| Because of global warming,grapes are usually characterised by high p H and low acidity.This results in wines with disturbed flavor and increased susceptibility of microbial spoilage.Organic acids adjustments are commonly used to improve the organoleptic characteristics of the wine.The aim of this work was the selection of Lactobacillus plantarum strains for their use as acidifying starter cultures to carry out a biological acidifification in low acidity grape musts.Eight selected L.plantarum strains were characterised according to their acidification capacity in pure fermentation and mixed fermentation with an indigenous Saccharomyces cerevisiae strain NX11424.Then a suitable mixed fermentation strategy was selected to increase wine acidity and improve wine quality.The main results are as followed:1.Eight L.plantarum strains were tested according to their lactic acid fermentation and mixed fermentation performances.All strains could adapt to the Chemically Defined Grape Juice Medium with high sugar and low acids during the pure fermentation process.These strains can also utilise glucose to produce lactic acid to achieve grape juice acidification,leading to the increase of total acids by 62.86% to 71.13%.Mixed fermentation with S.cerevisiae NX11424 showed that the inoculation of L.plantarum strains did not affect fermentation process markedly;however significantly increased total acids in wine after alcoholic fermentation,acidification degree rang from 0.83% to 90.00%.Nevertheless,the increase in total acids is accompanied by an increase of volatile acids.Finally,strains P533,P520,P519,P202 and P511 were co-fermented with S.cerevisiae NX11424 in Merlot for further evaluation.Results showed that strain P520 was the best performing strain in wine fermentation trials due to its high acidification rates(25.00%)and lactic acid yield(1.31 g/L).Additionally,it did not cause a significant increase in volatile acid content.Aroma analysis of wine samples shows that P520 and NX11424 mixed fermentation treatment significantly increased the content of higher alcohols,esters and fatty acids in wine,especially isoamyl acetate,ethyl citrate,ethyl phenylacetate,(Z)-3-hexen-1-ol,ethyl lactate and 2-phenylethyl alcohol.This would leads to potentially increasing floral and fruity aroma profile,thus enhancing the wine aroma complexity.2.Simultaneous and sequential inoculation of strains P520 and NX11424 were further conducted in Chemically Defined Grape Juice Medium with high sugar and low acids.Results show that:(1)Interaction between L.plantarum and S.cerevisiae was seen in both mixed fermentation trials.The effect of simultaneous inoculation on S.cerevisiae was not obvious,however,the maximum growth of L.plantarum was negatively impacted in this scenario.By contrast,in the sequential inoculation trail,the maximum population of S.cerevisiae was reduced compared to that in the simultaneous fermentation trial,but there were more viable cells detected at the end of fermentation.In addition,enhanced proliferation of L.plantarum was also observed during the first 3 days in the sequential inoculation trial.(2)Physical and chemical analysis showed that sequential inoculation fermentation increased wine acidity more significantly(74.06%)compared with the simultaneous inoculation treatment(40.25%).It also yield more lactic acid(15.98 g/L)than the simultaneous inoculation treatment(3.96 g/L).3.Simultaneous and sequential inoculation of strains L.plantarum P520 and S.cerevisiae NX11424(48 h)were used in Cabernet Sauvignon red wine fermentation(100 L).The results showed that:(1)In the early stage of fermentation,different inoculation treatments had no significant effect on the growth of S.cerevisiae,and the sequential inoculation treatment accelerated the death of S.cerevisiae in the late stage of fermentation.L.plantarum in the simultaneous inoculation treatment could not proliferate while in the sequential inoculation treatment,L.plantarum reached the maximum proliferation 2 days after inoculation.(2)Physical and chemical analysis and organic acid results showed that the sequential inoculation treatment significantly increased wine total acid(57.56%).The mixed inoculation treatment can significantly increase the lactic acid content of the wine,but the malolactic fermentation can not be completed at the end of the alcoholic fermentation.(3)Aroma analysis showed that the mixed fermentation treatment can increase the total amount of alcohols and esters(mainly ethyl acetate,ethyl lactate,hexanol)in wine,and reduce the content of acid substances in wine. |
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