NATURE OF FREE RADICALS IN FREEZE-DRIED FISHERY PRODUCTS 

 AND OTHER LIPID-PROTEIN SYSTEMS 



William T. Roubal' 



ABSTRACT 



The electron paramagnetic resonance spectrometer makes it possible to detect and study radicals which 

 are produced during lipid peroxidation in freeze-dried lipid-protein systems. In such systems, two gen- 

 eral types of resonances are observed. By studying effects of added antioxidants, added autoxidizable 

 lipid, and type of substrate, it is possible to differentiate and characterize the two signals which are ob- 

 served. It is postulated that the immobilized radicals observed in dry systems are the same as those 

 that are responsible for damage at the molecular level in o.\ygenated lipid-protein-water emulsions, 

 stored meats of normal moisture content, and in antioxidant deficiency states in man and animals. 



Fish from the sea are rich in polyunsaturated 

 fatty acids. Furthermore, when fish are pro- 

 cessed as a foodstuff, the unsaturated fatty acids 

 will, if unprotected, readily undergo lipid perox- 

 idation. 



In the presence of proteins, enzymes, nucleo- 

 tides and other classes of biological materials, 

 lipid peroxidation is radiomimetic, that is, it 

 produces similar if not the same effects as ion- 

 izing radiation — a damage mechanism which is 

 known to be mostly free radical in nature. Ac- 

 cordingly, such materials as freeze-dried fish 

 tissue, dried fish meals, and protein concentrates 

 incompletely freed of residual unsaturation, 

 are all prone to undergo various deteriorative 

 changes as a consequence of lipid peroxidation. 



Although much emphasis has been placed in 

 the past, and continues to be at present, on the 

 participation of radicals in events leading to 

 damage, radicals of the oxy or peroxy type have 

 not been directly characterized by electron para- 

 magnetic resonance (EPR) spectroscopy in liv- 

 ing systems or in emulsions for in these the 

 steady state concentration of radicals is univer- 

 sally low. Nevertheless, the EPR method re- 

 mains as the one method best suited for char- 

 acterizing radicals. 



' National Marine Fisheries Service Pioneer Research 

 Laboratory, Seattle, Wash. 98102. 



Manuscript received January 1971. 



FISHERY BULLETIN: VOL, 69, NO 2, 1971. 



This paper discusses recent research employ- 

 ing systems which, for the first time, are fa- 

 vorable for the detection and study of EPR 

 signals which arise with the onset of lipid oxi- 

 dation. Mechanisms for the formation of radi- 

 cals as well as reactions of radicals themselves 

 are discussed. 



MATERIALS AND METHODS 



Freeze-dried and isopropyl-extracted rockfish 

 myofiljrillar protein, and freeze-dried rockfish 

 sacroplasmic protein were provided by the 

 NMFS Technological Laboratory in Seattle. In 

 addition, a polyunsaturated fatty acid (PUFA) 

 concentrate (75':r C22:6 + 25^r C22:5) was 

 also provided by this laboratory. Freeze-dried 

 human serum albumin (Grade III) and bovine 

 serum albumin (BSA; crude powder) were 

 obtained from Sigma. Freeze-dried silver salm- 

 on light flesh was prepared from a slurry of 

 fresh fillet. All freeze-dried materials were 

 stored at — 60° C in the dark under nitrogen 

 prior to exposure to air. Lipid-protein mixtures 

 were prepared merely by thoroughly mixing 

 the C22:6 concentrate with protein, usually in 

 a ratio of 2: 1 (protein to lipid) by weight. All 

 oxidations were conducted in air at room tem- 

 perature. All EPR studies were conducted at 

 room temperature according to the procedures 

 of Roubal (1970). 



371 



