关键词: 小鼠法, 脂溶性贝类毒, 假阳性, 游离脂肪酸

Abstract:

Objective: To examine the changes in free fatty acid contents in oyster with storage temperature and storage time
for the purpose of exploring and analyzing the sources of false positive results in mouse bioassay for fat soluble shellfish
toxins. Methods: Methyl esterification of free fatty acids was carried out with boron trifluoride in methanol. The products
were analyzed by gas capillary chromatography with a column coated with a 100% cyanopropyl polysiloxane stationary
phase. Results: The total content of free fatty acids stored at −10 ℃ and −20 ℃ increased at first, then decreased, and
slowly increased again with prolonging time. When the sample was stored at 4 ℃, there was a slowly increasing trend. The
content of free fatty acids stored at −20 ℃ was significantly higher than at −10 ℃ at the same storage time. At all the three
storage temperatures, the contents of the highly toxic free fatty acid C20:5n-3 and the low toxic fatty acid C22:6n-3 kept increasing
throughout the storage period. Five months later, C20:5n-3 in oyster stored at −20 ℃ was 136.79 μg/g, which was 45% of the
lethal dose for mice. If 2.5-fold weight of the oyster sample was used, the mice would die, leading to false positive results in
mouse bioassay for fat soluble shellfish toxins. Conclusion: The high toxic free fatty acid in oyster samples was important
source of false positive results in mouse bioassay for fat soluble shellfish toxin, and the content of high toxic free fatty acid
in oyster samples presented an increasing trend at three temperatures as time goes by.

Key words: mice method, fat soluble shellfish poison, false positive, free fatty acid