Yeast Fermentation Modulates Aroma-Active Volatile Profiles and Bioactive Metabolites in Enzymatically Hydrolyzed...

Seaweeds are promising sustainable food resources, yet their utilization is limited by fishy off-flavors mainly derived from lipid oxidation. Although yeast fermentation is widely used for flavor modulation, species/strain-dependent aroma regulation in kombu (Saccharina japonica) slurry remains unclear. In this study, enzymatically hydrolyzed kombu slurry was fermented with five commercial yeasts (Saccharomyces cerevisiae, S. boulardii, Pichia kluyveri, Debaryomyces hansenii, and Zygosaccharomyces rouxii) to investigate metabolic and volatile changes. Distinct species/strain-dependent growth and substrate utilization were observed, with P. kluyveri showing the highest proliferation (5.42→7.44 log CFU/mL). D. hansenii exhibited stronger sugar (1058.51→525.21 mg/L) and mannitol consumption (150.34→58.75 mg/L) than that of other yeasts. In addition, fermentation shifted metabolism toward nitrogen pathways, producing multiple bioactive compounds including γ-aminobutyric acid and ornithine. Moreover, a total of 47 volatiles were identified. Based on the relative distribution of semi-quantitative responses, the aldehydes accounted for 52.00% of the summed volatile response in the control and 17.58%-39.60% after fermentation. Several lipid oxidation-derived compounds associated with grassy, fatty, mushroom-like, and marine-like odors, including 1-octen-3-one and unsaturated aldehydes, showed substantial decreases. In contrast, alcohols accounted for 44.09%-67.81% of the summed volatile response after fermentation, compared with 32.98% in the control, consistent with yeast redox metabolism and amino acid catabolism through the Ehrlich pathway. Higher alcohols, including isoamyl alcohol and 2-phenylethyl alcohol, also increased and are commonly associated with fruity and floral aroma characteristics. Overall, yeast fermentation modulated the metabolic and aroma-active volatile profiles of kombu slurry in a species- and strain-dependent manner. PRACTICAL APPLICATIONS: This study demonstrates the potential of selected yeasts to modulate the flavor-related chemical profile of enzymatically hydrolyzed kombu slurry through changes in volatile and non-volatile components. Yeast fermentation reduced several lipid oxidation-derived aldehydes and ketones associated with grassy, fatty, and marine-like off-odors, while promoting the formation of alcohols, esters, lactones, and amino acid-derived metabolites that may contribute desirable aroma and taste attributes. These findings provide a practical basis for developing fermented seaweed-based foods and/or non-alcoholic beverages with modified flavor-related chemical profiles, particularly for markets where the characteristic marine odor of seaweed limits consumer acceptance. However, sensory evaluation is required to determine whether these chemical changes result in improved aroma quality or consumer acceptability. The use of yeast fermentation after enzymatic pretreatment may therefore represent a feasible strategy for valorizing kombu biomass and expanding its application in sustainable functional food products.