| Pickle is a traditional flavor food formed by fermentation of microorganisms with fresh vegetables as raw materials.Although pickle have different production methods and flavores from place to place,they are all fermented by lactic acid bacteria.In this study,functional lactic acid bacteria with good production performance,extracellular polysaccharide production and certain stress resistance were screened from high-quality pickle water,the construction of fermentation probiotics and the determination of the optimal ratio of fermentation agents were carried out to optimize the fermentation process.Using different cabbage as raw materials,adding the fortified starter,in-depth research on the physical and chemical indicators,product sensory,bacterial community,organic acids and volatile flavor substances in the fermentation process,and the effects of raw materials on the fermentation process and product quality of pickle.The research results were as follows:(1)Isolate and purify 26 strains of lactic acid bacteria from commercially available pickle water,and select functional strains based on several indicators such as acid production rate,nitrite degradation rate,extracellular polysaccharide production,acid tolerance,and bile salt hydrolase activity,and finally screen three strains of lactic acid bacteria were produced.Three lactic acid bacteria were identified,ZY15 as(Lactobacillus plantarum),ZY19 as(Lactobacillus xiangfangensis)and JY12 as(Lactobacillus brevis).(2)Taking natural fermentation as a control,inoculate three pure strains and their mixed strains into vegetables for fermentation characteristic studies,determine the p H value,total acid content,nitrite content,and the number of lactic acid bacteria in pickles and make sensory scores.The results showed that the total acid content of pickle in the inoculated fermentation group was between 0.678-0.824%,which was higher than the control group's 0.516%.The nitrite content of the mixed bacteria fermentation group was relatively low at 1.58 mg/kg,and the single bacteria fermentation group was between 2.06-2.23 mg/kg,which was lower than the control group at 6.31 mg/kg.The number of lactic acid bacteria in the mixed fermentation group was lower,only 9.6×10~7 CFU/m L.The sensory evaluation performance is better in the mixed bacteria fermentation group and the natural fermentation group,with sensory scores of 88.5 and89.3.The results of pickle's starter optimization test showed that:the fermentation effect was best when the ratio of mixed bacteria was ZY15?ZY19?JY12=2?1?1.The mixed bacteria mixed with mature pickle water as a starter,can make up for the poor flavor of inoculated fermented pickle,and the optimal ratio of mixed bacteria and pickle water was 2?1.Through the orthogonal test,the best process conditions for pickle fermentation were determined as 5%salt addition,3%sucrose addition,30%starter addition,and 30?fermentation temperature.(3)Select four groups of cabbages with significant differences in material content to make pickle,and analyze the correlation between the raw materials and the fermentation of pickle.The results showed that the correlation coefficient between cabbage nitrogen content and total acid content in pickles was-0.941,indicating that the less nitrogen content was in the raw material,the faster the total acid was accumulated in pickle;cabbage nitrogen content and nitrite content were significantly positively correlated(P<0.05),and the peak value of"nitrous peak"reached during the fermentation of pickle was significantly different(P<0.05).The content of nitrite in mature pickle was between 1.16 and 1.79 mg/kg,and the food safety of pickle was not affected.The number of lactic acid bacteria in pickle is negatively correlated with the total phenol content of raw materials(P<0.05).The more phenolic substances in cabbage,the less the number of lactic acid bacteria in pickle.(4)The bacterial diversity of pickle fermented by different cabbages was analyzed.The results showed that the number of OTU in the NC group with relatively low nitrogen content among the four groups of pickle was highest,between 142 and 210.5.The Chao1 index was also higher than the other three groups,which showed that the colony abundance was the largest among the four groups of pickle.During the fermentation of pickle,Lactobacillus occupieds a dominant position from the beginning to the end.The species abundance increased in the middle of the fermentation.Bacterial diversity in pickle fermentation was early>late>middle.Therefore,the differences in the samples of the four groups of samples at different fermentation times based on PCo A analysis found that:as the fermentation progressing,the colony structure in pickles was changing.(5)The quality analysis of pickle fermented with different raw materials found that the organic acids in the 4 groups of pickle were mainly oxalic acid,acetic acid and lactic acid,with the highest oxalic acid content was 56.144 mg/g.With the fermentation,the oxalic acid content in pickle gradually decreased and the content of lactic acid,acetic acid and succinic acid gradually increased.The SPME-GC-MS combined method was used to analyze the volatile flavor substances in the four groups of pickles,and a total of 7 major flavor substances such as esters,alcohols,aldehydes,ketones,acids,phenols and alkanes were detected.The relative contents were 57.89%,58.86%,60.2%,77.3%and 13.12%,15.47%,20.1%and 0%,of which alcohols and aldehydes were relatively high.Pickle with high raw material nitrogen content and rich microbial diversity contained a large variety of aromatic substances and relatively high content.Correlation analysis of amino acid nitrogen(AAN),organic acids,volatile flavors and pickle sensory scores in pickle found that:AAN content was positively correlated with sensory scores of pickle,which played an important role in improving the quality of pickle;The sensory score was significantly positively correlated(P<0.05),which was the main component of the aroma of pickle;Organic acids were negatively correlated with sensory scores. |
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