Effect Of Temperature On Fermentation And Quality Of Doubanjiang

Doubanjiang is a traditional fermented condiment with unique flavor and taste,which is popular among consumers.Nowadays doubanjiang fermentation usually use open-system natural fermentation,which greatly depend on local climate and temperature.Doubanjiang fermented in different seasons had significant differences in quality.Doubanjiang produced in summer had higher quality with shorter production period while longer period with uncertain quality is observed in winter samples.Therefore,temperature had significant effect on doubanjiang production.However,the information of the influence of temperature on doubanjiang fermented has not yet been thoroughly investigated.This study aimed to measured and compared the physicochemical parameters,flavor compounds and microbial communities under different temperatures.Moreover,the growth and metabolism characteristics of key microorganisms in fermented doubanjiang under different temperatures were explored.Finally,a variable temperature fermentation technique was established.The main results are as follows:(1)Through analyzing the temperature variation regulations in different seasons,three fermentation groups(30℃ constant temperature,40℃ constant temperature and natural temperature)were prepared in lab scale.After tracking the physicochemical parameter during fermentation,the results showed that increasing fermentation temperature was beneficial for the accumulation of amino acid nitrogen and reducing sugar in the early-middle fermentation stage,the promotion of mash color and the formation of free amino acids and volatile flavor compounds.However,higher temperatures also led to higher concentrations of total acids and biogenic amines in doubanjiang.(2)Through amplification sequencing and RT-qPCR,the effect of temperature differences on the structure of microbial community was analyzed.Higher temperature significantly increased the abundance of Bacillus and Staphylococcus genera in doubanjiang while inhibited the growth of food-borne pathogens.Through redundancy analysis and correlation analysis,temperature was found significantly related to the metabolic ability of Bacillus,Staphylococcus and Aspergillus genera,thus leading to the changes of various compounds in doubanjiang.After further evaluation of the effect of temperature on the metabolic characteristics of key microorganisms,it was found that B.subtilis and S.carnosus had better ability to accumulate amino acid nitrogen,free amino acid and volatile flavor compounds at 30℃ constant temperature.Moreover,the levels of total acids and biogenic amines were relatively lower.(3)Based on the results of constant temperature fermentation and metabolic characteristics of key bacterial strains,four kinds of variable temperature fermentation techniques(40℃-30℃,40℃-25℃,30℃-25℃ and 15℃-50℃)were established.The results showed that the 40℃-30℃and 40℃-25℃ variable-temperature fermentation techniques led to better doubanjiang quality.Compared with constant temperature fermentation,the variable-temperature fermentation processes could not only accumulate amino acid nitrogen in the early fermentation stage,but also reduce the concentrations of total acids and biogenic amines in mash.Moreover,doubanjiang obtained by these two techniques with high temperature first and lower temperature afterwards had higher scores of sensory evaluations.