Turkish Journal of Agriculture and Forestry




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 (A_{420}) and using CIE-Lab color system. Analysis of kinetic data from A_{420} 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 A_{420} 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.


Citrus juice concentrate, nonenzymatic browning, color, storage, kinetic

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