| Bacterial cellulose (BC) is a biopolymer produced by some bacteria. It has unique physical and chemical properties and has been investigated in many fields such as medicine, food, separation membrane, and additives in the production of paper. A major challenge in BC production and applicaiotns is its relatively high cost. Searching for cheap fermentation substrates is an alternative way to reduce the cost, especially for carbon source. Therefore, production of BC should be focused on the use of cost-effective substrates or agricultural residues. In this research, cassava, sweet sorghum and sugar cane molasses were attempted as alternative raw materials for BC production.Fresh cassava was used to produce BC. A two-step enzymatic hydrolysis of fresh cassava by using thennostable α-amylase and glucoamylase was optimized by single factor experiment and response surface methodology. The optimal hydrolytic conditions for maximum yield of reducing sugars were as follows:liquefaction withα-amylase of123U/g cassava at87.5℃and pH6.0for53min and followed by saccharification with glucoamylase of133U/g cassava at62.2℃and pH4.5for86min. BC production in the cassava hydrolysates was compared with that in other carbon sources. The maximum BC yield was6.3g/L after7days of static cultivation in the cassava hydrolysates as carbon source, showing increases of43%compared to the yield in glucose-medium. The result demonstrated that cassava was capable of being developed as a potential excellent feedstock for BC production.Sweet sorghum is C4high energy crop that can be used as substrates for the production of sugar, syrup, alcohol, and fodder. In this study, the effects of kinds and amounts of nitrogen sources on BC production with sweet sorghum juice were investigated. Corn steep liquor (CSL) selected from organic nitrogen sources, and ammonium sulfate selected from inorganic nitrogen sources, performed better for BC production. The BC yields reached4.6g/L and4.0g/L respectively after7days cultivation. When16g/L CSL was used, BC yield of8.4g/L was reached. Compared with other nitrogen sources, CSL was an appropriate and economic nitrogen source. In addition, the concentration of the sweet sorghum, the time and the methods of the fermentation were dicscussed. It was found that the yield of BC reached16.9g/L, when the concentration was increased to125g/L. The yield of BC was24%higher than that in glucose-medium as same initial concentration of carbon souce of25g/L was used. The results demonstrated that sweet sorghum could be used as a potential carbon source for the production of BC.Sugar cane molasses is a residual stream of the sugar industries and contain rich fermentable sugars. In this paper, different pretreatment methods (H2SO4-heating treatment, heating treatment and untreated) of molasses and two microbial cultures(Gluconacetobacter xylinits and black tea fungus [Kombucha]) were compared. It was found that after the H2SO4-heat treatment, the reducing sugar and the total sugar were99.6g/L and100.4g/L, respectively. The BC yield was the highest, up to6.0g/L. When the concentration of the molasses was increased to80g/L, BC yield was increased to10.2g/L. In addition, when the H2SO4-heating treated molasses was used as carbon source, the BC yield in the culture of the Kombucha could reach12.0g/L. It showed that H2SO4-heating treatment was the best way for preparation of BC from molasses, and Kombucha performed better than G. xylinus.Further more, the BC membranes produced from fructose, glucose, cassava hydrolysate, sweet sorghum juice and molasses were compared by evaluating the properties of BC including water-holding capacity, microstructure and Young’s modulus. The results showed that the water-holding capacity was around98%, no big difference. The mechanical properties of the BC obtained from the five different carbon sources demonstrated a following order:fructose> glucose> sweet sorghum> cassava> molasses. |
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