Degradation of ascorbic acid in dried guava during storage

Retention of ascorbic acid (vitamin C) in dried guava during storage was studied. The effects of storage temperature: 30°C, 40°C, 50°C and water activity (aw): 0.43, 0.75, 0.84, 0.97 were investigated. The degradation of ascorbic acid follows a pseudo-first-order reaction. The rate constant increased about four to six fold when storage condition was changed from aw=0.43–0.97. The rate constants and corresponding water activities are related by a second-order polynomial equation. The effect of temperature on the rate constant followed the Arrhenius relationship. The activation energy of ascorbic acid degradation is found to be in the range 3.4–11.0 kcal/mol. An empirical equation, based on temperature, water activity and rate constant, is developed to predict shelf life of dried guava in respect of ascorbic acid retention.