The effect of additional skim and fermentation time on the amount of lactic acid bacteria and the pH of soyghurt

This study aimed to determine the effect of 5% skim and fermentation time on the number of lactic acid bacteria (LAB) of soyghurt. This study used completely randomized factorial design with 2 factors: skim addition and fermentation time. Standard soyghurt consisted of soybean juice, granulated sugar (5%), and starter (2%) containing Lactobacillus acidophilus, Lactobacillus bulgaricus, and Streptococcus thermophilus, fermented at 37oC for 10, 12, and 14 h. LAB were cultured in deMann Rogossa and Sharp (MRS) medium and then calculated by total plate count. The number of LAB in soyghurt with 5% skim addition is higher (1.76 x 108 CFU/ml) than soyghurt without 5% skim addition (5.9 x 106 CFU/ml). The number of LAB increased along with the length of fermentation. However, a significant difference in the average number of soyghurt lactic acid bacteria (p >0.05) are not found in 10 h, 12 h, and 14 h fermentation in both treatments. The longer fermentation time indicated that the pH of soyghurt was smaller. These results suggested that the addition of 5% skim and 14 h fermentation resulted in soyghurt with the highest number of LAB with pH of 3.25.