The Effects of Microbiological Biodegradation on Gum Arabic Structure and Molecular Mass

Abstract

Due to its wide spectrum of use in Food and Pharmaceutics industries, gum Arabic is considered as one of the strategic crops as well as one being the backbones of Sudan economy. In this study, eleven crude gum Arabic samples of Acacia senegal.var senegal were used to detect its potential for microorganisms’ enumeration. Four samples were donated by the Gum Arabic Company Ltd, harvested during seasons 2005 - 2008. Three samples were, commercial ones, collected from different market locations (Bahri, Omdurman and Khartoum). The remainder, four samples were taken from Dawaia ink of “Khalwies” (traditional ink used locally in Quran teaching schools. Gum Arabic is used to stabilize the activated charcoal (soot) in water to produce the ink. Some major parameters were, initially, determined to authenticate the gum samples. Average contents of control sample used for moisture, nitrogen, protein and sugar contents, viscosity, number average molecular weight and pH values were found to be 12%, 0.42%, 2.64%, 77%, 10 cps, 2.46×105 and 4.5, respectively The samples were sterilized and re-analyzed for the same major parameters. The results indicate no significant changes were observed between compositions of samples before and after sterilization except for protein composition which decreased from 2.77 to 1.85%.Different types of bacteria, fungi and yeast species were isolated from both gum Arabic and Dawaia ink samples. The mean values of bacterial loads were found to be 2.8×103, 3.7×104, 6.4×105 and 6.8×106 cfu/g for samples of season-years 2005, 2006, 2007, 2008, respectively. The mean bacterial load in commercial samples, were found to vary between 1.62×104, and 7.0×105 cfu/g, respectively. The bacterial loads in Dawaia ink samples (A, B, C and D) were found to vary between 3.5×102 and 2.3×106 cfu/g. The total viable count (TVC) of fungi in samples of season-years 2005- 2008, were found to be 4.0 ×10, 21.5 ×102, 16.5 ×103 and 10.0 ×106 cfu/g; respectively. The TVC of fungi in commercial samples were 10.6×103, 21.8 ×103, and 11.2 ×103 cfu/g; respectively. Whereas in Dawaia ink samples (A, B, C and D) fungi loads were found to be 16.0 ×105, 46.0×104, 19 ×102 and 3.5.05 ×103 cfu/g; respectively. A total of twenty five types of bacterial isolates were detected, fourteen of which were characterized as Bacillus spp (56% of total bacteria load). Seven isolates were Bacillus cereus, three were Bacillus thuringiensis, and two for each of Bacillus macerans and Bacillus licheniformis. Eight isolates from Cornebacterum spp (32%, of the total detected), and were identified as C. bovis, C. xerosis and C. murium. Two of the isolates were identified as Staphylococcus aureus and epidermis; one was Streptococcus faccium which represented 8% and 4% of the total detected, respectively. Thirty eight isolates of Bacillus genus were obtained from of Dawaia ink samples, seven species were identified as Bacillus which represented 18% of the total, three of them were Bacillus licheniformis and two were B. macerans, one, for each, of B. polymyxa and Micrococcus varians. About five Corynebacterium (13%) were found to be C. xerosis and C. murium.63% of the total isolates were found to be Streptococcus sp, 17 of which were Streptococcus faccium, five were Streptococcus faecalis, and two were Streptococcus bovis. Only one isolates for each of Staphylococcus epidermis and Micrococcus varians which represented 3% of the total isolates. With respect to yeast contamination, only trace amounts were found in the sample from season 2008, and identified as Saccharomyces cerevicia; while the others were devoid of any contamination of this group. Different types of fungi were isolated from crude gum Arabic samples and Dawaia ink. For example, Aspergillus niger, Fusarium moniliforme Rhizorpous nigricaus, Penicillium notatum, Penicillium citrconigrum and only one yeast Saccharomyces cerevisiae. Bio-fractionations of gum Arabic medium by microorganisms’ enzymes resulted in a decrease in pH, titratable acidity, viscosity, nitrogen and protein and sugars content; number average molecular weight (Mn). Gel Permeation Chromatography (GPC) showed the presence of arabinogalactan protein (AGP), arabinogalactan (AG) and glycoprotein (GP) in all the samples. However, AGP molecular weight has markedly increased from 3.80×106 to 22.69×106 in samples after biodegradation by Penicllium natatum, probably due to carbohydrates biosynthesis.