TEMPERATURE EFFECT ON YEAST ECOLOGY DURING PREFERMENTATIVE COLD SOAK IN MALBEC WINES

M. MESTRE; Y. MATURANO; R. MARTINEZ BEGUERÍ; B. KUCHEN; V. PESCE; M. TORO; M. COMBINA; F. VAZQUEZ

Congreso; XI Congreso General de Microbiología General SAMIGE; 2015

Prefermentative cold soak (CS) consists of the contact of fermentation solids (skins, seeds and occasionally stems) with the must in a non-alcoholic and low temperature environment (typically in the range of 0?15 °C) during variable time period (from 1-15 days) prior to the onset of alcoholic fermentation. Particularly the use of low temperatures results critical to the quantitativeand qualitative microbiological composition of the must during the prefermentative phase. Yeasts present during this stage can affect directly to final product, therefore is relevant to analyze. The main objective was to study the temperature impact on the biodiversity and dominance of yeasts species during prefermentative cold soak. Grape musts of Malbec from Lujan deCuyo-Mendoza were used. Stainless steel 100L tanks with 80L of must were used. Three different treatments were assayed: T1) CS 12±1°C, T2) CS 8±1 °C and T3) CS 2,5±1 °C. CS period was carried out during 7 days. Samples were taken in initialmust and during CS (Day: 2, 5 and 7). A representative percentage of each different colony was isolated, purified and identified by sequencing the D1/D2 domain of the 26S ribosomal gene. Classical ecology indexes were used to obtain the richness (total numbers of species), biodiversity (Shannon-Wiener index) and dominance (Simpson index) of the yeasts species found during CS treatments assayed. As a result, 9 species belonging to 5 genera were found on grape juice and throughout CS. In the initial grape juice, specify richness was 5 species (Hansenispora uvarum, Candida zemplinina, Pichia occidentalis, P. kudriadzevii and Saccharomyces cerevisiae). Seven yeast species were isolated and identified during the 3 CS treatments analyzed, but only 4 of them were present throughout the maceration stage (H. uvarum, C. zemplinina, P. occidentalis and S. cerevisiae). Furthermore, in spite of that all treatments presented the same number of species (7), genotypic distribution was different ineach treatment throughout the CS and across treatments. Considering the evolution of diversity and concentration of Dominance indexes, at the beginning of CS, all treatments registered the highest microbial diversity (1,7: T3; 1,3: T1 and T2) and the lowest index of dominance (0,21, 0,33 and 0,37 for T3, T1 and T2, respectively). CS treatments carried out at 2,5 ± 1 °C showed the highest Shannon indexes. Although differences were observed in the results obtained with the different maceration temperatures, it can be appreciated that H. uvarum, C. zemplinina and S. cerevisiae were the dominant species throughout cold soak period. Results obtained in this study suggest that the temperature is a factor responsible for the domain from one species over another one during maceration period. Furthermore, the temperature can exerts selection pressure onyeast ecosystem.