Physicochemical Characterization and Immunomodulatory Effect of Melanoidins from Vinegar Residue

There is currently a need for high-value applications of vinegar residue, a major byproduct generated during vinegar production, in order to benefit the environment and economic development. Melanoidins exist in vinegar residue as brown and bioactive macromolecules which are produced during the vinegar brewing process. However, the physicochemical characteristics and potential immunomodulatory activity of melanoidins from vinegar residue (VRM) have yet to be clarified. In this study, VRM exhibited structural heterogeneity, with a molecular weight of 9005.42 Da. Carbohydrates were the dominant component, accounting for 57.86 ± 3.36% (w/w), and xylose was the primary monosaccharide, with molar ratios of 53.15%. In addition, microstructural observations showed clear edges and a relatively smooth surface in VRM samples. Spectral analysis with FTIR showed that VRM has broad-spectrum ultraviolet absorption capacity and contains hydroxyl groups and unsaturated structures. Meanwhile, VRM exhibited higher antioxidant capacity than vinegar melanoidins according to ABTS and FRAP. Furthermore, the effects of VRM on immunomodulation were investigated in macrophages. VRM significantly induced phagocytic capacity and the secretion of NO, TNF-α, and IL-6. VRM at 800 ug/mL effectively exerted an immunomodulatory effect, which was associated with the TLR4-mediated NF-κB pathway. These findings demonstrate that VRM has a polysaccharide skeleton cross-linked with proteins and polyphenols, and possesses antioxidant and immunomodulatory properties. It will provide a novel and functional product for the efficient utilization of vinegar residue.