| Plum（Prunus salicina L.）,a member of the Rosaceae family,is an edible fruit consumed mainly in America,China,and Europe.However,the plum is respiration climacteric fruit,and storage-tolerance is poor after harvesting.What’s more,plum is highly seasonal and the mature period is relatively concentrated.Wine-making is one of major directions for plum.At present,the market plum wine is brewed by commercial yeast.However,excessive use of commercial yeast will bring flavor homogenization,lack of typicalness and characteristic,and other negative effects to plum wine.In recent years,more and more studies have shown that the mixed culture fermentation of non-Saccharomyces cerevisiae with S.cerevisiae can improve the quality of the fruit wine.However,most of current study concentrated on grape wine,plum wine has not yet been thoroughly explored as a subject of research.More importantly,different non-S.cerevisiae has different characteristic.And the research on the formation and change regular of plum wine during brewing is not systematic and comprehensive.Therefore,at first,this experiment assessed biochemical characteristics and mixed culture fermentation characteristics of four non-S.cerevisiae to select a match of mixed culture fermentation with huge potential.Then optimized inoculation strategy to enlarge the improvement effect of mixed culture fermentation.Finally,the dynamic changes of major components of plum wine during wine-making process were conducted in order to provide a scientific basis for the industrial application of mixed culture fermentation for plum wine.Results were showed as follow:（1）Biochemical characteristics and mixed culture fermentation characteristics Candida tropicalis,Issatchenkio orientalis,Metschnikowia pulcherrima,Hanseniaspora uvarum were compared.The results showed that:four non-S.cerevisiae attached maximum biomass and entered to stable phase within 24 h.All of four non-S.cerevisiae were able to withstand 350g/L glucose,3.5%citric acid,6%ethanol and 400 mg/L SO2,which met basic brewing requirements.Compared with S.cerevisiae pure fermentation（10 d）,mixed fermentation delayed the fermentation process（12～13 d）.The basic physical and chemical properties of different wines all met the national standards.Among all samples,Io-Sc had the highest volatile acid content（0.78 g/L）.In addition to Mp-Sc,mixed culture fermentation had a significant effect on the chrominance and hue of plum wine（P<0.05）.The analysis of aroma components combined with principal components showed that the aroma components of Mp-Sc were better than other wine samples.Among them,ethyl caprylate,ethyl caprate,ethyl laurate,and linalool were significantly improved and the odor?activity?value>1,which was beneficial to enhance the fruit flavor and floral.In summary,Mp-Sc was more suitable for brewing plum wine,which was beneficial to increase the complexity of aroma and improve quality.（2）This study describes the effect of variable factors on aroma and quality of plum wine include inoculum ratio（M.pulcherrima:S.cerevisiae=10:1,1:1,and 1:10）,as well as simultaneous versus sequential inoculation,with tested trials spanning 10:1sim,1:1sim,1:10sim,10:1seq,1:1seq,and 1:10seq,respectively.Results showed that during fermentation,M.pulcherrima growth was inhibited by S.cerevisiae.Compared to each simultaneous analog,sequential fermentation which was inoculated with the same yeast ratio consumed less sugar and produced lower ethanol content.Organic acids in each sample varied with the use of different inoculation strategies.A total of 48 aroma compounds were quantified,and 1:1seq sample was observed to be abundant in esters and terpenes but relatively low in higher alcohols,fatty acids,and phenols.Sensory evaluation of the variously-prepared samples revealed that 1:1seq sample featured a highly intense‘global aroma’,‘fruity’,and‘alcohol’notes.PCA illustrated that different inoculation protocols of mixed culture fermentation influenced plum wine aroma except 1:10sim.Ultimately,1:1seq was identified as a promising candidate for production of high-quality plum wine.（3）On the basis of the first two chapters,this chapter further studied the basic physio-chemical,organic acid,active ingredient,antioxidant activity,and aroma components,the formation and dynamic variation of aroma components during plum wine brewing process,including alcohol fermentation and aging.The results showed that after alcohol fermentation,the malic acid content decreased,lactic acid,acetic acid,citric acid and succinic acid content increased,but the type and content of organic acids in the aging stage were not significant（P<0.05）.During the brewing of plum wine,total phenol and total flavonoids showed the first decline in the rise,all of which reached the maximum at the end of the fermentation of the first day,respectively,from 3.86 mg/m L and 1.71 mg/m L.6 major phenolic substances were detected,which were mainly rutin and quercetin.After fermentation,DPPH,ABTS cation,and hydroxy free radical anti-oxidation activity of plum wine increased significantly,but the overall change in the ageing stage was not obvious（P>0.05）.The results of GC-MS and the PCA diagram of the electronic nose showed that,the plum wine flavor composition was significantly changed before and after fermentation（P<0.05）.The plum juice was rich in aldehyde,acid,and ketone substances,and after fermented ester substances were formed.Especially in plum wine sample when the aging was 40 d,ester and terpene substances reached maximum,phenylethyl alcohol,ethyl octoate,aromatic alcohol,and damascenone etc.were characteristic flavor.In summary,it was recommended to use the mixed fermentation of M.pulcherrima and S.cerevisiae with the initial vaccination ratio at 1:1 and sequence inoculation,the alcohol fermentation was 11 d,and the aging time was 40 d.Based on these condition,plum wine with better quality and higher activity component was acquired.The alcohol of the final product is 11.99%,the soluble solid is 6.30°Brix,the total acid content is 5.94 g/L,the total polyphenol content is 2.1 mg/m L,the total flavonoid content is 0.45 mg/m L,product taste was suitable and rich in flowers,and fruit flavor. |
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