Chymotrypsin inhibitor assay: expressing and standardizing inhibitor activity in absolute amounts of chymotrypsin inhibited

Authors: Liu, Keshun; Woolman, Michael - Mike

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/23/2022
Publication Date: 11/1/2022
Citation: Liu, K., Woolman, M.J. 2022. Chymotrypsin inhibitor assay: expressing and standardizing inhibitor activity in absolute amounts of chymotrypsin inhibited. Meeting Abstract. Available: https://www.iufostworldcongress-singapore.com/agenda

Interpretive Summary:

Technical Abstract: Historically, trypsin inhibitor activity in soybeans and other legume products has been of primary interest for measurement. However, as plant proteins are increasingly used for food or feed in recent years, there is a growing interest in monitoring chymotrypsin inhibitor activity (CIA) in these products. Recently, at our USDA lab, a robust method was developed for accurately measuring CIA. Like all previously reported methods, the new method expresses CIA as chymotrypsin units inhibited (CUI)/mg sample. This makes comparison of results among reports impossible. To solve the problem, we carried out a new study, using the newly developed method with three chymotrypsin preparations having different specific activities. We then determined the relationship between absorbance and chymotrypsin concentration for each enzyme preparation. Since conversion factors between CUI and chymotrypsin inhibited correlated highly with chymotrypsin specific activities, it became necessary to determine a standardized conversion factor against a reference chymotrypsin having a specific activity of 60 Na-benzoyl-L-tyrosine ethyl ester/mg protein. Upon standardizing against this reference chymotrypsin based on specific activities of the three chymotrypsin preparations, a standardized conversion factor of 1.7 between CUI and chymotrypsin inhibited was determined. The new method can now express results in mg chymotrypsin inhibited/g sample.