| Fermented vegetable is a product which is fermented from untreated or treated vegetable by using microorganisms carried by the raw material itself or by artificial inoculation of microorganisms.Besides the characteristics of pure sour taste,crispness,delicacy and appetizing,it has also attracted the attention of consumers and researchers because of its rich probiotic flora and various probiotic functions.At present,there are few studies on the structure of bacterial flora,the changes of antioxidant activity and their correlation in the process of continuous natural fermentation and natural fermentation with different formulas;the salt and acid tolerance of probiotic flora commonly used in inoculated fermentation,the synthesis of antioxidant activity,nitrite production and other physical and chemical indexes in the process of inoculated fermentation;and the traditional fermented vegetable products in Shaanxi Province.There are few reports on antioxidant activity and composition of bacterial flora.In this study,the biological characteristics of Shaanxi traditional fermented vegetable products,natural fermented vegetable,continuous natural fermented vegetable and inoculated fermented vegetable were studied,including microflora characterization,diversity of bacterial community structure,antioxidant activity and nitrite physical and chemical indicators.Through the experimental study,the following results are obtained:Biological characteristics of traditional fermented vegetable products on the market.Nineteen typical commercial fermented vegetable samples from Shaanxi Province were collected.Firstly,the microscopic characterization,antioxidant activity and physical and chemical indexes of the samples were analyzed.The results showed that the dominant bacteria in the samples were mainly coccus and bacillus.Ten of the 19 samples detected SOD activity,the highest was(100.54 ± 16.77)U/mL.The highest reduction power and DPPH free radical scavenging rate of each sample were(99.12±2.73)ug/mL and(96.75±0.71)%.The physicochemical indexes met the standard.Secondly,five samples(HBZ1,HBZ2,LHL2,LHL5,LHL6)with abundant bacteria were selected to analyze the diversity of bacterial community structure and fungal community structure using Illumina Miseq high-throughput sequencing technology.The results showed that the dominant bacterial flora were mainly Staphylococcus and Lactobacillus.The richness of Staphylococcus in HBZ1 was 59.59 %,the highest of the three OTUs belong to Bacilli and add up to 32.53 % in HBZ1,82.34 %,88.58 %,94.94 % and 93.74 % in the other four samples,respectively.The dominant flora of fungi were yeast.There were 13,15,9,7 and 9 species of fungi with relative abundance of more than 1% in the five samples.The highest abundance of fungi were Kazachstania bulderi,Pichia membranifaciens,Issatchenkia orientalis,Dipodascus Geotrichum and Kazachstania bulderi,accounting for 29.66 %,26.37 %,30.73 %,28.51 % and 50.75 %。Changes in biological characteristics of natural fermented vegetables.The microcharacterization,antioxidant activity and physicochemical indexes of continuous natural fermentation with different water addition(3000 mL,3500 mL),different formulations(condiments,medicinal and edible homologues,condiments and medicinal and edible homologues)were studied.The results showed that the dominant bacteria were bacteria at the end of fermentation.Compared with before fermentation,the antioxidant activity increased.SOD fluctuated during the process of increasing gradually,and the range of reducing power fluctuated and increased slightly.DPPH increased rapidly in the first two days and then stabilized at more than 91.00%.The highest SOD activity was(16.32±1.31)U/mL,the highest DPPH free radical scavenging rate was(95.60±0.15)% and the highest reducing power was(26.15±1.75)ug/mL.Different formulations had certain effects on the composition of bacteria in the process of fermentation of vegetables.The number of cocci increased gradually after the beginning of fermentation.There were more bacteria in the first two groups at bunch time,and cocci were more likely to adhere to vegetable surface;antioxidant activity increased gradually during fermentation.Among them,SOD activity showed an overall upward trend.The reducing power of the condiment group decreased slightly on the second day,while that of the other two groups showed an upward trend.DPPH free radical scavenging rate increased rapidly on the first day,and then fluctuated in the range of 89.54%-97.15%.The SOD activity and DPPH free radical scavenging rate of the drug-food homologue group were the highest,reaching the maximum values on the 7th day of fermentation respectively(16.58±1.37)U/mL and(97.15±0.60)%.Referring to the above results,continuous natural fermentation was carried out.The results showed that the first two generations were dominated by bacteria,yeasts and cocci appeared in the 3rd and 4th generations.After the 5th generation,the bacteria increased gradually.Bacillus is the dominant bacterial group in post-fermentation vegetables,and continuous natural fermentation has higher antioxidant activity than natural fermentation.Among them,the activity of SOD fluctuated with the highest SOD activity of(82.22±6.71)U/mL,and the reducing power showed an upward trend.The highest reducing power was(54.35 ± 2.84)ug/mL,which was 2.6 times higher than that before fermentation.DPPH radical scavenging rate increased rapidly in the 0th to 1st generation,and then fluctuated,the maximum was(99.09±0.50)%.Except for the total acid of continuous natural fermentation,the physical and chemical indexes of natural fermentation process were in line with the national standards.Changes of biological characteristics during inoculation and fermentation of vegetables.Firstly,the tolerance of 13 probiotics to salt concentration and pH was studied.The results showed that 13 probiotics grew better when the salt concentration was less than 7%,and the pH value was equal to 5~7.The changes of antioxidant and physicochemical properties during fermentation of vegetable inoculated with 10% inoculation using Lactobacillus plantarum,Lactobacillus casei,Staphylococcus lactis and Lactococcus lactis were studied.The results showed that the activity of SOD and the reducing power of DPPH increased rapidly in the first 3 days,and then fluctuated.SOD activity,reducing power and DPPH free radical scavenging rate reached the maximum on the 7th day,respectively(16.12±1.25)U/mL,(26.30 ±2.89)ug/mL,(93.23±0.18)%.Physical and chemical indicators were in line with national standards. |
