Improvement of freezing quality of food by pre-dehydration with microwave-vacuum drying

Partial dehydration through microwave vacuum drying has been applied to tuna, oyster and mackerel before freezing in order to reduce quality damages upon freezing and thawing. Samples were subjected to microwave vacuum drying at pressure of 4 kPa and temperature less than 25 degrees C in order to remove some water from the samples. Two freezing conditions, freezing chamber temperature at -20 degrees C and -80 degrees C, were used in this experiment. The experimental results showed that decreasing the water content in tuna could lower the freezing point temperature and made the freezing time become shorter. It was also found that removing some water in oyster and mackerel was effective to minimize the drip loss. After thawing, the pre-dehydrated mackerel showed better microstructure than mackerel that frozen without pre-treatment. Furthermore, good scores were given by a group of panelist in the evaluation on aroma, flavor, and general acceptability of mackerel that subjected to the pre-treatment.