Abstract
The article presents the results of a study on the effect of soluble plant dietary fiber on the viability of lactic acid bacteria and the microbiological stability of functional yogurt. The relevance of the study is determined by the need to increase the functional value of fermented dairy products and to ensure a stable level of probiotic microflora throughout the storage period. The object of the study was yogurt produced from pasteurized milk with a fat content of 1.0% using a starter culture containing Streptococcus thermophiles and Lactobacillus delbrueckii subsp. bulgaricus. Soluble plant dietary fiber was added at concentrations of 0.3%, 0.5%, and 1.0%. The viability of lactic acid bacteria was determined by the plate count method on MRS agar followed by colony-forming unit enumeration, and the results were expressed as log CFU/g. The analyses were performed on days 1, 7, and 14 of storage at 4 ± 2 °C. The results showed that the addition of plant dietary fiber did not exert an inhibitory effect on the development of lactic acid microflora. On the contrary, samples containing fiber demonstrated higher bacterial survival compared with the control sample. On the 14th day of storage, the number of viable cells in the control sample decreased to 7.6 log CFU/g, whereas at a concentration of 0.5% it remained at the level of 8.1 log CFU/g. The obtained data indicate the potential prebiotic effect of plant dietary fiber and its positive influence on the microbiological stability of the product. The concentration of 0.5% was found to be optimal, providing the best balance between microbial stability and technological characteristics. The developed product meets regulatory requirements and can be recommended for the production of functional fermented dairy products.