Changes in volatile compounds of red dragon fruit ( Hylocereus species ) juice during stepwise fermentation

In this study, red dragon fruit (RDF, Hylocereus polyrhizus) juice underwent stepwise fermented by Saccharomyces cerevisiae, Bacillus subtilis, and Lactiplantibacillus plantarum, and the volatile composition was analysed using E-nose and GC-IMS to identify the potential volatiles for the discrimination of different steps of fermented juice. The results indicated significant changes in the VOCs of RDF juice during stepwise fermentation, notably an increase in alcohols and a decrease in aldehydes during S. cerevisiae fermentation. In contrast, fermentation with B. subtilis resulted in no significant alterations in volatile compounds. Subsequent fermentation with L. plantarum induced notable changes, resulting in a decrease in ester content, and an increase in alcohol and ketone levels. Moreover, sulfur-containing compounds accumulated during S. cerevisiae fermentation, whereas their degradation occurred in fermentation stages involving B. subtilis and L. plantarum, contributing to the enhanced flavor profile of RDF juice. Furthermore, correlation analysis between VOCs and E-nose responses revealed that 2-propanol, 2-methylbutanal, methyl hexanoate, and 2-methylpropanal exhibited the highest correlation coefficients with S. cerevisiae and B. subtilis fermentations, whereas butyraldehyde, 1-nonanal, (Z)-4-heptenal, valeraldehyde, and methyl hexanoate were predominantly correlated with L. plantarum fermentation. This study provides insights for the further optimization of process development in the production of fermented RDF beverages.