Abstract
p-Anisidine value (AV) is an important and commonly-used index to determine the second oxidation statue of edible oils, but it sometimes cannot reflect the concentrations of all the secondary products, such as saturated aldehydes. An improved method for the determination of saturated aliphatic aldehydes (SAA) in docosahexaenoic acid (DHA)-rich oils has been developed in this study. This method reduces the aldehyde 2,4-dinitrophenylhydrazone adducts (DNPhydrazones) using 2-picoline borane, which can eliminate the analytical error caused by the isomerism of DNPhydrazone derivatives. We subsequently monitored the changes of SAA content during the oxidation of DHA-rich oil. Acetaldehyde (168.8 μmol kg−1 and propionaldehyde (78.5 μmol kg−) were the two main SAAs in fresh oil, and their concentrations increased to 824.8 μmol kg− and 811.9 μmol kg−, respectively, after oxidation for 50 hours at 80 °C. Furthermore, a Michael addition reaction was found to significantly reduce the AV of oxidized oils, from 172.5 to 11.7. Moreover, the concentration of SAAs showed no significant difference and could clearly identify the low-quality oil. These results demonstrate that SAA content might be a potential index to identify oxidized oils, which could provide a good supplementary value to the traditional AV index.
Practical applications: The method that has been developed in this study makes it possible to quantify saturated aliphatic aldehydes as markers of oxidation of oils, especially when the AV cannot correctly assess the levels of secondary products. It could serve as a supplement to the AV index and applied to oils, fats, and food products. This work provides quantitative data regarding the amounts of saturated aliphatic aldehydes that can be present in DHA-rich oils during the oxidation process. This data can be helpful for determining the mechanism of oil oxidation.
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