Abstract
The contamination of grape berries by Botrytis cinerea can drastically damage wine quality, in particular causing colour degradation. In musts obtained from botrytised grapes, SO2 addition is the main means of avoiding oxidation damage due to laccases excreted by the pathogen. However, consumers are becoming increasingly reluctant to accept SO2 addition to wine. Oenological tannins are used for fining wines because of their colloidal properties, and for wine colour stabilisation due to their ability to condense with anthocyanins. They are also known for their antioxidant and antioxidasic properties. They were thus investigated in the present study for their potential as an alternative to SO2 against laccase oxidation.The impact of various types of oenological tannins on musts and wines was studied once added to musts obtained from the Merlot cultivar, comprising 20 % and 50 % botrytised grapes. Laccase activity, antioxidant capacity, composition of phenolic compounds, spectrophotometric and CIELAB colour parameters were assessed in the musts and wines. Sensory analyses were also performed on 3-month-old wines to evaluate the visual, olfactory and gustative consequences of tannin addition. At a 50 % botrytisation rate, the addition of any type of oenological tannins (at a concentration of 100 g/hL) had no effect on laccase activity and did not protect phenolic compounds. However, at the same concentration and at a 20 % botrytisation rate, proanthocyanidin tannins from grape skin were found to be the most promising tannins with simultaneous protective effects, such as an inhibitory effect on laccase enzymes, protection of colour from complete degradation and preservation of some procyanidin compounds.Oenological tannins are promising candidates for protecting wines from Botrytis damage and they induce a differential effect according to their origin and structure. They could be used to reduce the amount of SO2 that is added during vatting. More research is needed to confirm and better understand the mode of action of various tannins at levels lower than the 20 % botrytised rate tested in the present study.
Highlights
Grey mold resulting from the pathogenic fungus Botrytis cinerea is a major grapevine disease, which is particulary prevalent in areas with temperate oceanic climates (Dubos, 1999; Elmer and Michailides, 2004; Martinez et al, 2005)
Oenological tannins are used for fining wines because of their colloidal properties, and for wine colour stabilisation due to their ability to condense with anthocyanins
The fungus preferentially develops on berries, it may infect leaves and inflorescences, with significant variations in severity of infection depending on both the ontogenic resistance of the host tissue, particulary the grape berry, and the transposon subpopulation of the pathogen (Elmer and Michailides, 2004; Martinez et al, 2005; Martinez et al, 2008; Deytieux-Belleau et al, 2009)
Summary
Grey mold resulting from the pathogenic fungus Botrytis cinerea is a major grapevine disease, which is particulary prevalent in areas with temperate oceanic climates (Dubos, 1999; Elmer and Michailides, 2004; Martinez et al, 2005). Anthocyanins and tannins, which are naturally present in grape berries, are used as substrates by laccases (Oliveira et al, 2011) These phenolic compounds play a major role in the organoleptic quality of wine since they contribute to colour stabilisation and mouthfeel balance in terms of both astringency and bitterness (Noble, 2002; Santos-Buelga and Freitas, 2009). In the presence of oxygen, laccases oxidise these substrates leading to the formation of quinones, which can polymerise and form brown compounds (Li et al, 2008; Pourcel et al, 2007; Salgues et al, 1986) This phenomenon, called ‟oxidasic haze”, is characterised by a degradation and/or instability of wine colour (Dubernet et al, 1975; Cheynier et al, 1995)
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