CsPbBr3 NCs Confined and In Situ Grown in ZIF-8: A Stable, Sensitive, Reliable Fluorescent Sensor for Evaluating the Acid Value of Edible Oils.

Rapidly and sensitively evaluating the acid value (AV) of edible oils is significant to ensuring food quality and safety. Cesium lead bromide perovskite nanocrystals (CsPbBr3 NCs) are an effective candidate for AV detection; however, their instability restricts wide applications. Herein, CsPbBr3@ZIF-8 was prepared by confining and growing CsPbBr3 NCs in situ into zeolitic imidazolate framework-8 (ZIF-8) to improve the stability, and a fluorescence sensor was established to evaluate the AV of edible oils. The results present that CsPbBr3 NCs (below 5 nm) with excellent optical properties were confined and grown in situ in micropores and mesopores of ZIF-8. Meanwhile, CsPbBr3@ZIF-8 had better long-term storage, ultraviolet-irradiation, and water-exposure stabilities, compared with CsPbBr3 NCs. Given the fact that free fatty acids (the major contributor of AV) decrease the fluorescence of CsPbBr3 NCs, the fluorescence intensities of CsPbBr3@ZIF-8 were negative-linearly related to oil AV (R2 = 0.9902) in 0.04-6.00 mg of KOH/g with a 0.06 mg of KOH/g limit of detection. Besides, the practical AV recovery was 92-101% with an average relative standard deviation of 2%. Furthermore, the detection time was 20 min. The response mechanism revealed that free fatty acids could remove surface ligands and increase surface defects to prompt the aggregation of CsPbBr3 NCs and the formation of lattice fringe dislocations, inducing a decrease in the fluorescence. Thus, a stable, sensitive, reliable sensor was established to evaluate the AV of edible oils.

An overview of the detection methods to the edible oil oxidation degree: Recent progress, challenges, and perspectives.

Oil oxidation, the main quality-deteriorated reaction, would significantly and negatively influence its quality and safety during processing and storage. Evaluating oil oxidation degree is an effective strategy to enable early warning and ensure food safety. Herein, principles, recent progresses, advantages and shortcomings, representative applications, current challenges and promising perspectives, and summary tables of traditional (titration), instrumental (chromatography and spectroscopy), and especially rapid detection methods (chemical colorimetric methods and portable miniaturized devices) for evaluating oil oxidation degree are presented and reviewed. It is believed that rapid detection methods are the most promising practical candidate for detecting oil oxidation. Also, the interaction between advanced data-processing techniques and detection methods, and the systematic integration of whole analytical processes is proposed as next-generation perspectives in the oil oxidation evaluation. We wish to provide the knowledge of oil oxidation degree determination and enlighten novel strategies.