Isolation And Identification Of Antifungal Lactic Acid Bacteria From Tibetan Mushroom And Its Antifungal Mechanism

Tibetan mushroom is a traditional dairy starter cultures of integrated nutrition with health care. It is different from foreign Kefir on appearance although has somewhat similarity. The herders used it for fermenting yogurt which mold can not grow in. Therefore, we screened antifungal lactic acid bacteria, which not only ensuring safety but also having great potential.In this paper, we screened two strains of lactic acid bacteria which have a good anti-mold effect from the Tibetan mushroom fermented milk. Considering ribosomal DNA by EcoRI restriction enzyme digestion and16S rDNA series of identification, they were identified as Lactobacillus paracasei.The two inhibitory strains basically had the same characteristics of antibacterial substances. They had good inhibitory effects to molds under the condition of pH not higher than6and the lower of the pH, the better of the antifungal effect. The antifungal activity was stable during heat treatment and was retained even after autoclaving at121℃and0.1MPa for20min. The antifungal activity had no significant decrease after treatment with proteolytic enzymes (trypsin, pepsin, protease K, and alpha-chymotrypsin).They had UV absorption in the region of200～220nm but the UV absorption of at about280nm was far from the210nm absorption amount.The inhibiting activity substance had a broad spectrum of antifungal activity to Gram-positive bacteria (Staphylococcus aureus) and Gram-negative bacteria (E.coli), but the antifungal activity was not obvious to a variety of yeast. The MIC of the antifungal activities for Penicillium oxalicum was0.05mg/mL, and the minimal bactericidal concentration (MBC) was26mg/mL.The antibacterial activity of crude extracts could lead mold spores deformation and the mold spore germination was delayed.Addition of13strains and/or25strains into the milk inoculated with either Lactobacillus bulgaricus strains or Streptococcus thermophilus strains, followed by application of milk spoilage fungi (Penicillium oxalicum each with104conidia mL-1) the yogurt spoilage was significantly delayed to Lactobacillus bulgaricus strains or Streptococcus thermophilus strains used alone.however, the observed LAB starter differences in curd time, pH value, consistency and texture were not significant (p>0.05).Significance and Impact of the Study:Tibetan mushroom can be used as a source of antifungal lactic acid bacteria.Their exploitation as biopreservative will help in prolonging shelf-life of yogurt.