Influence of packaging atmosphere on the formation of cholesterol oxides in gamma-irradiated egg powder

In a previous work the effect of ionising radiation on formation of cholesterol oxidation products (COPs) under aerobic conditions was studied. In the present work the influence of aerobic and anoxic conditions have been comparatively investigated to study the chemical changes of cholesterol in γ‐irradiated egg powder. The irradiation treatment was carried out with powdered egg packed under air and also under vacuum in polyethylene (PE) bags and in laminated, oxygen impermeable three‐layer (polyester‐aluminium‐polyethylene) foil to dosage levels 2 and 4 kGy at room temperature. The cholesterol oxidation is demonstrated by thin‐layer chromatograms. In the egg powder wrapped in PE bags the predominant cholesterol derivatives−7‐hydroxycholesterol isomers (α and β)—accumulated in significant amounts (increasing with dose) while vacuum‐packaging in laminated foil considerably suppressed the quantity of these products and prevented the formation of cholesterol 5α, 6α‐epoxide as well as 7‐ketocholesterol. Little or no change was observed in non‐irradiated (control) vacuum‐packed egg powder stored at approximately 22°C for up to 5 months. Peroxide values showed changes parallel to the formation of COPs.