Carnitine in milk: a survey of content, distribution and temporal variation

Acid-soluble free carnitine and short-chain acylcarnitines were released following a selective alkaline hydrolysis scheme and estimated with use of a coupled carnitine acetyl transferase–Ellman reaction. Liquid skim milk contained elevated total carnitine levels compared to whole milk, due both to the minor contribution of liposoluble long-chain acylcarnitines in milkfat and the higher solids-not-fat content. Data are also reported for a range of dried protein products derived from milk (1–64 mg/100 g), and the stability characteristics of endogenous carnitine are described. A study of a single lactating cow exhibited decreasing concentrations of total carnitine with time postpartum during transition from colostrum to mature milk (>9 mg/100 g to ca. 3 mg/100 g). Regional influences on bovine milk carnitine levels within Australasia were shown to be insignificant, while carnitine content in milk powders and pooled herd milk were relatively constant across a production season. Bovine milk was compared against samples of caprine, ovine, equine, human, canine and feline milks. A survey of anhydrous infant formulas indicated diverse carnitine contents (6.9–30.1 mg/100 g) as a consequence of their complex and varied compositions and the common practice of supplementation.