Analytical Methods for the Determination of Diamine Oxidase (DAO) Activity: A Comprehensive Review

Diamine oxidase (DAO) is an extracellular enzyme that plays a key role in the intestinal degradation of exogenous histamine. Given its association with histamine intolerance and its potential applications in food biotechnology and dietary supplements, the accurate determination of DAO activity has become essential in both clinical and food-related contexts. This review provides a comprehensive and critical evaluation of the analytical methods reported for the determination of DAO activity, including spectroscopic, radiometric, immunological, chromatographic, zymographic, mass spectrometric and electrochemical techniques. Their underlying principles, analytical performance, advantages and limitations, and suitability for different sample matrices are compared, distinguishing methods that measure catalytic activity from those that quantify DAO protein concentration. Particular emphasis is placed on the influence of the reaction substrate and assay conditions on the measured activity, and on the need to align substrate selection with the intended application, including the clinical investigation of histamine intolerance and the evaluation of DAO-based dietary supplements. This review offers practical guidance for selecting appropriate methods according to the analytical objective and identifies current challenges and priorities for the standardisation of DAO activity determination.