Biochemical and Morphological Changes in Grass Shrimp (Penaeus Monodon) Muscle Following Freezing by Air Blast and Liquid Nitrogen Methods

Abstract

Grass shrimp (Penaeus monodon) at prerigor stage were frozen at rates ranging from 3.41 to 16.1 cm/h by using an air blast freezer at –35C or a liquid nitrogen freezer at – 80, – 100 and – 120C. Immediately after freezing, the spacing between muscle fiber bundles was larger (21.3 ± 5.7 μm) in shrimp frozen at 3.4 cm/h than in shrimp frozen at 8.6 ∼ 16.1 cm/h (6.0 ± 0.6 to 8.8 ± 1.1 μm, respectively). The spacing between fibers increased during frozen storage at – 20C and remained different for slow and fast frozen samples within 4 weeks. The lysosomal fraction from fresh shrimp had more cathepsin D‐like activity (187 units/mg protein) than that from shrimp frozen at 10.2 cm/h (179 units/mg protein) and at 3.4 cm/h (86 units/mg protein). During frozen storage at – 20C the cathepsin D‐like activity of intact lysosomes decreased and was negligible after 4 weeks. The solubility of muscle protein in 0.6 M KCl was not consistently different in samples frozen by different methods and stored at – 20C for 4 weeks. Liquid nitrogen freezing produced frozen shrimp of higher muscle integrity than air blast. But the differences disappeared after one‐month storage at – 20C.

Effects of freezing and thawing on the quality changes of tiger shrimp (Penaeus monodon) frozen by air-blast and cryogenic freezing

“…The cutting force of the shrimps frozen at À70°C was similar to the fresh samples (p > 0.05) while those frozen at À100°C had the lowest cutting force which probably due to the cracking phenomena in the samples frozen at low temperature (Pan & Yeh, 1993). These findings were similar to that observed by Pan and Yeh (1993) that about 50% of the muscle cells surface cracking occurred in shrimps frozen at À120°C. Thus, freezing the shrimps at À70°C was selected for the best condition of cryogenic freezing.…”

“…The changes in temperature of sample during freezing for each batch was measured by using a thermocouple type T connected to temperature recorder (Yokogawa, LR 4210) and inserted at the second abdominal segment of a shrimp. The freezing rate (Pan & Yeh, 1993) was calculated from…”

“…The modified method of Pan and Yeh (1993) was used to prepare tissue for microscopic analysis. A light microscope (Nikon UFX-DX) and camera (Nikon FX-35DX) were used for observation.…”

“…So described above, many researches on frozen shrimp have been conducted (Kent & Stroud, 1999;Pan & Yeh, 1993;Srinivasan, Xiong, Blanchard, & Tidwell, 1998). However, as the shrimp is in the processing plant, it is frozen either in bulk by glazing with water and freezing in an air-blast freezer or individually frozen (IQF) using liquid CO 2 or N 2 .…”

Bioelectrical impedance analysis of frozen sea bass (Dicentrarchus labrax)

“…a Statistically significant difference (p < 0.05). Slow freezing has been reported to cause increased drip loss, and initial advantages of using fast freezing are reported (Chen and Pan, 1997;Pan and Yeh, 1993), although, in other studies of fast freezing, no advantage was observed (Cutting, 1977). However, in quality control of fish, it is been recommended that freezing should be fast.…”