Abstract:

This study was designed to investigate the influence of thawing on pork nutrition and the feasibility of detecting
thawed pork by low-field nuclear magnetic resonance (LF-NMR) technology. Five pieces weighed at 100 g were removed
from pork longissimus dorsi muscle along the direction of perpendicular to the muscle fibers, and four of these pieces were
frozen at -20 ℃ for 1, 3, 5 and 7 d, respectively and then thawed at 0–4 ℃ for 24 h. Another piece was used as control. The
exudate was collected to determine the contents of proteins, amino acids and mineral elements. Additional pork longissimus
dorsi muscle was divided into 8 2.5 cm thick pieces along the direction of perpendicular to the muscle fibers at 5 h
postmortem. These pieces were divided into four groups and stored at 0–4 ℃ for 0, 24, 48 and 72 h, respectively. One piece
in each group was frozen for 24 h at -18 ℃ and then thawed for 12 h at 0–4 ℃ and the other one was used as control. The
color parameters L*, a* and b* and NMR T2 were measured. The results showed that thawing could significantly increase
the total loss of proteins, mineral elements and amino acids, reduce the peak time (t21), area (A21) and area ratio (P21) of the
second peak (T21) of LF-NMR T2 relaxation time and increase the redness (a*). These four indexes of t21, A21, P21 and a* can
be used to detect thawed pork.

Key words: thawed pork, nutrition, low field nuclear magnetic resonance (LF-NMR), detection