The purpose of this study was to study the changes which occur in fish lipids with emphasis on cholesterol during processing. Frying, drying, and UV, solar and gamma-irradiation were selected as means of processing at different conditions. Cholesterol, cholesterol oxides, fatty acids, and volatiles were analyzed qualitatively and quantitatively to monitor the fish lipid changes during processing. The omega-3 fatty acids in mackerel were not significantly reduced by pan-frying. However, major amounts of the fish oil were physically lost during frying. The concentration of the omega-3 fatty acids in the oil released was significantly reduced, demonstrating the possible sensitivity to oxidation once the oil is removed from its natural state. When pollock was deep fat fried without batter, extensive absorption of the frying oil occurred. Batter coating appeared to protect the fillets against loss of moisture, absorption of cooking oil and dilution or loss of flavor volatiles. Oxidative interactions of cholesterol with other compounds were studied at 180 C for one hour. When triacylglycerols were added to cholesterol before heating at 180 C, the latter oxidized faster than cholesterol heated alone, and a relatively high amount of oxides was found. Dipalmitoylphosphatidylethanolamine and all the amino acids tested showed a protective effect, with cysteine and alanine being the most effective. When pure cholesterol, cholesterol in aqueous system, and cholesterol-containing squid were exposed under the UV radiation, cholesterol was destroyed in varying degrees depending on the wavelength, radiation time, and the state of cholesterol. Pure cholesterol and cholesterol in aqueous system were destroyed much faster than that in squid fish indicating some physical and chemical protection in fish muscle. Cholesterol in aqueous system produced higher amount of oxides suggesting different oxidative pathways when water is present. In all cases, the fastest and most severe destruction resulted from exposure at 312 nm. Solar radiation also resulted in certain degrees of cholesterol oxidation in squid. Gamma-irradiation induced cholesterol oxidation when exposed to high energy radiation. Cholesterol in aqueous system was destroyed faster than pure cholesterol and than the cholesterol in squid. (Abstract shortened with permission of author.)

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