The rancidity of coconut oil produced by mould action

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Abstract
This comprises (1) investigation of the products of the action of a typical Penicillium on coconut oil, (2) physiological experiments with Penicillium and Oidium lactis, and (3) a repetition of Dakin''s in vitro oxidation of fatty acids. Rancidity of coconut oil produced by a typical Penicillium is due essentially to methyl-amyl, methyl-heptyl and methyl-nonyl ketones. Methyl-amyl ketone occurs in the greatest quantity and is responsible for the characteristic "perfume" odor of the rancid fat. There are also present secondary alcohols corresponding to the ketones, ethyl alcohol, esters of the secondary alcohols and ethyl alcohol with caprylic (and probably other acids), and free fatty acids. Oxidation of fats by moulds is an example of B-oxidation and normally the keto-acid formed breaks up, forming a fatty acid containing 2 C atoms less, and acetic acid; but with Penicillium, absorption of poisonous fatty acids on the mycelium impedes respiration and the keto-acid splits to methyl-ketone and CO2. The poisoning capacity of the fatty acids towards Penicillium increases with molecular weight up to caprylic acid, then decreases. Only acids up to lauric acid are absorbed, consequently ketones of higher molecular weight than methyl-nonyl ketone are not formed. Fatty acids, with the exception of butyric and the lower acids, are more poisonous to O. lactic than to Penicillium Oidium, owing to its greater enzymic activity, decomposes the fatty acid normally to a lower acid and acetic acid. Secondary alcohols are probably, though not definitely proved, intermediate products of mold action. Dakin''s oxidation of saturated fatty acids has been repeated, but the formation of secondary alcohols could not be satisfactorily demonstrated.

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