Post Harvest Discoloration of Dark-Fleshed Fish Muscle: A Review

Discoloration of dark-fleshed fish species during storage and processing was mainly due to the reaction of myoglobin, a monomeric globular heme protein contributed to the pigmentation of red meat fish, alone and with other muscle components. Metmyoglobin formation caused by the autooxidation of myoglobin was a major factor influencing the darkening of dark-fleshed fish meat during iced and frozen storage. The increase in metmyoglobin content concomitant with a decrease in redness index of meat usually occurred during storage of dark-fleshed fish. Lipid oxidation was positively correlated with myoglobin oxidation and related to the discoloration of fish flesh. Aldehydic lipid oxidation products such as hexanal and hexenal potently induced the formation of metmyoglobin and the lowered whiteness of fish meat. Furthermore, a green pigment could be produced during heat processing in some dark muscle fish species such as tuna. Greening was generated when tuna myoglobin was reacted with other muscle components including trimethylamine oxide (TMAO) and cysteine. After heating, a single type of green pigment was formed and resulted in discoloration of cooked tuna meat. Furthermore, green pigmentation of tuna meat could be formed by the reaction of myoglobin with hydrogen peroxide, a by-product of lipid and myoglobin oxidations.