冻融对牦牛肉色、微观结构和蛋白质降解的影响

Impact of Freeze-thaw Cycles on Color,Microstructure and Protein Degradation of Yak Meat

牦牛肉经过冻融处理后(T0:新鲜牦牛肉;T1:冻融1次;T2:冻融2次),分别在4℃冷藏7 d,并在1、3、5、7 d测定其表面色泽(L*、a*、b*)、肌红蛋白氧化状态、高铁肌红蛋白还原能力、硫代巴比妥酸值、解冻损失率、蛋白质降解程度和肌纤维微观结构的变化。结果表明:T0组牦牛肉在冷藏过程中a*值和b*值显著降低,氧合肌红蛋白逐渐氧化为高铁肌红蛋白,高铁肌红蛋白还原能力显著降低,硫代巴比妥酸值和解冻损失率明显升高(P<0.05)。同时,肌球蛋白重链(200 k Da)、副肌球蛋白(97 k Da)、肌动蛋白(45 k Da)发生降解。随着冻融次数的增加,T1组和T2组牦牛肉在冷藏7 d后a*值分别比T0组显著降低了13.42%和20.02%,b*值则降低了9.94%和16.22%,氧合肌红蛋白相对含量降低了26.30%和53.53%,高铁肌红蛋白相对含量升高了18.03%和45.46%,硫代巴比妥酸值升高了20.55%和30.30%,解冻损失率升高了43.71%和121.14%(P<0.05)。T2组肌肉中蛋白质降解更明显,而肌纤维结构破坏程度也随冷冻-解冻次数增加而加重。综上可知,冻融循环会促进牦牛肉色劣变和脂质氧化、加速蛋白质降解、破坏肌肉结构、加剧汁液流失从而降低牦牛肉的品质。因此,减少运输和贮藏过程中的温度波动对保护牛肉品质具有重要意义。

To investigate the effect of freeze-thaw cycles（ T0： fresh meat,T1： one time freeze-thaw,T2：two times freeze-thaw） on the quality of yak meat,the yak meat samples were tested for color（ L＊,a＊,b＊）,myoglobin oxidation state,metmyoglobin reducing ability（ MRA）,thiobarbituric acid reactive substances（ TBARS）,thawing loss（ TL）,degree of protein degradation and muscle microstructure during refrigerated storage（ 4℃）. The T0 group showed significantly decreasing trends in a＊value,b＊value,oxymyoglobin（ OMb） content and MRA,while significantly increasing trends were observed in metmyoglobin（ Met Mb） content,TBARS value and TL（ P 0. 05）. Moreover,the degradation of myosin heavy chain（ 200 k Da）,paramyosin（ 97 k Da） and actin（ 45 k Da） were obvious during storage.With the increase of times of freeze-thaw cycles,the a＊values of T1 group and T2 group were decreased by 13. 42% and 20. 02% than that of T0 group after 7 d of storage,and the b＊values of T1 and T2 groups were decreased by 9. 94% and 16. 22%（ P 0. 05） than that of T0 group,respectively.Meanwhile,compared with that of T0 group,the OMb contents of T1 and T2 groups were decreased by26. 30% and 53. 53%,the Met Mb contents of T1 and T2 groups were increased by 18. 03% and45. 46%（ P 0. 05）,respectively. The TABRS and TL of T1 and T2 groups were increased by20. 55%,30. 30% and 43. 71%,121. 14%（ P 0. 05） than those of T0 group,respectively. The degree of protein degradation of T2 group was more serious than that of T0 group and T1 group,while the muscle microstructure damage was also increased with the increase of times of freeze-thaw cycles. In conclusion,freeze-thaw process could reduce the quality of yak meat by accelerating the deterioration of meat color,lipid oxidation and protein degradation,and damaging the muscle structure. Therefore,it is meaningful to reduce temperature fluctuation in the process of transportation and storage for protecting beef quality.