Abstract:

The aim of this study was to investigate the influence of irradiation and freeze-thawing cycles on myofibrillar
protein oxidation and eating quality of beef during postmortem aging. The longissimus dorsi was excised from the
carcass after exsanguination, and treated with irradiation (3 kGy) and freeze-thawing (3 cycles) individually after 3 days
of postmortem aging at 4 ℃. Then protein oxidation and degradation were investigated, and eating quality of the beef
was measured as well. The results showed the content of carbonyls increased by 1.53 nmol/mg protein in irradiated beef
while the contents of total sulphydryls and active sulphydryls decreased by 6.04 nmol/mg protein and 4.71 nmol/mg
protein, respectively. Similarly, the L* and a* values declined. The degradation of troponin-T and desmin was enhanced
by irradiation and correspondingly the shear force showed a reduction by 12.84 N (P ＜ 0.05). On the other hand, freezethawing
cycles could lead to an increase of carbonyls and a decrease of sulphydryls, but significantly increase beef shear
force by 23.96 N (P ＜ 0.05) and cooking loss by 11.67% (P ＜ 0.05). All these results demonstrated that freeze-thawing
cycles could cause protein oxidation, but remarkably reduce beef tenderness and water-holding capacity. Although having a
more significant impact on myofibrillar protein oxidation, irradiation could improve beef tenderness significantly.

Key words: irradiation, freeze-thawing cycles, protein oxidation, degradation, beef quality