DEGRADATION OF FISH MUSCLE DURING MECHANICAL DEBONING AND STORAGE WITH EMPHASIS ON LIPID OXIDATION

Deterioration of mechanically separated fish flesh as measured by extent of lipid oxidation and color change was studied using fresh mullet (Mugil spp.). The parameters studied included contact with iron surfaces, mechanical stress applied to the muscle during deboning, temperature of deboning drum, washing of deboned fish flesh, and postdeboning treatments including addition of antibiotic, sparging with nitrogen gas, cooking, freezing and thawing. TBA value was used as an index of lipid oxidation and the reflectance ratio of metmyoglobin to oxymyoglobin as an index of color change was determined using reflectance spectrophotometry. The degree of stress applied during deboning did not cause any significant variations in TBA value, whereas increased temperature of the deboning drum showed an adverse effect which became significant with prolonged storage. Contact of flesh with iron parts of the deboner resulted in a pronounced increase in TBA value of the flesh within the short span of time involved in the deboning process. Washing improved significantly product quality when the product was frozen for an extended period, but appeared to have no major advantage when stored under refrigeration and immediately processed. A marked rise in TBA value occurred during thawing with the effect being more pronounced with increased thawing time. The effect of thawing also became more pronounced with extended frozen storage. Ambient oxygen and microbial activity appear to have an insignificant role in lipid oxidation during storage. The lateral tissue (red muscle), tissue along the visceral cavity, and bone marrow exudate appeared to be the most susceptible to the development of oxidative rancidity. Rate of TBA value change was very rapid when these muscles had contact with iron surfaces.