Sphere-like Bacterial Cellulose:Producing Strains Screening And The Effects Of Fermentation Conditions On Its Synthesis And Structure

Bacterial cellulose(BC),especially sphere-like BC,as an excellent biological material,has been widely used in various fields.The application area has been limited since BC produced in agitated culture was mostly irregular lump,star-like,filamentous.Therefore,it is urgent to obtain a strain which can produce uniform sphere-like BC by strain screening.In this study,weight ratio and quantity proportion of sphere-like BC with median size were used as the assessment parameters,combined with the morphology and yield factors.Then the optimal strain was selected to produce sphere-like BC in agitated culture.This strain was used as production strain to study the effects of different fermentation conditions on the synthesis and structure of sphere-like BC.(1)30 Komagataeibacter nataicola stains were screened.The results showed that it was quite different for different strains under the same fermentation conditions even though they were the same species,possessed different abilities to produced BC.K.nataicola Y19 was the high yield strain which producted sphere-like BC.(2)The effects were significantly of synthesis of sphere-like BC by adding different concentrations of glucose,galactose,maltose,sucrose and fructose as the carbon source(p<0.05).The results showed that adding 50g/L fructose could obtain sphere-like BC with high uniformity and high yield.The yield was 0.842 g/L.The proportion of median sphere-like BC was 40.39%,the quantity proportion of sphere-like BC was 42.99%.(3)The rotation speed,depth of liquid,and diameter of fermentation beaker had significant influence on the synthesis of sphere-like BC in agitated culture(p<0.05).The results showed that the optimal fermentation conditions of sphere-like BC with high uniformity were as followed:rotation speed was 130r/min,depth of liquid was 2.40?2.75cm,diameter of fermentation beaker was 60mm.At this time,the proportion and the quantity proportion all more than 40%.(4)Our results showed that viscosity had significant influence on the synthesis of sphere-like BC in agitated culture(p<0.01).The BC yield increased as the viscosities increased and at 3.8mPa s(the addition concentration of agar,xanthan gum and potato starch were 0.64%,0.87%and 1.65%)it was the highest,they were 1.583g/L.1.517g/L and 1.613g/L.The uniformity was the best this time,the proportion of median sphere-like BC the highest.They were 47.32%,51.25%and 52.03%.The quantity proportions of sphere-like BC were 47.32%,51.25%and 52.03%.(5)The results of SEM showed the change of different carbon source and its concentration had no significant effect on the width of the filaments.The BC by adding galactose or maltose was looser and showed more aperture in the network structure,the BC by adding sucrose,fructose was opposite.XRD and FT-IR results indicated that the crystallinity of cellulose with sucrose or fructose was higher than the control,the crystallinity of cellulose with galactose or maltose was looser than the control.The crystallinity,crystal size and cellulose Ia of BC by adding high concentration of sugar were decreased.(6)The microstructure of sphere-like BC were affected greatly by viscosity.The resultant sphere-like BC was analyzed by using scanning electron microscopy(SEM),X-ray diffraction(XRD)and Fourier transforms infrared spectroscopy(FT-IR).The gaps and holes in the network structure increased with viscosity increase,especially the agar.With the hydrocolloid increasing,the impurities on fibrils didn't increase,but had smaller crystallinity and crystal size,and more cellulose Ip was formed.