A rapid fluorimetric method to estimate the heat treatment of liquid milk

A rapid and sensitive fluorimetric method is proposed to evaluate the heat treatment of commercial milk. This method is based on the simultaneous determination of protein denaturation by Trp fluorescence (lambda exc 290 nm; lambda em 340 nm) and formation of fluorescent advanced Maillard products (lambda exc 350 nm; lambda em 440 nm) in the milk fraction soluble at pH 4.6. The first reaction characterizes low heal treatments such as pasteurization or direct UHT sterilization and the second one becomes significant for indirect UHT treatments and for in bottle sterilization. Trp fluorescence of 80 commercial milk samples was correlated well with the soluble protein concentration evaluated by the Lowry method as well as the concentration of beta-lactoglobulin quantified by HPLC. The advanced Maillard products were poorly correlated to the furosine content. Furosine, formed during acid hydrolysis of the Amadori product,. increased linearly with time for a constant temperature, wile the fluorescence of the advanced Maillard products progressed exponentially. This method allows a wide characterization of heat processes and gives a rapid evaluation of the nutritional quality of milk proteins. (C) 1999 Elsevier Science Ltd. All rights reserved.