天然ニジマスの脂質について

Abstract

Fish culture industry for Salmo irideus GIBBONS has made a rapid progress with export of the frozen products increasing at such a rate as from 323 metric tons 1955 to 955 tons in 1958. Little information, however, is available at hand in regard to chemical properties of lipids of this species. The authors have carried out a survey on the lipids of wild rainbow trout with an expectation that the data would be useful in improving the method of procesing and the feed in culture for this fish. The fish used were caught by a gill net in Chuzenji Lake on May 27, 1961, and transported with ice to our laboratory in Tokyo. Body length, weight of the samples, and their visceral organs were examined (Table 1). Lipids were extracted respectively from liver, kidney, pyloric caeca, head, fatty tissue in abdominal cavity, and edible portion. Unsaponifiable matter was separated from fatty acid (Table 2 and Fig. 1). Mixed fatty acid of each portion remained within the range from 142 to 155 of iodine value and from 1.4600 to 1.4630 of reflex index at 40°C. As far as saturated and unsaturated acids concerned, however, liver oil was found to be different in composition from oil of other parts (Table 3 and Fig. 3). Among the samples from neck, middle, and tail regions of the dorsal muscle, the middle had a higher oil content, the oil being lower in reflex index that from other body parts. No positive relation, however, could be observed between the oil content and iodine value of the oil for any corresponding part of the muscle, for the latter varied from 105 to 137 according to a region as well as to the individual fish examined (Table 4 and Fig. 4).