The in situ metabolic characteristics of the yeasts involved in spontaneous fermentation process of Chinese light-style liquor are poorly understood. The covariation between metabolic profiles and yeast communities in Chinese light-style liquor was modeled using the partial least square (PLS) regression method. The diversity of yeast species was evaluated by sequence analysis of the 26S ribosomal DNA (rDNA) D1/D2 domains of cultivable yeasts, and the volatile compounds in fermented grains were analyzed by gas chromatography (GC)-mass spectrometry (MS). Eight yeast species and 58 volatile compounds were identified, respectively. The modulation of 16 of these volatile compounds was associated with variations in the yeast population (goodness of prediction [Q 2 ] > 20%). The results showed that Pichia anomala was responsible for the characteristic aroma of Chinese liquor, through the regulation of several important volatile compounds, such as ethyl lactate, octanoic acid, and ethyl tetradecanoate. Correspondingly, almost all of the compounds associated with P. anomala were detected in a pure culture of this yeast. In contrast to the PLS regression results, however, ethyl lactate and ethyl isobutyrate were not detected in the same pure culture, which indicated that some metabolites could be generated by P. anomala only when it existed in a community with other yeast species.
Spontaneous and solid-state fermentation has been used for thousands of years for the preparation of traditional foods such as bread, tempeh, yogurt, and cheese (1-3). Spontaneously fermented foods are generally characterized by a wide variety of tastes and textures, and sensory properties of the foods are generally determined by the involved microflora, besides the raw material (4, 5). With this in mind, it is therefore important to identify the functional microorganisms contributing to the formation of food flavors.The metabolic characteristics of lactic acid bacteria (LAB) and yeasts have been studied extensively (6-8), and their effects on food flavor have been highlighted through the detection of the corresponding metabolites in pure cultures. Although these studies have provided valuable information regarding the individual species, they take no account of the fact that the level of volatiles produced by a single species may be influenced by other species in a mixed-culture system. The different flavors of foods would be determined to a large extent by the in situ metabolic characteristics of different microorganisms. Several studies have already described the metabolic characteristics of mixed cultures with the aim of identifying the effects of individual strains on the generation of volatile compounds (9-12). For instance, the metabolic footprints of each strain of Saccharomyces in monoculture and mixed cultures were derived during wine fermentation (9). This showed that the volatile compounds produced in the mixed culture could not be predicted based on the volatiles observed in the monocultures of the same yeast species. Recent work i...