Screening Of Phenyllactic Acid Bacteria In Traditional Fermented Food And Optimization Process For Fermentation Conditions

Phenyllactic acid (PLA),2-hydroxy-3-phenylpropionic acid, it is a new type of antibacterial compound,which has been recently found in culture of lactic acid bacteria (LAB). The inhibitory properties of PLA havebeen demonstrated against both gram-positive and gram-negative. It has strong antibacterial activity in thecommon chemical preservatives and has become one of the lactic acid bacteria effective symbols ofanti-fungal ability. Moreover, Phenyllactic acid is stable in the condition of the acid and the heat, and is solublein the water. It can be evenly spread in the food system because of its safety and nontoxic, it has expected todevelop into a new type of preservative used in food industry. Therefore, the development and utilization ofphenyl lactic acid have been broaden in the application prospects. The main purpose of this study finally beable to screen out a maximum phenyl lactic acid production capacity of strains. The results are as follows:1. The screening of the strains of lactic acid in high yield Phenyllactic acidWith15kinds of traditional fermented foods for the separation of source, experiment separated out421lactic acid bacteria strains with the conventional plate; Taking antibacterial activity as an indicator, andapplying the methods of overlayer antagonistic and Oxford cup agar diffusion with the antibacterial test, theexperiment screened out32strains which have a strong inhibition to the Staphylococcus aureus and theEscherichia coli. By reverse high performance liquid chromatographic quantitative determined each straincontent of Phenyllactic acid. From the results, it is showed that LY-78has the highest Phenyllactic acidproduction capacity and is up to0.246g/L, moreve; it has a stable genetic nature.2. The identification of the Phenyllactic acid producing strain LY-78Based on the traditional bio-chemistry identification, the strain of LY-78was tested by gene amplificationand the gene sequence was measured by taking use of molecular biology method, the result were analyzed bycomparing with the16S rRNA/DNA gene sequence of the standard strains of lactobacillus. Then aphylogenetic dendrogragm was constructed. Combining with analysis of the phylogenetic dendrogragm andpartial sequences of16S rDNA, LY-78was classified as L.plantarum. The result was coincided with that oftraditional classification before.3. The optimization of LY-78lactic acid phenyllactic acid fermentation conditionsFor the production of Lactobacillus plantarum LY-78strains, On the basis of the single-factorexperiments, Orthogonal experiment to optimize the fermentation medium nitrogen source, inorganic salts,Using the response surface method to analyze the addition of glucose, Tween-80, Phenylalanine, Calciumcarbonate, separate optimized. The optimized medium composition is as follows: peptone10g/L, beef extract10g/L, yeast extract7g/L, hydrogen diammonium citrate3g/L, sodium acetate5g/L, dipotassium hydrogenphosphate2g/L, magnesium sulfate0.68g/L, manganese sulfate0.35g/L, and the phenylalanine add7.7g/L,the addition of glucose25.1g/L, the addition of Tween-808.7mL/L, the addition of Calcium carbonate12.8g/L. Single factor combined with response surface methodology to optimize the fermentation conditions, Theoptimized conditions are as follows: fermentation time74h,7%of the inoculum size, fermentationtemperature35℃, a double revolution100r/min, the initial pH7, the liquid volume to140mL/250mL. Mediaand culture conditions optimized, phenyllactic acid yield of2.13g/L and optimization of0.246g/L, comparedto the yield increased by7.65times. Confirmed by the study, a high yield phenyllactic acid lactic acid bacteria was isolated, determinationthrough morphological, physiological and biochemical indicators of16S rDNA molecular genetic analysiswere identified as follows: Lactobacillus plantarum. Up to0.246g/L; Lactic acid fermentation medium andafter the Self-optimizing Outcomes in fermentation process of35℃and74h, phenyl lactic acid yield of2.13g/L, Compared with optimized front of0.246g/L, the yield increased by7.65times.