Study On The Immobilized Fermentation Process Of New Fruit Vinegar

Chinese traditional vinegar has been dominated by rice vinegar,but the development and production of fruit vinegar is still in the stage of development.Fruit vinegar not only contains more rich nutrition,but also tastes better than rice vinegar,because fruit vinegar has more flavor substances like organic acids.And fruit vinegar contains abundant vitamins and polyphenols,which makes vinegar have better health functions such as anti-oxidation and cholesterol lowering.At present,the development and production of fruit vinegar are relatively backward in China,the main reasons for this issues are the high cost of fruit vinegar production and the immature processing technology of fruit vinegar,and in general,fruit vinegar is fermented from pure fruit juice.Based on this situation,yellow rice wine was added into the production of fuit vinegar as a part of raw material in this study,the purpose of that was to reduce the production cost of fruit vinegar and increase the flavor substance and functionality of fruit vinegar.In addition,the rate of producing acid was improved with fermentation by immobilization technology.We hope this can provide a new idea and method for the research and production of fruit vinegar.Kiwifruit wine and yellow rice wine were considered as raw materials to produce fruit vinegar in this paper.In the acetic acid fermentation stage,a suitable natural immobilized material was selected for immobilized fermentation,at the same time,the response surface method was employed to optimize the acetic fermentation conditions.Finally,the antioxidant properties and stability of the self-made fruit vinegar were studied.The main results of the study are as follows:1.14 strains of acid producing bacteria were obtained by sampling,screening,isolating and purifying.The five high acid-produced strains were classified into the genus of acetic acid bacteria based on the analysis of the sequences of 16S rDNA.Acetic acid bacteria strain with good acid-producing ability was selected for acetic acid fermentation of vinegar.2.Fruit vinegar fermented both by immobilized acetic acid bacteria with corncob,peanut shell,bagasse,straw,rice bran and sodium alginate as immobilized materials and by free acetic acid bacteria was compared,the results showed that the total acid content was 4.76 g/100mL by free acetic fermentation,and the total acid content of other immobilized materials after fermentation was in turn:bagasse(6.31 g/100mL)>corn cob(6.23 g/100mL)>peanut shell(5.85 g/100mL)>rice bran(5.80 g/100mL)>straw(5.67 g/100mL)>sodium alginate(5.11 g/100mL).Continuous fermentation of six batches of immobilized materials were carried out,and the average acid content of that was measured:corn cob(6.12 g/100mL)>peanut shell(5.84 g/100mL)>rice bran(5.76 g/100mL)>bagasse(5.70 g/100mL)>straw(5.52 g/100mL)>sodium alginate(4.92 g/100mL).Taking sensory evaluation,stability into consideration,corncob was chosen as the immobilized material.3.The aroma compounds of Kiwi vinegar,yellow rice wine vinegar and fruit vinegar fermented from mixed fruit wine and rice wine were extracted by headspace solid-phase microextraction(HS-SPME),identified by gaschromatography-mass spectrometry(GC-MS),and the characteristic organic acids of these three kinds of vinegar were detected by high performance liquid chromatography(HPLC).52 aroma components such as acids,alcohols and esters were isolated and identified,meanwhile,8 characteristic organic acids contents were determined.The results showed that there were 43 kinds of aroma components in fruit vinegar of rice wine and fruit vine,including 11 acids,10 alcohols,15 esters,all of them were higher than fruit vinegar fermented by pure fruit juice.The content of oxalic acid,tartaric acid,malic acid,ascorbic acid,citric acid and lactic acid in mixed vinegar were higher than pure vinegar when the proportion of yellow rice wine was lower than fruit wine.It also showed that the aroma compounds and content of characteristic organic acids in fruit vinegar could be increased when adding some yellow rice wine as raw material.At the same time,the addition of yellow rice wine was beneficial to improve the reducing sugar content of fruit vinegar,which made the fruit vinegar better.Taking sensory evaluation results and the total acid content into consideration,the ratio of kiwi wine and yellow rice wine was determined as 1:1.4.The single factor experiment was carried out for pH,pouring frequency,medium volume,temperature and inoculating volume,the results showed that the effects of initial pH value,medium volume and temperature were significant.The immobilized acetic acid bacteria had the best performance of producing acids when the fermentation initial pH was 3.5,medium volume was 100 mL/500mL,temperature was 32℃.Box-Behnken experiment design was used to analyze and optimize initial pH,medium volume and temperature and the optimal fermentation conditions were determined as follows:temperature was 31.3℃,medium volume was 84.2 mL/500mL,initial pH was 3.5.Under these optimal conditions,the actual total acids content was 6.39±0.27 g/100mL,which was basically consistent with the predicted value of 6.45 g/100mL.5.The sterilization process of fruit vinegar was studied with aerobic bacterial count,Vc loss rate and so on as the indexes,results showed the optimum amount of salt was 2%,and the optimum sterilization condition was 95℃,30 s.Under these conditions,sterilized fruit vinegar was kept at 38℃ in a thermostat for eight weeks,there were no obvious changes in the physical and chemical indexes,and the microbiological indexes met the standard.Antioxidative activity of self-made fruit vinegar and commercially available apple vinegar were studied through the determination of DPPH radicals,hydroxyl radicals and reducing capacity,the results showed that self-made fruit vinegar had stronger antioxidative capacity.