Carbohydrate composition of red wines during early aging and incidence on spoilage by Brettanomyces bruxellensis

Highlights

• Aging red wines contain many residual carbohydrates.

• Glucose, fructose and trehalose are preferentially consumed by B. bruxellensis.

• Higher amounts of these carbohydrates accelerate growth and wine spoilage.

• However, carbohydrate composition is not the main spoilage promoting factor.

Abstract

Wine is generally considered as hostile medium in which spoilage microbes have to manage with many abiotic factors among which low nutrient content. Wines elaborated in 8 wineries were sampled during the first summer of aging over two consecutive vintages, and analysed for carbohydrate composition. This revealed the systematic presence of many carbohydrates including those useful for the spoilage yeast Brettanomyces bruxellensis. However, during the first summer of aging, the changes in wine carbohydrate composition were low and it was difficult to assess how much carbohydrate composition contributed to wine spoilage by B. bruxellensis. Subsequent laboratory experiments in inoculated wines showed that the sugars preferentially consumed in wine by the spoilage yeast are d-glucose, d-fructose, and trehalose, whatever the yeast strain considered. The addition of these sugars to red wines accelerates the yeast growth and the volatile phenols formation. Although probably not the only promoting factor, the presence of high amounts of metabolisable sugars thus really increases the risk of “brett” spoilage.

Introduction

Aging and especially the first summer of aging is described as particularly favourable towards Brettanomyces bruxellensis development in Bordeaux vineyards (Chatonnet et al., 1992; Cibrario et al., 2019a, 2019b). B. bruxellensis can be found on grapes, in musts and wines and very often in wineries. Indeed, wine environment is one of its favourite ecological niche (Oro et al., 2019). In this context, it is considered a spoilage microorganism, because it converts the hydroxycinnamic acids extracted from grapes (mainly p-coumaric and ferulic acids) into volatile phenols (VP): 4-vinylphenol (4-VP), 4-vinylguaiacol (4-VG), 4-ethylphenol (4-EP) and 4-ethylguaiacol (4-EG) (Chatonnet et al., 1992; Rozpędowska et al., 2011). These molecules confer unpleasant aromatic notes to the wine and constitute one of the main defects of red wines nowadays (Romano et al., 2009; Schumaker et al., 2017).

To produce significant and detectable concentrations of these undesired molecules, the spoilage yeasts should first grow and become numerous enough (Gerbaux et al., 2002; Barata et al., 2008; Cibrario et al., 2019b). Recently, we showed that the genetic group of the strain(s) present and the cellar temperature were key factors modulating the yeast growth rate and thus the risk of spoilage. Nevertheless, the main factor was the wine itself, some being much more permissive to B. bruxellensis development than others (Cibrario et al., 2019a, 2019b). Though the species is described to display low nutritional requirements, one of the keys that could promote its rapid development in many wines is its ability to use many carbon sources as growth substrates (Dias et al., 2003; Conterno et al., 2006; Crauwels et al., 2017; Smith and Divol, 2018; Cibrario et al., 2019a; Da Silva et al., 2019). The wine carbohydrate content could thus contribute to increase its “permissiveness”. Indeed, different studies suggest that the wine carbohydrate composition could strongly differ from one domain to the other depending on the grape variety and oenological practices (Triquet-Pissard, 1979; Pellerin and Cabanis, 1998; Del Alamo et al., 2000; Ayestarán et al., 2004; La Torre et al., 2008; Ruiz-Matute et al., 2009; Rovio et al., 2011; Conde et al., 2015; Gougeon et al., 2019). The wine carbohydrate composition may also differ due to the activity of the active microorganisms during fermentations (Pellerin and Cabanis, 1998; Dols-Lafargue et al., 2007). In addition, during aging in barrels, the composition of the wine may also change due to the diffusion of wood carbohydrates, or due to the metabolism of the microorganisms present (Del Alamo et al., 2000).

We hypothesised that wines differ by their small neutral carbohydrate content and this may modify the risk of spoilage by B. bruxellensis. We thus measured the low molecular weight carbohydrate concentrations in many red wines, during two consecutive vintages. We then examined whether a link exists between the concentration and the nature of the carbohydrates present and the spoilage yeast growth or the volatile phenols formation in the barrels examined. Then, at laboratory scale, yeast growth and carbohydrate and volatile phenols concentrations were followed in wines, artificially enriched in carbohydrates or not, and inoculated with B. bruxellensis. The strains used were chosen to be representative of the recently highlighted genetic diversity of the species in wine (Avramova et al., 2018; Cibrario et al., 2019c).