AIMTo evaluate the correlation between the swelling equilibrium quantity (Seq), dissolution rate and amino group content which were used to estimate the degree of gelatin crosslinking, and the factors which influence the crosslinking, and to investigate the crosslinking mechanism of delayed dissolution of soft capsules.

METHODSThe swelling equilibrium quantity, dissolution rate and amino group content of formaldehyde-crosslinked capsule shells were determined. Gelatin structure was analyzed by means of DSC.

RESULTSA good lineal relativity was found between the swelling equilibrium quantity, dissolution rate and amino group content (r = 0.9953-0.9985). The Seq of capsule shells was influenced by high temperature, lighting and some additives. Glycine and sodium pyrosulfite might retard the decrease of Seq of capsule shells.

CONCLUSIONThe swelling equilibrium quantity, dissolution rate and amino group content exhibited the same rule in gelatin crosslinking extent. High temperature, lighting and some additives might induce gelatin crosslinking. Antioxidant such as glycine and sodium pyrosulfite might retard the crosslinking.