New Analytical Evidence of Discontinuous Oxidation in Dried Microencapsulated Lipids

Formation of hydroperoxy-, keto- and hydroxy-dienes was studied at 40 °C in fatty acid methyl esters (FAME) microencapsulated in a dairy-like matrix formed by lactose and sodium caseinate. The FAME were obtained from conventional sunflower oil and the microcapsules were prepared by freeze-drying of an oil-in-water emulsion. For comparative purposes a neat sample of FAME was also tested. Results showed that for a given content of hydroperoxydienes much more elevated amounts of secondary products were detected in the microencapsulated sample compared to the neat sample of FAME. The contents of keto- and hydroxy-dienes found in the microencapsulated FAME ranged as a whole between 6 and 31 wt% of the analyzed compounds, while the neat sample showed values lower than 1.5 %. Along with the fact that relatively higher contents of polymers were also found in the encapsulated sample, these results can be attributed to lipid droplets with very different oxidation states. On the one hand, the extract would be formed from droplets in early stages of oxidation containing hydroperoxides and very low contents of secondary products and, on the other, from droplets in advanced stages with decreased hydroperoxides and substantial contents of secondary products. Unlike the neat sample, hydroxy-dienes formed with significantly higher amounts than keto-dienes in the microencapsulated FAME, suggesting a possible chemical role of the encapsulation matrix.