Visual detection of edible oil oxidation by using chitin-based colorimetric sensor for aldehydes

Abstract

Traditional analytical methods for evaluation of lipid oxidation often rely on costly and sophisticated equipment or complex operations, which limit their application in daily life. Aldehydes are important compounds that are produced during the process of lipid oxidation, thus a good type of indicator for edible oil freshness. Herein, a chitin-based colorimetric sensor for aldehydes was developed and applied in visual detection of edible oil oxidation. The sensor was prepared by using Congo red and hydroxylamine sulfate to be incorporated into TEMPO-oxidized chitin nanowhiskers (TOChN) films. The sensing mechanism is based on the specific reaction in which hydroxylamine sulfate reacts with aldehydes, releasing sulfuric acid and leading to a decrease of pH, and finally inducing obvious color change from red to blue of the Congo red in the sensor films. Hexanal was chosen as model aldehyde to investigate the sensitivity and selectivity of the sensor films. As a result, the sensor films were highly sensitive and selective to aldehydes, with a detection limit of gaseous hexanal of 44.8 ppm and minor interference from other volatile organic compounds (VOCs). Additionally, to evaluate the effectiveness of the sensor films, their responses for real samples were also investigated. Surprisingly, the oxidation status of all seven sunflower oil samples was correctly identified by the sensor films, suggesting great potential of the colorimetric sensor for visual detection of edible oil oxidation.