Study On Superior Conditions For Saccharification And Ethanol Fermentation Of Rose Vinegar

Zhejiang rose vinegar,which was famous for its fresh rose color, was fermented with wild strains(such as yeast,bacteria,mildew and so on) and rice by method of surface liquid-state fermentation.Whereas the yield and quality of rose vinegar were considerably influenced by its long productive cycle,low utilization ratio of raw materials and bad stability of quality.Therefore,it is urgent to improve the traditional fermentation process.Submerged fermentation with the virtues of low cost,high yield and pure fermentation had been the general tendency of modern vinegar industry.Nevertheless,this method also had some disadvantages including short productive cycle,single material and lean enzymes,which let the flavor of rose vinegar inferior.Consequently,it is necessary to improve the flavor of vinegar by submerged fermentation. For these reasons,the saccharification and ethanol fermentation of rose vinegar were studied.Liquid culture of Aspergillus niger was used to improve the utilization rate of starch and provide reducing sugar for ethanol fermentation,and also generate some precursor substances of flavor compounds.Then the combinations of lactic acid bacteria and yeasts were used to ethanol ferment so as to improve the content of organic acids and volatile flavor components. Rose vinegar by liquid fermentation can approach to rose vinegar by traditional fermentation in aroma components.It can provide the theoretical basis for the industrial production of vinegar.The research results were as follows:1.Liquid culture conditions of AS3.4309 were optimized by single-factor tests and orthogonal tests.The results showed that the optimum composition of the medium and culture conditions were as follows:medium volume 50mL/500mL,corn starch 15%,corn steep liquor 7%,bran 5%,soybean flour 2%,(NH₄)₂SO₄ 0.15%;inoculation volume 10%,initial pH value 4.5,30℃,200r/min,culture 7 days.With the optimum culture conditions,the highest glucoamylase activity achieved at 1294.52U/g.2.Liquid culture of AS3.4309 was used in the saccharification of rose vinegar,to study starch conversion in the process of saccharification. The results showed that the optimum conditions for the saccharification of As3.4309 were as follows:fermentation time of AS3.4309 48h, inoculation volume 8%.Compared with the saccharification only by two kinds of enzymes,its efficiency of saccharification was improved 11.49%.3.The lactic acid bacteria AS1.130 was used to enhance the content of lactic acid in ethanol fermentation.The optimal fermentation conditions by the orthogonal test were as follows:inoculation volume 3%, fermentation temperature 30℃,and initial pH value 4.0.The content of alcohol can achieve to 6.6%;the total acidity 4.95g/100mL;the content of lactic acid(414.16mg/100mL) was improved 2.56-fold compared with ethanol fermentation without lactic acid bacteria(16.30mg/100mL), which approached to lactic acid content of solid-state fermentation vinegar.4.Lactic acid bacteria and yeasts were used in ethanol fermentation to improve the content of organic acids and volatile flavor components of rose vinegar.In this study,bacteria strains 1,2,3,4(1:K yeast,2: Torulopsis AS2.202,3:Candida AS2.1182,4:lactic acid bacteria AS1.130) as the original strain,to study effects of different combinations 1234,123,12,1 on the fermentation process and flavor components.The combination fermentation had no significance on the basic physical and chemical indicators:the content of alcohol can achieve to 5.5%,the total acidity 4.5g/100mL.Organic acids and volatile components in the rose vinegar were identified by high performance liquid chromatography (HPLC) and headspace gas chromatography-mass spectrometry (HS-GC-MS).This research suggested that test bacteria combination of 1234 was optimal,which had the highest content of non-volatile organic acids,especially tartaric acid and citric acid.The content of 2-butanone, 3-hydroxy-and phenyl ethyl alcohol as characteristic flavor components was significantly higher than the other three groups.5.Head space solid phase microextraction(SPME) technique was employed to extract volatile flavor components from rose vinegars. Volatile flavor components of rose vinegar were isolated and identified successfully by gas chromatography-mass spectrometry(GC-MS).An 851am polyacrylate(PA) fiber was selected to be the optimum fiber among three different fibers.Optimum adsorption time was 30 min at 60℃.Carboxylic acids,esters,alcohols and aldehydes were the major flavor compounds of rose vinegar.The characteristic aroma components in the vinegar were phenyl ethyl alcohol,acetic acid,ethyl acetate, 1-butanol,3-methyl-,butanoic acid,3-methyl-,2-butanone,3-hydroxy-, and 2(3H)-furanone,dihydro-5-pentyl-,which had high contents and low odor threshold.The research suggested that the flavor of improvement vinegar could approach to the traditional vinegar by liquid surface fermentation.The purpose to improve the flavor of liquid fermentation vinegar was achieved.