ROLE OF FORMALDEHYDE IN FORMATION OF NATURAL ACTOMYOSIN AGGREGATES INHAKE DURING FROZEN STORAGE

During frozen storage of certain lean species of fish, formaldehyde (F A) is formed, giving rise to changes in texture related to the formati on of aggregates of myofibrillar proteins. In order to study these agg regates a model system was prepared with natural actomyosin (NAM) (5 m g/ml) and increasing concentrations of formaldehyde. The system was st ored frozen at -20-degrees C for 2 months during which solubility in 0 .6 M NaCl, Ca2+ ATPase activity, cis-parinaric acid (CPA) hydrophobici ty, SH groups and sodium dodecyl sulphate (SDS) polyacrylamide gel ele ctrophoresis (PAGE) were measured. - FA caused an immediate loss of Ca 2+ ATPase activity and a decline in soluble protein and CPA hydrophobi city, an effect that was enhanced when the samples were frozen. The el ectrophoretic profiles of the proteins that remained soluble showed th at in both fresh and frozen samples, when FA reacts with NAM the first protein to be insolubilised is myosin, followed by actin, then the tr oponins and myosin light chains and lastly tropomyosin, depending on t he amount of FA and the reaction time. Aggregates of high molecular ma ss were found at early stages, probably as a result of covalent bindin g of myosin molecules. When the amount of FA or the frozen storage tim e was increased, these aggregates became insoluble, forming high-molec ular-mass structures and hence were not found in the soluble fraction.