3. Results and discussion
3.1. Effect of freezing methods
The proximate composition of the fresh shrimps were 79.75 ± 0.35 %moisture, 17.70 ± 0.42 %protein, 0.86 ± 0.05 %fat, 0.99 ± 0.01 %ash and 0.7 ± 0.17 %carbohydrate. The shrimps frozen by air-blast had the freezing rate of 6.8–7.4 cm/h while those frozen by the cryogenic freezing had the freezing rate of 11.8–21.9 cm/h (Table 1). The sam- ples frozen with air-blast freezing at the air velocity of 4 and 6 m/s had the %freezing loss significantly lower than those at 8 m/s (p 6 0.05). This may be due to the higher air velocity causing an excessive dehydration of the samples (Fennema et al., 1975). The samples frozen at the air veloc- ity of 4 m/s had the cutting force lower while those at the 8 m/s had the cutting force higher than the fresh samples. The shrimps frozen at the air velocity of 6 m/s had the cut- ting force similar to the fresh samples (p > 0.05). This may be due to the higher water removal at the surface during freezing at the higher air velocity. Therefore, the air-blast freezing at the air velocity of 6 m/s was selected for further studies of thawing and freeze–thaw cycle effects. For cryogenic freezing, it was found that all tempera- tures applied gave samples with similar %freezing loss (p > 0.05). The cutting force of the shrimps frozen at 70 C was similar to the fresh samples (p > 0.05) while those frozen at 100 C had the lowest cutting force which probably due to the cracking phenomena in the samples frozen at low temperature (Pan & Yeh, 1993). These find- ings were similar to that observed by Pan and Yeh (1993) that about 50% of the muscle cells surface cracking occurred in shrimps frozen at 120 C. Thus, freezing the shrimps at 70 C was selected for the best condition of cryogenic freezing.