Degradation of vitamin C in citrus juice concentrates during storage Original Research Article

Kinetics of ascorbic acid degradation in citrus juice concentrates (orange, lemon, grapefruit, tangerine) during an eight week storage at 28, 37 and 45 °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 °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 ± 0.67 to 80.02 ± 0.07 kcal mol−1. Significant correlation was obtained between HMF accumulation and ascorbic acid loss at all storage temperatures in all citrus juice concentrates.