Production Of Exopolysaccharides

SSF use in the production of exopolysaccharides such as xanthan and succinoglycan is growing. Xanthan is nontoxic and does not inhibit growth. It is nonsensitizing and does not cause skin or eye irritation. On this basis, xanthan has been approved by the United States Food and Drug Administration (FDA) for use as a food additive without any specific quantity limitations (131). Xanthan gum has been used in a wide variety of foods for a number of important reasons, including emulsion stabilization, temperature stability, compatibility with food ingredients, and pseudoplastic rheological properties (131). For recovering the xanthan, the cells are usually removed first, either by filtration or centrifugation (133). Further purification may include precipitation using water-miscible nonsolvents (isopropanol, ethanol, acetone), addition of certain salts, and pH adjustments (133). One SSF-based process for the production of xanthan gum utilized a bacterial culture of Xanthomonas campestris (134). The exopolysaccharide was produced on a number of agro-industrial residues or byproducts such as spent malt grains, apple pomace, grape pomace, citrus peels, and sugar beet molasses (137). With most of the substrates, the gum production was comparable to those obtained with SmF (130). Succinoglycan production by SSF with Agrobacterium tumefaciens on various solid substrates, including agar medium, spent malt grains, ivory nut shavings, and grated carrots, impregnated with a nutrient solution, showed the highest yield in static cultivation, reaching 42 g/l of impregnating solution, corresponding to 30 g/kg of wet substrate (135). The polymer production in a tray bioreactor was faster, but the final yield was lower (29 g/l of impregnating solution) (135).

SSF was performed using inert solid particles (spent malt grains) impregnated with a liquid medium. The gum was extracted from the fermented mass with seven volumes of water by shaking at 250rpm for 2h. It was filtered, centrifuged at 4000g for 10 min, followed by ultracentrifugation at 25000g for 20 min. The EPS was precipitated from the supernatant by the addition of 2% KCl, with 2-3 volumes of cold acetone. The precipitated xanthan was dissolved in 2% KCl, precipitated again with acetone, dried at 70°C. and weighed (136). The polymer yields obtained from SSF, as referred to the impregnating liquid volumes, were as follows: 38.8 g/litre xanthan from Xanthomonas campestris, 21.8 g/litre succinoglycan from Rhizobium hedysari and 20.3 g/litre succinoglycan from Agrobacterium tumefaciens PT45. These results made this technique promising as a potential application on the industrial scale. A further advantage of this fermentation process could be in the availability and low cost of substrates, which are obtained as byproducts or wastes from the agricultural or food industry (136). A comparison of SmF and SSF for the production of bacterial exopolysaccharides (EPS) showed that the latter technique yielded 2-4.7 times more polymer than the former on the laboratory scale (136).

Nutrition For Kids

Nutrition For Kids

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