Oenococcus oeni - interest in the production of wines: quantitative culture and molecular detection.
Oenococcus oeni (previously Leuconostoc oenos), named for oenology (oenology) is a Gram - positive bacterium, still, it can be seen in chains or pairs of round or oval cells, quimiorganotrofa, facultative anaerobe that obtains energy by breathing in oxygen and fermentation in its absence, very tolerant to low pH below pH 3.0 and above 10% ethanol, included in the group of lactic acid bacteria. It is the main lactic acid bacteria involved in malolactic fermentation of wine. There are various biotypes that are used as starting cultures (starter) to promote the organoleptic and microbiological stability of white and red wines. This bacterium stabilizes microbial communities wine consuming the available nutrients and decreasing the growth capacity of other microbes, but its malolactic fermentation may be beneficial or detrimental to wine production, depending on the grapes, the climate and the style of wine . In wine production they are essential both alcoholic fermentation and malolactic fermentation. There is a tendency to use Saccharomyces cerevisiae not only Oenococcus oeni and but also other different yeasts Kloeckera apiculata Saccharomyces as to improve the organoleptic characteristics, producing intermediate alcohols, monoterpenes and volatiles.
Oenococcus oeni is beneficial for wine and the entire field of oenology for its ability to perform malolactic fermentation, the crucial secondary fermentation in wine production converting malic acid to lactic acid. The final products of malolactic fermentation by Oenococcus oeni are made responsible for the aromas that are required in oenology. Although located in musts and wines, there are industrial strains are grown for use in wine production on a large scale.
The main function of malolactic fermentation is glucose and converting malic acid to lactic acid. They use the malic acid and lactic acid generating decarboxylate and carbon dioxide (CO 2). Oenococus oeni is heterofermentative, ie it generates multiple end products of the fermentation of sugars, such as ethanol, lactic acid, carbon dioxide (CO 2) and aromatic molecules as diacetyl.
This in wine, in low concentrations diacetyl confers a positive flavored hazelnut or caramel. However, when the diacetyl is above 5 mg / L generates a buttery flavor and is considered an alteration of wine. It is generated when there is little or no malic acid and citric acid is used. It is rare that diacetyl reach very high levels that could alter the wine.
An important aspect is that not all Oenococcus oeni strains produce the same aroma, but there are differences in metabolic processes carried out by the different variants of strains, because there are variations in utilization pathways sugars, system phosphotransferases II enzymes and exopolysaccharide cell wall, so the variations between strains and fermentation conditions can affect the overall quality of the wine. Winemakers use standardized industrial strains but many external and environmental variables dictate the effect on the wine. O.oeni is not the only lactic bacteria that can perform secondary fermentation. There are a variety of lactic acid bacteria which can dominate the bacterial community as temperature, nutrient content and SO 2 (sulfur dioxide), although this bacterium normally dominates secondary fermentation by extreme pH and ethanol tolerance.
Despite its importance, is not usually have specific and rapid to evaluate their presence and evolution during wine fermentation tests. Oenococcus oeni strains are difficult to grow, grow slowly and therefore it is difficult to study their characteristics. In addition, the culture media used except for its low pH, they are not selective for this species and definitive identification requires subculturing and corresponding biochemical identification. Currently you can detect its presence using amplification of the gene encoding the malolactic enzyme (MLE gene).