Abstract
Grapevine-associated microbiota influences wine organoleptic properties. Spoilage due to undesired microorganisms and biogenic amines (BAs) presence are two main constrains that must be seriously considered. In wine, BAs can originate from the grape berries or can be produced during fermentation, ageing or storage. This work aimed to understand if the high BAs levels observed in musts can have its origin in the microbial community present on grapes. The following methodologies were done: bacterial and fungal grapes communities' isolation, BAs quantification in grapes and musts and molecular amplification of the genes related to BAs production. For comparative purposes, microbial communities from grapes and musts from Douro (low BAs levels in musts) and Alentejo (high BAs levels in musts) were used. Higher number and diversity of bacteria were observed in Alentejo grapes comparatively to Douro ones. Filamentous fungi were predominant when compared with yeasts and the diversity was higher in Alentejo. BAs levels mainly due to putrescin were about ten times higher in grapes and musts from Alentejo. As bacteria isolated from Alentejo grapes showed a great BAs-production potential, namely putrescin, our results suggest a bacterial grape origin for the high putrescine levels found in fresh musts of this region.
Highlights
The production of wine is an important industry with a major economic and social impact in Portugal and in many other countries
Isolation was carried out using grape extracts in a non-selective broad medium for heterotrophic bacteria (NA medium pH 5.5 and 7.0: 0.5% peptone, 0.3% yeast extract and 1.5% agar) and in appropriate media for yeasts and filamentous fungi (yeast peptone glucose (YPG) supplemented with biphenyl and chloramphenicol, pH 5.0; Sabouraud dextrose agar (SAB) supplemented with chloramphenicol, pH 5.6; YPG supplemented with biphenyl, chloramphenicol and cycloheximide (YPGciclo), pH 5.0; SAB supplemented with chloramphenicol and cycloheximide (SABciclo), pH 6.9)
A semi-quantitative analysis allowed concluding that bacterial number was higher in Alentejo isolations comparatively to the Douro ones
Summary
The production of wine is an important industry with a major economic and social impact in Portugal and in many other countries. Microorganisms play a fundamental role on the entire process of wine production and strains responsible for wine fermentation are well known and studied, the grape-bunch associated microbial communities are still poorly characterized and their role in wine processing very much unknown [1,2,3]. Their influence on wine terroir is gaining relevance [3]. The aim of this work was to assess the microbial communities present on grapes from two Portuguese wine producing regions (Douro and Alentejo) with known differences in the levels of must BAs and correlate
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