Yeast population dynamics in five spontaneous fermentations of Malvasia must

The dynamics of the wine yeast strains presented in five spontaneous Malvasia wine fermentations have been studied. Samples were analysed for their microbiological characteristics and chemical substances. All 937 isolates were characterized using electrophoretic karyotyping and tested for their killer activity. The non-Saccharomyces population was identified using a combination of PCR-RFLP analysis of the rDNA spacer region and physiological testing. The fetal yeast population level in the must after sedimentation was 10(5) cfu ml(-1) and included the following genera: Candida, Metschnikowia, Hanseniaspora, Rhodotorula, Issatchenkia and Debaryomyces. However, Saccharomyces sp. was not detected in fresh must samples plated on YEPD medium. Based on the chromosome length polymorphism among 649 isolates from the subsequent phases of fermentation, 46 different electrophoretic patterns of Saccharomyces cerevisiae were distinguished The most abundant karyotypes were L-1 L-4 L-12 P-6. A sequential substitution of S. cerevisiae strains occurred during the different phases of fermentation. At the slow fermentation rate, karyotype Lq was most abundant in almost ail fermenters. AS the beginning of the tumultuous fermentation phase, She most frequent karyotype became L-1 followed by karyotype L-4 Finally, during the fermentation process, pattern L-4 was clearly replaced by karyotype L-1 followed by pattern L-12 Despite the same fermentation source (grape must), differences among five spontaneous fermentations were observed. The population dynamics of S, cerevisiae yeasts, especially the dynamics of the major S. cerevisiae strains (L-1, L-4, and L-12) were quite similar in all five fermenters in opposite to the minor strains of S, cerevisiae. (C) 2001 Academic Press.