Effects of Osmotic Dehydration Pretreatments on Qualities of Blueberries after Freezing-Thawing Process.

The effects of osmotic dehydration pretreatments on freezing-thawing qualities of blueberries were studied. Ordinary frozen at -18 °C and super low temperature quick freezing at -80 °C were set as the control groups, and static osmotic dehydration freezing and ultrasonic assisted osmotic dehydration freezing were set as experimental groups, then the freezing curves, drip loss, hardness, color, soluble solids contents, anthocyanins contents, peroxidase and polyphenol oxidase activities of blueberries were determined. The results showed that the freezing time of blueberries after static osmotic dehydration was shortened by 9.41% compared with ordinary slow freezing, and the soluble solid contents and hardness were significantly higher than those of other treatment groups (P<0.05), which could keep good color and appearance qualities, and effectively inhibit enzymes activities. Ultrasonic assisted osmotic dehydration pretreatment although improved the blackberries freezing rates compared with static osmotic dehydration freezing pretreatment, and presented similar effects on anthocyanins retention of blackberries with super low temperature quick freezing, other indicators were significantly lower than that of normal osmosis pretreatment group (P<0.05). The results showed that the two kinds of osmotic dehydration pretreatments presented superior effects than freezing storage at -18 °C, the static osmotic dehydration for freezing blueberries were more suitable for preserving the processing and edible qualities of materials, and ultrasonic osmotic dehydration pretreatment could effectively retain the anthocyanins of freeze-thawed blueberries. [ABSTRACT FROM AUTHOR]