Assessment of stability and bioactive compounds in yogurt containing novel natural starter cultures with the ability to promote longevity in Caenorhabditis elegans

Yogurt represent one of the oldest fermented foods containing viable lactic acid bacteria and many bio-active compounds that could exhibit beneficial effects on human health and train our immune system to better respond to invading pathogens. Streptococ-cus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus are commonly used for yogurt preparation under controlled temperature and environmental condi-tions. In this study, we investigated probiotic features of S. thermophilus BGKMJ1-36 and L. bulgaricus BGVLJ1-21 strains isolated from artisanal sour milk and yogurt by using Caenorhabditis elegans as an in vivo model system. Further, we evaluated content of total fat, saturated fatty acids, proteins, and lac-tose, as well as vitamins and AA of yogurt prepared from above-mentioned starter cultures during 21 d of storage at 4 degrees C to get insights of final product stabil-ity. We showed that S. thermophilus BGKMJ1-36 and L. bulgaricus BGVLJ1-21 strains applied in combination upregulated the expression of autophagy-related genes in C. elegans. Beside autophagy, we observed activa-tion of TIR-1-dependent transcription of lysozyme-like antimicrobial genes involved in the immune defense of C. elegans. Upregulation of these genes strongly corre-lates with an increase in the longevity of the worms fed with yogurt culture bacteria. Further, we showed that yogurt prepared with S. thermophilus BGKMJ1-36 and L. bulgaricus BGVLJ1-21, as a final product, is rich with vitamin B2 and dominant AA known by their pro-longevity properties. Taken together, our study pointed to the beneficial features of the tested starter cultures and yogurt and highlighted their potential to be used as a fermented food with added-value properties.