University of Khartoum

Effect of Growth Conditions on the Production, Composition and Viscosity of Xanthan Gum produced by Xanthomonas campestris

Effect of Growth Conditions on the Production, Composition and Viscosity of Xanthan Gum produced by Xanthomonas campestris

Show full item record

Title: Effect of Growth Conditions on the Production, Composition and Viscosity of Xanthan Gum produced by Xanthomonas campestris
Author: Taha, Leiza Hayder Mohammed
Abstract: The objective of this study was to optimize conditions for Xanthan gum production using locally recovered Xanthomonas campestris isolates. Symptomatic plants’ leaves and fruits were examined for the presence of Xanthomonas. Each sample was inoculated into Yeast extract Dextrose CaCO3 (YDC) medium and then cultured on selective Xanthomonas medium (SX). Cultural and microscopical tests indicated that most of the colonies detected were yellow, mucoid, convex, round and translucent with entire margins and smooth surfaces on YDC plates and the cells were all Gram negative rods. Isolates which conformed to growth characteristics described for Xanthomonas species (35 isolates) in this medium were considered as presumptive Xanthomonas isolates and those which showed other growth characteristics were excluded. Presumptive Xanthomonas isolates were then characterized biochemically using standard procedure. Biochemically, isolates were all able to grow at 35°C, to produce catalase and hydrolyze starch. The isolates produced acid from sucrose within two days but with different capacities. The identity of the 35 presumptive Xanthomonas isolates was confirmed by PCR using a X.campestris specific (conserved) gene. The 35 Xanthomonas isolates were screened for their ability to produce Xanthan gum by measuring their colony diameters and starch hydrolysis zone they produced. Xanthan yield (g/L) and viscosity, in sucrose medium, was also used as screening criteria. The tested isolates showed a wide range of variation in their capacity to produce Xanthan. Isolates Xan 7, 9, 26, 29 and 33 showed the highest Xanthan yield, the highest viscosity values and the largest starch hydrolysis zone and they were selected for further studies. To improve Xanthan gum productivity, the effect of a range of growth conditions, including initial pH, temperature, course of fermentation, H2O2 and EDTA addition on Xanthan gum productivity were studied in a series of experiments. Maximum concentration (83.33 g/L) was produced by Xan9 while minimum Xanthan yield (23.3g/L) was produced by Xan33 after three days of incubation. Other isolates have shown Xanthan yield in the range of 33.33-73.33 g/L (pH=7) at 30°C and 180 rpm under submerged fermentation conditions. The highest Xanthan yield was recorded for both isolates Xan9 and Xan26 when sucrose was used as the sole carbon source in the fermentation medium followed by glucose, fructose and the maltose. Very low Xanthan yields were obtained when lactose was used as the only source of carbon in the fermentation medium. The highest values of Xanthan yield for isolates Xan26 and Xan9 were recorded at 1.25mM H2O2. Although not consistent, addition of H2O2 after 24 hours seems to produce higher yields compared to other addition times. The time course of Xanthan yield by Xan9 and Xan26 was studied in batch fermentation using molasses as a substrate. For both isolates, the best yield was obtained at 96 hours of incubation after which no increments or significant reductions in Xanthan yield were observed. Scale up of Xanthan production by Xan26 in sucrose medium as well as in molasses-based medium was studied. Xanthan yield of 50 g/L (after three days of incubation) and 36 g/L (after seven days of incubation) were recorded in sucrose medium and molasses-based medium, respectively. Further research efforts are needed in order to characterize Xanthan, parameters such as Xanthan molecular weight, sugar composition and acetate and pyruvate contents, which are important Xanthan quality parameters, are to be determined.
URI: http://khartoumspace.uofk.edu/handle/123456789/20925
Date: 2016-05-01


Files in this item

Files Size Format View

This item appears in the following Collection(s)

Show full item record

Share

Search DSpace


Browse

My Account