Abstract
The disintegration of fish fat in cold storage has hitherto been considered as a chemical change due to oxidation, but the iodine values of the ether-extracts from fish remain almost constant during the storage, whereas their acid values develop rapidly. This fact means that the fatty substances in cold storage must be hydrolysed by means of the fat-hydrolysing enzyme, “lipase”
The observations on this subject have been considerably made, but no one has proved this enzyme action. Thus, I have researched whether the chemical changes of fat is caused by oxidation or by lipase, and at the same time I made observations on the lipase action at lower temperature.
The mackerels and sardines employed for sample were stored at -13°C, and after a certain period were extracted with alcohol and ether; and then the characteristics of the extracted substances were determined. The lipase action was observed with the fat-hydrolysing glycerinextracts from the intestine and stomach of mackerel.
The results obtained from the above experiments are summarised as follows: -
1. The characteristics of the fish body-fats in cold storage have the following variations. The acid value develops rapidly, but the iodine value shows no variation. The refractive index decreases, and the specific gravity is variable, a feature which seems to result from the hydrolysis of fat rather than from the oxidation.
2. Phosphatides (lecithin) may be also hydrolysed by means of a lipolytic enzyme as is the case with neutral fat, since the decreasing curves of the phosphor contents in the etherextracts are indicative of the action of enzyme. It was not, however, decided whether the hydrolysing enzyme was lecithase or lipase.
3. With regard to the contents of the free fatty acids in the ether-extracts, and the contents of the liquid acids and the solid acids in the free fatty acids, it was decided that the former two acids increase and the latter decrease; and this decrease and increase draw the curves on the lipolytic action. Therefore, at lower temperature lipase acts mainly on the unsaturated glycerides.
4. The hydrolysis of neutral ft ias not caused by the action of organisms (moulds, bacteria, etc.), but by the fat-decomposing enzyme, “lipase” The glycerin-extracts from the entrails of mackerels even at -13°C still have a strong decomposing power over fat, those from their intestines being much stronger. The limit of temperature so low as to destroy the lipase action was not yet determined.
5. The brine and the air freezing of fish have not brought any differences on the chemical changes of fat, neither the glazing nor unglazing of ice on fish making any difference whatever.
