Screening And Application Of Lactic Acid Bacteria Degrading Nitrite From Papaya

The study used papaya with different maturity as material to screening lactic acid bacteria (LAB) with excellent properties and the ability of efficient degradation of nitrite.63strains LAB were screened from papaya. Cultured for48hours with MRS+NaNO2medium, the63strains with ability of nitrite degradation were preliminary analyzed, and24strains of LAB with higher degradation rate were screened. The24strains LAB were rescreened, and finally selected six representative strains MGP1, MGP2, MGP11, MGP15, MGP16and MGP17. According to the results of physiological and biochemical analysis and16S rRNA gene sequence analysis, we concluded that MGP1, MGP11, and MGP16were Weissella confusa, MGP2was Lactococcus lactis subsp lactis., MGP15classed to Leuconostoc pseudomesenteroides, MGP17was Lactobacillus pentosus. MGP1, MGP11, and MGP16were the same species, so we chose MGP11, MGP2, MGP15and MGP17for the future study.To learn more about these four strains of nitrite degradation, the factors (carbon, nitrogen, NaNO2concentration, inoculation, vaccination age, initial pH value of the medium and temperature) that may affect the degradation rate of the strains were studied. The results showed that the four strains did not degrade nitrite when soluble starch was used as carbon source, degradation rate of the four strains were the highest when yeast extract used as nitrogen, lowest in ammonium sulfate and urea. The degradation rate of MGP2and MGP17are very high in nitrite concentration of100mg/kg-300mg/kg, slightly lower in sodium nitrite concentration of400mg/kg-500mg/kg; the degradation rate of MGP11and MGP15were the highest in nitrite concentration of100mg/kg, then with increasing concentration of sodium nitrite, degradation rate declined.The optimum inoculation amount of MGP2was2%when MGP2degraded NaNO2, vaccination age was12h, the most suitable pH value was in the range of5.0-7.0, the nitrite degradation rate was the highest in pH6.0, the degradation rate was high in the temperature range of25℃-40℃, the most suitable temperature was37℃. The optimum inoculation amount of MGP11was6%when MGP11degraded NaNO2, vaccination age was16h, the optimum pH value was in the range of5.0-7.0, the degradation rate of NaNO2was the highest in pH5.5; the optimum temperature of NaNO2degradation was in the range of30℃-40℃.When the inoculation amount of MGP11was4%, its degradation effects was the best; vaccination age was8h, the most suitable temperature range was30-37℃, optimum pH range was6.0-6.5. The optimum inoculation amount of MGP17was2%when it degraded NaNO2; vaccination age was12h; the optimum range of pH value was4.5-7.0, when the initial pH value of medium was5.5, its NaNO2degradation rate was the highest, the most suitable temperature range was25-45℃, the degradation rate was the highest at37℃Finally, MGP2, MGP15and MGP17were applied in to sauerkraut fermentation. Papaya with maturity of50%-60%as material, inoculated lactic acid bacteria to ferment papaya sauerkraut. The quality of papaya sauerkraut fermented with MGP2, MGP15and MGP17was better compared to papaya sauerkraut fermented with lactic acid bacteria came from other plants. We determined that the sensory evaluation of papaya sauerkraut fermented with the three strains mixture was the best in the single experiment. Based on the result of single experiment,the response surface method was used to optimized the fermentation process, optimum concentration of sugar and salt were3.8%,2.8%, inoculum amount was5%, and optimum temperature was31.23℃. According to the optimized the fermentation process, experimental rechecking was performed. The total acid of papaya sauerkraut was9.32g/kg, nitrite content have decreased to0, sensory evaluation score was90.67, which illustrated that the quality of papaya sauerkraut fermented with optimized fermentation process was better.