| Traditional vegetable fermented foods contain abundant lactic acid bacteria resources that need to be explored,providing scientific support for the industrialization and modern production of specialized vegetable fermented foods.Traditional industrial fermented vegetables have a long fermentation cycle,complex and uncontrollable bacterial strains,unstable quality,and outdated processes with low standardization,greatly limiting the further development of China’s fermented vegetable industry.With the application of direct fermentation agents,selecting high-performance specialized strains from specific fermented vegetables and preparing direct fermentation agents can greatly shorten the fermentation cycle,stabilize product quality,and provide a foundation for industrial mass production.The aim of this study is to screen highperformance strains specialized for fermenting ginger from industrial fermentation broth,and to prepare highly active direct fermentation agents through high-density cultivation and vacuum freeze-drying technology,creating a set of fermentation ginger production techniques suitable for practical production.By monitoring key parameters and metabolite changes before and after fermentation,technical support and theoretical guidance are provided for industrial production.The results of this study are as follows:(1)Determination of a specific strain for direct fermentation of ginger.102 strains of edible lactic acid bacteria were screened from 35 samples of ginger fermentation broth collected by the factory.After 16 S r DNA identification,39 strains were identified,including 32 strains of Lactobacillus plantarum,2 strains of Lactobacillus acidophilus,2 strains of Streptococcus pentosus,and 1 strain of Lactobacillus rhamnosus.The acidity and salt tolerance achievement test showed that 39 strains of lactic acid bacteria had p H in the range of 3.61～4.27,TA in the range of 10.09～16.89g/kg,and 10 strains of lactic acid bacteria had good salt tolerance under salinity of 4%,7%,and 10%.The nitrite reducing achievement test test of 10 strains of lactic acid bacteria showed that10 strains of lactic acid bacteria had good nitrite degrading capacity,and the degradation rate was more than 90%.Next,the acid resistance and bile salt tolerance of Lactobacillus plantarum NCU001792 were tested.Incubated in an acidic environment with p H=3,the acid resistance survival rate of Lactobacillus plantarum NCU001792 reached 83.3%.Incubated under 0.5% bile salt conditions,the survival rate of Lactobacillus plantarum NCU001786,Lactobacillus plantarum NCU001790,Lactobacillus plantarum NCU001800,and Lactobacillus plantarum NCU001810 reached over 80%.Six strains of lactic acid bacteria with better performance were screened for adhesion performance evaluation,among which Lactobacillus plantarum NCU001800 had strong adhesion ability,reaching 68.77%.The safety evaluation of the 6 strains of lactic acid bacteria showed that none of them had hemolytic activity,and all strains were resistant to some antibiotics,but the risk of drug resistance gene transfer was relatively low.Finally,according to the PCA score,it was found that Lactobacillus plantarum NCU001792 had the best performance and was used as the final specialized strain for ginger fermentation.(2)Optimization of high-density cultivation of Lactobacillus plantarum NCU001792.Under the composition conditions of the basic MRS culture medium,using the number of live bacteria as an indicator,a single factor experiment was conducted to optimize the types and concentrations of carbon source,nitrogen source,buffer salt,trace elements,and growth factors.Then,three significant factors were selected through PB experiment,including beef soaking powder,Vc,and yeast powder.Then,through the steepest climbing experiment,2% yeast powder,3.5% beef dipping powder,and 500mg/L Vc were selected as the center points for subsequent CCD.The optimal solution combination was ultimately determined as follows: the addition amount of beef soaking powder was 36.00g/L,the addition amount of yeast powder was 20.04g/L,and the addition amount of Vc was 0.49g/L.At this point,the number of viable bacteria after cultivation reaches 5.2 * 10^9 CFU/m L。 Subsequently,p H,temperature,inoculation amount,and shaking table speed were optimized through single factor experiments.The optimal static cultivation conditions were determined as follows: initial p H of 7.5,cultivation temperature of 30 ℃,inoculation amount of 3%,and shaking table speed of 220 r/min.Optimize the high-density cultivation conditions of Lactobacillus plantarum NCU001792 using a 3-L fermentation tank.Optimize the stirring speed,constant p H,different neutralizers,and different gas environments.The optimal combination obtained is: stirring speed of 200r/min,constant p H of 7,selection of 25% ammonia water as the neutralizer,and introduction of sterile air for cultivation.At this point,the bacterial concentration reaches 1.92 * 10^10 CFU/m L,which is 6.2times higher than that of ordinary MRS without optimized culture medium.(3)Optimization of vacuum freeze-drying conditions for Lactobacillus plantarum NCU001792.Through the influence of different protective agents on the freeze-dried survival rate of Lactobacillus plantarum NCU001792,it was determined that 12.5%sodium glutamate was the best freeze-dried protective agent,with a freeze-dried survival rate of 82.07%.Then,through a single factor experiment,the pre freezing time,centrifugal speed,the ratio of bacterial sludge to protective agent,and pre freezing temperature were optimized.The optimal solution combination was determined as follows: pre freezing time of 2 hours,centrifugal speed of 5000r/min,the ratio of bacterial sludge to protective agent of 1:1,and pre freezing temperature of liquid nitrogen freezing.At this time,the freeze-drying survival rate reached 83.1%.At this point,the number of live bacteria reaches 6.81 * 10^12 CFU/m L。(4)Optimization and determination of the direct fermentation process for ginger with Lactobacillus plantarum NCU001792 and quality monitoring of the fermentation process.Single factor optimization of seed quantity,sugar content,and salt content through sensory evaluation scores.The optimal process was determined as follows: the inoculation amount was 10^6 CFU/m L,the sugar content was 3%,and the salt content was 3%.On the 7th day,the direct fermentation of ginger has matured,with a p H of3.28 and a TA of 7.11 g/kg,greatly shortening the fermentation time.In the later stage of fermentation,the nitrite content in ginger through direct fermentation is 1.25 mg/kg,which is lower than other fermentation methods.During the fermentation process,a total of five organic acids were detected,namely oxalic acid,malic acid,lactic acid,acetic acid,and propionic acid.In the later stage of fermentation,the malic acid content,lactic acid content,and propionic acid content of direct fermentation ginger were higher than those of other fermentation methods.During the entire fermentation process,a total of 81 volatile flavor compounds were detected in the direct fermentation of ginger:30 alcohols,28 olefins,9 aldehydes,10 esters,and 4 ketones;A total of 47 volatile flavor compounds were detected in naturally fermented ginger,including 17 alcohols,15 alkenes,6 aldehydes,7 esters,and 4 ketones.Moreover,the content of volatile flavor compounds in directly fermented ginger was higher.Based on PCA analysis,it was found that there was no significant difference in volatile flavor compounds between direct fermentation and natural fermentation of Huangjiang on the 5th and 7th days,while there were significant differences in other groups.Based on OPLS-DA analysis,there are 32 differential metabolites between direct fermentation mature ginger and factory mature ginger samples,26 differential metabolites between direct fermentation mature ginger and natural fermentation mature ginger samples,and direct fermentation mature ginger has richer volatile flavor compounds. |
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