4 °C - the National Sea Grant Library

unit could be used with confidence to thaw shrimp blocks and be competitive, if not better, than the
conventional method. The next step was to use the unit in a plant environment, and to compare
quality attributes of shrimp thawed with both methods. Table 2 summarizes the results of the in-plant
experiments. The thickness, net weight, time required to thaw for the ohmic and control experiments,
the electrical energy used, and the C.O.P. for the ohmic experiments are shown.
e 2. erational Results from In-Plant Tests.
Test Thick. Net. Wt. Shrimp Thaw time Calc. Theor. COP
cm g /water min Watt-Hr Watt-Hr
Single 1: 1 6.35 - 6.67 1956 2.5 45
2 6.35 - 6.67 1930 2.17 45
Control :1 5.72 1784 1.47 50
2 6.99 1867 1.49 75
Single 2 5.4 1914 5.01 85
Control : 1 5.4 1860 4.04 75
2 5.72 1890 3.03 75
Single 3 : 1 6.99 2066 3.93 121
2 7.62 2150 4.37 121
Control : 1 7.62 - 8.89 1993 2.86 40
2 7.62 - 8.89 2089 3.01 40
Single 4 6 - 7.5 1807 2.23 77
Control : 1 5.8 - 7.1 1714 1.52 71
2 5.8 - 6.0 1896 2.24 71
Single 5 6.7 1855 1.92 170
Control : 1 6.7 1880 1.99 130
2 5.7 1851 2.08 130
Single 6 5.72 - 6.99 1486 1.18 104
Control :1i 5.4 - 6.35 1812 1.81 75
13.2 293.5 4.5
81.2 304.4 26.7
---
20.2
___
13
12.6
es_
32.3
m-w
81.6
_-
es_
101.9
-_-
2 6.03 1794 1.89 75
Note : The control samples were the shrimp thawed in the immersion tanks.
s-w _-
240.9 8.4
___ SW_
v-e _-
273.0 4.8
278.1 4.5
___ em_
287.4 11.2
___ _-
_- -_
305.9 26.7
mm- -
-- -
303.3 33.6
- -
- -
Table 2 shows the shrimp blocks used in the ohmic system and in the immersion were similar
in thickness, net weight, and shrimp/water ratio within each experiment. Generally, the immersion
thaw method was faster than the ohmic thaw method. However, optimization of the ohmic process
should reduce the time. One noticeable difference between the two methods is the temperature of
the shrimp after thawing. The temperature of the shrimp from the immersion method was much
warmer than the shrimp from the ohmic thawed shrimp. The temperature of the water in the
immersion tank was 28°C so the shrimp from this method was near 28°C. The shrimp from the
ohmic unit never reached above 12.7°C. Typical voltage, current, and cumulative watt-hrs of
quadrants vs. time are shown in Figure 1.
Microbiology Comparison
The shrimp and water from both methods of thawing were compared for aerobic microbial plate
counts. Table 3 gives the results of this study. The microbial count of the ohmic thawed shrimp and
water were on the same order of magnitude as that of the immersion thawed shrimp and water.