The effect of water activity on cholesterol oxidation in spray- and freeze-dried egg powders

The aim of the paper was to estimate the effect of water activity in spray- and freeze-dried whole egg and egg yolk powders on cholesterol oxidation during 3-months of storage at room temperature.Egg powders were divided into three groups. The first group of powders was not moisturized, the second and the third groups were moisturized to 8% and 12% of water content. The samples of powders placed in plastic bags without venting were stored for 3 months in darkness at room temperature. Directly after moisturizing of egg powders, the chemical composition (water, proteins, lipid) was measured. In fresh and stored powders the contents of cholesterol and oxysterols were estimated. Water activity was higher in egg yolk powders than in whole egg powders. Egg yolk powders contain less hydrophylic proteins and more hydrophobic lipids than whole egg powders. During storage the highest oxysterol accumulation appeared in egg powders with the lowest water activity; oxysterols accumulation was higher in whole egg powders than in egg yolk powders, and in spray-dried powders it was higher than in freeze-dried ones. Five oxysterols were identified and quantified. In not moisturized spray-dried whole egg powders these oxysterols were (as follows): 5α,6α-epoxycholesterol (5α,6α-EP) > 7α-hydroxycholesterol (7α-HC) > 5β,6β-epoxycholesterol (5β,6β-EP) > 7-ketocholesterol (7-KC) > 7β-hydroxycholesterol (7β-HC). During storage of powders, 5,6-epoxycholesterols (5,6-EP) were produced in the highest amounts.