Enzymatic determination of carnitine in milk and infant formula

A method has been developed for the routine estimation of carnitine in milk, milk powder and infant formula. Carnitine and its esters were measured following a selective alkaline hydrolysis scheme, with use of the coupled carnitine acetyl transferase-Ellman reaction to form the nitrophenolate anion chromophore. The method was automated using a centrifugal analyser to facilitate high sample capacity and improved precision. Endogenous total carnitine in whole milks varied between 20·2 and 28·1 mg/100 g solids, with free carnitine contributing 55–60% of the carnitine pool. A reliable estimate of the total carnitine content in milk is achieved from the sum of the acid soluble free and short-chain acylcarnitines, with the acid insoluble long-chain esters present at levels below the uncertainty of the methodology. Infant formulas demonstrated more diverse carnitine contents as a consequence of their complex and varied compositions and the increasingly common practice of supplementation.