Effects of Inoculating Timing of Selected Indigenous Lactic Acid Bacteria and Yeast on Fermentation in Red Synthetic Grape Juice Medium

Lactic acid bacteria can be inoculated at different stages of alcoholic fermentation during winemaking, but the influence of inoculation timing of indigenous lactic acid bacteria on wine is not well defined. The aim of this study was to investigate the influence of inoculation timing of Chinese indigenous lactic acid bacteria and commercial yeast on physiochemical parameters and the color of synthetic red grape juice. Three selected lactic acid bacteria 6-20, GZC3 and V22 were used to ferment the synthetic medium with Saccharomyces cerevhiae CECA. Two inoculation strategies were applied in the fermentation, including simultaneous and sequential inoculation, with single fermentation as the control. The sequential inoculation includes inoculating Saccharomyces cerevhiae 2 and 4 days prior to inoculating lactic acid bacteria and vice versa. The fermentation process was monitored by regularly measuring residual sugar, malic acid, and the colony numbers of both yeast and bacteria. After completion of fermentation, basic physiochemical parameters such as total acidity, volatile acidity, and pH were measured. Following this, total polyphenols and anthocyanins were determined by the Forlin phenol method and pH-differential method, respectively. Color parameters were then obtained through CIELab color space. Further, the correlation between color parameters and anthocyanin content was analyzed to evaluate wine color characteristics. Finally, Adobe Photoshop CS6 software was used to intuitively simulate the color of each wine sample. Results showed that there were significant differences in fermentation characteristics of simulated wine fermented by different inoculation strategies and these were strain-dependent. All strain pairs successfully completed alcohol fermentation (AF) in approximately 15 days. Malolactic fermentation (MLF) occurs simultaneously with or earlier than AF, depending on the inoculation timing of lactic acid bacteria. Not surprisingly, MLF was completed together with AF, or shortly after the depletion of residual sugar. Early inoculation of lactic acid bacteria was more conducive to MLF, whilst inoculation of yeast prior to lactic acid bacteria was more beneficial to AF. Particularly for CECA/6-20 mixed fermentations, AF took 2-4 days less when inoculating CECA prior to the inoculation of 6-20 compared to the rest inoculation strategies. Simultaneous inoculation of both S. cerevisiae and lactic acid bacteria had no significant effect on overall fermentation duration. The basic physicochemical parameters of all wine samples met the relevant national wine standards. In addition, the total phenol content and total anthocyanin level of most fermentation groups decreased significantly, and there was a significant correlation between these two parameters, though their correlation to CIELab color parameters was weak. With regard to wine colors, sequential inoculation resulted in darker colors compared to the simultaneous inoculation group. Interestingly, wine color was also species-specific, in particular, samples inoculated with Oenococcus oeni GZC3 were generally darker than that inoculated with Lactobacillus plantarum V22 and 6-20. To conclude, this study (dearly proved that our selected indigenous lactic acid bacteria strains were compatible with the commercial yeast CECA regardless of inoculation timing, thereby reducing the overall fermentation duration. Co-fermentation of yeast and bacteria would impact certain physiochemical parameters of wine. This study provides theoretical support and reference for efficient local production of high-quality red wine as well as helps promote the wide application of indigenous wine in China. © 2023 Chinese Institute of Food Science and Technology. All rights reserved.