Sample preparation
Yogurt milk with 12.0% dry matter was formulated using reconstituted skim milk powder. After heat treatment (90°C–15 min), cooling to inoculation temperature (40°C) and addition of yogurt starter culture, treatments were inoculated with different probiotic single strain cultures (106 cfu mL-1). The treatments were incubated at 40°C until pH of 4.5 ± 0.02 was reached. The yogurts were stored for 24 h at two different temperatures including cold or room temperatures (5 or 20°C, respectively). Therefore, eight treatments were produced; namely yogurts containing L. rhamnosus HN001 stored at 5°C (RY-5) or 20°C (RY-20), L. paracasei Lpc-37 stored at 5°C (PY-5) or 20°C (PY-20), L. acidophilus La-5 stored at 5°C (AY-5) or 20°C (AY-20), and B. Lactis Bb-12 stored at 5°C (BY-5) or 20°C (BY-20). Changes in pH decrease, redox potential increase and titratable acidity increase as well as the viability of probiotics per 6-h intervals during 24 h of storage were monitored.