Unraveling the mystery of ‘bask in daytime and dewed at night’ technique in doubanjiang (broad bean paste) fermentation

‘Bask in daytime and dewed at night’ technique is traditionally used in doubanjiang fermentation, however, the underlying mechanism behind this technique is still unrevealed. This study aimed to elaborate the roles of three key indexes in this technique, that are air, sunlight, and mash turnover, on doubanjiang quality through the design of doubanjiang fermentation. The results showed that the exposure to air or sunlight was beneficial for doubanjiang to yield reddish-brown luster color, less acidity and balanced flavor. On the contrary, blocking of air and sunlight could accumulate higher acidity (4.75 ± 0.01 g/100gdw), amino nitrogen (2.08 ± 0.07 g/100gdw), alcohols (36.9 g/kg) and esters (26.9 g/kg). Regular mash turnover was mainly involved in making different mash layers exposure to air or sunlight equally through homogenizing mash layers. Different conditions also have been suggested to affect the microbiota dynamics by amplicon sequencing and RT-qPCR. Based on RDA analysis, Pediococcus, Meyerozyma, Bacillus and Zygosaccharomyces were predicted to be related to the changes of physicochemical properties or volatile compounds in different conditions, and their function was validated by simulated fermentation. This study would unravel the underlying scientific meaning of ‘bask in daytime and dewed at night’ technique in doubanjiang fermentation.