Five model systems dissolved in 50 mM Na-phosphate buffer (pH6) were prepared with 50 g/l lactose (systemA), 50 g/l lactose +30 g/l sodium caseinate (system B), skimmed milk containing lactose (49 g/l) and protein (32 g/l) (system C), 25 g/l glucose (system D) and 25 g/l glucose +30 g/l sodiumcaseinate (system E).