Effects of frying conditions on the formation of heterocyclic amines and trans fatty acids in grass carp (Ctenopharyngodon idellus)

The effects of frying temperature and the number of frying cycles on the formation of heterocyclic amines (HAs) and trans fatty acids (TFAs) in grass carp were investigated. 9t-18:1 FAs was detected in all samples. The TFA contents of samples fried at 150–210 °C were not significantly different (P > 0.05). The content and number of different types of HAs increased with increasing frying temperature. 9H-pyrido[3,4-b]indole (Norharman), 1-methyl-9H-pyrido [3,4-b]indole (Harman), and 2-amino-3,7,8-trimethylimdazo[4,5-f]quinoxaline (7,8-diMeIQx) were detected in most of the tested samples. The differences in the surface colour (ΔE) increased with frying temperature, and ΔE of samples fried at 170 °C was significantly higher than that of 150 °C (P < 0.05). The analysis of different cycle times revealed that the TFA levels increased with an increase in the usage period of the frying fat, and 9t,12t-18:2 FAs was detected after the 40th frying cycle. As the number of frying cycles increased, the number of different types of HAs increased, seven types of HAs were detected after the 25th frying cycle.