Selection Of Strain With High-Yield Bacterial Cellulose And Optimization Of Fermentation Process

It's not only plants can synthesize cellulose, but some animals and micro-organisms also have this ability. The cellulose produced by micro-organisms is called"bacterial cellulose (BC)".Compared with the other two kinds of cellulose, BC has several excellent characteristics, such as: superfine, ultrapure, ultra-intensity, high water content, and better biology adaptability. These characteristics make BC has special application. At present, BC has been successfully applied to food processing, paper processing, medical domain and biochemical engineering domain. As a new kind of biomaterial in 21 century, BC has a bright future, however, comparatively high cost give some restriction on its application. In order to improve the yield of BC and reduce its cost, a strain (J2) with high yield of BC was initially selected from buckwheat vinegar on whose surface grew much thicker membrane and the characteristics of the strain J2 was researched, then the parameters of fermentation process were optimized which established the basis for industry. The property of the cellulose membrane was studied and its apparent structure and ultra-micro-structure were observed which gave some direction to its application. The results of this research were as follows:â‘ a strain(J2) with ability to produce high yield of BC was selected from buckwheat vinegar. After the configuration and physiological and biochemical property were studied, the strain was primarily ascertained to belong to Gluconobacter.â‘¡The seed medium and seed cultivation conditions were confirmed. The seed medium components were as follows: glucose 7%, yeast extract1%, K₂HPO₄ 0.5%, MgSO₄ 1.5%,ethanol2%. Using this medium, the yield of BC could be enhanced and was as 1.8 times as that using initial cultivation medium. The optimum cultivation conditions were seed age 24h, rotation speed 150r/min, inoculums amount 7%.â‘¢The stationary fermentation medium was confirmed. The components of it were as follows: carbon source3%(glucose:sucrose =1:2), yeast extract 0.33%, FeS04 0.4%,ZnS04 0.09%,K₂HPO₄ 0.1%,MgSO₄1%,malic acid 0.3%, ethanol 0.7%.Under this fermentation medium, the yield of BC was as 1.35 times as that under initial fermentation medium. â‘£The main components of the cellulose membrane produced by J2 was mensurated, and the apparent structure and ultra-micro-structure were observed. The water content in wet membrane was 98.94%; the water content in dry membrane after absorbed water was 81.74%; cellulose content in dry membrane was 88.85%, protein content was 7.67%, and fat content was 1.5%. The apparent structure of both wet and dry membrane were different under different disposing methods; the results of ultra-micro-structure observed with SEM was that vacuum freeze-drying way and ordinary drying way could change the ultra-micro-structure of membrane.