Surface application and impact of Yarrowia lipolytica grown in cheese whey as adjunct culture for innovative and fast-ripening Caciotta-like cheeses

Cheese whey represents a significant challenge for the dairy industry due to its high chemical and biochemical oxygen demand. However, when utilized as a substrate for microbial growth, it can yield microbial biomass suitable for various food sector applications. In this study, two strains of Yarrowia lipolytica (RO3. and Y3) were cultivated to approximately 7.9 log CFU/mL on cheese whey and subsequently applied as culture adjuncts on the surface of Caciotta-type cheese. The cheeses were produced on an industrial scale and stored at 6 °C for 35 days, during which microbiological (plate counting for total mesophiles, yeasts, lactic acid bacteria, Pseudomonas spp., and Enterobacteriaceae), chemical (water activity, pH, color), proteolytic (SDS-PAGE), lipolytic (Folch method with gas chromatography analyses), and volatile molecule profiles (solid-phase microextraction combined with gas chromatography-mass spectrometry) were analyzed, along with sensory evaluations. Although Y. lipolytica levels declined during storage, its application accelerated the ripening process, enhancing proteolysis and increasing the content of unsaturated fatty acids (25 % for RO3. vs. 19 % in the control) in the cheese paste. Additionally, it promoted the development of ripened cheese aroma compounds (e.g., butanoic, hexanoic, and decanoic acids) on the cheese rind, particularly in cheeses treated with strain Y3. Overall, the findings demonstrate that Y. lipolytica represents a promising approach for valorizing food industry by-products, transforming them into innovative ingredients for sustainable and circular production systems. However, strain selection is crucial, as only Y. lipolytica RO3. produced cheeses with the desired ripening characteristics.