Impact of somatic cell count on milk and dahi: Changes in physico-chemical, microbiological, rheological and metabolic characteristics

This study investigates the impact of somatic cell count (SCC) levels in raw cow milk on the quality characteristics of dahi , a traditional Indian fermented milk product. Milk samples were categorized into healthy (HM), subclinical mastitis (SCM), and clinical mastitis (CM) groups based on SCC. Dahi was prepared using three starter cultures (( Streptococcus thermophilus , Lactococcus lactis, Streptococcus thermophilus , and Mesophilic mixed strain dahi culture NCDC 167) and two temperature-time combinations (85 °C/30 min and 90 °C/15 min). Physicochemical, textural, and microbiological analyses were performed to assess the resulting dahi quality. Results indicated that increased SCC levels in raw milk led to a significant (p < 0.05) increase in protein and ash content in dahi , while lactose content decreased. Whey syneresis was substantially affected by SCC, culture type, and temperature-time combination. Dahi prepared from milk from healthy cows using 90 °C/15 min treatment and Lactococcus lactis and Streptococcus thermophilus culture had the lowest whey syneresis (25.95 ± 0.93 %), highest firmness (1.63 ± 0.02 N) and acidification rate (4.87 × 10 −3 pH units/min). Furthermore, metabolomics analysis revealed distinct metabolite profiles among the SCC groups as indicated by Principal Component Analysis and VIP score plot analysis thereby, highlighting differentially expressed (p < 0.05) metabolites in milk and dahi related to mastitis. Specifically, increased SCC was associated with alterations in metabolites involved in carbohydrate and lipid metabolism. These findings provide valuable insights into optimizing dahi production by considering SCC levels in raw milk and selecting appropriate starter cultures and processing conditions. • Increased SCC in milk: Higher protein & ash, decreased lactose in dahi (p < 0.05). • Whey syneresis & textural attributes in dahi affected by SCC, culture, temperature. • Healthy milk (90 °C/15 min): decreased syneresis, increased firmness. • Metabolite profiling demonstrates alterations in lactose, benzoic acid, glycerol. • SCC alters metabolites in carbohydrate & lipid metabolism of milk and dahi.