Effect of organic acids, grape juice and pH on growth and aroma compounds production in Oenococcus oeni from wines

CARMEN MATURANO; FABIANA M. SAGUIR

Tucumán

Congreso; Argentino de Microbiología General “SAMIGE del Bicentenario; 2011

Lactic acid bacteria (LAB), preferably <i>Oenococcus oeni</i>, play an important role in winemaking by undertaking the malolactic fermentation (MLF), which improves the quality wine. Diacetyl produced during MLF at low concentration and in combinations with other compounds can impart yeasty, nutty, toasty aroma to wine. Nevertheless little information is available on this physiological aspect in LAB wine. So, the aim of this work was to investigate the influence of pH, organic acids and grape juice on growth and diacetyl, acetoin and 2,3 butilenglicol production in <i>O. oeni</i> strains from Argentinian wines. The microorganisms were grown in MRS broth with 15% tomato juice, pH 4.8 (control) and added individually or combined with (g/l): L -malate 2; citrate 0.7 and 10% grape juice in place of tomato juice. The  pH 3.8 effect was also investigated. In control medium the growth extent varied according to analyzed strain and it was related with the diminution of pH. The strains grew to final biomass of among 4.90x10⁷ and 3.09x10⁸ cfu/ml, while at pH 3.8 the final biomass ranged of among 1,10x10⁷ and 5.75x10 ⁷ cfu/ml. Addition of organic acids and grape juice to control, in general, increased significantly growth, being L-malic and citric acids almost completely consumed.  At pH 3.8 this stimulatory effect was also observed by approximately 50%. In control the production of diacetyl, acetoin and 2,3-butanediol by <i>O. oeni</i> strains ranged of among 0.2 and 7 mg/l. When pH was adjusted at 3.8 the MS21 and MS27 strains showed the highest aroma compounds production (5.1 ± 0.32 and 4.91 ± 0.53 mg/l) for 6 and 5 days, respectively. In the other strains diacetyl, acetoin and 2,3 butilenglicol formation was also detected but in concentrations lower than 4 mg/l. In presence of both organic acids and grape juice, pH 4,8, all strains except MS52,  produced lower than 5 mg/l of the aroma compounds. In general, at pH 3.8 it decreased detecting values lesser than 3.65 mg/l in the MS21, MS27, MS29 and MS49 strains. In conclusion, although in general, a decrease in cell growth and aroma compounds was observed at pH 3.8 as regards to those obtained at pH 4.8, an interesting finding was that the majority of <i>O. oeni</i> strains were able to growth and to produce the aroma compounds in concentration lower than 4 mg/l at the lowest pH. So they would have adequate characteristics for potential use in winemaking. However, the variability of this production among strains makes convenient to considerer this as a point of strain selection to obtain starter which will give better sensory qualities to wine