Changes in the state of water and ATPase activity during dehydration procedures of white croaker myofibrils were investigated in the presence of various amino acids by monitoring the desorption isotherm profile and myofibrillar Ca-ATPase activity.Amino acids were classified into four groups by their effect on myofibrillar Ca-ATPase inactivation; (1) amino acids exerting marked suppressive effect on inactivation such as Na-Glu and Na-Asp, (2) those exerting moderate suppressive effect such as Gly and Ala, (3) those exerting little or no effect on inactivation such as Val, Leu, and Ile, and (4) those accelerating the inactivation including hydrophobic amino acids.The addition of acidic amino acids exhibiting a remarkable suppressive effect on ATPase inactivation increased the content of monolayer and multilayer water adsorption of myofibrils.
The fatty acid composition in horse mackerel caught off Nagasaki, off Tsushima Island, and in the middle of the East China Sea was investigated. The ratios of monoenoic and polyenoic acids to the total fatty acids in the Nagasaki and bull trawl catch specimens had a negative correlation. The docosahexaenoic acid (DHA; 22:6n‐3) ratios of total fatty acids in summer‐caught specimens were lower than those in winter‐caught specimens, and this tendency was significantly clearer in smaller‐sized fish, while DHA levels in tissues varied little throughout the year. Consistently high levels of DHA were found in various fishing areas, which suggests that horse mackerel offers a stable source of DHA.
The chemical components and body color of horse mackerel caught between July 1997 and May 2000 were studied. The fish were caught with small‐ to medium‐sized purse seine offshore from Nagasaki and from Tsushima, and with bull trawl seine and medium‐ to large‐sized purse seine in the East China Sea. The crude lipid content of the fish caught offshore from Tsushima was higher than that of the others, and there were no significant differences among the other catches. The extractive nitrogen content of the fish caught with bull trawl seine was somewhat lower than that of the others. The body colors of the fish differed from those suggested by their common names: Kuroaji (black), Kiaji (yellow), and Shiroaji (white). The crude lipid content and body color indicated that there was no difference in quality among the catches, with the exception of the crude lipid content of the Tsushima catch.
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