The kinetics of nonenzymatic browning in citrus juice concentrates (orange, lemon, grapefruit and tangerine) during 8 weeks of storage at 28, 37 and 45 oC were investigated. Browning development was followed by measuring absorbance at 420 nm (A420) and using CIE-Lab color system. Analysis of kinetic data from A420 values suggested a zero-order reaction for nonenzymatic browning, while changes in L* and b* parameters followed a first-order reaction. Activation energy for nonenzymatic browning determined by A420 values ranged from 17.60 to 35.27 kcal mol-1, while those for L* and b* parameters were 6.67-28.99 kcal mol-1 and 15.38-34.2 kcal mol-1, respectively. Activation energies were higher in orange (28.99-35.27 kcal mol-1) and tangerine (27.84-33.1 kcal mol-1) juice concentrates than those in grapefruit (6.74-27.81 kcal mol-1) and lemon (6.67-17.6 kcal mol-1) juice concentrates. The lower activation energies determined for grapefruit and lemon juice concentrates indicated that nonenzymatic browning reactions are favored in these samples.
展开▼
