The effect of frozen storage on the sulfhydryl content of pork patties
is illustrated in Fig. 3b. The concentration of sulphydryls in all groups
decreased (P ≤ 0.05) during frozen storage, demonstrating that the
frozen stored patties were susceptible to protein oxidation. On day 0
of storage, the initial sulphydryl concentrations of all groups were in the
range of 68.4–69.7 nmoles/mg, indicating that no effect of the added
antioxidants on the sulphydryl contents. These initial concentrations
decreased (P ≤ 0.05) with the storage time to reach on day 60 values
in the range of 46.8–51.3 nmoles/mg, which did not differ (P N 0.05)
among each other. This indicated that protein oxidation had already
started, and the effect of the added antioxidants was not significant.
When the frozen storage was prolonged to 120 days and, thereafter, to
180 days, sulphydryl concentrations in all groups continued to decrease
(P ≤ 0.05), but the decreasing rate turned out to be lower (P ≤ 0.05)
than that observed on day 60 of storage. As a result, the mean sulphydryl
concentration of the CONT group decreased from 68.4 to 46.8 nmoles/
mg (21.6% loss of sulphydryls) on day 60, to 35.7 nmoles/mg (47.8%
loss of sulphydryls) on day 120, and to 31.6 nmoles/mg (53.8% loss of
sulphydryls) on day 180 of frozen storage. The higher loss of sulphydryls
on day 180 indicated more intense oxidation of proteins as storage time
progressed. These results are consistent with studies reporting losses of
65.8 and 33.8% in the sulphydryl content of chicken thigh and breast
meat after 6 months of frozen storage (Soyer et al., 2010).