Isolation and Purification of Gellan Gum
Optimization of fermentation parameters alone is not enough to ensure high yield of gellan gum. The next crucial step after the completion of successful fermentation is the recovery and purification of gellan.
Recovery of gellan gum
In the recovery process described by Kang et al. (12), the culture broth is first heated to 90–95 °C for 10–15 min. The heating step not only kills the cells, which remain with the capsular polysaccharide, but also gently reduces the viscosity of the broth and this facilitates mixing during precipitation. The polysaccharide is separated from the cells by filtration or centrifugation. Cell-free supernatant was added to ice-cold isopropyl alcohol and the mixture was kept at 4 °C for 12 h for complete precipitation of gellan gum. The precipitate formed was then recovered by centrifuging. After gellan recovery, the product was dried at 55 °C for 1 h. Perhaps lyophilization of gellan could offer another alternative for formulating dry gellan powder (29). Clarified gellan gum was obtained by filtration of the hot fermentation broth with cartilage filters (0.2 µ), followed by precipitation with isopropyl alcohol (12).
Purification of gellan gum
The gellan gum obtained after alcohol precipitation was washed repeatedly with acetone and ether, dissolved in deionised water and dialyzed against deionised water by using dialysis tubing with molecular mass cut-off of 12 000–14 000. After dialysis for 2–3 days with four or five changes of deionised water, the solution was lyophilized to formulate dry gellan powder. Chromatographic methods like gel filtration chromatography (GFC) can also be used for the purification of gellan gum, although any such report has not yet been available.
Deproteinization of gellan gum
Deproteinization is a technical bottleneck in the purification of viscous water-soluble polysaccharides. Wanget al. (38) investigated the effectiveness of several methods of deproteinization including Sevag method, alkaline protease, papain and neutral protease for deproteinization of crude gellan gum. The results revealed that using
Sevag method deproteinization efficiency of 87.9 % was achieved, but recovery efficiency of gellan gum (28.6 %)
was unsatisfactory, making it unsuitable in industrial applications. Deproteinization by alkaline protease was
most suitable with high polysaccharide recovery (89.3 %) and high deproteinization efficiency (86.4 %)
Sevag method deproteinization efficiency of 87.9 % was achieved, but recovery efficiency of gellan gum (28.6 %)
was unsatisfactory, making it unsuitable in industrial applications. Deproteinization by alkaline protease was
most suitable with high polysaccharide recovery (89.3 %) and high deproteinization efficiency (86.4 %)
