不同杂交品种肉牛背最长肌纤维组织学结构与嫩度对比研究

选择16个月龄的西门塔尔牛、夏洛莱牛、红安格斯牛品种高代杂种牛以及草原红牛,在相同饲养管理条件下育肥180d后屠宰。研究品种对肉牛背最长肌纤维组织学结构及嫩度的影响。结果表明：草原红牛肌纤维直径最大为（48．16±2．98）μm,肌节长度最短为（1．84±0．09）μm,剪切力值最大为（7．31±0．46）N,背最长肌肌肉嫩度较其他品种差;红安格斯牛肌纤维直径最小为（37．77±3．21）μm,肌纤维肌节长度最长为（2．08±0．09）μm,剪切力值最小（5．70±0．74）N,背最长肌肌肉嫩度较其他品种好。     

Measurement of Muscle Exudate Protein Composition as an Indicator of Beef Tenderness

The objective of this study was to determine the relationship between the protein composition of muscle exudates and meat tenderness in beef. Frozen, intact beef strip loins (n = 24) were each divided into 3 equal portions (anterior, middle, and posterior). Steaks were removed from each portion, individually vacuum packaged, thawed at 4 °C, and aged for 0, 7, or 14 d. After the designated aging period, exudate was collected from the packaging and 1 steak from each strip loin portion was utilized for shear force measurements. Muscle exudates were analyzed for protein content (biuret assay) and composition (sodium dodecyl sulfate–polyacrylamide gel electrophoresis). Shear force decreased (P < 0.0001) with aging from 0 to 14 d. The protein concentrations of the muscle exudates were not influenced by the aging period and were not related to the amount of exudate expressed. Electrophoretic analyses of the muscle exudates indicated that with aging the relative abundance of 4 proteins decreased (P < 0.01) and 10 proteins increased (P < 0.05) within the protein profiles of the exudates. The relative abundance of the 167, 97, and 47 kDa proteins in exudates at day 0 were significantly correlated (|r| = 0.57 to 0.77) to shear force at day 14. These data demonstrate that exudate protein composition changes with postmortem aging and beef tenderness.     

Evaluation of the Tenderness of Beef Top Sirloin Steaks

Top sirloin butts and strip loins were obtained from both sides of 20 U.S. Choice beef carcasses and cut into six steaks (2.54 cm thick). These steaks were assigned randomly to one of six aging treatments (0, 7, 14, 21, 28 or 35 days). Top sirloin steaks were less tender and more variable in tenderness than top loin steaks. This difference in tenderness appeared to be due to higher amounts of collagen in top sirloin steaks and a tendency toward lower collagen solubility, shorter sarcomere length and higher (less tender) fragmentation index.     

Consumer Acceptability of Beef Steak Tenderness in the Home and Restaurant

Acceptability of beef steak tenderness in home and restaurant environments was evaluated by 62 consumers. Steaks (loin, ribeye, or bottom and top round) were consumed by each panelist in their home and in a fine dining restaurant. Each consumer rated steaks for tenderness and overall acceptability in the home (over a 2-mo period) and one steak per week (over a 7-wk period) in the restaurant. Acceptability for steaks consumed at home and in the restaurant ranked between 3 (moderately tough) and 4 (slightly tough) on an 8-point scale. The Warner-Bratzler Shear force transition level for beef tenderness acceptability in the home was between 4.6 and 5.0 kg and in the restaurant between 4.3 and 5.2 kg. The unacceptable level of beef steak tenderness was ≤4.3 kg. Results suggested that consumers were more critical of beef tenderness in the home than in restaurants. Consumer responses may have been influenced by receiving free meals in the home or restaurant, as well as by the dining environment.     

不同中心温度对牛肉胶原蛋白特性及嫩度的影响

本研究通过水浴加热牛肉使其达到不同的中心温度来探究胶原蛋白特性对嫩度及质构特性的影响,为煮制牛肉嫩度特性提供理论基础。将牛半腱肌肉在100℃水浴下加热至中心温度60℃、70℃、80℃、90℃、和100℃,通过测定其剪切力、蒸煮损失、水分含量、质构特性、胶原蛋白含量及热溶解性、共价交联以及扫描电镜等指标来探究嫩度的变化机制,最后通过相关性分析得出影响嫩度的关键因素。结果表明,随着中心温度的升高,牛半腱肌剪切力、胶原蛋白的含量及其热溶解性、羟赖氨酸吡啶啉、硬度、弹性、黏着性与咀嚼性增加;赖氨酸吡啶啉、凝聚性、胶黏性和回弹性下降。胶原蛋白含量以及可溶性胶原蛋白的溶解变性很大程度上影响了牛肉的嫩度,肉的弹性和咀嚼性与胶原蛋白含量以及共价交联有关,牛肉硬度下降与肌束膜肌内膜的完整性遭到破坏有关。     

光谱技术预测牛肉嫩度研究进展

肉的嫩度是肉品品质的首要指标。多年来,牛肉嫩度一直是肉品学者关注的焦点,而牛肉嫩度的检测是近年来研究的热点之一。本文从光谱谱信息和牛肉内部成分的关系及光谱成像和牛肉外部特征的关系两方面,简要阐述牛肉嫩度检测的光谱技术特点。主要介绍国内外近十年来在牛肉嫩度检测方面所采用的近红外(NIR)、高光谱、多光谱、荧光光谱和可见光谱技术研究进展,讨论现有技术的局限性,并指出未来牛肉嫩度检测技术的发展方向。     

不同加热方式对牛肉嫩度和杀菌率的影响

本文研究变频微波和水浴两种低温加热方式对牛肉加热过程中嫩度、保水性和微生物杀死率的影响。以牛大腿腱子肉为实验材料,在两种低温加热方式下经不同加热温度和加热时间处理后,检测肉品各项指标。结果表明:微波加热时间短;微波加热温度每降低5℃,加热时间缩短且节能10%~15%。微波加热牛肉的肉汁渗出率明显小于水浴加热。两种加热方式下牛肉的剪切力都是随加热温度的升高呈波浪形趋势;加热温度为60℃时,剪切力达到最大值,继续升高到65℃,剪切力为最小值。微波加热牛肉的剪切力小于水浴加热;当微波加热温度为65℃保温4~6 min时,剪切力较小。牛肉水分保留率与肉汁渗出率密切相关,线性方程为y=-0.323x+99.49(R2=0.927)。两种加热方式下,温度高于60℃都能杀死99%以上的微生物。综合分析得出结论:在变频微波500 W、控温65℃条件下加热42 g(±2)牛肉4~6 min,肉品品质较好。     

Effect of electrical stimulation,delayed chilling and post‐mortem aging on the quality of M. longissimus dorsi and M. biceps femoris of grass‐fed steers

BACKGROUND: Roughage‐based low‐input beef production systems are gaining increasing interest owing to the perceived ecological advantages and potential health benefits associated with the favourable fatty acid composition of such beef. The low plane of nutrition may on the other hand yield less tender beef by affecting growth, carcass weight and fatness and therefore, indirectly, early post‐mortem (p.m.) proteolytic enzyme activity and sarcomere shortening. This study aimed to examine delayed chilling and electrical stimulation as promising techniques to control early p.m. muscle metabolism in a way that improves the tenderness of beef from purely grass‐fed steers in comparison with that from steers receiving a finishing diet with concentrates. RESULTS: Electrical stimulation decreased the pH at 1.5 and 3 h p.m. in the M. longissimus dorsi (LD) and M. biceps femoris (BF) of the treated carcass sides as well as the maximum shear force in the LD, while delayed chilling had no effect on pH or texture. The interactions of carcass fatness with electrical stimulation (P = 0.025) and delayed chilling (P = 0.089) indicated more pronounced effects of the p.m. treatments on beef texture in leaner carcasses. CONCLUSION : Electrical stimulation, but not delayed chilling, could markedly improve pasture beef texture and reduce the aging period needed for proper tenderisation. Copyright © 2008 Society of Chemical Industry     

冷鲜牛肉贮藏过程中线粒体变化与肌红蛋白氧化状态的相关性

为探索冷鲜牛肉贮藏过程中线粒体功能结构的变化,采用透射电子显微镜与原子力显微镜对线粒体内、外部超微结构的检测来确定贮藏时间对肌细胞线粒体变化的影响。结果发现：在4 ℃贮藏过程中（0～21 d）,Flameng线粒体评分从0.986 8升高到2.533 8,表明线粒体结构完整性逐渐降低;线粒体膜电位与线粒体呼吸控制率、ATP含量均呈极显著正相关,相关系数分别达到0.936、0.926（P＜0.01）,说明线粒体结构与功能之间关系密切;线粒体呼吸控制率与氧合肌红蛋白相对含量呈极显著正相关（r＝0.885）（P＜0.01）,线粒体膜电位与高铁肌红蛋白相对含量呈极显著负相关（r＝－0.902）（P＜0.01）,表明线粒体结构、功能变化与肉色稳定性有密切的关系。     

电刺激对牛背最长肌中钙激活酶活性及嫩度的影响

通过对中国杂交黄牛(鲁西黄牛×西门塔尔)牛背最长肌中Calpains活性及剪切力值的分析,研究了电刺激对牛背最长肌宰后成熟过程中Calpains活性及牛肉嫩度的影响。结果表明:电刺激显著提高了μ-calpain的活性(P<0.05),降低了calpastatin对μ-calpain的抑制作用,提高了牛背最长肌的嫩度,缩短了牛肉的成熟时间;但电刺激仅在宰后成熟1h,显著提高了m-calpain的活性(P<0.05);宰后成熟24h、3d,与对照组之间差异不显著(P>0.05),试验结果证实,电刺激通过对Calpains体系的影响,改变了牛肉的成熟速度,显著的改善了牛肉的嫩度。     

不同杂交肉牛背最长肌脂肪酸含量分析

分析研究不同杂交肉牛背最长肌肉脂肪酸含量.选择年龄、体质量和体况接近的安格斯、利木赞、西门塔尔牛与本地黄牛的杂交公牛18头;按不同杂交牛种分为1组(AG×L)、2组(LM×L)、3组(SM×L),每组为6头,各组随机选择3头屠宰,取其背最长肌为材料.结果表明:不同杂交肉牛SFA含量为3组优于1组和2组,皆以棕榈酸和硬脂酸含量为主,且硬脂酸含量3组和1组显著高于2组(P＜0.01; P＜0.05); MUFA含量为2组优于1组和3组;PUFA含量为3组优于1组和2组,且皆以亚油酸和花生四烯酸含量为优势;总脂肪酸、二十碳五烯酸、n-6 PUFAs和n-3PUFAs含量及PUFA/SFA(P/S)比例为1组优于3组和2组,其n-6/n-3 PUFAs比值为3组优于2组和1组.     

不同杂交肉牛背最长肌氨基酸含量分析

分析研究不同杂交肉牛背最长肌肉氨基酸含量。试验选择年龄、体质量和体况接近的安格斯、利木赞、西门塔尔牛与本地黄牛的杂交公牛18头;按不同杂交牛种分为1组(AG×L)、2组(LM×L)、3组(SM×L),每组为6头,各组随机选择3头屠宰,取其背最长肌为实验材料。结果表明:1)不同杂交肉牛粗蛋白(CP)及总氨基酸(TAA)、必需氨基酸(EAA)和风味系游离氨基酸(FAA)含量为试验1组>2组>3组;其氨基酸组成即EAA/TAA和EAA/UAA(非必需氨基酸)为试验1组>3组>2组(P>0.05)。2)氨基酸评分,根据FAO/WHO模式比例,其蛋氨酸、缬氨酸是限制性氨基酸,其他必需氨基酸含量均高于FAO/WHO标准值。     

肌肉嫩度的影响因素及pH调节牛肉嫩化技术研究进展

嫩度是牛肉的重要品质指标,提高牛肉嫩度可以显著提高牛肉品质。大量研究表明,调节pH能有效改善牛肉嫩度、提高牛肉的品质,且该嫩化方法安全有效、成本较低,正在受到越来越多学者和企业的关注。本文综述了决定肌肉嫩度的主要因素、pH调节嫩化技术的机理及国内外pH调节改善牛肉嫩度的应用的研究进展,为新型牛肉嫩化技术的研究与应用提供参考。     

The Effects of Marination and Cooking Regimes on the Waterbinding Properties and Tenderness of Beef and Bison Top Round Roasts

ABSTRACT: The combined effect of marination and different cooking regimes on the cooking yield and palat-ability of bison and beef top round roasts was investigated. Semimembranosus (SM) muscles from beef and bison top rounds were injected with a marinade to achieve 20% extension by weight and 0.5% sodium chloride and 0.3% sodium tripolyphosphate levels and then subdivided into 4 roasts and cooked by following 4 cooking regimes: cooking at a constant temperature of 75°C (control; C); similar to the control treatment except that roasts were held at an internal temperature of 55°C for 45 min (Hold45) or 90 min (Hold90) prior to final cooking at 75°C; initial cooking at 55°C with a 5°C increase in oven temperature every hour (Step-up) until the 71°C internal temperature was achieved. Cooking yield, expressible moisture, purge, and shear force of processed roasts were determined. Marination by injection improved the yield and tenderness of beef and bison SM roasts. The cooking yield for injected samples (78%) was significantly (P < 0.05) higher compared with noninjected controls (68%). Injected SM roasts from bison had lower cooking losses than those from beef, whereas control samples from these 2 species did not differ in their cooking yields. Injected beef SM was more tender than bison SM; however, marination significantly reduced the shear force values of SM roasts for both species (i.e., shear force values of 82 N in control samples was reduced to 63 N in injected ones). The cooking regimes, Hold45, Hold90, and Step-up (which allowed a longer time at 55 to 60°C), gave products with lower ( P < 0.05) shear force values than those of the controls. Based on the cooking yield and time involved, the Hold 45 treatment performed the best.     

线粒体膜通透性转化孔促进剂苍术苷对宰后牛肉线粒体损伤及嫩度的影响

明确线粒体膜通透性转换孔促进剂苍术苷对宰后牛肉线粒体膜通透性、嵴结构、细胞色素c释放等损伤水平变化及嫩度的影响,揭示损伤导致细胞色素c释放激活细胞凋亡酶改善肉品嫩度的作用。选取成年杂交黄牛背最长肌,对比分析经过苍术苷处理（处理组）和未处理（对照组）牛肉样品在4℃条件下分别存放0、12、24、72 h和120 h后,检测线粒体超微结构、膜电位、释放至胞浆中细胞色素c含量、细胞凋亡率、细胞凋亡酶-3和肌原纤维小片化指数等指标变化。随着宰后时间延长,线粒体嵴结构明显减少,并发生肿胀、破裂等变化,线粒体膜电位显著下降、细胞色素c逐渐释放,在宰后72 h起提高细胞凋亡酶-3活性和细胞凋亡率,肌细胞逐渐发生凋亡,肌原纤维蛋白小片化程度提高;与对照组相比,苍术苷处理提高了线粒体嵴结构破坏、膜电位下降和细胞色素c释放等线粒体损伤水平,加速了宰后牛肉肌细胞的凋亡和肌原纤维小片化。线粒体膜通透性转换孔的开放显著影响宰后牛肉线粒体损伤水平,经过苍术苷处理的线粒体除外膜通透性提高外,内膜嵴结构也发生明显变化。线粒体内外膜协同作用,共同调控细胞色素c释放,影响宰后牛肉嫩度变化。     

育成期营养水平对育肥皖南牛背最长肌不同部位肉品质的影响

研究育成期营养对育肥皖南牛背最长肌的上脑、眼肉和西冷的肉品质的影响。30头去势的体质量相近的7月龄皖南牛,随机分成5组,各组根据体质量的1.9%、1.6%、1.3%、1.0%和0.7%补充育成期精料饲养到24月龄进行育肥,在各组饲养程序相同条件下育肥期3个月屠宰。结果显示:育成期按1%体质量饲喂精料的G1.0组的p H值、大理石纹、系水力、蒸煮损失和嫩度等肉品质都优于其他各组,且G1.0组组内不同部位不同肉品质变化范围小、一致性强,皖南牛具有生产大理石纹甚至雪花牛肉的潜质。     

Textural and Ultrastructural Changes in Carrot Tissue as Affected by Blanching and Freezing

ABSTRACT: The impact of blanching and freezing conditions on firmness retention and ultrastructural changes in the cell wall and middle lamella of carrot tissues were studied. Freezing caused extensive degradation of cell wall pectins as evident from the rapid loss in tissue firmness. High-temperature short-time blanching (100°C, 0.58 min.; 90°C, 2.12 min.) retained firmer texture than low temperature long time blanching (80°C, 11.64 min.; 70°C, 71.1 min.). Freezing at rapid rates of -4.5°C/min and -2.4°C/min showed less softening than slow rates of -0.19°C/min and -0.05°C/min. Softening was further enhanced in blanched-frozen carrots. Severe structural damage due to growing ice crystals and substantial loss of pectic material were seen at slower freezing rates.     

Progressive ultrastructural changes in the casein matrix during the ripening of inadequately acidified feta cheese

This study investigated the ultrastructural changes underlying the undesired softening of insufficiently acidified feta cheese during cold storage. Experimental feta cheeses with a range of pH values before brining were manufactured by allowing the cheese blocks to ferment overnight at 3 temperatures (35, 20, and 3°C), which resulted in pH values of 4.80, 4.88, and 5.17, respectively. Cheese blocks were stored in pH-adjusted whey brine solutions for up to 120 d, at which point significant decreases in the cheese firmness were confirmed with compression and shear tests. Samples for transmission electron microscopy were taken during the make procedure, after overnight fermentation, and after 7 and 90 d of cold storage. Increasing the initial pH from 4.80 to 5.17 resulted in a fundamentally different ultrastructure at d 90, with the protein matrix as the continuous phase having markedly decreased density compared with the typically open porous and discontinuous protein matrix of high density in the low-pH control feta cheese. Ultrastructural changes were progressive, and the first signs were evident after only 20 h (the overnight fermentation), when fine, proteinaceous material dissociated from the edges of the casein strands into the serum phase. By d 7, the serum phase was completely filled with the loosely aggregated casein closely surrounding the spheroidal fat globules. A further breakdown of the protein matrix was observed after 90 d, with the complete loss of open porous network structure. Image analysis quantitatively confirmed the progressive and significant decrease in density of the protein matrix. In summary, this is the first study to provide a comprehensive and in-depth view of the progressive and most likely irreversible ultrastructural changes that lead to this textural defect.     

Quantifying the extent of variation in the eating quality traits of the M. longissimus dorsi and M. semimembranosus of conventionally processed Irish beef

The aim of this investigation was to quantify the scale of variation in the eating quality of two commercial beef muscles, M. longissimus dorsi (LD) and M. semimembranosus (Sm). Both the LD and Sm were excised from steers (n=81) and heifers (n=81) (classification grade O4H, O4L, R4H, R4L) within 48 h postmortem, vacuum packaged and stored at 4?°C until tested for eating quality at 14 days postmortem. Quality measurements analysed were: pH, Warner Bratzler shear force, sensory attributes, sarcomere length, Hunter L a b muscle and subcutaneous fat colour and chemical composition. Extent of variation in many eating quality measurements, with the exception of most sensory attributes and subcutaneous fat colour, depended on gender, classification grade or a combination of both. The LD was more variable than the Sm for most quality attributes and heifers were more variable than steers. No one carcass grade was more variable over all attributes analysed; with different grades causing higher or lower variances within certain attributes. Knowledge of the current scale of variation in the eating quality of beef is required by the meat industry, and is one that requires further research.