Development Of Blueberry Vinegar And Changes Of Flavor Substances In Different Post-fermentation Stages

Blueberry is a fruit rich in many kinds of nutrients.Besides anthocyanins,other nutrients include conventional vitamins,polysaccharides,essential amino acids,proteins and edible fibers.Some mineral nutrients are also high.The storage temperature of fresh blueberry should be 2-6?.During transportation,it should not exceed 12?.Generally,it can only be stored for about 15 days.The flavor of fresh blueberry will change over a long period of time.Therefore,freezing is the main method of preservation of blueberry raw materials in industry.The production of blueberry vinegar is a way to transform the seasonal fruit value and prolong consumption.The production and development of blueberry vinegar not only conforms to the national agricultural policy,but also solves the problem of a large amount of waste of blueberry fresh fruit.In this paper,using frozen blueberry as raw material provided by Genhe Wild Blueberry Processing Plant,the optimum femientation conditions of two stages of fermentation of blueberry vinegar were studied,and the optimum production technology of blueberry vinegar was finally determined.Meanwhile,the changes of flavor substances in blueberry vinegar at different post-fermentation stages were explored and analyzed.The main results are as follows:1.The optimum technological conditions of ethanol fermentation of blueberry vinegar were obtained by single factor and orthogonal test.The optimum technological conditions were as follows:ratio of material to liquid 1:1,initial pH 3.6,yeast inoculation 0.2 g/L,fermentation temperature 25?,fermentation time 5 days.The results showed that the alcoholicity was 8.3%vol,the pH was 3.78 and the soluble solids content was 5.8%.And the wine is bright dark puqple red,bright color,fruity aroma,long aftertaste.2.Using blueberry fruit wine as base wine,the optimum technological parameters of acetic acid fermentation of blueberry fruit vinegar were studied by single factor test and response surface test.The optimum conditions for acetic acid fermentation were determined as follows:Difa acetic acid bacteria were selected for fermentation with inoculation of 1.0 g/L,shaking speed of 201 r/min,initial pH 4.0 and fermentation temperature of 30?.Under these conditions,the acetic acid content of blueberry fruit vinegar was 5.422 g/100 mL,with strong vinegar aroma and sweet and sour taste.3.The antioxidant activity of blueberry vinegar was determined.The results showed that the scavenging rate of blueberry vinegar to DPPH was 67.73%,to·OH was 82.81%,and to·O 2-was 49.45%.This indicated that the antioxidant activity of blueberry vinegar brewed by this method was strong.4.Gas chromatography,electronic tongue and electronic nose were used to detect the changes of aroma components in fruit vinegar at different fermentation stages.The results were as follows:(1)The results of gas chromatography showed that there were differences in aroma substances between the new vinegar liquor at the end of main fermentation and the fruit vinegar liquor at different stages of post-fermentation.The highest content of aroma substances in the vinegar liquor at the 20th day of post-fermentation was 99.9848%,which contained 9 aroma substances,including 5 alcohols and 4 esters.(2)The results of electronic tongue test showed that the acidity response value of blueberry vinegar was the highest on the 10th day after fermentation.The acidity response value of blueberry vinegar decreased significantly on the 20th day after fennentation,but increased gradually on the 30th and 40th day after fermentation.Bitter taste existed on the 10th day after fermentation,and weakened on the 20th day,but continued post-fermentation also caused the trend of increasing bitterness response value.After 30 days,the response value of astringency decreased to the lowest,then increased;the response value of fresh blueberry vinegar was the highest at 20 days after fermentation,and there was a significant downward trend in the continuous fermentation;the change trend of salty response value of blueberry vinegar was first increased and then decreased during the whole post-fermentation period;the sweet response value of blueberry vinegar liquor after 20 days fermentation was the largest.To sum up,the best fermentation time of blueberry vinegar is 20 days.Under this condition,blueberry vinegar has no impurities,rich fruit flavor,sweet and sour taste.(3)The results of electronic nose test showed that the variance contribution rates of PCA and PLS of blueberry vinegar were 98.76%and 98.72%respectively,which were more than 85%,indicating that both methods were effective.The total contribution rate of PCA to principal component variance was higher than that of PLS,which indicated that PCA was better than PLS in distinguishing blueberry vinegar.Comparing the results of PCA and PLS,the distribution of blueberry vinegar after 20 days of post-fermentation in PCA was far,while that of blueberry vinegar after 30 days of post-fermentation in PLS was far.The reason may be that the esters produced by the reaction of organic acids and alcohols in blueberry vinegar after 20 days and 30 days of post-fennentation were more and higher,which resulted in the difference of odor composition between the other groups.