BROWNING OCCURRING BY HEATING OF SHELLED OYSTER STORED AT FROZEN TEMPERATURE

Causes of undersirable browning which occur as a result of heating of shelled oysters stored at -35-degrees-C and characteristics of brown pigments produced were investigated. Peroxide values (100-500 meq/kg lipids), which were measured by HPLC, of lipids in potential browning portions were more than ten times larger than those in normal portions, and nearly half of the polyunsaturated fatty acids of the former lipids had been oxidized during storage at -35-degrees-C for 6 to 16 months. Discoloration by steaming resulted in a decrease in peroxide value and polymerization of oxidized glycerides. Brown polymers obtained after steaming for 20 min were lipophilic but not hydrophilic. They were fluorescent substances composed of 2-5 molar oxidized glycerides, mainly triglycerides, having intact saturated fatty acids and oxidized polyunsaturated fatty acids, and of nitrogeneous compounds (1.0-1.5%N).