Elimation of the "pH effect" in cell fragility determinations
Love, R.M.; Muslemuddin, M.
Nature 228(5272): 681-682
1970
ISSN/ISBN: 0028-0836 PMID: 4920020 Document Number: 24026
When fish is stored frozen, the properties of the flesh slowly change so that the thawed material becomes tougher, with consequent problems for the food industry. Research in the field has been hindered by the lack of convenient methods for measuring the phenomenon. Love and Mackay1,2 devised a simple technique in which 200 mg of muscle is subjected to a standard gentle homogenization in 20 ml. dilute formaldehyde (the "cell fragility" technique). Fresh fish is disintegrated to the myofibrillar level, but after freezing and thawing increasingly less disintegration occurs as the cold-storage period is increased; after about 12 weeks at −14° C, only intact cells are present. The extent of disintegration is assessed from the light-scattering characteristics of the homogenate, which are measured in a colorimeter. The soft tissue of fresh fish forms an opaque "soup" of high absorbance, whereas tissue which has toughened is shredded to a few strands, most of the suspending medium remaining clear and giving a low reading in the colorimeter. It was later discovered, however, that the readings were influenced by the p H of the muscle3,4 in such a way that toughening attributable to low p H, without cold storage, gives rise to a high absorbance, whereas toughening in the frozen state gave a low absorbance reading. This method was therefore useless for quality control of frozen fish unless the p H could be determined also. The routine determination of p H along with cell fragility has been suggested5, but this would make quality control more tedious without guaranteeing accurate assessment of storage history. Though an experienced operator can distinguish by eye between homogenates of high p H–low absorbance density and cold storage–low absorbance, this requires skill and leaves room for doubt about values obtained in different laboratories.