Trypsin inhibitor from duck albumen: Purification and characterization

Egg albumen is a potential source of trypsin inhibitor (TI), which has been widely used to improve textural property of surimi or surimi-based food products. TI from duck albumen was isolated and purified using ammonium sulfate precipitation at 20%-40% saturation and affinity chromatography using trypsin-CNBr-activated Sepharose 4B column. TI was purified with purity and yield of 111.8-fold and 0.6%, respectively. The purity of inhibitor was confirmed using Native-PAGE as indicated by the presence of single band. Molecular weight of purified TI was 43 kDa based on SDS-GAGE and gel filtration. The purified TI remained unchanged at temperatures below 60°C and the pH in the range of 7-9. The inhibitory activity of TI was decreased with the addition of salt higher than 5%. Inhibition kinetic study revealed that purified TI from duck albumen was uncompetitive inhibitor and the inhibition constant (Ki) was 508 nM. TI from duck egg albumen could serve as a food grade inhibitor for controlling undesirable proteolysis. PRACTICAL APPLICATIONS: Duck egg albumen has been known to be rich in protease inhibitors, which can be used as a protein additive to enhance gelling properties of surimi or surimi-based products. Therefore, it is of interest to isolate and purify TI from duck egg albumen. Information regarding characteristics of TI from duck albumen could be beneficial for further applications, in which duck albumen is better exploited.