Microbial interaction dynamics of Candida oleophila and Starmerella lactis-condensi with Saccharomyces cerevisiae in winter-melon beer fermentation

Candida oleophila YS209 and Starmerella lactis-condensi MN412 are non- Saccharomyces yeasts isolated from sugar-rich environments. The ecological behaviour of these yeasts in brewing systems remains poorly understood. This study investigated their interaction dynamics with Saccharomyces cerevisiae US-05 in a winter-melon beer fermentation using sequential and co-inoculation strategies. Yeast population dynamics, physicochemical parameters, volatile organic compounds, antioxidant properties, and sensory attributes were evaluated. Initial yeast concentrations ranged from 5.74 to 6.53 Log CFU/mL, with S. cerevisiae reaching 7.16 Log CFU/mL in monoculture. Non- Saccharomyces populations decreased after day 6 but increased following fruit juice addition. In sequential fermentations, C. oleophila reached 6.10 Log CFU/mL. Sequential inoculation with C. oleophila YS209 resulted in higher glycerol production (3.15 g/L) and enhanced ester synthesis (182.32 mg/L), with ethyl octanoate as the predominant compound. Finished beers showed ethanol contents ranging from 6.07 to 6.28% (v/v). Winter melon beers exhibited higher total phenolic content (681–827 mg GAE/L) than raw juice (475.8 mg GAE/L) and increased antioxidant capacity (+109%). Sensory analysis showed more fruity and floral attributes, particularly in sequential fermentations. Overall, C. oleophila YS209 and St. lactis-condensi MN412 influenced yeast succession and fermentation outcomes, supporting their potential application as functional bioflavouring yeasts in fruit-based beer fermentation.