Variation in growth of candidate lactic acid bacteria isolated from ‘dadih’ under varying total solids concentration and incubation times

Abstract

Dadih is a traditional fermented milk from West Sumatra, Indonesia, which is made by naturally fermenting fresh milk inside bamboo tubes. While this traditional method gives dadih its unique flavor and texture, producing it on a larger scale consistently requires the use of controlled starter cultures. This study, therefore, aimed to have the optimal combination of total solids concentration and incubation time for milk fermented by lactic acid bacteria (LAB) starters isolated by dadih. Five individual LAB starters STARTER 11, STARTER 21, STARTER 25, STARTER 29, and STARTER 41 were tested in four different milk-based media: plain cow's milk (as a control), evaporated cow's milk, cow's milk added with 5.0% cream milk powder, and cow's milk added with 10% skim milk powder and 8.0% cream milk powder. Each medium was homogenized, pasteurized at 85 ℃ for 30 m, inoculated with a 3.0% LAB starter, and incubated for 24, 30, 36, 42, and 48 h. The outcome showed that the total solids concentration had a substantial effect on pH (p = 0.032) and curd formation (p = 0.041), but not on titratable acidity (p = 0.117). In the study, the control treatment using plain cow's milk had the lowest pH (4.66 ± 0.02) and the highest titratable acidity (0.45 ± 0.00), suggesting that LAB thrived best under these conditions and produced a stable, well-formed curd. By contrast, milk has a higher total solids content. Specifically, cow's milk with 10% skim milk powder and 8.0% cream milk powder has fermented more slowly, having weaker acidification and softer curd, likely due to reduced bacterial activity. Extending the incubation period to 48 h substantially increases acid production and curd firmness, resulting in the best coagulation consistency. Overall, plain cow's milk devoid of solids has a longer incubation time, creating the most favorable environment for LAB, which results in optimal acidification and a stable, firm curd.