贮藏时间、温度以及提取方法对高铁肌红蛋白还原酶活力的影响

高铁肌红蛋白还原酶是和肉色相关的一类酶,它可以阻抗引起肉品褐变的高铁肌红蛋白的生成,从而延长肉品货架期。为了更好地了解它的特性,本文研究了贮藏时间、温度以及提取方法对高铁肌红蛋白还原酶活力的影响,以及酶活力和高铁肌红蛋白相对含量的相关性。实验结果显示,经过高铁氰化钾氧化但不经硫酸铵盐析的二号样活力最高,在-30℃的贮藏条件下其活力比4℃时高,在贮藏9～15d时酶活力和高铁肌红蛋白相对百分含量呈负相关。      

高铁肌红蛋白还原酶与肉色关系研究进展

高铁肌红蛋白还原酶是肌肉中存在的可以还原高铁肌红蛋白的一类酶,它与肉色的关系是国内外研究的热点课题。本文对高铁肌红蛋白还原酶以及肉色稳定性关系的国外研究现状进行了概括,包括高铁肌红蛋白还原酶的概述、酶活力的测定方法、影响酶活力的因素、酶纯化的研究、还原过程的机理研究、酶活力和肉色稳定性关系等内容。最后分析了高铁肌红蛋白还原酶在肉品护色领域的研究所面临的问题,从而为以后的研究提供一些新的思路。      

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。      

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。     

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.     

乳酸盐对冷却牦牛肉色泽稳定性及高铁肌红蛋白还原的影响

以牦牛背最长肌为实验材料,通过向牦牛肉糜中添加三种不同种类的乳酸盐（乳酸钙,Ca L;乳酸钾,KL;乳酸钠,Na L）和不同浓度的Ca L（0.1%、0.3%、0.5%）,研究了在（4±1）℃冷藏条件下乳酸盐对牦牛肉肉色稳定性和高铁肌红蛋白还原系统的影响。结果表明:经过7 d的贮藏,0.3%的乳酸盐可以抑制牦牛肉糜a*值的下降,但会使肉色变暗;可显著抑制牦牛肉贮藏过程中MbO₂的氧化（p<0.05）,抑制Met Mb含量的上升,提高MRA,且Ca L处理组的效果最显著（p<0.05）。添加不同质量分数的Ca L后,0.3%Ca L处理组的a*值上升速度显著高于其他3组（p<0.05）,但会使肉糜L*值降低;不同浓度的Ca L均可抑制牦牛肉贮藏过程中Mb O2的氧化（p<0.05）和Met Mb的生成（p<0.05）,并显著提高MRA（p<0.05）和肉色稳定性,其中添加0.3%的Ca L对稳定和保持肉色的作用最明显。      

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。     

不同包装冷却肉在贮藏过程中高铁肌红蛋白还原系统活性变化

在冷却肉的贮藏过程中,其肌红蛋白(Mb)被氧化为高铁肌红蛋白(MetMb),导致了冷却肉的褐变。研究了CO气调包装和真空包装条件下,冷却肉自身的还原系统活性变化规律及其对肉色稳定性的影响。结果表明:CO-MAP的包装护色效果最好,但是对MetMb含量下降和脂肪氧化没有明显作用;在19d的贮藏期内,肌肉中MetMb还原酶活力稳中有升,在其作用下,肉中MetMb含量不断下降,从第9天开始保持平稳,MetMb维持在较低的水平。结果表明,肌肉中MetMb的含量不仅与还原酶系统的活力有关,还与肌肉中自身的电子传递体NADH的含量有关。同时对肌肉中脂肪氧化程度变化的研究表明,TBA值与MetMb含量的变化趋势有一定的相关性。     

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。     

琥珀酸钠和线粒体共同作用对牛肉高铁肌红蛋白含量的影响

高铁肌红蛋白(MetMb)的形成是造成肉色褐变的主要原因。MetMb的还原对于保持肉色鲜红非常重要。本文提取了牛心中的线粒体,研究了在高活性线粒体中,琥珀酸钠对MetMb相对百分含量的影响。结果表明:随着pH增加,MetMb相对百分含量显著下降。在不同线粒体浓度下,随着贮藏时间的延长,MetMb的含量先下降而后又上升。琥珀酸钠含量不变,线粒体浓度越高,MetMb含量越低,而线粒体浓度不变,琥珀酸钠浓度在16mmol/L和24mmol/L时,被还原的MetMb的百分比显著多于其他组。      

Effect of postmortem time on the metmyoglobin reductase activity, oxygen consumption, and colour stability of different lamb muscles

The aim of this research was to characterize the lamb M. longissimus dorsi (LD), M. semitendinosus (ST), and M. psoas major (PM) muscles for differences in instrumental colour, tissue oxygen consumption rate (OCR), mitochondrial respiration control ratio (RCR), metmyoglobin reductase activity (MRA), and the relative proportions of myoglobin (Mb) redox forms. LD, ST, and PM muscles were stored for 6 days at 4 °C. Changes in the instrumental colour (CIE L*-value, a*-value, b*-value, Chroma-value, and Hue-value), OCR, RCR, MRA, and relative proportions of Mb redox forms during storage were evaluated. LD revealed the lowest MetMb accumulation and highest colour stability. Muscles with higher colour stability had lower levels of OCR, higher MRA, and less MetMb accumulation. Colour stability and MRA for the lamb muscles were LD > ST > PM. The correlation coefficients among the main parameters were also investigated in this research. The correlation coefficients between a*-value and OxyMb within the same muscle were highly significant (r = 0.951, 0.974, 0.828; P < 0.05). MRA of the muscles was negatively correlated (r = ?0.810, ?0.942, ?0.971, P < 0.05) with the relative percentage of MetMb. The results of the present study suggested that OCR, RCR and MRA contribute to variation in colour stability of different lamb muscles.     

光照条件对冷却猪肉MetMb还原活性及色泽稳定性的影响

冷却肉中的肌红蛋白很容易受到光的作用而发生褪色,导致颜色劣变.本文采用猪冷却肉为原料,在相同光照强度(40～ 80Lux)下,研究不同波长光照对冷却猪肉肉糜中MetMb还原酶活性及肉色稳定性的影响.结果表明:不论托盘包装还是真空包装,避光与其他光照条件(紫光、绿光、红光、白光)对肉的色泽影响差异显著(P<0.05);真空包装有利于保持肉中MetMb还原酶活性.     

Effect of storage temperature and time on egg white protein

Eggs stored up to six weeks at temperatures of 5, 20 and 30 °C at 60% rel. humidity were investigated regarding their egg white protein composition. The proteins were separated on a C₄-column by HPLC. Specific lysozyme activity was determined using the Micrococcus lysodeikticusmethod, and the lysozyme content was quantified via HPLC. The results showed no significant changes in the activity and content of lysozyme, during storage. Conalbumin content was quantified by HPLC and iron binding capacity. No significant changes in the content could be observed during storage. Changes however, in the HPLC elution pattern of ovalbumin were observed at a reduced retention time. Furthermore, the isoelectric point of ovalbumin became slightly more acidic. These changes of ovalbumin are in accordance with the formation of S-ovalbumin during storage. As the changes are influenced more by the storage temperature than by storage time, this leads to the conclusion that more care should be taken on a consequent storage of eggs under refrigerated conditions.     

贮存温度和时间对山楂汁品质的影响

目的:研究不同储藏温度下山楂汁中组分及品质的变化情况。方法:将同一浸提工艺得到的山楂汁,分别在4、25、37℃下放置,每隔2、4、6、8、10d取样测定,以透光率、总色度、可溶性固形物、蛋白质含量、总酸、有机酸为考察指标,研究不同温度下各参数的变化规律。结果:透光率、总色度、褐变度、褐变指数随温度升高而升高;相同贮存温度下,随着贮存时间的延长,可溶性固形物的含量逐渐降低,最后趋于平稳。相同贮存时间下,37℃条件下贮存的山楂汁的蛋白质含量略有下降,4℃和25℃条件下储藏的山楂汁的蛋白质含量下降幅度较大,最后趋于稳定。原始山楂汁液中总酸的含量为24.27g/kg,随着贮存时间的延长,37℃贮存下山楂汁中总酸的降幅最大,较起始阶段降低13.1%;结论:相同贮存条件下,山楂汁透光率、总色度、褐变度、褐变指数均与温度成正相关;相同贮存时间下,低温条件固形物含量相对较高,一定程度上可以降低蛋白质含量而更加有利于汁液的稳定性;低温贮存能更好的保留山楂汁中的有机酸以及更大程度的保证山楂汁的口感。      

Effect of time before storage and storage temperature on survival of Salmonella inoculated on fresh-cut melons

The effects of a waiting period at room temperature ( approximately 22 degrees C) before refrigerating fresh-cut watermelon, cantaloupe and honeydew pieces contaminated with Salmonella on survival of the inoculated pathogen were investigated. Whole cantaloupes, honeydew melons and watermelons were washed with water, and fresh-cut pieces from individual melons were prepared and inoculated with a five strain cocktail of Salmonella at 10(5)cfu/ml. Populations of aerobic mesophilic bacteria, yeast and mold and Pseudomonas spp. were higher for fresh-cut cantaloupe than for fresh-cut watermelon and honeydew immediately after preparation. Populations of Salmonella, aerobic mesophilic bacteria, yeast and mold and Pseudomonas ssp. in fresh-cut melons left at room temperature for up to 5h before refrigeration were significantly (P<0.05) higher than populations in fresh-cut melons stored at 5 degrees C immediately after preparation. Populations of Salmonella recovered in fresh-cut melon after inoculation with the cocktail of Salmonella strains averaged 2 log(10)cfu/g for all three types of melons. Populations in fresh-cut watermelon and honeydew pieces declined by 1 log when stored immediately at 5 degrees C for 12 days, while the populations in fresh-cut cantaloupe did not show significant (P>0.05) changes. Populations of Salmonella in fresh-cut melons stored immediately at 10 degrees C for 12 days increased significantly (P<0.05) from 2.0 to 3.0 log(10)cfu/g in watermelon, 1.9 to 3.0 log(10)cfu/g in honeydew and 2.0 to 3.6 log(10)cfu/g in cantaloupe pieces. Holding freshly prepared, contaminated fresh-cut melon pieces at 22 degrees C for 3h or more prior to refrigerated storage would increase the chances of Salmonella proliferation, especially if the fresh-cut melons were subsequently stored at an abusive temperature.     

储藏温度和时间对混浊苹果汁混浊稳定性的影响

为了提高混浊苹果汁的混浊稳定性,选用红富士苹果为原料,通过将其在不同条件下(温度和时间)贮藏,研究对苹果汁混浊稳定性和苹果中果胶含量及其性质的影响。结果表明,随着时间的延长,在两种温度(4℃和12℃)下,果汁浊度保留率和混浊稳定性均提高,而且,苹果pH值和果胶含量增加,果胶酯化度和相对分子质量降低。相对于低温(4℃)而言,室温(12±1)℃更有利于提高果汁的浊度保留率和稳定性。因此,苹果通过室温贮藏能够明显改善果汁的混浊稳定性。在考虑出汁率的情况下,浊度保留率由12.91%提高到25.51%;不考虑出汁率时,浊度保留率则提高到42.39%。     

Effect of storage time and temperature on structure,mechanical and barrier properties of chitosan-based films

The mechanical (tensile strength, elongation at break, mechanical work of deformation) and barrier (water vapor permeability and water vapor uptake) properties of chitosan films produced with acetic and lactic acids have been studied as a function of storage time, molecular weight of chitosans, concentration of plasticiser and the storage temperature. It was demonstrated that mechanical properties of chitosan-based films can be improved to a great extent during storage at low temperatures in freezer and refrigerator. Transition of chitosan molecules during storage in the solid state to more extended conformations and free volume changes are considered as mechanisms for the improvement of mechanical and barrier properties of chitosan films. The best mechanical properties are achieved for chitosan films produced with acetic acid and plasticized by the addition of 20% of glycerol. Sharp decrease in water vapor permeability has been demonstrated for thinner chitosan films and related to more dense packing and orientation of linear chitosan macromolecules.