Lactic acid bacteria from Patagonian red wines

By Natalia S. Brizuela, E. Elizabeth Tymczyszyn and L. Semorile

Winemaking is a complex microbial process in which yeasts and lactic acid bacteria (LAB) play a significant role. Yeasts consume sugars to produce ethanol and lead the alcoholic fermentation (AF). The malolactic fermentation (MLF) is responsible for the conversion of L-malic acid to L-lactic acid and CO2, causing a reduction of titrable acidity, and a small increase in the pH of wine. MLF also leads to enhanced microbial stability and is usually believed to improve the complexity of wine aroma, which is linked to the LAB enzymatic activity (Cappello et al., 2017; Iorizzo et al., 2016; Liu, 2002). Several organic acids, in addition to L-malic acid, could be metabolized by LAB during MLF, such as, acetic, citric and tartaric acids. The balance of organic acids has a strong impact on wine taste, being the total consumption of L-malic acid the premise to reduce acidity and astringency of wines (Volschenk et al., 2006).
Oencoccus oeni is the major bacterial species find in wines during spontaneous MLF due to high tolerance to harsh wine conditions (Wibowo et al., 1985). However, O. oeni can also be detected with other LAB, mainly Lactobacillus spp., and in particular Lactobacillus plantarum species (Lonvaud-Funel et al., 1999, Lerm et al., 2011, Bravo-Ferrada et al., 2013, Valdés La Hens et al., 2015). Some strains of O. oeni and Lb. plantarum are able to produce enzymatic reactions that modify the wine aroma profile (Cappello et al., 2017; Tristezza et al., 2016). Although the presence of a broad range of enzymes in wine LAB have been documented (glycosidases, esterases, phenolic acid decarboxylases, citrate lyases) (Liu, 2002; Ugliano et al., 2003, Matthews et al., 2004, Grimaldi et al., 2005a, 2005b), information on the role of these bacterial enzyme activities including their potential use in winemaking is still limited (Cappello et al., 2017).
Argentinean North Patagonia is one of the southernmost winegrowing regions of the world that has optimal agro-ecological conditions for high quality viticulture, in which the Pinot noir varietal has found the optimal conditions to express its full oenological potential (Crisóstomo, 2007). Although the flavor of Pinot noir wine could vary among wine regions, and according to winemaking practices, in general it has a fruity and spicy bouquet (Feng et al., 2017; Girard et al., 1997; Guinard et al., 1987). In Patagonian red wines, MLF occurs spontaneously and randomly, mainly by action of native Lb. plantarum and O. oeni strains (Figure 1) (Valdés La Hens et al., 2015).

In order to avoid delay and spoilage during this process, the use of malolactic starter cultures is an option. However, the commercial cultures are formulated with strains from other wine-growing regions and their use could negatively affect the properties of wine terroir (Bokulich et al., 2014; González-Arenzana et al., 2012). The selection of autochthonous strains, best adapted to regional winemaking conditions, is desirable.
In previous works, we have isolated and characterized several Lb. plantarum and O. oeni strains from Merlot and Pinot noir Patagonian wines, including psychrotrophic strains able to conduct microvinification assays at low temperature (10 °C) (Fig 1) (Bravo-Ferrada et al. 2013, Bravo-Ferrada et al. 2014, Valdés La Hens et al., 2015, Manera et al. 2017). Studies of tolerance to wine stress factors in wine-like medium or in sterile wine, as well as the analysis of some enzymatic activities and the screening of aroma related genes, allowed us to select the best candidate strains to formulate regional starter cultures for MLF (Bravo- Ferrada et al., 2013; Bravo-Ferrada et al., 2016; Brizuela et al., 2017; Valdés La Hens et al., 2015). We also have studied the ability of previously selected O. oeni and Lb. plantarum strains to modify the volatile compounds profile after inoculation in sterile and non-sterile Pinot noir wine. We found that O. oeni strains could produce an adequate level of diacetyl and a higher concentration of fruity esters, which are characteristics of Pinot noir wines, whereas Lb. plantarum strains showed a better capacity to consume L-malic acid (Brizuela et al., 2018).
These results allow us to suppose that properly selected strains of both species will be able to induce and successful complete the MLF, at different temperatures, could offer an interesting advantage to improve the sensory attributes and the wine quality. In order to achieve this goal, it is expected to be able to design regional malolactic starter cultures, easy to use in the winery, and able to highlight the regional terroir.

Those interested in a longer length report can download the working paper at:
https://www.sciencedirect.com/science/article/pii/S0963996917308864

The academic staff of LMM is composed by specialized personnel in the areas of Biotechnology, Molecular Biology and Microbiology. Since 2007 the group is working in different aspects of the lactic acid bacteria involved in malolactic fermentations of Patagonian red wines. Currently, studies under development include the following topics:

• Preservation of native Patagonian O. oeni and Lb. plantarum strains.
• Optimization optimization of dehydration – rehydration processes of LAB strains of oenological interest.
• Evaluation of changes in the volatile profile red wines by native O. oeni and Lb. plantarum strains.
• Selection of psychrotolerant native LAB strains to formulate malolactic starter cultures suitable for fermentations at low temperatures.
• Analysis of changes involved in the bacterial adaptation to harsh wine environment.
• Application of high-throughput sequencing to evaluate the yeasts and bacterial communities associated with wines from the South of Buenos Aires province.

All these studies have been reflected in more than 100 papers in specialized journals and books chapters, over of 250 congress communications, and more than 50 research projects funded by national and international organizations. This research has been complemented with a formative activity that has been reflected in 10 defended thesis and some others to be defended shortly.

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