The influence of addition of various sweet potatoes (Ipomea batatas) extract to total count of cells and antioxidant activity in yogurt

Abstract

Retnati, Andriani MAM, Fauza G. 2009. The influence of addition of various sweet potatoes (Ipomea batatas) extract to total count of cells and antioxidant activity in yogurt. Biofarmasi 7: 68-76. The aim of this research was to determine the influence of addition of various sweet potatoes extract to the total count of cells and the antioxidant activity in yogurt. Yogurt was made from fresh milk, skim milk, white sweet potato, orange sweet potato, purple sweet potato, and pure culture of Streptococcus thermophilus 0040 and Lactobacillus bulgaricus 0041 in straight MRS agar. Fresh milk, skim milk powder (5%, b/v), and sweet potato extract (10%, v/v) was pasteurized at 90oC for 15 minutes, cooled to the temperature between 40-45oC, inoculated with 2.5% S. thermophilus and L. bulgaricus with a proportion of 1.4:1, and then incubated at a temperature of 40oC for 15 hours. Yogurt without an addition of sweet potato extract was used as control. The parameters measured in this experiment were the total count of cells with TPC (Total Plate Count) method and the antioxidant activity with DPPH (2,2- diphenyl-1-picrylhydrazyl) method. Samples were taken at one hour interval to examine the total count of cells, while the antioxidant activity was collected at three hours interval. The result of each analysis was plotted into graphics which describing the relation of total bacteria and antioxidant activity with fermentation time. ANOVA was employed to analyze the data. If there was a significant difference, it should be followed by Duncan Multiple Range Test (DMRT) at a significance level α=0.05. The result of this research showed that the addition of various sweet potatoes extracts increased the total count of cells and the antioxidant activity in yogurt. The total count of cells showed no significant different for each sample, it meant that the different colors in sweet potato did not influence the total count of cells. However, yogurt with orange and purple sweet potato extract addition had a significant difference on the antioxidant activity with control and yogurt with white sweet potato extract. In conclusion, the difference colors in sweet potato influenced in the antioxidant activity in yogurt significantly. Sweet potato is potential for milk substitute in yogurt production due to oligosaccharide content and antioxidant activity.