Study On Extraction Process Of Extracellular Polysaccharide-gellan Gum

Extracellular polysaccharide gellan gum is one of the industrially useful microbial exopolysaccharides due to its stability and high gelling efficiency. Because of its high viscosity, the extraction work is very difficult. Current researches are mainly focusing on its fermentation rather than extraction. In laboratory, fermentation broth is largely diluted to reduce its viscosity, and remove the cells by centrifugation, the method is obviously uneconomical for industrial production. In this paper an extraction process for gellan gum was developed including cell removing, decolorization, deproteinization and Ca2+ removing. The total process was as follow:The first step decolorization:add 3% HCl (v/v) solution into the broth to precipitate crude gellan gum (gellan gum mixed mainly with cells). The volume of 3%HCl solution is equal to the initial fermentation broth.Then filtrate the precipitate with Plate and Frame Filter(PFF) to get the filter cake(crude gellan gum), and squeeze the cake to remove HCl solution as much as possible. Then the cake was immersed in industrial alcohol of 1.5 cake volumes, and adjusts pH to 7, after 40min, remove alcohol and main pigment by filtration.The second step cell removing:dissolve the crude gellan gum in water (the ratio of water volume to initial broth was about 2:1).Then adjust pH to 10,and keep the solution at 80℃for 25min to make gellan deacetylated. After that the cells were flocculated by adding 0.0045mol/L CaCl2 into the solution (pH10,80℃)and removed by filtration with PFF using industrial filter cloth of 200 mesh along with diatomite as filter aid at pressure of 0.25MPa.The third step Ca2+ removing and further removing of cells:add 0.0045mol/LNa2CO3 into permeation liquid, filtrated the liquid by PES membrane of 0.45μm pore at 90℃,0.7MPa using PFF.The fourth step deproteinization and further decolorization:after cell and Ca2+ removing,0.3% alkaline protease (w/v) was added and the solution was kept at 55℃for 4h to remove protein.after that add 0.5% H2O2 and keep the solution at 75℃,pH8 forl5 min to remove pigment absolutely. The last step precipitate and drying:add equal volume of 3%HC1 into the solution, then get the precipitate by filtration,and wash it with alcohol and adjust the pH to7, then remove the alcohol by filtration again.At last drying the refined gellan gum at 50℃. The molecular weight, gel strength, transparency, and total recovery of deacetylated gellan gum was 1130000,890g/cm2,79.9%,71% respectively.