Research On Direct Bacterial Fermented Vegetable Compound Starter

Fermented vegetables preserve most of the nutrients in raw vegetables,are rich in nutrients and are good for your health,It is one of the many standing foods on the table of many consumers,but the stability and safety of fermented vegetable products caused by insufficient processing technology,natural fermentation-based fermentation and nitrite accumulation have always existed,and direct investment Compound starter can shorten the fermentation cycle of kimchi,help standardize,specialize and unify the production and processing of kimchi,and improve the quality,safety and stability of fermented products.Therefore,in this study,lactic acid bacteria with excellent performance were isolated and identified from naturally fermented peppers.On this basis,the compound fermentation agent was compounded,and then the lactic acid bacteria high-density cultivation process,immobilization method,and freeze-drying protection agent ratio were compared Research,the main research content and results are as follows:(1)Isolation and identification of excellent strains.From the commercially purchased and laboratory-made fermented peppers,80 strains of suspected lactic acid bacteria producing calcium-soluble circles,Gram-positive,and catalase-negative bacteria were isolated.Their growth activity,acid production capacity,and nitrite degradation capacity were The indicators were screened multiple times to obtain two suspected lactic acid bacteria strains with excellent performance.The two strains screened and the Lactobacillus plantarum LP-7501S screened by the research team in the early stage were subjected to growth curve measurement.The time is not much different,and the growth habits are similar,indicating that these three strains are suitable for compounding,and then the two strains selected are molecularly identified.The results show that both strains are Lactobacillus fermentum,named LF-8001 and LF-8002,the growth activity and acid-producing ability of these two strains are better than those of other strains isolated,and the nitrite degradation ability is above 95%,respectively 95.86%and 98.69%.(2)Determination of the ratio of compound starter.Taking the acid production capacity,nitrite degradation capacity,and sensory evaluation as indicators,the best compound starter formula is:LF-8001:LF-8002:LP-7501S=3:3:2,and the fermentation is carried out.The nitrite content of fermented peppers is lower than that of single strain fermentation and naturally fermented peppers,and the sensory evaluation of peppers fermented according to this composite starter formulation is significantly better than single strain fermentation,which is close to natural fermentation to mature peppers.The color of fermented peppers is naturally bright red,and the texture is relatively uniform.It has the unique fermentation aroma of fermented peppers.The aroma is rich,the sour and spicy is moderate,and the flavor is coordinated.(3)High-density cell culture of lactic acid bacteria.The three strains of the compound starter formula were cultured in high density,using the concentration of bacteria as an indicator,through a single factor experiment on the initial p H,inoculation amount,culture temperature,the type of added nutrient factors and the type of neutralizer.Based on the experiment,an orthogonal experiment was designed to determine the best high-density culture method for the three strains:The high-density cultivation method of LF-8001 is:using 2%zucchini juice as an additional nutrient factor,using K₂HPO₄ solution as a neutralizing agent,adjusting the initial p H of MRS medium to 7,and inoculating 6%LF-8001 at 30?From constant temperature cultivation to stable period,the bacterial concentration of LF-8001 reached 1.08*10¹⁰ CFU/ml,which was 9.6times that of non-high density cultivation.The high-density cultivation method of LF-8002 is:using 2%potato juice as an additional nutrient factor,using Na OH solution as a neutralizer,adjusting the initial p H of MRS medium to6.5,inoculating 5%LF-8002 at 36?From constant temperature cultivation to stable period,the bacterial concentration of LF-8002 reached 1.32*10¹⁰ CFU/ml,which was 9.3 times that of non-high density cultivation.The high-density cultivation method of LP-7501S is:using 2%cucumber juice as an additional nutrient factor,using Na2CO3 solution as a neutralizer,adjusting the initial p H of MRS medium to 7,and inoculating 5%LP-7501S at 32?From constant temperature cultivation to stable period,the bacterial concentration of LP-7501S reached 8.77*10⁹ CFU/ml,which was10.1 times that of non-high density cultivation.(4)Immobilization of lactic acid bacteria.The three strains in the compound starter formulation were immobilized separately.Based on the embedding rate and nitrite degradation rate,combined with the physical parameters of the immobilized pellet,a single factor test was carried out on the mixing ratio,temperature and calcium chloride concentration.Based on the single-factor experiment,an orthogonal experiment was designed to determine the optimal immobilization method for the three strains:LF-8001's immobilization method is:take a solution containing 1.2%sodium alginate+0.5%sodium carboxymethyl cellulose as the immobilization solution,and mix the bacterial solution and immobilization solution in a ratio of 1:4,and then drop by drop Slowly drop into 4%calcium chloride solution and fix it at a constant temperature of 25?for 2h.Under this condition,the embedding rate is high.The immobilized pellet has a nitrite degradation rate of 91.23%and a bacterial concentration of 1.49*10¹¹CFU/g.LF-8002's immobilization method is:take a solution containing 1.2%sodium alginate+0.5%sodium carboxymethyl cellulose as the immobilization solution,and mix the bacterial solution and immobilization solution in a ratio of 1:4,and then drop by drop Slowly drop into 3%calcium chloride solution and fix at a constant temperature of 25°C for 2h.Under this condition,the embedding rate is high.The nitrite degradation rate of the immobilized pellet is 89.23%,and the bacterial concentration is 1.98*10¹¹CFU/g.The immobilization method of LP-7501S is:take a solution containing 1.2%sodium alginate+0.5%sodium carboxymethyl cellulose as the immobilization solution,and mix the bacterial solution and immobilization solution at a ratio of 1:4,and then drop by drop Slowly drop into 4%calcium chloride solution and fix it at a constant temperature of 30?for 2h.Under this condition,the embedding rate is high.The immobilized pellet has a nitrite degradation rate of84.61%and a bacterial concentration of 7.84*10¹⁰CFU/g.(5)Freeze drying of lactic acid bacteria.Using the freeze-drying survival rate as an indicator,the types of protective agents that have better protective effects on the three strains of bacteria are obtained through test screening.The three protective agents of trehalose,sorbitol,and lactose have good protective effects on LF-8001,so that The survival rate of freeze-drying is greatly improved,all of which reach more than 50%;while the three protective agents of skim milk,sorbitol,and sucrose have good protective effects on LF-8002 and LP-7501S.Then through the response surface optimization test,the best freeze-dried protective agent formula for the three strains is:The best protective agent ratio of LF-8001 is:use a solution containing 8.72%trehalose+8.44%sorbitol+1.64%lactose as the protective agent,the immobilized pellet and the protective agent are mixed in a ratio of 1:2,in Under this condition,the survival rate of freeze-dried cells is82.46%;The best protective agent ratio of LF-8002 is:take a solution containing 22.96%skim milk+12.78%sorbitol+17.53%sucrose as the protective agent,the immobilized pellets and the protective agent are mixed in a ratio of 1:2,in Under this condition,the survival rate of freeze-dried cells is 83.49%;The best protective agent ratio of LP-7501S is:take a solution containing 24.66%skim milk+12.26%sorbitol+18.92%sucrose as the protective agent,the immobilized pellet and the protective agent are mixed in a ratio of 1:2,Under this condition,the survival rate of bacterial freeze-drying is 86.44%;(6)Application of direct-injection starter in vegetable fermentation.The prepared direct-injection composite starter was applied to the fermentation of peppers,and its nitrite content was significantly lower than that of single fungus powder fermentation and naturally fermented peppers during fermentation and maturity.Nearly naturally fermented to mature peppers,the color is naturally bright red,with a rich fermentation aroma unique to fermented peppers,moderate sour and spicy,harmonious flavor,and more uniform texture.