J Food Biochem. 2019;e12841. wileyonlinelibrary.com/journal/jfbc | 1 of 8 https://doi.org/10.1111/jfc.12841 © 2019 Wiley Periodicals, Inc. 1 | INTRODUCTION Over decades, bioprocesses especially separation and purification of protease inhibitors have drawn attention. Purification is a criti‐ cal step prior to molecular characterization of protease inhibitor (Elizeu, Adeliana, Luciana, Adriana, & Ana, 2012). Protease inhibi‐ tors have physiological functions and possess a key function in the regulation of different biological pathways such as transcription, apoptosis, breakdown of intracellular protein, and invasion of cell cycle, in which proteases are associated (Choi, Park, & Kim, 2002). In food processing, protease inhibitors have been used as the food additives to improve textural property of several food products, e.g., surimi‐based products, meat ball, and sausage (Klomklao, Benjakul, Kishimura, Osako, & Simpson, 2016). Trypsin inhibitor (TI) is one of the most common serine protease inhibitors, which belong to Kunitz and Bowman‐Birk families and could be found in various sources from plants as well as pancreas of animals (Choi et al., 2002; Elizeu et al., 2012). Egg albumen is the cheapest source of several bioactive compounds including protease inhibitors (Datta et al., 2009). Duck egg albumen or egg white has been considered as a po‐ tential source of protein (8.8%) of total weight (Huang & Lin, 2011). Albumen proteins have multiple functional properties including gell‐ ing, emulsifying, vitamin, and iron‐binding properties, thus widening its use in food industry (Naknukool, Hayakawa, Sun, & Ogawa, 2008). Received: 26 December 2018 | Revised: 4 February 2019 | Accepted: 3 March 2019 DOI: 10.1111/jfbc.12841 FULL ARTICLE Trypsin inhibitor from duck albumen: Purification and characterization Tran Hong Quan 1,2 | Soottawat Benjakul 1 1 Faculty of Agro‐Industry, Department of Food Technology, Prince of Songkla University, Hat Yai, Thailand 2 Faculty of Applied Biological Sciences, Department of Food Technology, Vinh Long University of Technology Education, Vinh Long, Vietnam Correspondence Soottawat Benjakul, Faculty of Agro‐ Industry, Department of Food Technology, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand. Email: soottawat.b@psu.ac.th Funding information Prince of Songkla University Abstract 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 pres‐ ence 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 control‐ ling 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. KEYWORDS affinity chromatography, albumen, duck egg, kinetic inhibition, trypsin inhibitor