Studies on quantitative determination of fat in micro-organisms

Abstract

Great difficulty is experienced in extracting fat from wet or dried micro-organisms. It has been suggested that a large portion of the fat they contain may be held in physical or chemical combination by some ingredient of the protoplasm and various preliminary treatments have been developed to free it from such combination. Three of the simplest are that of Larson and Larson for bacteria 1 which depends on simultaneous drying and extraction by acetone, followed by ether extraction of the solid residue and the acetone extract; I. S. MacLean's method used on yeast 2 which consists in boiling with normal HCl, washing and then extracting with ether in a Soxhlet; and the method developed by C. R. Smith for work on edible pastes, in which he boils the sample with alcoholic ammonia, and then extracts with ether.

The work here reported was done on Oidium Lactis. In the first experiment a two weeks'growth was drained by suction and divided into three portions, one of which was treated by each of the above methods without previous drying. The residues as well as the extracts were dried to constant weight and the total dry weight of the samples obtained by addition. The MacLean method is impractical on moist samples, as an unmanageable mucilaginous brown material results from the acid treatment. The acetone method gave 1.21 per cent. ether extract; the alcoholic ammonia method gave 6.13 per cent. No further studies were made on the lipoids thus extracted, as drying to constant weight, either in an oven at 100° or in a vacuum dessicator over P₂O₃ at room temperature, results in a hard, semitransparent brown material, insoluble in petroleum ether, only a portion of which is soluble in ethyl ether.