Nutrient-rich algal innovation: exploring the amino acid profile, flavor, antioxidant, immunomodulatory, and cytotoxic properties of Chara corallina protein sauce powder.

BACKGROUND: The exploration of sustainable and functional plant-based protein sources has gained momentum amid rising global demands for health-oriented food innovations. This study investigates the nutritional and biofunctional properties of a powdered protein sauce derived from Chara corallina, a freshwater macroalga recognized for its high protein potential. RESULTS: Dried C. corallina fronds (17.3% protein) were fermented with Aspergillus sojae using koji and moromi processes under open-air conditions. The resulting sauce was freeze-dried into algal protein powder (APP-C). Amino acid analysis revealed significant increases (P ≤ 0.05), especially in tryptophan (16.09%), nearly absent in unfermented C. corallina. This highlights APP-C as a rich dietary source of tryptophan, a serotonin precursor linked to mood and immune health. Aspartic acid, glutamic acid, and cysteine were also elevated, while methionine was absent. These changes enhanced umami flavor and reduced sweetness. APP-C exhibited no cytotoxicity at concentrations of 3.90-500 μg mL-1 across RAW264.7 macrophages, human dermal fibroblast (HDF) cells, and rat skeletal muscle (L6) cells, with > 90% cell viability confirmed by the thiazolyl blue tetrazolium bromide (MTT) assay. Antioxidant potential was evidenced by significant up-regulation (P < 0.05) of superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) messenger RNA (mRNA) expression in HDF cells under oxidative stress induced by hydrogen peroxide (H2O2). Moreover, immunomodulatory assessments of APP-C revealed dose-dependent stimulation of nitrite production, phagocytic activity, and gene expression (lysozyme M, tumor necrosis factor-α, and interleukin-8) in RAW264.7 cells (P < 0.05). These findings exhibited strong antioxidant and immunomodulatory activity. CONCLUSION: APP-C represents a promising fermented functional food from sustainable, health-promoting freshwater algae. © 2026 Society of Chemical Industry.