Identification And Screening Of Lactic Acid Bacteria For Fresh-keeping Usage And Optimization Of Fermentation Condition

Lactic acid bacteria and its fermentation production for fresh-keeping usage attract attentions of many researchers because of its nontoxicity and stronge inhibitory activity against many bacerias associate with food spoilage; while chilled meat is becoming a consume trend because of its fresh appearance and good taste.However, the preservation of chilled meat has been the chock point of its marketing development. So the object of this study was to screen lactic acid bacterias as natural food preservtives and apply them to chilled meat.5 stains of lactic acid bacteria was screened from the collection of ACCC, the supernate of which exhibited strong inhibitory acticity against Escherichia coli,Staphylococcus aureus,Bacillus cereus,Listeria monocytogenes and Pseudomomas fluorescens. According to the morphological features, physiological and biochemical features with 16S rDNA sequence analyse of the strains, 11118, 10171 and 11095 were identified as LactobacilIus plantarum, while 11050 and 11052 were identified as Lactobucillus casei.The supernate of the 5 strains screened was steady in acid conditions (about pH4) and remained about 80% baceriostasis activity after boiled at 121℃for 20 minutes. Excluded hydrogen peroxide and lactic acid, the inhibitive activity of them was decreased and even totally lost after treatment with papain, which showed that inhibitory materials included the contents with the the features of protein, could be classed as bactericin.Different factors were investigated such as the ingredients of medium, temperature, pH and inoculating amount on inhibitory activity of the supernate in order to optimize the fermentation condition. The optimum incubation time was 16h, the optimum temperature was 37℃, the optimum broth initial pH was about 6, while the optimum inoculating amount and medium component varied from strains to strains:1. The optimum inoculating amount of 11118 was 2% and its optimum medium component was: sucrose 2.5%, soybean peptone 2.5%, NaAc 0.7%, K₂HPO₄ 0.2%, Tween-80 1mL, H₂O 1000 mL;2. The optimum inoculating amount of 11050 was 3% and its optimum medium component was: lactose 2%, soybean peptone 3%, NaAc 0.5%, K₂HPO₄ 0.1%, Tween-80 1mL, H₂O 1000 mL;3. The optimum inoculating amount of 11052 was 4% and its optimum medium component was: glucose 2.5%, peptone 1.6%, yeast extract 0.8%, NaAc 0.5%, K₂HPO₄ 0.3%, Tween-80 1mL, H₂O 1000 mL; 4. The optimum inoculating amount of 10171 was 4% and its optimum medium component was: sucrose 2%, soybean peptone 3%, NaAc 0.5%, K₂HPO₄ 0.1%, Tween-80 1mL, H₂O 1000 mL;5. The optimum inoculating amount of 11095 was 4% and its optimum medium component was: maltose 2%, soybean peptone 2%, NaAc 0.5%, K₂HPO₄ 0.3%, Tween-80 1mL, H₂O 1000 mL.The fermented production of the 5 strains was applied as fresh-keeping agent on chilled pork, with the total bacteria as the parameter to value the effects of storing. When stored at 4℃, the total bacteria of the comparision group was about 10 times more than that of the groups treated with the supernate of the 5 strains, in which situation the shelf life of chilled pork could be extended about 1d; while after stored at 28℃for 8h, the total bacteria of the comparision group was more than 10⁶CFU/g and the other groups were less than 10⁵CFU/g. The fermented production of 10171 exhibited the best effect on the preservation of chilled pork.