Growth and metabolism of halophilic Candida versatilis and Tetragenococcus halophilus in simultaneous and sequential fermentation of salted soy whey

This study investigated various strategies: mono-, simultaneous and sequential fermentation of halophilic Candida versatilis and Tetragenococcus halophilus to valorize salted whey, a side stream of salted tofu (pressed beancurd) production, with an ultimate goal of creating a soy sauce-like condiment. Growth, glucose, organic acids were monitored throughout fermentation, while free amino acids and volatile compounds were analyzed on the final days. In monoculture fermentation, both C. versatilis and T. halophilus thrived in salted soy whey. However, in co-culture fermentation, an antagonistic relationship was observed, wherein C. versatilis growth was slightly suppressed and T. halophilus was significantly inhibited. In C. versatilis-involved fermentations, no significant (p > 0.05) differences in key volatile and non-volatile chemical components were found among various fermentation modes. Key soy sauce-like volatile compounds, such as 4-ethylguaiacol and 4-ethylphenol, were detected in all C. versatilis-fermented salted soy whey, while T. halophilus primarily functioned as a lactic and acetic acids producer. This study highlights the potential of mixed culture fermentation involving soy sauce yeast and lactic acid bacteria for eventually developing a soy sauce-like condiment from salted soy whey, with C. versatilis playing a crucial role in flavour development. The findings suggest that fermenting of a single culture of C. versatilis in lactic acid-adjusted salted soy whey could be a viable and efficient choice for future production of soy sauce-like condiment.