2.7. Production and analysis of probiotic yogurt
Lactobacillus plantarum SY11 and L. plantarum SY12 were cultivated in MRS broth at 37 °C for 24 h and harvested by centrifugation at 8000 × g for 20 min at 4 °C. The harvested cells were washed twice and freeze-dried for use as yogurt starter.
The production of probiotic yogurt was carried out using 3 different samples. Pasteurized milk (1 L; Seoul milk, Korea) was purchased at a local supermarket, repasteurized at 90 °C for 10 min and cooled down to 40 °C. The milk samples were then inoculated with a mixed culture (1:1) of S. thermophilus TH-4 (Chr. Hansen, Denmark) and another LAB strain (L. plantarum SY11, L. plantarum SY12, or L. acidophilus CH-2). These inoculated milk samples were incubated at 40 °C until a pH of 4.4–4.5 was reached.
Microbiological and physicochemical of the 3 samples were performed. The pH and titratable acidity (TA) was measured using a pH meter and titration with 0.1 N NaOH, respectively (Lee, 2001). LAB counts were estimated using bromocresol purple (BCP) plate count agar (Eiken Co., Tokyo, Japan).