Air Drying of Guava: (II) Kinetics of Vitamin C Degradation at Different Temperature

Farzana Sharmin, Md Syduzzaman, Md Nazrul Islam

Abstract: In Bangladesh, the production of Guava (P. guajava, family: Myrtaceae) is ample and needs to be stored properly during off-seasons. Drying is one of the efficient and low-cost preservation techniques. But during the drying process, the vitamin C rich Guava lost a significant amount of vitamin C primarily due to oxidation. This study was conducted to analyze the drying behavior of guava on the stability of vitamin C during drying and storage. The drying was done by using a Cabinet dryer at a constant airflow rate and constant or variable temperature. The higher the drying temperature, the higher is the loss of vitamin C content of guava, and loss of vitamin C during 2.5 hr of drying was observed and found to be 43% to 69% of vitamin C was destroyed during drying at the temperature range of 50-60?. The activation energy value for degradation of vitamin C was calculated as 14.73 kcal/g-mole, which is proof of temperature dependency. Activation energy values for the degradation of vitamin C could be used to optimize process variables to retain more vitamin C in the processed product. Considering short-season availability, fresh guava was stored at 30?C, 4?C, and -18?C temperature, and the effect of storage temperature on vitamin C content was determined. The rate constant were 0.13, 0.1, and 0.03 mg% day?? at 30, 4, and -18?C, respectively, and the activation energy value for degradation of vitamin C was calculated to be 3.00 kcal/g-mole.

Keywords: Vitamin C, Kinetics, Guava, Drying