Japanese quail given 20 parts per million of mercury as methylmercury in diets containing 17 percent (by weight) tuna survived longer than quail given this concentration of methylmercury in a corn-soya diet. Tuna has a relatively high content of selenium and tends to accumulate additional selenium when mercury is present. A content of selenium in the diet comparable to that supplied by tuna decreased methylmercury toxicity in rats. Selenium in tuna, far from being a hazard in itself, may lessen the danger to man of mercury in tuna.
The effects of storage temperature and antioxidant treatment on the chemical and nutritive properties of herring meal were studied. The following observations were made:
Low‐temperature (−20°C.) storage promoted more rapid decrease in ether extractability and in iodine value of the ether extract than did storage at 25.5°C.
Antioxidant treatment prevented the decrease both in ether extractability and iodine value of the extract.
Binding of the lipid into a complex from which the lipid was extractable with acetone only after HC1 treatment occurred early in the storage period. After six weeks the amount of lipid in this fraction decreased, presumably as a result of further oxidation and polymerization into more refractory compounds.
Pepsin digestibility tests showed that BHT‐treated meal contained the lowest amounts of undigestible nitrogen. Meals subjected to −20°C. contained the most undigestible nitrogen.
All meals were similar in nutritive value as protein or vitamin‐B supplements in chick diets, composed of natural ingredients, even after storage for nine months. As the sole source of protein in a purified diet, the meal kept at −20°C. from time of processing promoted slower growth than the other meals.
Various chemical characteristics of fish meals pertaining to the protein and lipid components were determined and their relation to different biological estimates of protein quality were studied. The results demonstrated the practical importance of selecting appropriate biological assays in order to avoid underestimating or overestimating protein quality. Pepsin digestibility of the crude protein remaining in the meals after chloroform–methanol extraction was significantly correlated with biological estimates of protein quality. Meals of initially high supplementary protein value declined in value to a greater extent than did meals of lower quality. The level of available lysine present in the meals declined with storage but biological tests indicated that a combination of several amino acids rather than any single amino acid was limiting to supplementary protein value.
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