Kinetics of ascorbic acid degradation in citrus juice concentrates (orange, lemon, grapefruit, tangerine) during an eight week storage at 28, 37 and 45 degrees C were investigated. The loss of ascorbic acid at each temperature followed a first-order kinetic model. Activation energy was determined in the range of 12.77 +/- 0.97-25.39 +/- 1.98 kcal mol(-1). Ascorbic acid retention after storage at 28, 37 and 45 degrees C was about 54.5-83.7%, 23.6-27% and 15.1-20.0%, respectively. Since hydroxymethylfurfural (HMF) is one of the decomposition compounds of ascorbic acid degradation, its formation was also investigated. HMF accumulation fitted to a zero-order kinetic model and activation energy ranged from 43.41 +/- .67 to 80.02 +/- 0.07 kcal mol(-1). Significant correlation was obtained between HNIF accumulation and ascorbic acid loss at all storage temperatures in all citrus juice concentrates. (c) 2005 Elsevier Ltd. All rights reserved.