解冻猪肉品质和基于LF-NMR技术的检测方法

Applicability of LF-NMR to Detect Quality of Thawed Pork

研究解冻对猪肉营养品质的影响,并研究利用低场核磁共振技术检测解冻猪肉的可行性。选择10条宰后5 h内的猪背最长肌,每条通脊沿垂直于肌纤维方向取质量为100 g的肉块5块,1块空白,其余在-20℃冷冻1、3、5、7 d后在0~4℃条件下解冻24 h后收集汁液,测定蛋白质含量、氨基酸含量和矿物元素含量。选择宰后5 h内的猪背最长肌10条,分别沿垂直于肌纤维方向分切厚度为2.5 cm的肉块8块,分成4组,每组2块肉样,分别在0~4℃中贮藏0、24、48、72 h后,各组各取1块于-18℃中冻藏24 h后在0~4℃中解冻12 h,另一块不处理,然后测定肉色(L*、a*和b*)、低场核磁共振横向弛豫时间(T2)。结果表明,解冻会使猪肉蛋白质、矿物元素和氨基酸的流失量显著增大;解冻会导致猪肉低场核磁共振弛豫时间T2中第2个峰(T21)的峰时间(t21)、峰面积(A21)和峰面积比(P21)减小,色差中的红度值(a*)增大。可以利用t21、A21、P21、a*这4项指标检测解冻猪肉。

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.