Influence of muscle glycometabolism and lipid oxidation on the discoloration mechanism of dark muscle of cultured yellowtail <i>Seriola quinqueradiata</i>

Abstract

The discoloration of yellowtail dark muscle begins at the boundary part between dark muscle and ordinary muscle, and progresses toward the body surface side. To gain a deeper understanding of this phenomenon, we examined the processes of glycolysis and lipid oxidation in the two types of muscle. The glycolysis analyses indicated that an increase of lactic acid and decline of pH occurred at the boundary between dark muscle and ordinary muscle. An in vitro experiment using dark muscle extract showed that the decline of pH promoted the oxidation of myoglobin. An in vitro experiment using a mixture of extracted lipid and myoglobin from the dark muscle showed that the oxidation of phospholipid promoted the oxidation of myoglobin. Thus, we conclude that the discoloration, caused by the decline of pH at the boundary between dark muscle and ordinary muscle, progresses toward the body surface with oxidation of the phospholipid.

Potential of fluorescence fingerprints for fish meat authentication: Differences in freshness evaluation in white and dark meat at frozen state

“…A gradual decrease of pH was observed throughout the storage period, and this could be attributed to the degradation of ATP and the production and accumulation of lactic acid in the fish muscle (Lougovois et al., 2003). In addition, because of the higher accumulation rate of lactate in white muscle during anaerobic glycolysis, the pH decreasing rate of white meat was higher than that of dark meat of fish during ice storage periods (Kubo et al., 2018).…”

“…IMP contributes to the pleasant, fresh flavor of the meat, and enhances the umami flavor, especially in meaty foods, whereas HxR accumulation is associated with the progressive loss of desirable fresh fish flavor, that is, the development of a bitter off‐taste (Fletcher et al., 1990; Howgate, 2006; Kawai et al., 2002). Moreover, pH is considered a complementary freshness index; during postmortem anaerobic glycolysis, a higher amount of lactic acid is accumulated at the boundary of white and dark meat; thus, pH drops there more rapidly, causing the oxidation of myoglobin (discoloration), and progresses toward the body surface with the oxidation of phospholipid in dark meat of fish (Kubo et al., 2018; Listrat et al., 2016; Sohn et al., 2005).…”

“…Dark muscle is called slow skeletal muscle and mostly lies along the lateral line of a fish and is used for slow cruising (Jiao et al., 2019; Ochiai & Ozawa, 2020). During postmortem storage and processing of fish, dark meat deteriorates faster than white meat due to the remarkable variation of oxidative and glycolytic enzyme profiles between these two muscles (Jiaoa et al., 2019; Kubo et al., 2018; Listrat et al., 2016; Ochiai & Ozawa, 2020). In fact, dark meat has a higher concentration of the pigment myoglobin, which is low in soluble protein, glycogen, and glycolytic enzymes except hexokinase, but high in lipid, oxidative enzymes, and Ca 2+ ‐ATPase activity; the opposite situation exists in white meat of red‐fleshed fish including trout, mackerel, and yellow tail (Cassens & Cooper, 1971; Johnston, 1977; Kubo et al., 2018; Listrat et al., 2016; Rescan et al., 2001; Watabe & Hashimoto, 1980; Watabe et al., 1983).…”