A simple and sensitive fluorescence-measuring technique was developed to assess extent of lipid oxidation in freeze-dried meats. Solvent extracts of reconstituted stored samples were assayed by fluorimetry. Spectra of "oxidized" meats show maximum excitation and emission wavelengths of hex = 350 and hem = 440 nm, respectively. At hem of 440 nm, "unoxidized" meats show three peaks in excitation spectrum at hex1 = 308, hex2 = 318 (max.), and hex3 = 350 nm. However, at hex of 350 nm, these samples show a peak at Aem = 476 run. The intensity ratio of hex3 or hem over hex2 are useful as sensitive and reliable "internal standards" of lipid oxidation. Presence of 100 ppm TBHQ (monotertiary butylhydroquinone), absence of oxygen, and compression of meat before freeze-drying, which protect against oxidation also result in corresponding reductions of these ratios.

The oxidation of membrane lipids of freeze-dried Milk Fat Globule Membranes (MFGM) was studied using a fluorescence technique involving two different extraction procedures to obtain lipophilic fluorescent chromophores. MFGM underwent extensive lipid oxidation when stored under air, at controlled temperature and humidity and fluorescent compounds were formed with excitation maxima at 350 nm and emission maxima at 440 nm. Direct extraction of fluorescent compounds with an organic solvent mixture (CIsCH:CHsOH 2: 1 v/v) gave reproducible results reflecting well the progress of oxidation. Solvent extraction after previous reconstitution (to original water content) of the dry samples was less satisfactory.

iron, which alters it from a ferric to a ferrous state.Effects of ionizing radiation on beef pigments were studied by determining the absorption spectra of myoglobin solutions and the reflectance spectra of radiation-sterilized beef slices. Bovine and ovine oxymyoglobin (MbO,) and met(ferri)myoglobin (metMb) were extracted, purified, and treated with gamma radiation. Increasing dose and temperature of gamma radiation produced increasing shifts in characteristic peaks and progressive decreases in the Soret bands of these pigments. The total color difference (AE), computed from tri-stimulus values of reflectance spectra of radiation-sterilized beef, showed similar dependence of color on radiation dose and temperature. Re-irradiation of beef allowed to brown in air caused the unstable red pigment to re-form. The presence of oxygen in the container during radiation-sterilization reduced the red color formation. The results show that ionizing radiation reduces the heme iron of the brown pigment of cooked meat (globin myohemichromogen) to an unstable red pigment (globin myohemocbromogen), which, upon exposure to air, reverts to the original ferric (brown) pigment.Clark and Richards (197 1) reported that gamma irradiation of beef metMb with 1 Mrad changes it to a compound that has characteristic absorption peaks at 542 and 582 nm and a Soret band at 411 nm. These authors suggested that a chole-heme protein is formed by rupture of the hemin nucleus, which is still principally attached to the denatured globin.Richards and Morrison (1971), who studied color changes in beef exposed to pasteurizing doses of gamma rays, showed that irradiation of samples packaged in oxygen-permeable film produced less red color than irradiation of comparable samples packaged in oxygen-impermeable film. Giddings and Markakis (1972) suggested that there are two myoglobin derivatives produced by gamma irradiation of ferrimyoglobin solutions. When the solution is anoxic before irradiation, a reductive oxygenation (via hydrated electrons from water radiolysis) to Mb02 takes place. In solutions containing oyxgen, ferrylmyoglobin (quadrivalent myoglobin) is generated via Hz OZ.

To investigate changes in structure and function of milk fat globule membrane (MFGM) components due to oxidation of membrane lipids, freeze‐dried MFGM were stored under controlled temperature and relative humidity (RH) conditions. It was found that while membranes underwent extensive lipid oxidation when stored under air, fluorescent compounds were formed. These compounds exhibited fluorescence with excitation maxima at 350 nm and emission maxima at 440 nm; which were similar to those of the fluorescent substances derived from the reaction of oxidized fatty acids and primary amines. Formation of high molecular weight proteins was detected by SDS‐PAGE in samples stored under air, but not in samples stored under nitrogen and was also affected by time and relative humidity. Activity of xanthine‐oxidase, an important prooxidative agent, was greatly influenced by temperature and complete inactivation was observed when MFGM's were stored at 37°C, 50% RH for 1 day.