Monitoring microbial succession and metabolic activity during manual and mechanical solid-state fermentation of Chinese cereal vinegar

Chinese vinegar solid-state fermentation (SSF) has been using traditional manual operation (TO) for a long history. Recently, mechanical operation (MO) is being applied. However, the fermentation periods and organic acids pattern of TO and MO are different. In this research they were compared considering the microbial diversity and succession, and the effects of fermentation conditions on microorganism metabolism were analyzed using in vitro and in vivo methods. TO has a higher lactic acid/acetic acid ratio (0.399) than MO (0.351). They differ in the middle-early, middle, and middle-late stages, whereas the later stages of both show similarities. Acetic acid bacteria (AAB) and lactic acid bacteria (LAB) are predominant microorganisms in SSF process. Acetic acid and lactic acid are mainly produced at the upper and lower of fermentation containers, respectively. Oxygen content is positively related to AAB metabolism, whereas negatively related to LAB metabolism. Heat generated by bio-reaction will inhibit the growth of AAB after the middle stage. The more sufficient mass and heat transfer is responsible for the higher activity of microbial metabolism in TO than in MO, resulting in a shorter fermentation period. •The fermentations of cereal vinegar by manual operation (MO) and mechanical operation (TO) were compared.•Fermentations by TO or MO arrive at the same end by different time curves.•The more sufficient mass and heat transfer is responsible for the higher metabolic activity in TO than in MO.•Acetic acid bacterial and lactic acid bacterial are mainly responsible for those differences.