Grape marc project

Figure 1: grape marcs.

INTRODUCTION

Grape marc consists of the solid parts of grapes, containing grape skins, seeds and sometimes stalks which remain after juice extraction and represents the main solid waste of the wine-making process (Figure 1). Grappa is a traditional alcoholic beverage produced in Italy from steam distillation of grape marc (EEC, 1989). During the manufacturing process of white grape varieties, marc is separated from grape juice before must fermentation [1]. The marc is sent to the distillery where they are stored, generally in sealed plastic tunnels, for a period ranging from a few days to several weeks. During this period sugars present at 5 to 15% (w/w) in grape marc, are converted into ethanol to reach a

final concentration of 4–10% (w/w). Generally, microbial starter cultures are not added and thus many undefined biochemical reactions take place due to the activity of the natural microflora. Yeasts are essential to the process of alcoholic fermentation [2-5] while bacteria are responsible both for the aromatic characteristics and for the most frequent off-flavours present in the distillate [6-10]. The aim of this study was to investigate the composition, evolution and dynamics of bacteria during storage of grape marc. To perform a detailed characterization of the cultivable and non-cultivable bacterial species we have sequenced two regions of the 16S rRNA gene overlapped to the ipervariable regions V3-V4 and V5-V6 (Figure 2) using next-gen sequencing (454-FLX sequencing with Titanium chemistry). In prokaryotes, the 16S ribosomal RNA (rRNA) genes are essential and occur in at least one copy in a genome [11] and they are also present in all the mitochondrial genomes [12]. The universality of the genes makes them an ideal target for phylogenetic studies and taxonomic classification [13]. The products of the rRNA genes can fold into a complex, stable secondary structure, consisting of stems and loops [14]. The sequences of some of the loops are conserved across nearly all bacterial species because of the essential functions involved, whereas the features of the structural parts are largely variant and specific to one or more classes [15,16]. Since the invention of the polymerase chain reaction (PCR) technique [17], the variant regions, V1–V9, of the 16S rRNA genes (rDNAs) have been used for species identification [18].

Figure 2: schematic representation of the 16 rRNA gene, the variable regions are colored in grey. Arrows represent the primers used for PCR amplification.

REFERENCES

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