Effect of storage on nonenzymatic browning of apple juice concentrates

Kinetics of nonenzymatic browning in Golden Delicious and Amasya apple juice concentrates during 4 months are investigated. Apple juice concentrates were at 65, 70, 75°Bx of Golden Delicious variety, stored at 5, 20, 37 °C and Amasya variety, stored at 37, 50, 65 °C. Colour development was measured by browning index (A420) and the CIE-Lab colour system. Browning level of all apple juice concentrates increased according to a zero-order reaction kinetic. Activation energies for 65–75°Bx of Golden Delicious and Amasya apple concentrates ranged from 21.4 to 21.0 kcal/mol and 33.7 to 32.5 kcal/mol, respectively. Influence of soluble solids content on browning was negligible. HMF concentration, in Golden Delicious apple juice concentrates, was between 0.52 and 963 mg/kg, and between 0.52 and 190 mg/kg in Amasya apple juice concentrates.