Yoghurt starter cultures as a source of bioactive bacteria: influence of inoculum type on syneresis and bacterial content of the final product

Abstract

Yoghurt, as the most popular fermented dairy beverage, has been attracting increasing consumer interest due to its nutritional, probiotic and sensory qualities. A key stage in yoghurt production is lactic fermentation, during which lactic acid bacteria convert lactose into lactic acid, resulting in the coagulation of milk proteins. Currently, there is a noticeable trend towards a return to traditional fermentation methods and home-based yoghurt production, alongside growing popularity of yoghurts enriched with probiotic bifidobacteria. The aim of this study was to compare the physicochemical and microbiological properties of four yoghurt variants: two prepared using commercial starter cultures and two via inoculation with natural yoghurt. The analyses focused on bacterial counts (Lactobacillus spp., Streptococcus thermophilus, Bifidobacterium spp.), titratable acidity and the phenomenon of syneresis, i.e. the separation of whey. The obtained results demonstrated that yoghurts produced using commercial yoghurt as the inoculum contained higher levels of lactic acid bacteria and bifidobacteria. Differences were also observed in the levels of syneresis and acidity, depending on the fermentation method employed. Microscopic observations corroborated the microbiological culture results. This study confirms that both the preparation method and microbial composition significantly influence the quality and shelf-life of yoghurt. Furthermore, it was shown that centrifugation time and speed are critical factors in syneresis determination, whereas sample mass does not significantly affect the outcome.