le48 J. Agric. zyxwvutsrq Food Chem. 1992, 40, 1948-1952 Time-Dependent Postirradiation Oxidative Chemical Changes in Dehydrated zyxwv Egg Products Branka Katugin-Raiem,' Branka Mihaljevib, and Duhn Raiem Ruder BogkoviE Institute, 41000 Zagreb, Croatia Radiation-induced oxidative chemical changes in whole egg and egg yolk powder were followed in time after irradiation as a function of dose, dose rate, and storage atmosphere. In evacuated samples of whole egg powder the decay of lipid hydroperoxides (LOOH) was pseudo-first order zyxw (k zyxwv = 0.088 day1), while carotenoids did not decay at all. In the presence of air both lipid hydroperoxides and carotenoids decayed during postirradiation storage. The decay of LOOH could be treated by dispersive kinetics with the measure of dispersion, a = 0.51 f 0.05, independent of dose, and the effective lifetime T inversely related to dose. The decay of carotenoids could also be treated by dispersive kinetics, with the values of a decreasing with increasing dose. The effective lifetimes of carotenoids did not depend on dose in samples irradiated in vacuum. In samples irradiated and stored in air the effective lifetimes decreased with dose, faster in egg yolk than in whole egg powder. The complex nature of postirradiation kinetics in solid food systems is discussed. INTRODUCTION Egg is a basic raw material used in many areas of the food industry (Horn, 1977). Dried egg has the additional advantages of easier handling, lighter weight, and longer storage time, while retaining excellent functional prop- erties. However, dehydrated eggs also present a number of microbiological and chemical problems. Drying does not necessarily kill the entire pathogenic microflora, and additional microbicidal treatment is often necessary (Bomar, 1970). Chemical problems with dehydrated eggs are often caused by the large surface area, which makes dried products particularly susceptible to oxidation (Hubbard et al., 1989). Exposure of egg powder to agents promoting oxidative deterioration is usually avoided by adhering to the principles of good manufacturing practice; however, deliberate exposures to heat (ICMSF, 1980) or radiation (Farkas, 1988)are needed to pasteurize or sterilize foods. Drying and irradiation are intended to improve the stability and hygienic status of egg, respectively, as well as the status of the food products which contain it. On the other hand, radiation-induced oxidative chemical changes may persist in dry egg after the irradiation has ended, causing undesirable organoleptic changes. Thus, the temporal stability accomplished by drying becomes compromised by the means to accomplish the hygienic quality. Often, a delicate balance of risk and benefit must be considered when solutions made available by technology are evaluated. The consideration of risks and benefits involved in irradiating foodshas resulted in the recommendation made by the Joint Expert Committee on Food Irradiation (JECFI, 1980)that the wholesomeness of irradiated foods should be evaluated on the basis of radiation chemistry criteria. This requires quantitative knowledge of radia- tion-induced chemical changes in irradiated foods. We have shown earlier that a 2.4-kGy dose of y irradiation was adequate for a Salmonella inactivation factor of lo3 in egg powder (MatiE et al., 1990) without adverse effects on the organoleptic properties of the product, which begin to deteriorate above 3 kGy in air (Katdin-Raiem et al., 1989). However, some peroxidation was unavoidable on irradiation, even under vacuum (Katdin-Rdem et al., 1992). Considering the postirradiation persistence of free radicals in irradiated egg powder (Diehl, 1972) and postirradiation changes of lipid peroxides in irradiated solid food model systems (Wills, 1980), it is conceivable that radiation-induced hydroperoxides in dry egg products will also continue to change after irradiation. This work deals with the time dependence of lipid hydroperoxides (LOOH) in irradiated dry whole egg and egg yolk powder, as well as with the hydroperoxide-mediated postirradiation changes of carotenoids. These changes were followed as a function of dose, dose rate, and storage atmosphere, and the complex nature of postirradiation kinetics is discussed. MATERIALS AND METHODS Materials. Commercial samples of whole egg powder and egg yolk powder were obtained from two manufacturers of dehydrated food products, several batches from each. Determination of Lipids. The amount of lipids in samples was determined by extraction with a 2:l mixture of chloroform- methanol in a Soxhlet apparatus or by shaking with a cold deaerated solvent mixture (Warren et al., 1988). Dry whole egg samples contained between 42 and 51% lipids, while dry egg yolk contained about 61 % lipid. The profile of fatty acids in the lipidic component was determined by gas chromatography of methylated fatty acids on a 2-m, 3 mm i.d., column filled with 15% OV 275 on Chromosorb WAW 80-100 at 170 "C with 13 mL/min Nz and flame ionization detector (FID)(Christie, 1982). Retention times were determined with authenthic compounds. Quantitation was carried out using the methyl ester of hepta- decanoic acid as an internal standard and assuming the FID response factor 1 for fatty acid methyl esters relative to the standard. The major unsaturated fatty acids, oleic and linoleic, were between 21 % in whole egg and 29 % in egg yolk and between 2.5% in whole egg and 4.2% in egg yolk, respectively. To account for the variability of the contents of lipids among the samples, the level of lipid hydroperoxides was expressed per unit mass of lipid (L) (millimoles of LOOH per kilogram of L). Determination of Carotenoids. Carotenoids were deter- mined in a CHCls-MeOH extract by spectrophotometry against a blank (an extract of whole egg powder irradiated with 20 kGy or of egg yolk powder irradiated with 40 kGy to destroy the characteristic absorption of carotenoids). The absorbance of the longest wavelength peak of carotenoids at 478 nm was used. Sample Preparation, Irradiation, and Dosimetry. Sam- ples weighing 10-50 g were sealed in polyethylene pouches in the presence of air. Samples to be irradiated and stored in vacuum were evacuated and sealed in laminated aluminum pouches using 0021-8561/92/1440-1948$03,00/0 0 1992 American Chemical Society