Degradation of vitamin C in citrus juice concentrates during storage

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.