Effects of Freeze-Drying Process on Antioxidant and Some Physical Properties of Cherry Laurel and Kiwi Fruits

Abstract

Freeze-drying is a trend method for the preservation of thermosensitive and nutritive food products. In this study, two different fruits, kiwi fruit with high ascorbic acid content and cherry laurel fruit with high phenolic content, were selected to study the freeze-drying effect on these compounds. Ascorbic acid content, total phenolic content and antioxidant capacity of kiwi and cherry laurel fruits were determined before and after freeze-drying process. Ascorbic acid content of kiwi and cherry laurel fruit were 205.14±21.33 and 3.00±1.02 mg/100 g dry matter, respectively. Total phenolic content of kiwi and cherry laurel fruits were 262.66±19.97 and 1056.78±90.73 mg GAE/100 g dry matter, respectively. Ascorbic acid contents did not change, while antioxidant capacities increased by freeze-drying process for both fruits. The total phenolic content of cherry laurel fruits increased significantly after freeze-drying in contrast to the total phenolic content of kiwi fruits. Color values changed with freeze-drying, the lightness and yellowness values increased significantly for both fruits (p<0.05). The rehydration ratios of freeze-dried kiwi and cherry laurel fruits were found similar at 25 and 40C. The rehydration ratio in water at 40C increased more quickly in the beginning of immersion than the ratio at 25C. The results of this study showed that freeze-drying method is highly recommended for the preservation of nutritive values of these fruits and off-season products.