As reported previously1); peroxide number may well be used to express the degree of oxidation of fish oil in so far as that degree remains still not too large. However, it was not the case when the oxidation had extremly advanced. Therefore, the author tried now to find out some appropriate property changing in parallel to the degree of oxidation or discoloration of oil in fish products. Following the advice of Prof. Nonaka, Tokyo University of Fisheries, the author confirmed the significane of oxidized acid produced during the oxidation of fish oil.
In each case, when B. H. A. was not used, not only the fish oil (the sardine oil once used in the prcvious experiment) itself, but the dried fish (Saurel and Anchovy) was greatly discolored. Farther more, the extent of oxidized acid (petroleum ether insoluble) remained especially small in the case of the oil or the dried products processed with B. H. A. (see Table 1 to 4).
It has been concluded, after all, that there is a close relation between the oxidized acid content and the appearance and quality of the oil or the dried fish.
1) S. OTANI, K. TAKAYANAGI and T. MATSUHASHI: Bull. Jap. Soc. Sci. Fish., 19, (9) 947-951 (1954).