Identification of fermentation time markers in caipu, a kind of traditional Chinese food

Caipu is a popular pickled dry radish originated in China with promoting digestion and anticancer effects. The older caipu is considered to possess greater edible and medicinal values. But its composition changes during long term storage are still unclear. In this study, the properties of caipu stored for different years were compared to identified markers of different storage time points. Caipu undergoes significant color change during fermentation, turning dark after 10 years. The SEM results showed that cell structures in caipu were gradually destroyed over time. The protein and fat contents of 10 to 40-year-old caipu were significantly higher than those of 1-year-old caipu, and that the protein and fat contents of 20-year-old caipu reached peaks, at 14.0% and 13.2%, respectively. Moreover, the 16S rRNA and ITS analysis results showed that bacterial and fungal diversity decreased after fermentation. Finally, 67 kinds of volatile organic compound (VOCs) were identified by GC-MS. Among them, benzoic acid, furfural and tetradecamethyl cycloheptasiloxane were the most accumulated VOCs after fermentation and contributed to the distinctive aroma and flavor of caipu. In all, this study revealed the composition changes of caipu at different fermentation times, which will be beneficial for improving the processing of radish-based foods. • After caipu has been fermented for different years, its nutrients, microstructure, and microbial community have undergone remarkable changes. • The older caipu, which has been fully fermented, contains more nutrients. • Most types of volatile organic compounds (VOCs), as well as the greatest quantity of ketones, aldehydes, and esters, have been identified in caipu fermented for 20 years.