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 degrees Brix) produced by the combined membrane-evaporation technique was studied at storage temperatures of 4, 14, and 24 degrees 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 degrees C. Rates of vitamin C degradation ranged from 4.79 x 10(-4) to 3.13 x 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.