Screening And Application Of Fermented Mustard Lactic Acid Bacteria

Brassica juncea is an important fermented vegetable in the country,and fermented Brassica juncea is a kind of food with Chinese regional characteristics.Typical examples are Hunan mustard,Sichuan kimchi,Guizhou sauerkraut,etc.It has a refreshing taste,promotes appetite,helps digestion,and is deeply loved by people.The market demand is really large.Traditional natural fermented Brassica juncea has many factors that are not easy to control,such as long fermentation cycle,easy to be contaminated by bacteria,high nitrite content and other pollution during fermentation,etc.The flavor and quality of fermented Brassica juncea are difficult to guarantee.In order to realize the industrial production of fermented Brassica juncea and ensure its flavor quality,artificial inoculation of lactic acid bacteria during the fermentation process can shorten the fermentation time and reduce the fermentation cost,and the application of lactic acid bacteria to ferment Brassica juncea greens can well monitor and improve the stability and safety of the product.Therefore,this paper isolates,screens and identifies lactic acid bacteria with excellent fermentation performance from naturally fermented Brassica juncea and studies its growth characteristics,and explores the optimal growth environment of the strains;the selected lactic acid bacteria strains are compounded to prepare direct starter,using single factor and response The surface method optimizes the fermentation conditions of Brassica juncea greens.The developed lactic acid bacteria starter is subjected to fermentation application research,and the optimal fermentation conditions are obtained through optimization.The direct injection type lactic acid bacteria starter is put into fresh Brassica juncea greens to make fermented Brassica juncea greens.Compare the physicochemical properties of samples with naturally fermented Brassica juncea greens.The indicators and sensory quality provide a certain scientific theoretical basis for the standardized and large-scale production of fermented Brassica juncea with direct injection of lactic acid bacteria starter inoculation.The results are as follows:1.Isolation,screening and identification of excellent lactic acid bacteria strains.In this experiment,39 strains of lactic acid bacteria were isolated from traditional natural fermented Brassica juncea.By comparing their growth ability,acid production ability,nitrite degradation ability and antibacterial ability,10 excellent Lactobacillus strains were screened.After physiological and biochemical tests and 16S r DNA molecular biology identification,the identification results showed that 8 strains were Lactobacillus plantarum and 2 strains were Lactobacillus brevis.BJ-1 Lactobacillus plantarum and BJ-31 Lactobacillus brevis were selected as the test strains in this study to develop the direct-cast sauerkraut starter.2.Research on the growth characteristics of fermentation strains.Through the growth research of the fermentation strains,the growth trend of the two strains is the same.The growth period is 0?4 h for the delay period;4?18 h is the logarithmic phase;after 20 h of culture,it enters the stable phase.When the studied strains were cultured at different p H,when they were cultured at p H 3.0,the strains were observed for 28 h.At 0?14 h,the strains had almost no growth.However,as the culture time extended,the strains gradually adapted to the acidic environment,and the strains began to show with exponential growth,the strain exhibits good acid tolerance;when it is cultured at p H 4.0?7.0,the growth rate of the strain is slow in the delay period within 0-4 h,and the growth is rapid within 4?20 h,and enters logarithmic growth.After 28 hours of culture at p H 6.0,the OD_600nmvalues of BJ-1 and BJ-31 strains reached 1.696±0.012 and 1.687±0.013 respectively,indicating that the strain is suitable for growth in a moderately acidic environment;research Lactobacillus plantarum BJ-1 and the growth ability of Lactobacillus brevis BJ-31 at different temperatures,it can be concluded that the growth of these two strains is better under the conditions of 20?37?,and when the fermentation is cultivated at 35?,the maximum OD_600nmvalue is reached respectively The nitrite tolerance of Lactobacillus plantarum BJ-1 and Lactobacillus brevis BJ-31 was studied,and it was found that both strains have good tolerance to Na NO₂at 200 mg/kg.When cultured with Na NO₂concentration,the OD_600nmvalues of strains BJ-1 and BJ-31 could reach above 1.6.3.Study on the ratio of direct injection lactic acid bacteria starter strains.Under the same fermentation conditions,Lactobacillus plantarum BJ-1 and Lactobacillus brevis BJ-31 were compounded in different ratios to obtain a 2:1 ratio.The p H decreased quickly and the acid production rate was fast during fermentation.The total acidity of the fermentation was 7 days.The content is 1.2±0.03 g/100g,the p H is3.73±0.07,and the sensory score is 31.72±0.65.4.The optimization of fermentation conditions and physical and chemical indexes of Brassica juncea greens with direct-input lactic acid bacteria starter.Using sensory evaluation as an indicator,single factor and response surface methodology were applied to optimize the fermentation conditions of Brassica juncea greens.The best fermentation conditions were obtained:the addition of lactic acid bacteria starter was 0.7%,the fermentation time was 5 days,and the fermentation temperature was23°C.Using natural fermented Brassica juncea as a control,the lactic acid bacteria starter fermented Brassica juncea products were tested using the best fermentation conditions.The results showed that the finished product of Brassica juncea fermented with lactic acid bacteria starter was better,with a sensory score of 31.12±0.67.During the fermentation of Brassica juncea greens,inoculating lactic acid bacteria starter for fermentation can speed up the fermentation speed and reach the end of fermentation ahead of time.Through the determination of the fermented Brassica juncea index,the p H is 3.46±0.2,the total acid content is 1.25±0.02 g/100g;reducing sugar content It is0.545±0.17%;nitrite contains 0.557±0.189 mg/kg,and the nitrite content is low,which is lower than 120.11%of naturally fermented Brassica juncea.Brassica juncea fermented with lactic acid bacteria starter contains a higher lactic acid content of2099.30±12.84?g/m L.Compared with natural fermentation,lactic acid content in mustard fermented with lactic acid bacteria starter is increased by 13.50%,and succinic acid content is increased by 36.42%.Its sour taste and delicious taste for natural fermentation,is consistent with the results of sensory evaluation.In this study,using HS-SPEM/GC-MS technology to determine that the lactic acid bacteria starter fermented Brassica juncea has a total of 34 volatile flavor components,with a total relative content of 76.52%,consisting of esters,nitriles,aldehydes,acids,and alcohols.The relative content of esters,ketones,sulfides,alkanes and other compounds in 9 categories is the highest among the total volatile components,reaching 55.91%,followed by nitriles with a relative content of 7.71%,followed by Alcohols(5.85%)>Aldehydes(2.25%)>Alkanes(0.90%)>Ketones(0.89%)>Sulfides(0.86%)>Dimethothiazine(0.86%)>Acids(1.42%)>5-methylthiazole(0.35%).Esters and nitriles are the main components of volatile components,which add aroma and clear fragrance to fermented Brassica juncea.The lactic acid bacteria starter fermented Brassica juncea is superior to natural fermentation in sensory evaluation.Lactobacillus starter fermented Brassica juncea greens produce acid at a fast rate,and Lactobacillus plantarum and Lactobacillus brevis have the ability to degrade nitrite,so that the content of nitrite in fermented Brassica juncea is low,and it is superior to traditional natural fermented Brassica juncea in terms of organic acids and volatile components.It can improve the production efficiency of fermented Brassica juncea greens,and improve the stability of the quality of Brassica juncea greens and the safety of eating.