Effect of alpha-, gamma-, and delta-tocopherol on the distribution of volatile secondary oxidation products in fish oil

Summary

The relative ability of α-, γ- and δ-tocopherol (TOH) to influence the distribution of volatile secondary oxidation products in fish oil was studied, with particular emphasis on oxidation products expected to be important for adverse flavour formation. Purified fish oil samples with 100 ppm or 1000 ppm of the different tocopherols were analysed by dynamic headspace analysis of the volatiles formed after 2, 5 and 8 d of storage at 30 °C. The tocopherol type and concentration affected not only the overall formation of volatile secondary oxidation products, but also the composition of this group of oxidation products. Principal component analysis of the data obtained suggested that high tocopherol hydrogen-donating power, i.e. a high tocopherol concentration or the use of αTOH as opposed to γTOH or δTOH, directs the formation of hydrocarbons, unsaturated carbonyl compounds of relatively high molecular weight, as well as the formation of cis,trans isomers of unsaturated aldehydes. Although an active inhibitor of overall volatile formation, αTOH at a high concentration thus appears to direct the formation of the more flavour-potent aldehydes, such as those linking the carbonyl group with ethylenic conjugated unsaturation.