Preparation Of Bacterial Cellulose From Molasses By Using Different Strains

Bacterial cellulose(BC)is an extracellular metabolite polysaccharide produced by microorganisms,which is a novel nanostructured cellulosic material.High purity,strong water absorption,good tensile strength and strong biocompatibility enable BC to be a superior candidate,for broad application prospects in food additives,biomedicine,functional materials,papermaking applications and other fields,as compared to plant cellulose.However,due to its low productivity and relatively expensive culture medium,fermentation cost is high to limit its large-scale industrialization and commercial application.Therefore,it is of the great significance to find a lowcost,wide-ranging industrial and agricultural by-product as a raw material for BC production.Molasses is a by-product of the sugar industry enriched with a large amount of sugars,which can be used for the fermentative production of bacterial cellulose.In this paper,molasses is used as raw material to produce BC,analyze the sugar content in molasses and explore the acid treatment conditions.By optimizing the conditions for acid treatment of molasses,its detoxification was done in different ways,and then used in the medium to produce BC.The effect of strain type and nitrogen source type on BC membrane production was studied by using double-detoxified molasses acid solution as carbon source.In the later stage of the experiment,the yield,microstructure and tensile properties of BC films obtained under different conditions were compared to provide a theoretical basis for the further development and utilization of BC.The specific experimental results are as follows:Firstly,the sugar content analysis of molasses revealed that the total sugar content in molasses was 49.48%,the reducing sugar content was 21.20%,indicating that the reducing sugar content only accounted for half of the total sugar content,because Acetobacter xylinum can only use monosaccharides and oligosaccharides,so it needs to be acidified to molasses.Based on the single factor experiment,the effect of various dilute acid treatment conditions on the yield of reducing sugar was investigated by using the dilute sulfuric acid pretreatment.Taking the reducing sugar yield and reducing sugar concentration as indicators,the orthogonal optimization experiment was carried out on the basis of single factor.The optimal process conditions for the acidolytic molasses solution were as follows: 5 times water dilution,sulfuric acid concentration 1 mol/ L,acid hydrolysis temperature 90 ° C,acid hydrolysis time 240 min,the reducing sugar concentration under this condition is 114.81 g / L,reducing sugar yield is 42.52%,close to the total sugar content of molasses.The molasses acid hydrolysate was detoxified in different ways and then was used as the medium carbon source to prepare bacterial cellulose by using Acetobacter xylinum DHU-ATCC-1.The results indicated that the pure BC yield of the double-detoxified acid solution was the highest(4.96 g/L),which was 1.47 times than that of the glucose control group(3.38 g/L).The effect of activated carbon detoxification was second,and the yield was(3.79 g/L)is also higher than the glucose control group.The mechanical test results showed that the bacterial cellulose membrane cultured with molasses as the carbon source is mechanically weaker than the control glucose carbon source in any way.The X-ray diffraction pattern analysis showed that the crystallinity of BC prepared by using molasses as carbon source was lower than that of the control group.The activated carbon detoxification group was 91.87%,following the glucose group,92.60%.The doubledetoxification group BC film had poor crystallinity 69.38%,the reason for the analysis may be that the introduction of a large amount of Ca2+ during the detoxification process leads to a decrease in crystallinity.By infrared spectroscopy and electron microscopy,it was found that the detoxification method had almost no effect on the composition and three-dimensional network of the BC film.In addition,the effect of different strains and different nitrogen sources on BC membrane was investigated by using double-detoxified molasses acid solution as carbon source.The order of BC yield in this experiment was DHU-WX-1(7.68 g/L)> DHU-ATCC-1(4.18 g/L)> DHU-ATCC-23770(0.49 g/L),the tensile strength characterization indicated that the BC membrane obtained by DHU-WX-1 strain in the molasses medium had the worst mechanical properties.The crystallinity of the BC membrane obtained from the molasses acid solution medium and the control glucose medium were sequentially ranked,and all followed the same trend as;DHU-ATCC-1 > DHU-WX-1 > DHU-ATCC-23770.While considering the effects of nitrogen source on BC membrane,doubledetoxified molasses was used as carbon source,organic nitrogen source corn syrup and inorganic nitrogen source ammonium sulfate were suitable as nitrogen sources for producing bacterial cellulose,and DHU-WX-1 was used as the model strain.The yield of BC membrane obtained by the strain was 5.47 g/L and 3.99 g/L,respectively.The mechanical properties analysis suggested that the nitrogen source had little effect on its Young's modulus.Infrared spectrum analysis showed that the type of strain and the type of nitrogen source had no effect on the composition of the BC membrane.