The increase of air-velocity from 4 to 6.5 m/s as well as the reduction of freezing temperature from35 to 60 C did not show significant difference to the yield or freezing loss after a freeze– thaw cycle of the samples. Freezing loss was caused by partial denaturation of proteins taking place during freezing. Generally, slowfreezingwill give higher liquid loss than fast freezing. Large ice crystals were formed in slow freezing and grew larger during the storage, and caused water loss by osmosis. The ice crystals will damage the cell tissue, leading to high drip loss (Boegh-Soerensen & Jul, 1985). Comparing to this, the freezing loss of black tiger shrimps, size 80–90 shrimps per kilogram was 2.14–3.43 and 1.83 g/100 g shrimp for the samples frozenwith air-blast at 4–8 m/s and cryogen at 70 C(Boonsumrej et al., 2007). Air-blast freezing
and freezing by liquid nitrogen are used extensively in many sea- food industries. The freezing by shelf freezer showed slowest freezing rate leading to highest freezing loss. However, plate freezer used in food industries would obtain higher freezing rate since the plates can be moved together to improve the contact between surfaces of the food (Fellows, 1993) while the shelf freezer used in the experiments described here could not be moved. The samples frozen after the treatment of sodium bicarbonate containing traces of citric acid and sodium chloride tended to give white shrimps
with less toughening meat.