| Malolactic fermentation (MLF), activated generally by lactic acid bacteria, is an important processing step for cider production. It makes final cider have a nice flavor and softer taste. Traditionally, Oenococcus oeni is always used for MLF in cider. Few researches involve the applications of other lactic acid bacteria in cider-making.The objectives of this study were to:(1) use a seleceted Leuconostoc mesenteroides WZ3O-2 to start the MLF in cider; (2) investigate its influences on the sensory quality of cider; (3) optimize the technological parameters of strain WZ30-2 in order to produce good quality cider; (4) examine the effects of strain WZ30-2 on the levels of malic and lactic acids before or after MLF; and (5)obtaine a profile of major aromatic components from WZ30-2-fermented cider products according to GC/MS data. The following are main results.1. Strain WZ30-2 adapted to cider surroundings very well, activating MLF when it was added to cider. The growth of strain WZ30-2 was influenced by temperature, pH, alcohol content. Compliant index, reflecing the sensory quality of cider in quantitative, showed that good growth of strain WZ30-2 was helpful in softering acidity and improving mouth-feel of the final cider products.2. The main factors influencing MLF were fermentation temperature (A), pH (B) and inoculum concentration (C) according to compliant index. A regression model between the compliant index and pH, temperature, inoculum size of strain WZ30-2 was Y=3.46+0.091A+0.7000B-0.2000C-0.1300AB +0.3900AC+0.089BC-0.4900A2-0.6000B2-0.3000C2. The optimal parameters for cider MLF included a fermentation temperature of 21.62℃, pH at 3.54 and inoculum size of 4.63%. The determined values of compliant index from three repeated experiments averaged to 3.66, closed to its predicted value (3.69). The cider products made with the optimal processing were characterized by clearness, golden color and harmonious taste without precipitation. 3. Organic acids analysis showed that MLF started after strain WZ30-2 was inoculated into cider for 2 days, and lasted about 6 days based on changing in malic and lactic acids. The level of malic acid decreased by 3789.81mg/L, and that of lactic acid increased by 2250.31mg/L after the completion of malolactic fermentation.4. GC-MS was used to analysis the volatile compounds of ciders processed with malolactic fermentation.51 compounds from malolactic-fermented ciders were confirmed by mass spectrometry-search and artificial map analytical, including 10 esters,15 alcohols,7 organic acids,8 ketones and other compounds. After the completion of the malolactic-fermented cider,46 compounds' contents grew up significantly, only 5 compounds' contents decreased. Compared to the malolactic-free fermentation ciders, the levels of volatile compounds from the malolactic-fermented ciders were higher. Especially, significant differences existed in the levels and proportions of glycerin, isosorbitol, 1,3-dihydroxy-2-acetone,isoamylol,9,12-octadecadienoic methyl diene, acetamide and acetic acid due to the changes of cider processing. Malolactic fermentation increased the total content of volatile organic compounds, and partly changed the content and proportion of volatile organic compounds, thus producing the cider products that contain rich-full aroma components.In summary, this is first report that Leuconostoc mesenteroides WZ30-2 was used to process cider throughout its malolactic fermentation. All the works lay theoretical and applied foundations for the industrial production of cider based on the optimized MLF technology of Leuconostoc mesenteroides WZ30-2.
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