The objective of this study is to identify the effect of two commercial Lactobacillus cultures, Lactobacillus plantarum (A) and a mixture of Lactobacillus rhamnosus, Lactobacillus plantarum and Lactobacillus paracasei, on the control of mold contamination, nutrients, texture and sensory qualities of stirred yogurt. The results demonstrated that these two cultures exerted different degrees of inhibition on mold growth. Culture B led to higher degree of mold inhibition than culture A when added at the manufacturer recommended amount (A: 2.0 × 106 CFU/mL, B: 1.38 × 107 CFU/mL). In contrast, culture B at 2.0 × 106 CFU/mL had less inhibition capability than culture A. The flavor of yogurt was adversely affected by culture B, while culture A showed no effect during the shelf-life period. Compared with the control group, the nutrients and texture of yogurt with culture A or B were not changed greatly. In conclusion, Lactobacillus cultures can inhibit the growth of mold in yogurt, where its bacteriostatic ability is related to the species and concentration of strains added.

The objective of this study was to determine the growth curves and antibacterial activity of two different strains of Lactobacillus salivarius. Streptococcus mutans, Porphyromonas gingivalis and Staphylococcus aureus were selected to perform antibacterial tests in vitro by the Oxford cup method. The results showed that the logarithmic growth phase of the two strains of Lactobacillus salivarius began respectively at 2 and 4 hours after inoculation and ended both at 8 hours, and the stationary phase began at 14 and 16 hours, respectively. It was proved that the bacteria cultures of both strains of Lactobacillus salivarius and their metabolites had antibacterial activity against Streptococcus mutans, Porphyromonas gingivalis and Staphylococcus aureus, and the antibacterial activity against Streptococcus mutans and Porphyromonas gingivalis was stronger than that against Staphylococcus aureus. Also, for both strains, neither bacterial sludge nor metabolite with an adjusted pH value (7.0) had antibacterial activity. Antibacterial activity of both strains of Lactobacillus salivarius came mainly from their metabolites, and it were acid or acid-dependent materials that play a key role in the antibacterial activity of metabolite.