Encapsulation of urease in alginate beads and protection from α-chymotrypsin with chitosan membranes

Urease was encapsulated in alginate beads coated with chitosan, poly-L-lysine or poly(methylene co-guanidine) membrane to exclude α-chymotrypsin and other proteases. Urease in uncoated alginate was highly susceptible to 21.6 kDa α-chymotrypsin, with 98% of the activity lost within 10 min exposure. Chitosan and poly-L-lysine membrane coating provided 50 and 12% activity retention respectively after exposure, while poly(methylene co-guanidine) membrane both inactivated urease and failed to provide protection from protease hydrolysis. Lyophilization of the beads caused shrinkage, and rehydrated beads did not swell to their original diameter, effectively reducing permeability. This was evident through a large improvement in protease exclusion for both chitosan-coated (89% activity retention) and uncoated (71%) beads. Results with trypsin were similar to that observed with α-chymotrypsin, likely due to similarity in molecular weight. A higher level of exclusion and urease protection within chitosan coated alginate beads was observed with higher molecular weight proteinase K.