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| Nondestructive Physical Methods Differentiates Unfrozen from Frozen-thawed Grouper (Epinephelus drummondhayi) |
| CAI Ting;ZOU Jia;LUO Yongkang;SHEN Huixing |
| 1.College of Food Science and Nutritional Engineering,China Agricultural University,Beijing 100083; 2.College of Science,China Agricultural University,Beijing 100083 |
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Abstract Electric conduction property of unfrozen and frozen-thawed grouper was studied by measuring their impedances under different frequencies.The impedances varied as frequency change. The change ratio of impedances(Q value)of the unfrozen grouper on the 1st,3rd,5th and 7th day were 40.0%,30.7%,25.0%,21.9%respectively.The Q value of the frozen-thawed grouper which had been frozen at the temperature of-20℃for two days was 16.2%on the first day it thawed.The Q value of the frozen-thawed grouper which had been frozen at the temperature of-30℃for two days was 13.4%on the first day it thawed.Although impedances of unfrozen and frozen-thawed grouper decreased as frequencies increased,change ratio of impedance of unfrozen grouper was evidently more than that of frozen-thawed ones.Therefore,it is feasible to identify unfrozen and frozen-thawed grouper using change ratio of their impedances compared with 20%.
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2009, Vol. 23 
