Screening Of Lactic Acid Bacteria With Antifungal And Its Application In Food

Lactic acid bacteria(LAB) are widely distributed in the natural environment,such as traditional Chinese fermented foods and animal intestine, which can produce acidics and antagonidtic metabolites for control spoilage and pathogenic bacteria.There hava been many studies about LAB that can inhibit Penicillium expansum and Aspergillus niger, it provides theoretical basis for LAB as bio-protective agent to control corruption flamentous fungi. In this paper, LAB with strong antifungal activity were isolated from kimchi, Northeast Suancai and soybean paste. The antagonistic substances and antagonistic mechanism of LAB were preliminarily analysed. In additionly, LAB as bio-preservatives were applied in bread and Fuji apple.The main results obtained in this study were as follows:1. A total of 29 LAB strains with strong antagonistic activity to Penicillium expansum and Aspergillus niger were isolated from kimchi, Northeast Suancai and soybean paste by dissolved calcium circle, Gram stain, catalase test and double agar diffusion methods. Strains SC3 and PC3 were screened from 29 LAB strains. The antibacterial rate of strain SC3 recived 61.92% and 65.96% for Penicillium expansum and Aspergillus niger, respectively. Strains SC3 and PC3 were screened from 29 LAB strains. The antibacterial rate of strain PC3 reached 62.62% and 76.03% for Penicillium expansum and Aspergillus niger, respectively. Strains SC3 and PC3 were identified as Lactobacillus plantarum and Lb. sakei, respectively, according to physiological and biochemical test and molecular biological analysis.2. The antagonistic activity was mainly existed in cell-free supernatants(CFS)for two LAB strains. The CFS produced by strain SC3 and PC3 had antibacterial activity within pH 3.0-4.0, and possessd thermal stability treatment with 121℃ for 30 min. The antagonistic activity of CFS treated with neutral protease, pepsin and papain was not significant difference with control groups. The results showed that the antagonistic substances produced from by strains SC3 and PC3 were preliminarily determined as acids compouds.3. The content of organic acids produced by strain PC3 were measured by gas chromatogramphic-mass spectrometer. The results indicated tha the retention time of acetic acid, propionic acid, lactic acid and phenyllactic acid were 2.499 min, 3.049 min,12.379 min and 5.39 min, respectively. The content of acetic acid, propionic acid and lactic acid was 5.831μL/mL, 0.09μL/mL, 61.708μL/mL and 1.863μg/mL respectively.The result of scanning electron microscopy illustrated that the spores treated with CFS were seriously deformed with apparent holes and dissolved dead, which conforms to the carpet type model in the field of antibacterial mechanism. In other words, the surface of phospholipid bilayer in the cell membrane was attacked, resulted in distorting of celland killing the cell.4. The application effects of lactic acid bacteria PC3 on sliced bread and Fuji apple has been verified according to the changes in sensory quality, water content, PH value, POD, PPO, total phenols and flavonoid of the sliced bread and Fuji apple under the action of antibacterial substances. The findings showed that strain PC3 prolonged the shelf life of sliced bread and Fuji apple, and the activity of the protective enzymes in apple such as POD and PPO was improved after being treated by the supernatant of the bacterial strain PC3. In addition, the content of phenols and flavonoid in fruit also increases significantly to improve the postharvest disease resistance of Fuji apple.