Optimization Of Kiwi Juice Fermented By Probiotic And Analysis Of Aroma Components

Kiwifruit is popular because of its high nutritional value,sweet and sour taste.However,it is not easy to store after harvesting.At present,kiwifruit is easy to cause waste and loss of resources due to its single type of processed products.On the other hand,the use of probiotic lactic acid bacteria to ferment fruit and vegetable juices is a new type of functional health food that is popular among the public,which not only saves resources,but also enhances the nutritional value of the products,at the same time give the product a new flavor.In this paper,two probiotic lactic acid bacteria with acid and bile-tolerant ability and suitable for kiwifruit fermentation were screened to ferment kiwi juice,its fermentation process is optimized.Key indicators in the fermentation process are monitored.The effects of different fermentation strains and different fermentation substrates on the aroma of fermented kiwi juice were analyzed.The main research contents and conclusions are as follows:(1)Sensory scores and viable counts were used as indicators to select probiotic lactic acid bacteria strains suitable for natural kiwi juice fermentation,which are tolerance to low pH conditions and to bile salt.Secondly,the fermentation conditions of kiwi juice were optimized.the optimal fermentation conditions of Lactobacillus plantarum 21805 and Lactobacillus acidophilus 20250 were as follows: ratio of two probiotic strains,1:1;inoculums size,3%;fermentation time,24 h;and temperature,36℃.Under these conditions,sensory score was 81.45 points and viable cell count was 2.185×108 CFU/mL.(2)The kiwi juice fermented by the optimized fermentation process was detected and analyzed.The physical and chemical indicators of kiwi juice during fermentation and the dynamic changes of total aroma showed that the fermentation process is accompanied by a decrease in the pH and the sugar content,and an increase in the total acid content.In addition to the elevated levels of pyruvic acid,lactic acid and shikimic acid,the rest of the organic acid content decreased.The organic acid of the kiwi juice after fermentation is mainly composed of citric acid,lactic acid,quinic acid and malic acid.The results of electronic nose showed that the difference in flavor among different fermentation stages is mainly from terpenes,and other alcohols,alkanes,aromatic compounds,etc.The fermentation aroma is formed from 8 h,and 12 h is a key time point for producing aroma composition,and the late stage is a key stage for production the flavor of fermented kiwi juice.(3)The kiwi juice was fermented by single bacteria and mixed bacteria,and the kiwi juice of 4% malic acid,4% glucose and 4% citric acid was separately fermented by mixed bacteria to detect the aroma substances of the kiwi juice after fermentation.The results showed that the main aroma substances in each fermentation group were trans-2-hexen-1-ol,cis-3-hexen-1-ol,trans-3-hexen-1-ol,isovaleraldehyde,trans-2-hexenal,acetaldehyde,ethyl acetate,ethyl propionate,methyl butyrate,ethyl butyrate,damasthone,alpha-terpineol.Mixed fermentation can well retain the aroma substances produced by single-fermentation fermentation,and can also generate more aroma substances,and improve the aroma substance content of the fermented kiwi juice.The fermentation substrate also has an effect on the synthesis of aroma substances,and the 4% glucose fermentation group can produce more aroma species and content.The differences in each fermentation group are mainly reflected in terpenes,esters,and aldehydes.The electronic nose also showed similar results:mixed fermentation can produce more aroma substances.Compared with the addition of citric acid and malic acid,the addition of 4% glucose produces more aroma and produces more alcohols and aromatic compounds than unadded.And their overall aroma is closer.The aroma of the fermented kiwifruit can be further improved by the addition of glucose.