Acidic Beverage Fermentation Using Citrus Juice and Antimicrobial Activity of the Fermented Beverage

In this experiment, citrus juice was fermented by Gluconacetobacter hansenii TF-2, an isolate from tea fungus to develop a new type of acidic beverage. The juice broth is made by fermenting of $11{\sim}17%$ (v/v) juice and sweetened with sucrose (initial sucrose $10^{\circ}Brix$). The fermentation by G. hansenii TF-2 was initiated by adding 5% (w/v) of seed gel (pellicle, tea fungus) which was previously cultured in the same medium (fresh juice broth) and the fermentation was carried out in a dark incubator at $28{\sim}30^{\circ}C$ for about 15 days. During the fermentation a pellicle grew on the surface of the fermenting fluid and acids were produced. Fermented fluid (beverage) was centrifuged at 7,000 rpm for 15 min for further analyses. The highest amount of the other metabolites including organic acids were observed in 5 to 10 days. Major acids were acetic acid (fermented citrus beverage, CB). After 15 days of fermentation, organic acid content such as acetic acid in fermented beverage was measured to be $183.5{\sim}186.6\;ppm$. Free sugars content in CB were 56.8%, 35.1%, 40.7% and 63.2% of unfermented sucrose, glucose, fructose and sorbitol, respectively. When the growth rate of inhibitory effect of the fermented beverage was measured by using several species of food-related bacteria, the beverage fermented with CB exhibited the strongest inhibition against gram-negative (E. coli and Sal. Typhimurium). Its inhibition rate was between $71.9{\sim}94.0%$ at CB. Fermented beverage has shown effectiveness for antimicrobial activity against some species of food-related bacteria.

감귤과즙을 이용한 산형음료 발효 및 발효음료의 항균효과

감귤과즙으로 새로운 산형음료 개발을 위해 tea fungus로부터 분리한 G. hansenii TF-2 균을 이용하였다. 과즙배지는 $11{\sim}17%(v/v)$의 과즙에 초기 당도를 $10^{\circ}Brix$로 하였다. G. hansenii TF-2에 의한 발효는 과즙배지에 활성화시킨 seed gel을 5%(w/v) 첨가하여 $29{\pm}1^{\circ}C$에서 15일 배양하면서 5일 간격으로 측정하였다. 발효 동안 발효액 표면에는 막을 생성하고 액에는 다양한 유기산을 생성하였다. 분석에 사용한 발효액은 7,000 rpm에서 15분간 원심분리 하여 사용하였다. $5{\sim}10$일 사이에 유기산 등의 기타 대사산물의 함량이 가장 높았다. 발효가 진행되면서 malic acid, acetic acid, itric acid, succinic acid, fumaric acid 등의 다양한 유기산이 생성되었으며, 특히 발효 전반에 acetic acid가 관여하였다. 주요 산으로는 acetic acid이었다. 발효 15일째 측정에 의하면, acetic acid 함량은 $183.5{\sim}186.6\;ppm$이 검출되었다. 배양 동안 CB11의 유리당은 sucrose, glucose, fructose 그리고 sorbitol이 확인되었으며 각각 56.8%, 35.1%, 40.7%, 63.2%가 검출되었다. 음용 시 식품에 관련된 세균에 대해 CB11가 $71.9{\sim}94.0%$의 저해율을 나타내었으며 그람 양성균 보다는 그람 음성균에서 더 효과적이었다.