冷鲜牛肉高铁肌红蛋白还原酶的粗分离与性质

以不同部位冷鲜牛肉(背最长肌、腰大肌)为原料,采用硫酸铵盐析法对其高铁肌红蛋白还原酶(Met Mb R)进行粗分离,并对分离所得酶液的适宜温度及p H进行研究,旨在为提高冷鲜牛肉的肉色稳定性奠定基础。结果表明,原料冷鲜牛背最长肌和牛腰大肌粗酶液的分子量主要范围均为14.3～97.2 k Da。原料冷鲜牛背最长肌高铁肌红蛋白还原酶酶活为94.33 U/m L,在70%硫酸铵饱和度下可主要沉淀得高铁肌红蛋白还原酶,从而达到粗分离的目的。粗分离所得的牛背最长肌高铁肌红蛋白还原酶适宜温度30～45℃,适宜p H 6.5。原料冷鲜牛腰大肌高铁肌红蛋白还原酶酶活为53.60 U/m L,在70%硫酸铵饱和度下可主要沉淀得高铁肌红蛋白还原酶,从而达到粗分离的目的。粗分离所得的牛腰大肌高铁肌红蛋白还原酶适宜温度35℃,适宜p H 6.0～6.5。     

冷却肉中高铁肌红蛋白还原酶的特性及其与肉色泽稳定性之间的关系研究

以冷却牛肉为实验材料,对冷却牛肉中高铁肌红蛋白还原酶与肉色泽稳定性之间的关系以及高铁肌红蛋白还原酶的还原条件和还原途径进行了探讨.研究发现,高铁肌红蛋白还原酶活性越高,肉的色泽也越稳定.高铁肌红蛋白还原酶在体内作用时是NADH依赖性的并且需要细胞色素b5作为其电子转移激活剂,其在体外作用时必须有亚铁氰化钾参与下才可起到还原作用.该酶的最适pH为6.5,最适作用温度25℃,但在pH6.0,温度10℃时仍有相当的活性.     

牦牛背最长肌高铁肌红蛋白还原酶提取工艺的优化

为研究牦牛背最长肌高铁肌红蛋白还原酶的最佳提取条件,本实验以牦牛背最长肌为研究对象,以高铁肌红蛋白还原酶活力为考察指标,在单因素试验的基础上,采用响应曲面分析法,以高铁肌红蛋白还原酶活力为响应值,对磷酸盐缓冲液、Tris-HCl和柠檬酸-柠檬酸钠缓冲液3 种提取液的pH值、浓度和料液比3 个因素进行优化。结果表明：各因素对酶活力的影响大小顺序依次为提取液的pH值＞料液比＞浓度;最佳提取参数为磷酸盐缓冲液pH 7.22、料液比1∶2.25（m/V）、浓度2.12 mmol/L,在此条件下酶活力为73.92 U/L,与理论预测值的相对误差为0.86%,说明本实验所建立的模型在实践中具有可行性。     

高铁肌红蛋白还原酶活力与肉色稳定性关系的研究

本文通过对冷却肉采用CO气调包装和真空包装在4±1℃贮藏,研究了高铁肌红蛋白还原酶活性变化规律及与肉色稳定性之间的关系,并研究了不同实验条件下高铁肌红蛋白还原酶的特性。结果表明:高铁肌红蛋白还原酶在宰后2周内仍然存在较高活性,其活性作用可使肉中的高铁肌红蛋白含量持续下降,对肉的色泽稳定起着重要的作用;在pH6.5,酶的活性最大,温度10℃时,该酶活性依然很好,可通过创造无氧、pH6.5左右的环境,使该酶发挥活性来调节肉的颜色。     

乳酸钙对牛肉糜色泽稳定性的影响

为研究乳酸钙对牛肉糜色泽稳定性的影响,将牛背最长肌绞碎成肉糜,分别添加0.1%、0.3%、0.5%的乳酸钙溶液,研究在(4±1)℃的冷藏条件下,肉糜肉色稳定性、色素含量、脂肪氧化及高铁肌红蛋白还原酶活性随时间的变化。结果表明：在7d的贮藏期内,添加不同质量分数乳酸钙均可有效抑制高铁肌红蛋白的生成和脂肪氧化的发生,并显著提高高铁肌红蛋白还原酶活性和肉色稳定性,但会使肉糜L*值显著降低(P＜0.05)。其中0.3%的乳酸钙对稳定肉色有显著作用,护色效果明显。     

紫外照射和温度波动对冷鲜肉肉色稳定性的影响

以不同部位冷鲜猪肉(背最长肌、后腿肉、腰大肌)为对象,研究肉样在2种贮藏条件(实际销售贮藏条件:4℃-13 h-紫外照射,0℃-11 h-避光;实验室设置条件:4℃-24 h-紫外照射)下色泽、肌红蛋白含量、高铁肌红蛋白还原酶活等的变化,旨在为提高冷鲜肉在销售贮藏期间的肉色稳定性提供依据。结果表明:实验室条件下,3个部位(背最长肌、后腿肉、腰大肌)冷鲜猪肉的色泽感官评定、a*值、氧合肌红蛋白含量和高铁肌红蛋白还原酶活性等均显著优于实际销售条件(P<0.05),实验室条件下更利于不同部位冷鲜猪肉的贮存。另外,在实验室条件下,3个部位中猪背最长肌肉色最稳定,其次是后腿肉,腰大肌肉色稳定性最差。     

高铁肌红蛋白含量和高铁肌红蛋白还原酶活性与冷鲜肉肉色稳定性关系的研究

以皖白Ⅲ背最长肌和腰大肌为研究对象,研究了冷藏1～9d肉样肉色稳定性与高铁肌红蛋白含量和其还原酶活性的关系.结果表明,腰大肌亮度(L*值,P＜0.01)极显著低于背最长肌,而红度(a*值,P＜0.05)显著高于背最长肌;a*值随储藏期延长呈下降趋势,L*值和b*值呈整体上升趋势;三者表明储存期越长,肉色将越暗.a*值与高铁肌红蛋白含量呈弱负相关性;而与还原酶活性呈中等程度正相关,其中3、5、7d二者正相关达到显著性水甲(p＜0.05).根据研究结果建议冷鲜肉储藏期不宜超过5d.     

肌肽对牛肉糜肉色及脂肪氧化的影响

在牛背最长肌中添加肌肽(C_9H_(14)N_4O_3),研究在4±1℃冷藏条件下,不同浓度(0.05%、0.1%、0.5%、1.0%)肌肽对牛肉肉糜高铁肌红蛋白(MetMb)还原酶活性、色素含量、脂肪氧化及肉色稳定性的影响.结果表明:在7d的贮藏期内,添加不同浓度肌肽均可有效抑制肉糜MetMb含量上升、提高高铁肌红蛋白还原酶活性,并与无添加组有显著性差异(P<0.05),0.1%、0.5%浓度肌肽对抑制脂肪氧化、稳定肉色有显著作用,护色效果较理想     

牛不同部位肌肉高铁肌红蛋白还原酶活力及耗氧率对肉色稳定性的影响

为了研究牛不同部位肌肉的高铁肌红蛋白还原酶活力(MRA)和肉的呼吸耗氧强弱对肉色泽稳定性的影响,本文以牛的三个部位的肌肉:背最长肌(LL)、半腱肌(ST)、腰大肌(PM)为研究对象,4℃避光贮藏5d,测定MRA、肌红蛋白(MMb)含量、耗氧率(OCR)等,探究肉色稳定性与牛肉部位、MRA和呼吸耗氧率之间的关系。结果表明,三种肌肉中,背最长肌的色泽稳定性最好,腰大肌最差,半腱肌介于中间;MRA越高的肌肉,肉色越稳定;OCR越低的肌肉,肉色越稳定。     

保鲜膜包裹对冷鲜肉贮藏中肉色稳定性的影响

选取3个部位冷鲜猪肉(背最长肌、腰大肌、后腿肉)为原料,研究肉样在有无保鲜膜包裹的情况下(4 ℃贮藏24 h)色泽、肌红蛋白含量、高铁肌红蛋白还原酶活性等的变化,为提高冷鲜肉在贮藏过程中色泽的稳定性提供参考。结果表明:在无保鲜膜包裹情况下,3个部位冷鲜肉的色泽感官评分、a~*值均显著高于有保鲜膜包裹(P0.05);在有保鲜膜包裹情况下,3个部位冷鲜肉的弹性感官评分、表面干湿度感官评分、L~*值、氧合肌红蛋白含量、高铁肌红蛋白还原酶活性均显著高于无保鲜膜包裹(P0.05)。综合考虑,为最大程度地保持并提高冷鲜肉在贮藏过程中良好的色泽与其他外观品质,建议在其实际贮藏过程中采用保鲜膜包裹。     

Aging and Processing Affect Color, Metmyoglobin Reductase and Oxygen Consumption of Beef Muscles

Color stability and various biochemical properties were determined in bovine longissimus dorsi and psoas major at different times postmortem (8 hr to 21 days) and during retail display. Surface metmyoglobin accumulation, metmyoglobin reductase activity and oxygen consumption rate were affected by muscle type, postmortem aging, and fabrication method (p < 0.01). Psoas steaks had greater metmyoglobin accumulation, lower metmyoglobin reductase activity, and greater oxygen consumption than longissimus steaks. However, color stability of muscles was similar after grinding, which increased oxygen consumption. Color was most stable in steaks fabricated at 4 or 7 days postmortem. The order of color stability was knife-cut steaks > saw-cut steaks > ground muscle.     

Metmyoglobin reductase activity in porcine m. longissimus dorsi muscle

Reduction of metmyoglobin by metmyoglobin reductase extracted from porcine m. longissimus dorsi was found to depend on the presence of NADH and to a lesser degree on the presence of an electron transfer mediator (ferrocyanide). The porcine metmyoglobin reductase was found to reduce equine metmyoglobin and metmyoglobin isolated from pigs hearts using a method described for bovine metmyoglobin. A linear increase in the rate of reduction as a function of amount of enzyme extract was observed, while the rate as a function of NADH concentration increased to a saturation level. In the pH range 6.0-7.1, the rate of reduction of porcine metmyoglobin by porcine metmyoglobin reductase increased at decreasing assay pH, apparently approaching a maximal rate around pH 6. From the temperature dependence of the maximal rate of the enzyme catalyzed reduction of porcine metmyoglobin an apparent activation energy of 33 kJ mol(-1) was calculated. Porcine metmyoglobin was also reduced by NADH in a non-enzymatic reaction, with a rather similar activation energy showing (i) that porcine metmyoglobin is more closely associated with the reductase complex than bovine metmyoglobin and not so easily separated, or (ii) that porcine metmyoglobin reduction is more facile as a non-enzymatic reaction and less dependent on electron transfer mediators compared to bovine metmyoglobin reduction.     

Metmyoglobin reducing activity and colour stability of ovine longissimus muscle

Characteristics of metmyoglobin reducing activity in ovine longissimus were determined, and its effect on colour and colour stability of muscle was investigated in two experiments. In the first experiment vacuum packed ovine longissimus samples were incubated at 5–35°C during the first 16 h post mortem (n=8 per treatment). Metmyoglobin reducing activity was negatively affected by incubation temperatures above 30°C, but colour and colour stability were little affected at 24 h post mortem and after 2 weeks of vacuum storage at 2°C. In the second experiment the effects of pre-slaughter stress and electrical stimulation on metmyoglobin reducing activity, colour and colour stability of ovine longissimus (n=40) with an ultimate pH below 5.8 were investigated. Neither of the treatments had an effect on metmyoglobin reducing activity or colour parameters. The relatively large variation in metmyoglobin activity and colour parameters allowed correlation analysis. Metmyoglobin reducing activity was not correlated to colour or the colour stability parameters. The results of the present study indicate that metmyoglobin reducing activity is not the primary determinant of colour or colour stability of ovine longissimus muscle.     

OXYMYOGLOBIN IN BOVINE MUSCLE SYSTEMS AS AFFECTED BY OXIDIZING LIPIDS, VITAMIN E AND METMYOGLOBIN REDUCTASE ACTIVITY

Oxymyoglobin and lipid oxidation were examined in low and high vitamin E (α-tocopherol) bovine M. longissimus thoracis et lumborum (LD) homogenates and in subcellular fractions of LD. Investigation of the effects of temperature (4, 22, 37C) and pH (5.5, 6.4, 7.2) on lipid and oxymyoglobin oxidation indicated that oxymyoglobin oxidation increased with increasing temperature (P < 0.05) and was higher at the low pH (P < 0.05). Lipid oxidation increased with temperature (P < 0.05) only at pH 5.5. The inclusion of 45 μM Fecl₃/ascorbate (1:1), at pH 5.5 and 4C, led to significant increases (P < 0.05) in lipid oxidation but significant oxymyoglobin oxidation occurred only when the extent of lipid oxidation exceeded a threshold level. Oxymyoglobin and lipid oxidation were significantly lower in LD fractions derived from high vitamin E muscle compared to low vitamin E muscle. α-Tocopherol did not interact directly with oxymyoglobin to suppress oxymyoglobin oxidation but a positive unit effect of muscle α-tocopherol on metmyoglobin reductase activity was observed.     

注射水和氯化钙溶液对宰后猪肉肉色及其稳定性的影响

目的：探讨注射水和氯化钙溶液对宰后冷藏期间猪背最长肌肉色及其稳定性的影响。方法：猪背最长肌于宰后1.5h注射肉质量分数5%的水和200mmol/L氯化钙溶液,分别测定其冷藏期间肉色a*值、总色素含量、高铁肌红蛋白(MetMb)相对百分含量、MetMb还原酶活性等指标。结果：注射氯化钙溶液能降低肉中a*值、总色素含量、MetMb还原酶活性和乳酸脱氢酶-B(LDH-B)活性,增加MetMb相对百分含量和丙二醛(MDA)含量。注水能降低肉中总色素含量和MetMb还原酶活性,增加MetMb相对百分含量。结论：注射水和氯化钙溶液均能降低宰后冷藏期间猪背最长肌中总色素含量,增加MetMb相对百分含量,从而加快猪背最长肌的褪色,不利于其冷藏期间新鲜肉色的维持。     

Reduction of Metmyoglobin by Extracts of Bovine Liver and Cardiac Muscle

Enzymatic reduction of metmyoglobin (in vivo) was investigated using a partially purified metmyoglobin reductase from bovine cardiac muscle. Greater substrate reduction (P<0.05) occurred at pH 6.3 versus 7.0 or 7.3 and at 375°C compared to 22°C using either partially purified cytochrome as or potassium ferrocyanide as reaction mediators. Differences in effectiveness between potassium ferrocyanide and the cytochrome b, preparation were dependent on specific pH/temperature conditions. The cytochrome preparation alone (i.e. without metmyoglobin reductase) reduced metmyoglobin at a rate comparable to that of the reductase. At 22°C the cytochrome b=, preparation assay displayed much slower re-oxidation than the cardiac reductase/ferro-cyanide assay (48 vs 2 hr, respectively).     

Metmyoglobin reductase activity in bovine muscles

Cow muscles (Longissimus dorsi, Tensor fasciae latae, Psoas major, Diaphragma medialis), with different colour stabilities, were used to measure 'Metmyoglobin reductase activity' in different conditions. The effects of pH and temperature on in vitro metmyoglobin reduction were analysed. The highest metmyoglobin reductase activity was localized in microsomes and in more or less intact mitochondria by means of differential centrifugations. The most unstable muscles, from the colour point of view, presented the highest reducing activities and no differences were noted between activities measured in aerobic or anaerobic conditions.     

Metmyoglobin Reducing Capacity of Fresh Normal, PSE, and DFD Pork During Retail Display

Fresh pale, soft, exudative (PSE), dark, firm, dry (DFD), and normal pork were stored under light or dark conditions at 4°C for 7 days. Sample pH, metmyoglobin reductase activity, oxygen consumption rate, and relative surface metmyoglobin and oxymyoglobin contents were determined. DFD pork had the highest metmyoglobin reductase activity and oxygen consumption rate. Enzyme activity of PSE was lower than that of normal pork, but no difference existed in oxygen consumption rate between PSE and normal samples. Metmyoglobin reductase activity dropped slowly during meat storage; oxygen consumption rate sharply decreased during the first day of storage. Both metmyoglobin reductase activity and oxygen consumption rate declined more rapidly in the light. Results can help develop guidelines for display and packaging of pork.     

Effects of pH and temperature on metmyoglobin solubility in a model system

From a series of experiments heating metmyoglobin solutions at pH 5.0 through 7.0, the effects of temperature and pH on the thermal stability of metmyoglobin were investigated. The percent metmyoglobin denatured at temperatures from 25 to 80 °C was determined. pHs lower than 6.5 caused metmyoglobin denaturation at various temperatures from 25 to 80 °C, but it was particularly apparent when pH was < 5.6. Thermal stability of metmyoglobin increased as pH increased. Metmyoglobin denaturation occurred at 55 °C at pH 5, however, denaturation did not occur until 60 °C at pHs from 5.3 to 7.0. A slower heating rate (0.9 °C/min) resulted in more metmyoglobin thermal denaturation than a faster heating rate (1.3 °C/min) when the temperature was above 55 to 60 °C. The denaturation caused by low pH alone was reversible, while that caused by high temperature was not. Techniques which increase muscle pH, such as the injection of sodium bicarbonate, could effectively improve the color condition of PSE meat.