Fermentation time and quality characteristics of yogurt produced using traditional and starter cultures in the Sidama region of Ethiopia

Abstract Smallholder dairy farming in the Sidama Region of Ethiopia predominantly produces traditional yogurt (ergo), which is characterized by variable fermentation times and inconsistent product quality. This study evaluated the effectiveness of a single strain starter cultures (Yoba, Lacticaseibacillus rhamnosus ) and a mixed strain culture (YF904, Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus) in improving fermentation time, as well as the physico-chemical and sensory quality of yogurt produced from a raw milk. Yogurt was prepared from uniform batches of milk collected from local cooperatives using four fermentation methods: spontaneous fermentation (SP), back-slopping (BS), and with two starter cultures. Physico-chemical analyses (pH, titratable acidity, fat, protein, and total solids) were performed, and fermentation time was recorded. Sensory evaluation was performed by 30 consumer panelists using a 5-point hedonic scale. Starter cultures yogurts had lower fat content (3.5% in both cultures); however, only Yoba probiotic yogurt showed a higher protein content (4.5%). Fermentation time was markedly shorter with starter cultures (11–14 h) than with SP and BS methods (18–24 h). Sensory results showed that Yoba probiotic yogurt was the most preferred, with sensory index values ≥ 0.80 for flavor, texture, color, and overall acceptability, followed by YF904, while traditionally fermented yogurt scored lower. These findings demonstrate that starter-culture based yogurt production improves fermentation efficiency, nutritional composition, and sensory quality. Adoption of starter cultures is recommended to enhance yogurt consistency and quality, and further research should explore additional cultures and characterize local fermentation bacteria.