Effect of temperature on chemical compounds of Cupei (precursor of bran vinegar) during in-situ aging and revelation of functional microorganisms in the process

Abstract

The precursor of Chinese traditional bran vinegar (Cupei) is usually carried out by in-situ aging to improve the quality. Temperature and microbial activity are potential factors that impact Cupei properties during aging. However, little is known about the effect of temperature on Cupei and the functional microorganisms during this stage. In this study, changes of important compounds and potential functional microorganisms were determined, and the relationships between them were investigated during aging at different constant temperatures. Results showed that free-amino acids (e.g., Leu, Glu, Ala, Ile, Thr, His, and Met), organic acids (e.g., lactic acid, l-malic acid, and phenyllactic acid), sugars, and flavor compounds (e.g., esters, aldehydes, and phenols) of Cupei were significantly impacted by bacterial growth and the Maillard reaction during in-situ aging, which was temperature-specific and time-specific. Based on Illumina sequencing, the Bacillus and Oceanobacillus were revealed to significantly impact the properties of Cupei. B. sporothermodurans, B. oleronius, B. ruris, B. thermoamylovorans and some unidentified Oceanobacillus bacteria that were potential functional bacteria. Furthermore, we proposed gradient constant temperature and bio-perturbation strategies for improving aging efficiency based on this study. Overall, our study provided an understanding of roles of temperature and microbes on in-situ aging of Cupei.