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Abstract
Microbial interactions are fundamental during milk fermentation, determining the product final characteristics. Galactomyces geotrichum, Lactobacillus plantarum and Enterococcus faecalis are among the most common microorganisms in the Colombian Kumis. The aim of the research was to evaluate the yeast–bacteria interactions in milk fermentation at 28 °C. UHT (Ultra-High Temperature) milk was inoculated with single- or multiple-strains associations and analysed periodically to determine the microbial counts, organic acids and total free amino acids (FAA). The results evidenced different growth performance of the strains in single or co-culture, with a positive effect of G. geotrichum KL20B on the lactic acid bacteria (LAB) growth performance. All the strains consumed citric acid after 6 h of incubation with E. faecalis KE06 as the major consumer; however, all the co-cultures showed an early metabolism of citrate but with a low intake rate. In addition, the interaction between G. geotrichum KL20B and E. faecalis KE06 led to a low accumulation of acetic acid. Formic acid fluctuated during fermentation. The strains interaction also led to an increase in ethanol content and a lower accumulation of FAA. In conclusion, the three strains co-culture enhances the LAB viability, with high production of lactic acid and ethanol, as a consequence of adaptation to the environment and substrate exploitation. To our knowledge, this is the first time in which it is showed that G. geotrichum KL20B could be used to compensate for the slow acid-producing ability of Lb. plantarum and E. faecalis in milk, underlining that this consortium applies some mechanisms to regulate the growth and milk composition in acids and ethanol content.
Highlights
IntroductionDuring milk fermentation, microbial interactions play an important modulatory role in this particular ecosystem
During milk fermentation, the composition and frequency of species within the microbiota, as well as the amount of final bio-products are influenced by the environmental conditions encountered by microbial cells, the available energy sources and the growth-stimulating or -inhibiting factors.during milk fermentation, microbial interactions play an important modulatory role in this particular ecosystem
Considering that acid production is an important phenomenon associated with fermented milks manufacture, in this work we evaluated the effect of the interaction of the same strains on the production of organic acids, ethanol and amino acids during the fermentation of milk at 28 ◦ C for 48 h, in order to better understand the real contribution of each strain on growth dynamics and metabolites production
Summary
During milk fermentation, microbial interactions play an important modulatory role in this particular ecosystem. The impact of the process variables and their changes during continuous propagation enables the microbial association to endure even for years [1]. In fermented milks such as Kefir, Koumis, Kumis, Viili, Longfil, Laban, Amasi and Kurut, the co-occurrence of yeasts and lactic acid bacteria confers particular treats to the products. Yeasts are believed to be essential in the production of these fermented milks, since their presence is usually in a high number. In Kumis, a traditional low alcoholic fermented cow milk produced in rural and urban
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