Effect Of Salt Reduction On Doubanjiang Fermentation

Doubanjiang,a traditional Chinese fermented food,is deeply loved by the public.But it is controversial because of its high salt concentration which may affect human health.With the popularity of low-salt eating habits and the improvement of consumers' healthy diet awareness in recent years,reducing daily dietary salt intake become a trend in the food industry.Doubanjiang has high salinity,so reducing the salinity of doubanjiang has become research hotspot in recent years.However,salt plays an important role in the fermentation of doubanjiang.The reduction of salinity may cause many quality problems about the production of doubanjiang,such as deterioration of flavor and breeding of polluting microbes.In this experiment,in order to clear the influence of salt reduction on the production of doubanjiang,the physicochemical parameters,flavor and microbial dynamic changes of different salinity doubanjiang were detected and compared.And a lactobacillus,which has ability to inhibit conditional pathogenic bacteria,was screened from the sauce from the doubanjiang mash to lay the foundation for the development of low-salt doubanjiang fermentation process.The main conclusions are as follows:By testing the physicochemical parameters of commercially available doubanjiang,it was confirmed that the lowest salinity of normal-salt Doubanjiang was 10.0 g/100 gfw.Three sets of doubanjiang samples which had lower salt concentration(5.5 g/100 gfw,7 g/100 gfw and 8.5 g/100 gfw)than commercial doubanjiang were prepared under laboratory conditions.The physicochemical parameters during fermentation were analyzed,it is found that the decrease of salinity is benefit to the accumulation of amino acid nitrogen,the increase of amino acid concentration and the production of various functional substances.However,higher concentrations of total acids and biogenic amines were also found in low salt doubanjiang.At the same time,the color and body shape of doubanjiang both deteriorate with the decrease in salinity.The volatile flavor compounds of doubanjiang with different salinities were determined by GC-MS.The results showed that the reduction of salinity is beneficial to the accumulation of volatile flavor compounds,but when the salt content is less than 8.5 g/100 gfw,doubanjiang would lose pyrazine-like flavor compounds which has sauce-flavored.Amplicon high-throughput sequencing was used to analyze the influence of salinity reduction on the microbial composition of doubanjiang fermentation process,and it was found that the doubanjiang with lower salinity had more types of microbes.At the same time,some conditional pathogenic bacteria like Klebsiella,Cronobacter and Acinetobacter were detected in low salt doubanjiang.However,when the salt content is 8.5 g/100 gfw,the abundance of conditional pathogens were relatively low and no Acinetobacter was detected.The correlation between flavor compounds and microbial communities was further analysised by mathematical statistics.It showed that Millerozyma,Bacillus and Enterobacter have a positive effect on the formation of volatile flavor compounds,while Staphylococcus and Enterococcus have a negative impact on flavor production during the fermentation of doubanjiang.Combining the physicochemical parameters,flavor compound analysis and microbial kinetic analysis of doubanjiang,8.5 g/100 gfw was finally determined as the target salinity.In order to inhibit the conditional pathogenic bacteria including Klebsiella pneumonia,Bacillus cereus and Cronobacter sakazakii produced under low-salt conditions,the traditional coating separation and antibacterial experiment were adopted.A strain,which had obvious inhibitory effect on Klebsiella pneumoniae and Bacillus cereus was obtained from the doubanjiang mash by two-stage screening,and it was named as Lactobacillus plantarum2-12-2 through molecular biology identification.Lactobacillus plantarum 2-12-2 had little effect on the normal growth of functional flora in doubanjiang.A preliminary study on its antibacterial mechanism revealed that Lactobacillus plantarum 2-12-2 mainly secretes a protein-like bacteriocin to inhibit the growth of Klebsiella pneumoniae and Bacillus cereus.Lactobacillus plantarum 2-12-2 was applied in the actual fermentation process of low-salt doubanjiang.It was found that Lactobacillus plantarum 2-12-2 could effectively inhibit the growth of Klebsiella pneumoniae and Bacillus cereus in the fermentation process of low salt doubanjiang,and ensure the normal fermentation of it.