Effect of operating conditions in freeze-drying on the nutritional properties of blueberries.

The effect of particle size, use of infrared radiation, and type of freeze-drying (vacuum or atmospheric) on some nutritional properties of blueberries was investigated. Ascorbic acid was decreased in freeze-dried blueberries compared with fresh fruit, while polyphenols were decreased in atmospheric freeze-drying-unlike in vacuum freeze-drying, where this nutritional property was increased. Antioxidant activity of freeze-dried blueberries did not differ significantly from that found in fresh fruits. In order to minimize the impairment of the nutritional properties of freeze-dried blueberries, it is suggested to use infrared radiation, a relatively small particle size and vacuum freeze-drying.