EFFECT OF IRON AND LACTOSE SUPPLEMENTATION OF MILK ON THE MAILLARD REACTION AND TRYPTOPHAN CONTENT

New liquid UHT milks supplemented with iron (0.9-4 mg/100 ml), vitamin C (1-7 mg/100 ml), lactose (2-4 g/100 ml) and linoleic acid (200-400 mg/l 100 ml), named growth milks, have recently become available to sa tisfy the specific nutritional needs of children aged 1-3 years. But t he iron-vitamin C mixture could activate the lactose-induced Maillard reaction and tryptophan (Trp) oxidation in proteins. We have therefore examined the Amadori product and Trp concentrations of these milks. F orty-two commercial growth milks from five firms were analysed for the Maillard reaction and the soluble protein Trp content and compared wi th 64 UHT milks. The furosine concentration of total proteins was two to four times higher in 'growth' milks than in standard UHT milks, ind icating a proportional loss of available lysine. The Trp fluorescence of undenatured proteins soluble at pH 4.6 was almost three times lower in 'growth' than in standard milks and Trp concentration 36% lower su ggesting destruction of this oxidation-sensitive amino-acid. The mecha nism of Trp destruction remains to be elucidated, and the roles of iro n and Amadori products determined.