Comparative study of basic characteristics of ordinary and dark muscle in skipjack tuna (Katsuwonus pelamis)

Differences between ordinary and dark muscle of skipjack tuna (Katsuwonus pelamis) including proximate composition, flavor, color, texture, and freshness were investigated. Ordinary muscle had a higher crude protein content, but a lower crude lipid content than dark muscle. Alcohols (30.41%) and aldehydes (25.56%) were the prominent flavor compounds present in ordinary muscle, whereas hydrocarbons (39.51%) and ketones (21.81%) were more abundant in dark muscle. Different L*, a*, and b* values were also observed. Texture profile analysis (TPA) showed that dark muscle had higher values for adhesiveness, and lower values for cohensiveness, chewiness, and resilience. After mechanical breaking, large myofibril fragments were observed in ordinary muscle under phase contrast microscopy, but not in dark muscle. Freshness indices, including K values, total volatile basic nitrogen (TVB-N), and thiobarbituric acid (TBA) values of dark muscle were higher than for ordinary muscle.