Lipid distribution and recovery during salt fractionation of cod muscle

Lipids and particularly free fatty acids have been implicated in the denaturation of fish muscle proteins in the frozen state. A fuller understanding of this phenomenon can only be obtained with knowledge of the distribution of lipids at the subcellular level and of their behaviour when muscle proteins are isolated. Attempts were made to determine the lipid distribution between myofibrils, supernatant and subcellular particles and to follow the extraction of lipid during the preparation of actomyosin and structural lipoproteins. It was found that whole cod muscle homogenates incubated at 0° for 24 h do not show phospholipase activity. Separation of cell particulate matter and supernatant by centrifugation causes considerable hydrolysis and loss of phospholipids even after 2 h at 0°. The losses are enhanced by time and by the extraction of proteins and accompanying lipids into strong salt solutions. Phospholipase‐C‐like activity appears to cause a considerable proportion of the lipid loss. These phenomena, which are thought to be largely due to oxidation, are not observed in the summer months. Attempts to determine the lipid distribution in tissues by subcellular fractionation when lipid recovery is not quantitative may lead to seriously erroneous conclusions.