Development of Indigenous Streptococcus thermophilus Multi-Strain Starter Culture Blend for Dahi Production

Abstract

Present study aimed to develop an indigenous Streptococcus thermophilus multi-strain starter culture blend for the preparation of dahi. A total of 89 raw milk and curd samples were collected for the isolation of Streptococcus thermophilus strains. Based on the morphological and genotypic methods 24 isolates were characterized as Streptococcus thermophilus strains. These strains were evaluated for the presence of Als and epsA gene and assessed for acid production, textural, flavour and sensory properties in 11% (w/v) Reconstituted Skimmed Milk. From the 24 S. thermophilus strains, 17 and 15 strains were found positive for Als and epsA gene respectively. Three strains exhibiting desirable characteristics such as reduced curd formation time, optimal pH and titratable acidity, and improved curd quality were selected for blend formulation, and their compatibility was evaluated using cross-streak and spot assay techniques. Among these, blend D1 (St1:St7:St17 in a 1:1:1 ratio) demonstrated better performance, with a curd-setting time of 3.20 ± 0.05 h, pH of 4.48 ± 0.01, titratable acidity of 0.68 ± 0.02 %LA, and a total viable lactic count of 9.87 ± 0.04 log CFU/mL. The developed blend thus offers a promising option for dahi manufacture and can be conveniently adopted by small and medium scale manufacturers.