Use of probiotic yeasts with biocontrol activity for fermentation of ewe's milk.

BACKGROUND: There are sufficient scienctific studies that support the benefit that fermented dairy products produce in those who consume them. Traditionally, cow's milk has been the most commonly used milk but there is a growing interest in the development of new dairy products, substituting cow's milk with milk from other sources, as well as in the use of microorganisms in fermentation to replace artificial preservatives or treatments that may affect the chemical and organoleptic characteristics of the product. For these reasons, the aim of the present work was to understand the behavior of five potential probiotic yeasts during the fermentation of ewe's milk and to consider their potential use as biocontrol agents. RESULTS: Saccharomyces cerevisiae 3 and Hanseniaspora osmophila 1056 provided the most promising kinetic parameters in the different salt, temperature and pH conditions tested in their technological characterization. The profiles of organic acids and volatile compounds after the fermentation period was noteworthy for contributing to the final aroma of the dairy product. Sensory analysis revealed the sour taste of all samples, and S. cerevisiae 3, Lachancea thermotolerans 1039, and H. osmophila 1056 stood out for an accentuated cheese flavor. In addition, all strains showed biocontrol activity; they reduced the mycelium of the mycotoxigenic molds. CONCLUSION: Saccharomyces cerevisiae 3 and H. osmophila 1056 could be inoculated along with bacterial starters to provide a functional fermented beverage with improved flavor. These strains also have an added value as they act as biocontrol agents. © 2022 Society of Chemical Industry.

Safety Evaluation of Yeasts With Probiotic Potential.

This work has evaluated the safety aspects of 20 yeast strains, isolated from food environments, selected in previous works due to their probiotic potential. Among the different strains, there are Saccharomyces and non-Saccharomyces yeasts. Before safety evaluation, differentiation of Saccharomyces cerevisiae strains was done by PCR amplification of inter-δ region with pairs of primers δ2-12 and δ12-21, which showed that they were all different from each other and also had different profiles to Saccharomyces boulardii (the only commercial probiotic yeast). The non-Saccharomyces ones were already known. The evaluation tests carried out were antibiotic and antifungal resistance, production of biogenic amines, deconjugation activity of bile salts, and different enzymatic activities: coagulase, deoxyribonuclease, hemolysin, proteolytic, and phospholipase. None of the studied strains demonstrated coagulase, hemolytic or DNase capacity (clear virulence factors), although all of them showed protease activity, some showed phospholipase activity, and half of the yeasts were capable of conjugating bile salts. Regarding antimicrobial compounds, all were resistant to antibiotics but showed sensitivity to the antimycotics used. Nevertheless, only one strain of Hanseniaspora osmophila was excluded for use in the food industry, due to its high production of tyramine.