A new chemical method for quantifying total aldehydes in frying oils and its correlation with the para-anisidine value

Abstract: Thermal decomposition of hydroperoxides during frying generates a number of secondary oxidation products, with carbonyl compounds predominating. p-Anisidine Value (p-AV) is the most prominent official method for quantifying these carbonyl compounds, utilizing the reaction between carbonyls, principally 2-alkenals and 2,4-dienals, and p-anisidine reagent. It is well known, however, that despite the success of the p-AV test, the data is generally skewed toward the unsaturated carbonyl compounds and the reagent is considered as highly toxic, limiting its acceptability in some food processing settings. The method proposed in the current study utilizes the reaction between carbonyl compounds, specifically aldehydes, and purpald reagent (4-Amino-3-hydrazino-5-mercapto-1,2,4-triazole). Unlike the p-AV, the purpald test is specific to aldehydes with negligible interference from other functional groups (e.g. ketones, carboxylic acids, esters). Interestingly, the reaction between aldehydes and purpald reagent is skewed toward saturated aldehydes by nearly the same factor that the p-AV is skewed towards unsaturated aldehydes, providing a complimentary information to the p-AV on the nature of secondary aldehydes formed during thermo-oxidative degradation of lipid hydroperoxides. Further, a strong correlation was found between the purpald method  and the p-AV method, providing the opportunity for indirect determination for p-AV in food processing settings where the p-anisidine reagent is considered unacceptable with regard to environmental health and safety. Challenges and limitations of the proposed chemical method are also presented.