The conversion of grape must to wine is a complex biochemical process mediated by highly specialised micro organisms, yeasts and bacteria. The primary role of wine yeast is to catalyse the rapid, complete and efficient conversion of grape sugar into ethanol, carbon dioxide and other minor, but important, metabolites without the development of off-flavours. Winemakers have started to use strains isolated from their own geographical regions to produce wines with peculiar sensorial properties and reproducible quality. Indigenous yeasts with oenological potential are considered autochthonous and are present on the surfaces of undamaged grapes and their success depends on the sum of physical, chemical and biotic factors. In the spontaneous fermentation of grape must, there is a progressive growth pattern of indigenous yeast, with the final stage invariably being dominated by alcohol-tolerant strains of Saccharomyces cerevisiae. Traditionally, the identification and characterisation of yeast species and strains has been based on morphology and physiological properties. In recent years, techniques developed in molecular biology have provided an alternative to these traditional methods and are an important tool in solving industrial problems. An investigation was carried out in order to characterize the yeast population present in the spontaneous fermentation of "Negroamaro" must, an important grape cultivar for the industrialized production of The Salento (south-eastern Italy) wine. The objective of this study was the identification and characterization of natural yeast flora with peculiar technological and oenological properties from "Negroamaro" grapes collected from different vineyards of the The Salento and grown in organic and non-organic conditions. Identification and characterisation of yeast species and strains was carried out by morphological, physiological, biochemical and molecular methods by sampling the micro flora present on grape skin and in the must during spontaneous fermentation, at different stages. The colonies from each sample were selected on the bases of morphological and physiological characteristics and the isolated population was identified at genus level by PCR analysis of the internal transcribed ITS1- 5,8S - ITS2 region. Further identification was carried out by RFLP analysis of the above amplified fragments and of the amplified d interspersed element. On non-organic cultivated grape skin Hanseniaspora uvarum, Metschnikowia pulcherrima and Issatchenkia orientalis were observed, whereas on the skin of organic cultivated grapes Kluyveromyces thermotolerans, Issatchenkia terricola, Candida incomunis and Candida stellata were also found. In the first stage of fermentation (d=1.125 g/l) a population similar to that present on the grape skin was identified. In the following fermentation stages (d= 1070-1.000 g/l) only Saccharomyces cerevisiae was found and a higher number of strains was identified in must from non-organic grapes than in that from organic grapes. The technological properties (ability of the strains to utilise different carbon sources, production of ethanol, glycerol and hydrogen sulphite, surviving in dry conditions, etc.) of the selected S. cerevisiae strains were studied. The dominant S. cerevisiae strains identified in fermented musts showed potentially important enological characteristics.
POPULATION DYNAMICS OF YEASTS IN "NEGROAMARO" MUST DERIVED FROM ORGANIC AND NON-ORGANIC CULTIVATION
GRIECO F;CAPPELLO MS;BLEVE G;ZACHEO G
2004
Abstract
The conversion of grape must to wine is a complex biochemical process mediated by highly specialised micro organisms, yeasts and bacteria. The primary role of wine yeast is to catalyse the rapid, complete and efficient conversion of grape sugar into ethanol, carbon dioxide and other minor, but important, metabolites without the development of off-flavours. Winemakers have started to use strains isolated from their own geographical regions to produce wines with peculiar sensorial properties and reproducible quality. Indigenous yeasts with oenological potential are considered autochthonous and are present on the surfaces of undamaged grapes and their success depends on the sum of physical, chemical and biotic factors. In the spontaneous fermentation of grape must, there is a progressive growth pattern of indigenous yeast, with the final stage invariably being dominated by alcohol-tolerant strains of Saccharomyces cerevisiae. Traditionally, the identification and characterisation of yeast species and strains has been based on morphology and physiological properties. In recent years, techniques developed in molecular biology have provided an alternative to these traditional methods and are an important tool in solving industrial problems. An investigation was carried out in order to characterize the yeast population present in the spontaneous fermentation of "Negroamaro" must, an important grape cultivar for the industrialized production of The Salento (south-eastern Italy) wine. The objective of this study was the identification and characterization of natural yeast flora with peculiar technological and oenological properties from "Negroamaro" grapes collected from different vineyards of the The Salento and grown in organic and non-organic conditions. Identification and characterisation of yeast species and strains was carried out by morphological, physiological, biochemical and molecular methods by sampling the micro flora present on grape skin and in the must during spontaneous fermentation, at different stages. The colonies from each sample were selected on the bases of morphological and physiological characteristics and the isolated population was identified at genus level by PCR analysis of the internal transcribed ITS1- 5,8S - ITS2 region. Further identification was carried out by RFLP analysis of the above amplified fragments and of the amplified d interspersed element. On non-organic cultivated grape skin Hanseniaspora uvarum, Metschnikowia pulcherrima and Issatchenkia orientalis were observed, whereas on the skin of organic cultivated grapes Kluyveromyces thermotolerans, Issatchenkia terricola, Candida incomunis and Candida stellata were also found. In the first stage of fermentation (d=1.125 g/l) a population similar to that present on the grape skin was identified. In the following fermentation stages (d= 1070-1.000 g/l) only Saccharomyces cerevisiae was found and a higher number of strains was identified in must from non-organic grapes than in that from organic grapes. The technological properties (ability of the strains to utilise different carbon sources, production of ethanol, glycerol and hydrogen sulphite, surviving in dry conditions, etc.) of the selected S. cerevisiae strains were studied. The dominant S. cerevisiae strains identified in fermented musts showed potentially important enological characteristics.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
