Rates of vitamin C loss and discoloration in clear orange juice concentrate during storage at temperatures of 4-24 °C

The rate of vitamin C degradation in clear orange juice concentrate (80.2 °Brix) produced by the combined membrane−evaporation technique was studied at storage temperatures of 4, 14, and 24 °C for 19 weeks. Absorption at 420 nm and CIE L*, a*, b* color parameters were determined to evaluate color changes due to nonenzymic browning during storage. Calculated values of reaction rate constants indicated that vitamin C degradation occurred slowly in clear orange juice concentrate at 4 °C. Rates of vitamin C degradation ranged from 4.79 × 10-4 to 3.13 × 10-2 per week. The activation energy for vitamin C degradation was on the order of 34.3 kcal/g·mol. Main color changes in stored clear orange juice concentrate in amber glass vials were due to increases in b* value and chroma. Keywords: Clear orange juice concentrate; vitamin C; color; browning, membrane