Abstract
Malolactic fermentation (MLF) in wine is an important step in the vinification of most red and some white wines, as stands for the biological conversion of l-malic acid into l-lactic acid and carbon dioxide, resulting in a decrease in wine acidity. MLF not only results in a biological deacidification, it can exert a significant impact on the organoleptic qualities of wine. This paper reviews the biodiversity of lactic acid bacteria (LAB) in wine, their origin, and the limiting conditions encountered in wine, which allow only the most adapted species and strains to survive and induce malolactic fermentation. Of all the species of wine LAB, Oenococcus oeni is probably the best adapted to overcome the harsh environmental wine conditions and therefore represents the majority of commercial MLF starter cultures. Wine pH is most challenging, but, as a result of global warming, Lactobacillus sp. is more often reported to predominate and be responsible for spontaneous malolactic fermentation. Some Lactobacillus plantarum strains can tolerate the high alcohol and SO2 levels normally encountered in wine. This paper shows the potential within this species for the application as a starter culture for induction of MLF in juice or wine. Due to its complex metabolism, a range of compositional changes can be induced, which may positively affect the quality of the final product. An example of a recent isolate has shown most interesting results, not only for its capacity to induce MLF after direct inoculation, but also for its positive contribution to the wine quality. Degrading hexose sugars by the homo-fermentative pathway, which poses no risk of acetic acid production from the sugars, is an interesting alternative to control MLF in high pH wines. Within this species, we can expect more strains with interesting enological properties.
Highlights
Malolactic fermentation (MLF), the process of biological de-acidification in winemaking, is based on the l-malic acid decarboxylation to l-lactic acid and CO2
This paper reviews the biodiversity of lactic acid bacteria (LAB) in wine, their origin, and the limiting conditions encountered in wine, which allow only the most adapted species and strains to survive and induce malolactic fermentation
We have identified two different timings throughout the winemaking process for inoculating wine LAB into the wine: co-inoculation with yeast or sequential inoculation, when selected wine lactic acid bacteria are added at the end of, or just after the completion of, alcoholic fermentation (AF)
Summary
Malolactic fermentation (MLF), the process of biological de-acidification in winemaking, is based on the l-malic acid decarboxylation to l-lactic acid and CO2. In EP0398957B1 [7], they disclosed a method of introducing an important freeze-dried biomass of L. plantarum directly into must or fruit juice to induce MLF without significant consumption of sugars present in the must or fruit juice and substantially without any production of volatile acidity This malolactic bacteria strain had little alcohol tolerance and had been unable to survive in the fermented wine. The cycloserine resistant mutants of lactic acid bacteria had been proposed for use to induce malolactic fermentation in wine having high alcohol levels, but, as outlined above, alcohol tolerant L. plantarum strains can be isolated from nature. Despite the good alcohol tolerance of this pure Lactobacillus plantarum culture with the homo-fermentative metabolism of hexose sugars, its most interesting application is in co-inoculation (inoculation 24 h after the wine yeast) without any risk of volatile acidity production during MLF even under high pH conditions. Diverse enzymatic activities, which could contribute to the wine aroma profile than O. oeni
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