Quality criteria of crude and processed gum arabic

The physico-chemical and microbiological characteristics of crude commercial grade and processed gum arabic samples (Acacia senegal gum) of Kordofan origin (El Obeid) season 1995/96 were studied. The crude samples which were hand picked selected, kibbled gum, gum siftings, gum dust and composite samples were provided by the Gum Arabic Company (GAC). The processed samples were prepared from the composite gum by freeze, drum and spray drying. A clarified gum dust sample was also prepared by atmospheric air drying. Each sample was characterized physically and chemically, and the microbial counts were enumerated, using different analytical techniques which included high performance liquid chromatography (HPLC), X-ray fluorescence, viscosity, optical rotation, emulsifying capacity, sorption isotherms and some other routine analyses. Dehydration of gum arabic concentrate (30-45%) have shown that drum drying was the most productive method. Moisture content of crude gum arabic samples ranged between 6.95 to 10.53%; while that of processed samples was 8.79 to 15.77%, optical rotation-25.38 deg to -35.71 deg and -28.57 deg to -31.82 deg; optical density at 340 nm was 0.063 to 0.320 and 0.104 to 0.253; emulsifying capacity at 650 nm was 0.515 to 0.550 and 0.542 to 0.611; intrinsic viscosity was 7.30 to 12.20 gE-1 cmE-3 and 13.20 to 13.30 gE-1 cmE-3; and molecular weight was 201, 806 to 337, 266 and 364, 910 to 367, 674. Construction of sorption isotherms have revealed that all samples have water activity of a sub(w) 0.65 which is the critical a sub(w) for microbial growth. Gim arabic in nodule or kibbled forms could be stored at 30 deg C at or belw 52% relative humidity, fine ground gums at or below 43% relative humidity and processed samples at 33-43% relative humidity. Microbial growth was only detected in some of the processed samples at relative humidity of 86%. Chemical characterization have shown a total ash content of 3.09 to 7.05% in crude samples which decreased to different levels in processed samples. A similar pattern was obtained in acid insoluble matter. All samples were free from starch or dextrin, and tannins. The nitrogen and crude protein of crude gums were 0.227 to 0.461% 1.417 to 2.898% which decreased after processing. All crude and processed samples exhibited slight acidic nature (pH 4.63 to 4.98). The element composition of all samples revealed in addition to K, Ca, Mg and Na, trace amounts of Ti, V, Cr, Mn, Fe, Co, Ni, Zn, Br, Rb, Sr Y; and Zr. The concentration of total heavy metals; As; and Pb were all within the permitted levels. In most cases these elements increased after processing. High performance liquid chromatography revealed the presence of L-rhamnose, L-arabinose and D-galactose in all crude samples with a total sugar content of 66.54 to 88.01. Freeze, drum and spray drying resulted in a decrease in total sugar content to different levels. Colourimetric determination of uronic acids gave a range of 20.41 to 24.60% which increased slightly after processing. High performance liquid chromatography also revealed the presence of alanine, arginine, aspartic and glutamic acids, cystine, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine therionine, tyrosine and valine; but in different concentrations in the different samples. While freeze and drum drying resulted in an increase in some aminoacids and a decrease in other; spray drying resulted in an increase in all aminoacids. Total enumeration of bacteria, moulds and yeast gave a bacterial load of 4.5x10 to 8.5x10E4 colony forming units (CFU)/g and 1.0x10E3 to 6.9x10E5 CFU/g in crude and processed gums, respectively. The mould count was 0.3xsquare 10 to 1.5xsquare 10 in crude and from nil to 1.5x10E3 in processed samples. Yeast were destroyed during processing but they tolerated freeze drying. All samples showed complete absence of pathogenic bacteria