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Background and Objectives: 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. Materials and Methods: 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 28 °C, 72 h and 200 rpm). The fermentation medium was centrifuged at 5°C and 21055  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  g), the xanthan dry weight was determined. Results: 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. Conclusion: 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.

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Background and objective: Propionibacteria are capable of producing many important industrial products such as propionic acid, vitamin B12 and bacteriocins. Also these bacteria show some probiotic health benefits and produce prebiotics as stimulator of intestinal bacteria. The aim of this research is evaluation of pH control on production of biomass propionic, acetic and lactic acids in fed-batch system, with feeding of molasses and lactose as carbon sources of co-fermentation of Propionibacterium freudenreichii ssp. shermanii and Lactobacillus acidophilus. Materials and methods: Fermentation was conducted in a 3-liter fermentor containing base medium and molasses as the carbon source in which lactose was fed after 36th hat temperature at 30 °C. Total fermentation time was 96 hand sampling was done in every 24 h intervals to measure the biomass and organic acids. Two treatments were compared to each other: in one trial, pH was maintained at 6.5 by using NaOH 1N, but in another, during fermentation pH was not controlled. Content of biomass and organic acid were measured by freeze drying and HPLC methods, respectively. Results: The final concentration of the dependent variables for the two treatments with and without pH control obtained as following (g/L): biomass 1.97±0.07 and 1.72 ±0.07, propionic acid, 4.87±0.13 and 4.16±0.04, acetic acid 4.87±0.13 and 4.16±0.04 and lactic acid 7.93±0.06 and 6.10±0.09. Conclusion: In this study it was shown that production of mentioned organic acids was not affected significantly by adding NaOH for control of pH in medium. Keywords: Propionibacterium freudenreichii subsp. dhermanii, Propionic acid, Fed-batch system, Molasses