Apple Vinegar Fermented By Gluconacetobacter Xylinus And The Effect Of Bacterial Cellulose For Fermentation

Fermented apple vinegar was brewed with yeast wine and inoculated Gluconacetobacter xylinus RF4 successively through taking apple juice as material,which flavor characteristics was better than formulated products. In the implementation of the process, a layer of bacterial cellulose pellicle was found on the liquid surface at the middle and later periods of the fermentation, as the increase of fermentation time, the pellicle became thicker and thicker, it was a typical form of surface aerobic fermentation. This paper preliminary discussed the mechanism that the formation, existence and intactness of bacterial cellulose pellicle have effect on Gluconacetobacter xylinus producing acid, the results provide a theoretical foundation for optimizing the production process and equipment design.This paper discussed the differences between stepwise fermentation and synchronous fermentation in fermentation time, acidity and sensory evaluation;Researched the influence of the bacterial cellulose pellicle on producing acid during fermentation, compared the differences of ADH enzyme activity between cellulose pellicle and fermented liquid, discussed the differences of fermentation between inoculating cellulose pellicle and liquid, and the influence of acid between static fermentation and shake flask fermentation.Determined the relationship in acid production rate, the ADH enzyme activity and total number of bacteria within 32 hours for two kinds of cultivation, compared differences of oxygen consumption in three kinds of cultivation, compared oxygen consumption between static fermentation and shake flask fermentation.Used solid phase micro extraction and gas chromatography- mass spectrometry(SPME-GC-MS) detection, determined volatile aroma components in three kinds of apple vinegars that come from market, stepwise fermentation and synchronous fermentation.The main results are as follow:1. The acidity increased to 4.32g/100 m L in 12 days by stepwise fermentation; for synchronous fermentation, the acidity increased to 4.86g/100 m L in 10 days. Both ofthem had great taste and full of the aromas of apple and the vinegar, the synchronous fermentation vinegar taste was better.2. Prevented the formation of the bacterial cellulose pellicle would result in the stagnation of producing acid; the initial formation of the pellicle was sank to the bottom of the liquid or taken out would both lead to producing acid were significantly suppressed immediately; the fermentation would produce acid normally under the condition of cellulose pellicle keeping intactness. The results showed that the bacterial cellulose pellicle formation and floating on the fermented liquid surface had a direct effect on acid production,its existence and intactness played a key role in the fermentation system.ADH enzyme activity in cellulose pellicle was 56 times of that in fermented liquid, the bacterial cellulose pellicle was the main place of acetic acid production.Inoculating cellulose pellicle would produce acid faster than inoculating liquid containing bacteria. So, time would be shortened effectively by inoculating cellulose pellicle at the beginning of the fermentation.The acidity increased to 4.32g/100 m L in 8 days by static fermentation at the acetic acid fermentation period, but shake flask fermentationwas hardly produce acid.So, static fermentation was better than shake flask fermentation to produce acid.3. Keeping static fermentation after 5 days, the acidity was rising, acid production rate was also accelerating, the ADH enzyme activity of fermented liquid under cellulose pellicle had almost nothing changes, the total enzyme activity in the fermentation system had been on the rising, the number of bacteria in fermented liquid was decreasing slowly, but the total number of bacteria was increasing.The bacterial cellulose pellicle grew up again after had removed it, the Gluconacetobacter xylinus began to consume oxygen and produce acid. ADH enzyme activity in the fermented liquid achieved the maximum 0.333 U/g on 20 h, the number of bacteria in fermented liquid achieved peak on 24 h(bacteria count(8.35±0.44)E+04 CFU/m L),and then both of them began to decline; the total ADH enzyme activity and bacterial content have been increasing, which mean as the formation of the bacterial cellulose pellicle, the Gluconacetobacter xylinus began tomove to pellicle to ferment.The bacterial cellulose pellicle floated on the level integrity on 24 h, acid production rate reached the highest 0.065g/100 m L·h, the oxygen consumption also rate reached the maximum 0.383ppm/h, it was confirmed that the presence of the pellicle and integrity would make Gluconacetobacter xylinus consume oxygen effectively, which was the characteristic of surface fermentation.The headspace oxygen content almost unchanged by shake flask fermentation,however, when the bacterial cellulose pellicle floated on the level, the oxygen consumption rate rapidly accelerated by static fermentation. It showed that the formation of pellicle played a key role in oxygen consumption, which further confirmed the characteristic of surface fermentation.4. Fermented apple vinegar had the same main kinds of flavor substances, 9kinds of volatile aroma components were detected which belong to alcohols, acids and ester, the main substances were acetic acid, ethyl acetate and ethanol. There were also 9 kinds of volatile aroma components were detected which belong to acid, ester and aldehyde in mixing apple vinegar, the main substances were ethyl acetate, 2-hexene aldehyde and 2- methyl ethyl butyrate.