ABSTRACT Ropy fermented milk is a traditional dairy product with a viscous texture largely attributed to exopolysaccharide (EPS)-producing lactic acid bacteria (LAB). However, texture and stability also arise from complex microbial interactions with yeasts and molds. This study examined the combined effects of an EPS-producing LAB ( Lactococcus lactis subsp. cremoris APL15), yeast ( Kluyveromyces marxianus var. marxianus TY1), and mold ( Geotrichum candidum ) in broth and non-homogenized milk. In broth, EPS production by L. lactis was most strongly enhanced during live co-culture with both fungi, while growth and acidification were unaffected. In milk, K. marxianus accelerated early acidification, whereas G. candidum reinforced textural integrity and formed a patchy surface layer typical of traditional products. After 14 days of storage, L. lactis survival was highest in the L. lactis + G. candidum group compared with yeast-containing groups, suggesting that the mold buffered yeast-associated inhibition. Mixed cultures also improved viscosity, cohesiveness, and firmness, particularly with G. candidum , despite no significant differences in EPS yield. To our knowledge, few studies have systematically evaluated LAB–yeast–mold synergy in ropy fermented milk, thereby providing new ecological insight and guiding starter culture design to enhance the quality and authenticity of traditional fermented dairy products.
Chen et al. (Mon,) studied this question.