[Comparison of bench-scale production of xanthan by xanthomonas campestris in solid state and submerged fermentation]

ABSTRACT

Xanthan gum is an important natural biopolymer with numerous applications in various technologies, specially food industry. In this research, microbial production of xanthan by Xanthomonas campestris PTCC1473 from sugarcane molasses and date sugar in submerged fermentation [SmF] and also dried date waste [cake produced after pressing] in solid state fermentation [SSF] were compared. The Plackett-Burmann design [PBD] was used in this study. Chemical composition and characteristics [dried cell weight, nitrogen, moisture, ash and pH] of the substrates were determined. Yeast malt broth [YMB] and yeast malt agar [YMA] were used as maintenance and inoculum preparation media, and incubation was performed in a shaker incubator [at 28degreeC, 72 h and 200 rpm]. The fermentation medium was centrifuged at 5degreeC and 21055 multiplied by g for 50 minutes and the supernatant separated from the pellet for further xanthan extraction. After precipitation of xanthan by isopropanol, resuspension and further purification by centrifuge [at 2056 x g], the xanthan dry weight was determined. The effects of several variables, including the kind and concentration of carbon [date sugar and sugarcane molasses], nitrogen [ammonium nitrate and diammonium phosphate] and phosphorus [KH2PO4], temperature, shaking, and size and age of inoculum, on the yield were determined. The most effective variables were found to be the type of carbon and nitrogen sources in the medium. It can be concluded that both the yield [% w/w of xanthan/consumed sugar] and productivity [g/g.day xanthan/consumed sugar] are higher in SmF [22.4 and 7.46] than in SSF [13.3 and 4.43]. In addition, date extract results in a higher productivity than date waste and sugarcane molasses. The xanthan yield could be increased by changing the composition and physical conditions of the culture medium