Yeast population dynamics in five spontaneous fermentations of Malvasia must

The dynamics of the wine yeast strains presented in five spontaneous Malvas ia wine fermentations have been studied. Samples were analysed for their mi crobiological characteristics and chemical substances. All 937 isolates wer e characterized using electrophoretic karyotyping and tested for their kill er activity. The non-Saccharomyces population was identified using a combin ation of PCR-RFLP analysis of the rDNA spacer region and physiological test ing. The fetal yeast population level in the must after sedimentation was 1 0(5) cfu ml(-1) and included the following genera: Candida, Metschnikowia, Hanseniaspora, Rhodotorula, Issatchenkia and Debaryomyces. However, Sacchar omyces sp. was not detected in fresh must samples plated on YEPD medium. Ba sed on the chromosome length polymorphism among 649 isolates from the subse quent phases of fermentation, 46 different electrophoretic patterns of Sacc haromyces cerevisiae were distinguished The most abundant karyotypes were L -1 L-4 L-12 P-6. A sequential substitution of S. cerevisiae strains occurre d during the different phases of fermentation. At the slow fermentation rat e, karyotype Lq was most abundant in almost ail fermenters. AS the beginnin g of the tumultuous fermentation phase, She most frequent karyotype became L-1 followed by karyotype L-4 Finally, during the fermentation process, pat tern L-4 was clearly replaced by karyotype L-1 followed by pattern L-12 Des pite the same fermentation source (grape must), differences among five spon taneous fermentations were observed. The population dynamics of S, cerevisi ae 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 th e minor strains of S, cerevisiae. (C) 2001 Academic Press.