Non-organic solvent extraction of capsaicinoids from oil combined with fluorescent lateral flow immunoassay strips for on-site identification of illegally recycled waste cooking oil†

The illicit use of recycled waste cooking oil poses a threat to food safety, yet there is currently a lack of on-site identification methods. This study targets a key component of recycled cooking oil, capsaicinoids, and establishes a rapid detection method for identifying illegally recycled waste cooking oil on-site. The method involves extracting capsaicinoids from the oil using a non-organic solvent extractant, and then detecting it using fluorescent lateral flow immunoassay (LFIA) strips. The preparation conditions of LFIA test strips were first optimized in this study. Subsequently, a 0.02 mol L⁻¹ solution of dimethyl-β-cyclodextrin was optimized as the extractant for capsaicin. The optimized sample extraction conditions involve a sample-to-extractant volume ratio of 1:2 and an extraction time of 1 minute, with a total extraction and detection time not exceeding 15 minutes. This method demonstrates a limit of detection (LOD) for natural capsaicin in oil samples of 0.14 μg kg⁻¹, with a detection range spanning 0.46 to 81 μg kg⁻¹. The method yields recovery rates between 88.76% and 115.79%, with coefficient of variation (CV) values ranging from 1.80% to 13.37%. Cross-reactivity rates for dihydrocapsaicin and synthetic capsaicin exceed 90%, while the impact of common contaminants or additives in other edible oils on detection is minimal. In conclusion, this approach fulfills the technical criteria mandated by the China Food and Drug Administration for distinguishing capsaicin compounds in recycled oil, offering advantages such as simplicity, rapidity, and “green” operation, making it suitable for rapid on-site identification of illegally recycled waste cooking oil.