Abstract: Monopterus albus with different freshness (stored for 1, 2, 3, 4 and 5 days at 4 ℃) was used to investigate the changes of moisture loss, chemical forces and protein structure during heating and to explore the mechanism of quality deterioration during storage. The results indicated that protein degradation took place in low-freshness Monopterus albus, resulting in a higher rate of moisture loss during heating. During heating, ionic bonds and hydrogen bonds in Monopterus albus proteins were gradually destroyed, and hydrophobic interaction and disulfide bonds gradually became the major forces. When heating Monopterus albus stored for 1–2 days, hydrophobic interaction gradually increased, while disulfide bonds gradually increased at the early stage of heating and then did not change significantly at the late stage. Hydrophobic interaction and disulfide bonds in Monopterus albus stored for 3–5 days were reduced significantly at the late heating stage. The analysis of protein structure showed that the degree of protein unfolding in low-freshness Monopterus albus increased during heating, and hydrophobic groups were more likely to be buried inside, which was consistent with the trend of hydrophobic interaction. In conclusion, Monopterus albus with a longer storage time was more prone to protein degradation with a greater degree of protein unfolding and greater burying depth of hydrophobic groups, resulting in a reduction in hydrophobic interaction and disulfide bonds, consequently a higher rate of moisture loss and texture deterioration. This study provides preliminary theoretical support for the clarification of the mechanism of quality deterioration of Monopterus albus with different freshness after cooking.

Key words: Monopterus albus, cold storage, heating, protein