38. The Inactivation of Lipase in Dairy Products by Traces of Heavy Metal Salts

Abstract

Traces of heavy metals in amounts up to 25 parts per million have the property of inhibiting the action of lipase in butter from unpasteurised sweet cream in varying degrees depending on the concentration of the metal and on the metal itself. Copper was the most potent metal of those studied, iron, nickel, cobalt, manganese, and chromium being less active, while tin and aluminium had no effect. The acidity produced was accompanied by fat-peroxide formation in amount varying directly with the acidity. This was attributable to the free oleic acid formed. The depression of lipase activity by the various metals varied directly with their catalytic power in inducing fat oxidation later, and it is suggested that destruction of lipase was catalysed by the traces of heavy metals according to their varying powers of activating oxygen. Lipase as a compound naturally associated with fats might thus be looked on as a natural “antioxygen.”