Production of a Probiotic Soy-Soursop Yogurt Containing Lactobacillus rhamnosus yoba 2012

There is an increasing demand for functional food products developed from local resources. In this work, Lactobacillus (Lb.) rhamnosus yoba 2012 and Streptococcus thermophilus were used to produce a soy-soursop probiotic yogurt. Soy milk was supplemented with soursop pulp in amounts of 0%, 5%, 10%, and 15%. The mixtures were pasteurized at 85 °C for 15 s, cooled, inoculated with a starter and incubated at 45 °C for 24 h. Samples were taken at 0, 2, 4, 6 and 24 hours for analysis of pH, acidity, and Lb. rhamnosus yoba 2012 counts. Consumer acceptability and willingness to purchase were determined after 24 h of fermentation. The most acceptable sample was analyzed for nutritional composition. Lb. rhamnosus grew in the soy-soursop yogurt up to 8.1-9.3 log cfu/mL. The highest cell growth was observed in yogurt containing 5% soursop whereas the lowest was observed in yogurt containing 15% soursop. Yogurt pH reduced to 3.9-4.4, with 15% soursop having the lowest pH (p<0.05). Titratable acidity increased to 0.6%-0.9% lactic acid. All the yogurts were accepted although those containing 15% soursop had the lowest scores (5 = neither like nor dislike). There were no yeasts, molds or coliforms detected during the 21 days of cold storage (4 ℃) of all the yogurt. Therefore, adding soursop to soymilk produces a satisfactory probiotic soy-soursop yogurt.