The vitamin D activity of butter. II. The complex nature of the antirachitic action of butter. III. An attempt to elucidate the nature of the labile factor in butter antirachitic for the rat. The antirachitic potency of lard, olive oil, egg oil and the fatty acids of butters and lard
Kon, S.Kazimierz; Booth, R.Gordon
Biochem Jour 28(1): 111-120, 121-130
II. The antirachitic potency (AP) of high-level yeast butter and of irradiated butter could be recovered practically completely in the non-saponifiable residue, while the butter from cows on summer pasture, or given cod liver oil, suffered a more or less marked loss in the course of saponification. These butters were definitely more resistant to saponification than the autumn and winter butters reported on previously. Confirming previous work, over 75% of the AP of autumn and winter butters was either destroyed or diverted to another fraction on preparation of the non-saponifiable residues. The greater the initial AP of the butter, the greater the proportion of the AP recoverable in the non-saponifiable residue. It is suggested that at least 2 factors antirachitic for the rat are present in butter: a factor not recoverable in the non-saponifiable residue, and the usual vit. D, which is resistant to saponification. By exposure to summer conditions or by feeding highly antirachitic substances the concn. of the stable factor but not of the labile factor of butter can be markedly increased. Direct irradiation of the butter also leads to the formation of the stable factor only. Attempts to achieve a chemical separation of the labile and stable antirachitic factors of butter by extraction with alcohol failed; contrary to Zucker's findings, the AP of a high grade cod-liver oil could also not be extracted by this method. III. Tested on rats, lard, both home rendered and American, was found to possess an antirachitic activity of the same order as that of butter. Like that of butter, the activity of lard is impaired by saponification, the degree of loss being greater in the lard of lower activity. Fatty acids prepared from various butters exhibited a slight but definite AP which could not be attributed to incomplete removal of the non-saponifiable residue. This activity was roughly proportional to the amt. of fatty acid fed and was independent of the original activity of the butter. Butter incorporated in the diet produced a lower antirachitic effect than a similar amt. of butter fed separately. The original AP of an autumn butter, largely lost after saponification, could be recovered practically completely when the non-saponifiable residue was given along with the fatty acid incorporated in the diet. Although the loss of AP in various samples of butter might be explained by assuming the existence of a new labile antirachitic factor, the authors believe at present that this phenomenon could be at least as adequately, and certainly more simply, explained by the antirachitic effect of fat as such. If this be true, then, unless the labile factor is definitely proved to be antirachitic also for other species besides the rat, values obtained by accepted methods for the antirachitic activities of butters are ca. 2-5 times too high; and values obtained by direct feeding of highly potent butters are correct. While the general AP of the labile factor is still in question, the only safe course in ascertaining the vit. D activity of butter is to submit it to saponification and feed to rats the non-saponifiable residue only.