Diacetyl production by Oenococcus oeni strains from wines Turing growth under different culture conditions.

MATURANO CARMEN; SAGUIR FABIANA M.

Villa Carlos Paz Códoba

Congreso; VI Congreso Argentino de Microbiología General; 2009

Sociedad Argentina de Microbiología General (SAMIGE)

 Lactic acid bacteria (LAB) are associated with the wine making process by inducing malolactic fermentation (MLF), that consists in the conversion of L- malate to L-lactate and carbon dioxide. As a consequence of this reaction, the total acidity decreases and the organoleptic properties and biological stability generally improve. Diacetyl is considered one of the most important flavor produced during MLF. This compound at low concentrations (and in combinations with other wine aroma compounds) will impart yeasty, nutty, toasty aroma. Diacetyl can be reduced further by wines LAB to acetoin and 2,3- butanediol. In a previous work we selected the MS9 strain of Oenococcus oeni from Argentina wine by its ability to produce diacetyl, acetoin and 2,3 butanediol in concentration lower than 5 mg/l at the end of exponential growth in MRS medium. The aim of this study is to analyze the influence of some components normally found in wine on the diacetyl, acetoin and 2,3 production during growth of the MS9 strain in basal medium. At the same time the behavior of the commercial PSU strain is investigated. Cells are grown in MRS broth with tomato juice, 15%, pH 4.8, (BM) and added with (g/l): L -malate 2; citrate 0.7; SO2 0.08 and/or grape juice 10% in place of tomato juice. Growth is measured by determining the colony forming units (cfu), diacetyl, acetoin and 2,3-butanediol and L-malic acid spectrophotometrically. In BM, the MS9 strain develops with a maximum growth rate and final cell concentration of 0.29 h-1 and 5.01x108 cfu/ml, respectively. The PSU strain shows similar growth rate but a final cell population 9.6% higher than MS9 strain. Organic acids and/or grape juice addition to BM stimulate the final biomass, especially when all substrates are included. Thus, in this last condition, the MS9 and PSU strains grow at 6.03x108 and 1.39x109 cfu/ml, respectively. In BM, both strain produce 4.6 and 4.0 mg/l of diacetyl, acetoin and 2,3 butanediol, respectively. Only citric acid stimulates the aroma compounds formation as compared to BM and this effect is maximum in stationary growth phase (4.98 and 4.68 mg/l for the MS9 and PSU strains, respectively). In both strains, L-malic acid is always completely consumed.  In conclusion, the MS9 strain that displays in general, a similar behavior than the commercial strain as regards to its ability to produce the aroma compounds and malolactic activity under the tested conditions could have adequate characteristics for its potential use in winemaking. Finally, the assessment of the biochemical property in study such as diacetyl production should be considered as a quality criterion for selecting starter cultures for the wines aroma improvement.