Assessing nutritional quality of milk-based sport supplements as determined by furosine

Milk proteins have a strong position in the sport nutrition markets, such as sport supplements for highly trained athletes, apart from bodybuilders. Furosine, a well-known index for the availability of lysine and subsequently of the extent of the Maillard reaction, was evaluated in different common ingredients used for formulation, as well in commercial sport supplements. Furosine content ranged from 2.8 to 1125.7 mg/100 g protein in commercial sport supplements being usually lower in samples containing mainly whey protein isolates or casein, as compared with whey protein concentrates. It is estimated that 0.1–36.7% of the lysine content is not available in this type of products. The use of high quality ingredients for the manufacture of sport supplements reveals important, since it could be the major source of protein intake of certain group of consumers in high or moderate training regime. Furosine is an appropriate indicator to estimate the nutritional quality of sport supplements. A reference value of 70 mg furosine/100 g protein content in dried sport supplements could be set up for controlling the quality of milk-based ingredients used in the formulation. Samples with higher levels are suspected of use of low quality milk-based ingredients or inappropriate storage conditions.