The Optimization Of Lactobacillus Acidophilus NX2-6 Medium For Antibacterial Production And Its Application In The Cherry Tomatoes Preservation

In recent years,the media constantly exposed food preservatives accidents,people gradually realized that many problems because of chemical preservatives,Because of its safety、pollution and other features,biogenic preservative slowly come.into people’s attention.Lactic acid bacteria is an internationally recognized intestinal probiotic which can improved flora.So it can be directly used in food.Many studies have shown that lactic acid bacteria can produce inhibitory substances in fermented foods,Further more it has become the new bio-preservatives potential.In this study,Based on preliminary laboratory research on Lactobacillus acidophilus NX2-6,We optimizate modified MRS medium for Lactobacillus acidophilus NX2-6,and study the preparation of fermentation broth lyophilized and apply freeze-dried powder in fresh cherry tomatoes,the main results are:1.Optimization of Low-skim-milk whey soy medium(LWS)Lactobacillus acidophilus NX2-6:On the basis of modified MRS medium,by single factor we ensure the factors which acidophiluS generate antibacterial activity,these are lactose,skim milk,enzymatic soy flour,enzymatic whey powder,yeast extract,sodium acetate,Tween-80,K2HPO4·3H2O.Because the high price of skim milk,and it easlly to form macromolecules,which maybe make for the difficult of segregation of antibacterial substances,so the content of skimmed milk is fixed at 10 g/L.Built on of the single factor,PB experiments ensure key factors which can influence antimicrobial activity of antibacterial substances of Lactobacillus acidophilus NX2-6,Taking Box-Behnken Design(BBD)experiments,we can ensure the key factors,enzymatic soy flour,enzymatic whey powder,Tween-80,The medium consist of enzymatic soy flour 58.7 g/L,enzymatic whey powder 13.9 g/L,Tween-80 36.1 g/L,yeast extract 2.5 g/L,lactose 40 g/L,sodium acetate 10 g/L,skim milk lOg/L,After three times parallel tests,the last inhibition zone is 21.82 ± 0.14mm.On the other hand,the inhibition zone of modified MRS medium is 13.47 ± 0.09mm,In a word,which improve 1.6 times.2.Preparation of lyophilized powder of Lactobacillus acidophilus NX2-6 fermentation:(1)The preparation of Lactobacillus acidophilus NX2-6 low-skim-milk fermented food medium broth lyophilized powder and potency:20%corn flour are added into the fermentation supernatant,then the complex are freeze-dried,the freeze-dried powder was reconstituted to the original volume by 0.02 mol/L hydrochloric acid,the titer of which is 28610.19 IU/ml.(2)The preparation of Lactobacillus acidophilus NX2-6 LWS broth lyophilized powder and potency:15%corn flour are added into the fermentation supernatant,then the complex are freeze-dried,the freeze-dried powder was reconstituted to the original volume by 0.03 mol/L hydrochloric acid,the titer of which is 35091.34 IU/ml,which can effectively restrain Gram-positive and Gram-negative bacteria,and can better restrain Gram-positive bacteria growth.3.The preservative effect of Lactobacillus acidophilus NX2-6 antibacterial substances on cherry tomatoes preservation:By determining the effect of compound preservative on rotting rate,weight loss,firmness,a*/b*and other indicators during storage of cherry tomatoes,The results showed that the compound preservative can effectively delay the rotting rate of cherry tomatos,reduce water transpiration,delay fruit softening.The results of POD activity,SOD activity,TSS show that the compound preservative can effectively clear the fruit peroxides,free radicals and other substances,cut down the nutrients of cherry tomatoes,so that the fruit can maintain a high nutritional value.In a word,N.4 group(1%alginate+LWS fermentation broth + 0.05%ε-PL)is the best preservative compound.