Efficient Bacterial Cellulose Production from Buffered Fruit Juices

Abstract

Bacterial cellulose (BC) is an exopolysaccharide produced by numerous bacterial species including Acetobacter. BC has many advantages such as high tensile strength, water holding capacity, and biodegradability. The problems are low BC yield and high production cost. To solve the problem various carbon sources have been researched to produce BC. In Southeast Asia, coconut water is commonly used as carbon source to produce BC called nata de coco. However, there have been very few attempts to produce BC from juices of other fruit sources, such as pear, apple, and grape, which are major fruits produced in East Asia including South Korea. Since those fruits have relatively low pH because of organic acids, the control of pH is necessary to achieve the maximum BC production yield. In this study, optimum fermentation conditions of the strain KCCM 41431 were investigated to achieve the maximum BC production using response surface methodology (RSM). Also, the BC fermentation characteristics of various fruit juices and optimum conditions for the BC production with buffered media were investigated. The factors for RSM were screened through literature review, and the effective factors and range of the factors were selected by one factor at a time research. Three effective factors, fructose (X1), agar (X2), and agitation speed (X3), were set for the optimization. Among the variables agitation speed (X3) showed 95% significance. The coefficient of determination (R2) of the BC production was 0.7048, indicating that the three variable model could explain 70.48% of the total variation in response. The optimum condition for BC production was decided to be 112 g/l of fructose concentration, 0.55% (w/v) of agar concentration, and 133 rpm of agitation speed. The predicted maximum BC production was 19.55 g/l and the experimental BC production at these conditions was 17.07 g/l. Acetate buffer and citric-phosphate buffer were used to control pH of fruit juice media. A.xylinus KCCM 41431 was inoculated and BC fermentation was performed for 10 days. In buffered fruit juice media, BC productions were 1.67, 1.44, 2.54 fold higher than those of pure pear, apple, and grape juice, probably due to the reduction of acid stress. Even though apple juice contained high concentration of total sugar, the BC yield was low due to its high concentration of organic acids. The BC production was inhibited at high buffer concentration (>200mM). The results demonstrated that BC production from various fruit juices depended on concentration of organic acids, concentration of buffer solution, and type of buffer solution. The maximum BC production was 17.02 g/l in 75mM acetate buffered pear juice media. The maximum BC production from buffered fruit juice was comparable to the RSM result. The result of this study suggested the feasibility of BC production from various fruit juices.