Straight-chain C13-C18 fatty acids, added together with aspartic acid to a biotin-free medium, are capable of promoting the growth of baker's yeast under aerobic conditions. The effect of biotin is compensated by oleic acid and palmitoleic acid, and the influence of elaidic acid, like that of stearic or palmitic acid, is only slightly less marked. The addition of long-chain fatty acids, or their ethyl esters, did not noticeably influence the fatty acid content of yeast, although the addition of oleic or palmitoleic acid caused an accumulation of the acid concerned, and correspondingly a clear diminution of the other unsaturated component. The elaidic acid taken up by the yeast was not isomerized to oleic acid, but was as such capable of replacing oleic acid in promoting the growth of yeast. Normally, the fraction of C18:1 acids of baker's yeast mainly contained oleic acid and small amounts, less than 5 %, of elaidic acid, and about 5 ,% vaccenic acid, in its cis-form, and traces of the trans-form.
Tridecanoic acid, taken up by baker's yeast from the medium, was converted into pentadecanoic acid, and, to some extent, to heptadecanoic acid; increases occurred in the amounts of the corresponding mono-unsaturated acids, tridecanoic, pentadecanoic and heptadecanoic. On the addition of palmitic acid -1-14C at the first stages of growth, a more distinct accumulation of activity was discernible in the C16 acids when biotin-poor baker's yeast was grown, than was the case with biotin-containing yeast. The situation was reversed with ClS acids, and the activity continued to accumulate in the Cls acids of biotin containing yeast.
Bottom-fermenting brewer's yeast contained amounts of C8-C12 fatty acids which considerably exceeded those in baker's yeast. Moreover, palmitic and palmitoleic acid, along with linoleic and linolenic acid, were found more abundantly, although less oleic acid was found in brewer's than in baker's yeast.