Screening Of Excellent Antioxidative Oenococcus Oeni Strains And Research On Promoting The Quality Of Wine

Oenococcus oeni is the main lactic acid bacteria responsible for conducting malolactic fermentation(MLF) in wines. Its main advantages are their capacity to cope with a hostile wine environment: low pH, high ethanol and SO2 concentration. The beneficial properties of O. oeni strains should not be ignored, although they are scarce in the final bottled wine. Recently, some O. oeni strains were found to have anti-inflammatory and immunomodulatory potential etc. Antioxidant ability is one of the important probiotic properties for lactic acid bacteria. However, the antioxidant properties and the gastrointestinal tract environment tolerances rarely studied in O. oeni strains. Research on promoting the quality of wine by excellent antioxidative O. oeni strains has been little investigated. In addition, reduced glutathione(GSH) is a tripeptide with antioxidant activity. It plays an important role for the quality of wine. In wine making, it could prevent the oxidation of grape juice and the browning of white wine, and protect various aromatic compounds and prevent the formation of off-flavour compounds in wines. However, little is known about the relationship between GSH and the quality of wines after MLF and the effect of GSH on the growth and fermentation performance of O. oeni strains.The antioxidant properties in vitro of O. oeni strains were determined, and excellent antioxidative O. oeni strains were selected. The viabilities of these strains in simulated gastric and intestine juice and bile solution were measured and analyzed in this study. Then, the effects that wine MLF by using these strains alone or in combination with GSH on the final wines were further investigated. Moreover, the influence on wine quality after MLF that the pre-adaptation culture O. oeni strain has made was investigated. The main results were as follows:(1) For the tested 20 O. oeni strains, the antioxidant properties of O. oeni strains depended on the strains and the evaluation methods used. Lactobacillus bulgaricus CICC 6032 was kept as a control. O. oeni SD-1e, SD-2gf, 31-DH, SD-2d, SD-2a and SD-2ee have a better antioxidant capacity were selected. Moreover, the tested O. oeni strains exhibited good survival abilities in simulated gastric and intestine juice and had high bile resistance abilities. However, they had low tolerant capacities and cell surface hydrophobicities compared with the control.(2) When O. oeni SD-2d, 31-DH and SD-2a with high antioxidant properties were used to carry out Cabernet Franc wine MLF, the concentrations of gallic acid, syringic acid, vanillic acid, rutin, morin,(-)-epicatechin and trans-resveratrol of the final wines were increased, and the antioxidant activities of the final wines were enhanced. Moreover, the values of ?E* were bellow 3 for the Cabernet Franc wines fermented by O. oeni strains with different antioxidant properties. Therefore, it was difficult to recognize the colour difference for these wines after MLF on the vision.(3) When 20, 40 or 60 mg/L GSH were added to pre-MLF wines before conducted Cabernet Franc wine MLF, respectively, the concentrations of benzoic acid, syringic acid, vanillic acid, p-coumaric aicd, chlorogenic acid, caffieic acid, rutin, morin, quercetin,(-)-epicatechin, trans-resveratrol and coumarin in wines after MLF were increased, and the antioxidant activities of these wines were enhanced. Moreover, the values of ?E* were bellow 2 for the final wines fermented by pre-MLF Cabernet Franc wines with or without addition GSH. Therefore, it was difficult to recognize the colour difference of these final wines on the vision.When 20 or 40 mg/L GSH were added to pre-MLF wines before wine MLF, the concentrations of isoamyl alcohol, nonanol, 2-phenylethanol, ethyl acetate, isoamyl acetate, ethyl butanoate, ethyl hexanoate, ethyl octanoate, ethyl decanoate, ethyl(E)-hex-2-enoate, ethyl phenyl acetate, ethyl vanillate, diethyl succinate, geraniol, benzaldehyde of these final wines were increased, and the concentrations of volatile components of alcohols, esters, terpenoids and aldehydes of the corresponding final wines after MLF were increased. GSH played a protective role in some aromatic substances of Cabernet Franc wine to a certain extent.The addition of 40 mg/L GSH to pre-MLF wines could help to improve the antioxidant properties and the concentrations of aromatic compounds of the final Cabernet Franc wines.(4) GSH could promote the growth of O. oeni SD-2a strain in acid stress(pH 3.2) and ethanol stress(12% ethanol) environment. During mid-log growth phase of O. oeni SD-2a in the FMATB culture medium(pH 3.2) with 150 mg/L GSH, the transcriptional levels of mleA, hsp18, clpP and citE of O. oeni SD-2a were improved. O. oeni SD-2a exhibited a better growing ability and fermentation power in the wine-like medium with 60 mg/L GSH. During the initial stage of MLF in the wine-like medium with 60 mg/L GSH, the transcriptional levels of hsp18 and clpP of O. oeni SD-2a were improved.(5) O. oeni SD-2a could be cultured by the acid pre-adaptation FMATB culture medium(pH 3.5) with 150 mg/L GSH before MLF. This culturing method could incresea the growing ability and fermentation power of O. oeni SD-2a in wine-like medium. Moreover, during the initial stage of MLF in the wine-like medium, the transcriptional levels of hsp18, citE, clpP, cts R and rml B of the pre-adaptation cultured O. oeni SD-2a were improved. When the pre-adaptation cultured O. oeni SD-2a was used to carry out Cabernet Franc wine MLF, the concentrations of total phenols, total flavonoids, flavanols, oligo proanthocyanidins, syringic acid, salicylic acid, vanillic acid, chlorogenic acid, qercetin and trans-resveratrol were increased, and the antioxidant activities of the final wine were improved. Moreover, the red hues(a*) and color saturation(C*) of the final wine were improved.