Transformation of Microbial Negative Correlations into Positive Correlations by Saccharomyces cerevisiae Inoculation during Pomegranate Wine Fermentation

The application of starter is a common practice to accelerate and steer the pomegranate wine fermentation process. However, the use of starter needs a better understanding of the effect of the interaction between the starter and native microorganisms during alcoholic fermentation. In this study, high-throughput sequencing combined with metabolite analysis was applied to analyze the effect of commercial Saccharomyces cerevisiae inoculation on the native fungal community interaction and metabolism during pomegranate wine fermentation. Results showed that there were diverse native fungi in pomegranate juice, including Hanseniaspora uvarum , Hanseniaspora valbyensis , S. cerevisiae , Pichia terricola , and Candida diversa Based on ecological network analysis, we found that S. cerevisiae inoculation transformed the negative correlations into positive correlations among the native fungal communities and decreased the Granger causalities between native yeasts and volatile organic compounds. This might lead to decreased contents of isobutanol, isoamylol, octanoic acid, decanoic acid, ethyl laurate, ethyl acetate, ethyl hexadecanoate, phenethyl acetate, and 2-phenylethanol during fermentation. This study combined correlation and causality analysis to gain a more integrated understanding of microbial interaction and the fermentation process. It provided a new strategy to predict certain behaviors between inoculated and selected microorganisms and those coming directly from the fruit. IMPORTANCE Microbial interactions play an important role in flavor metabolism during traditional food and beverage fermentation. However, we understand little about how selected starters influence interactions among native microorganisms. In this study, we found that S. cerevisiae inoculation changed the interactions and metabolisms of native fungal communities during pomegranate wine fermentation. This study not only suggests that starter inoculation should take into account the positive features of starters but also characterizes the microbial interactions established among the starters and the native communities. It may be helpful to select appropriate starter cultures for winemakers to design different styles of wine.