by a reduction in endogenous fluorescence intensity. SDS-PAGE analysis revealed that prolonged aging led to partial degradation of myofibrillar protein, with the simultaneous formation of high-molecular-weight aggregates. The proportion of oligopeptides below 1000 Da in MDP was elevated, among which glutamate was determined to be the most abundant amino acid. Regarding immunomodulation activity, 3-year-aged dried abalone MDP exhibited the most potent stimulation of RAW264.7 cell proliferation rate at 236.37%, whereas 0-year-aged dried abalone MDP elicited the strongest phagocytic activity at 42.79%. In contrast, 0-year-aged dried abalone MDP was shown to induce the highest secretion of 1.53 μM NO and 19.18 ng/mL TNF-α when administered alone. A synergistic effect was observed when 5-year-aged dried abalone MDP were co-administered with LPS, resulting in a remarkable increase of TNF-α from 45.50 to 122.89 ng/mL and IL-6 from 5.72 to 19.52 ng/mL. Furthermore, the combined application of 5-year-aged dried abalone MDP and LPS effectively upregulated the expression of CD80 from 7.41% to 94.22% and CD86 from 51.30% to 68.87%. These findings suggest that the aging process likely induces Maillard reactions in dried abalone, thereby potentiating the immune-activating properties of its digestion products.