The phospholipids of pork muscle, and their relation to the post-mortem rate of glycolysis

The phospholipids of pork longissimus dorsi muscle were investigated. The proportions of the major phospholipid components appeared to be constant in different regions of the same muscle, although the total lipid-P varied widely. Homogenates of the muscle were fractionated by differential centrifuging - ‘myofibrillar’, ‘mitochondrial’, ‘reticular’, and ‘final supernatant’ muscle fractions being obtained. Sarcoplasmic reticulum appeared to be present very largely with the fibrils in the ‘myofibrillar’ fraction, which contained 40–78% of the total lipid-P. The percentage composition of the phospholipids was similar in the first three sub-cellular fractions, while the fourth contained less of the ‘kephalin’ component. During fractionation of the muscle, substantial losses of phospholipids occurred; the possible origin and cause of these losses are discussed. The sum of lipid-P in the first and third subcellular fractions, containing sarcoplasmic reticulum, showed a highly significant negative correlation with pH₁, (muscle pH 45 minutes after slaughter) which represents an approximate index of the rate of post-mortem glycolysis in the muscle. The significance of this correlation is discussed.