Sarcoplasmic proteins influence water-holding capacity of pork myofibrils

Water-holding capacity (WHC) is one of the main pork quality characteristics. The objective of this study was to determine the influence of (denaturation of) sarcoplasmic proteins on WHC. Myofibrils extracted from red, firm, non-exudative (‘normal’) and PSE (pale, soft, exudative) pork longissimus muscle were combined with sarcoplasmic extracts (with or without proteins) from PSE and normal pork longissimus samples. Weight increase of myofibrils (mg increase mg⁻¹ myofibrillar protein) was used as a measure of WHC. When combined with protein-containing sarcoplasmic extract from normal pork, WHC of myofibrils from PSE (2.6 mg mg⁻¹) and normal (2.8 mg mg⁻¹) pork was higher (P < 0.05) than when combined with sarcoplasmic extract from PSE meat (1.3 mg mg⁻¹ for PSE and 1.9 mg mg⁻¹ for normal myofibrils). Protein-free sarcoplasmic extracts were prepared by heating the extracts for 30 min at 80 °C. WHC of myofibrils combined with protein-free sarcoplasmic extract from PSE and normal pork was not significantly different. WHC of myofibrils combined with protein-free extract was lower than WHC of myofibrils combined with protein-containing extract. Ionic strength or pH could not explain the observed differences. It was concluded that sarcoplasmic proteins do influence WHC. The mechanism of this influence still needs to be determined. © 1999 Society of Chemical Industry     

Protein denaturation and water-holding capacity in pork muscle

Summary. The water-holding capacity of the myofibrils from longissimus dorsi muscles of Large White pigs, selected on the basis of their rate of fall in pH post-mortem, has been compared with the ultimate pH, the protein extractability in M potassium chloride and the adenosine triphosphatase (ATPase) activities. It was found that any loss in water-holding capacity of the myofibrils could be attributed, mainly, to the extent of denaturation, occurring in the myofibrillar protein, as a result of a rapid fall in pH postmortem. It was also found that the ultimate pH had a small, but significant, influence on the water holding capacity.     

四种无磷持水物质对猪肉糜保水性的影响

采用单因素实验和正交实验的方法研究,并优化了四种无磷持水物质卡拉胶、山梨糖醇、大豆分离蛋白、海藻酸钠对猪肉糜及其制品保水性的影响。单因素实验结果表明：这四种无磷持水物质对增强猪肉糜及其制品的保水性均有一定的效果,且随着添加量的增加,解冻产品得率和蒸煮产品得率不断提高,即产品的出品率不断提高,但用量应适当,添加量过大,反...     

Measuring water-holding capacity in pork musculature with a tensiometer

The water-holding capacity (WHC) of post-mortem porcine musculature is an important quality trait, and it is desirable for the industry to assess its variations ,for purposes of evaluating and processing pork products. There are several procedures to accurately determine WHC, but most are either too slow, too expensive or are impractical for commercial application. Since WHC is also important when examining the characteristics of soil, scientists routinely use an instrument called a tensiometer for this measurement. Therefore, we explored the potential application of this technique for assessing WHC in post-rigor pork muscle. The cost, potential speed and invasive application of the tensiometer in muscle were attractive characteristics. A sample (29) of pork loins, representing considerable variation in WHC were used to test the applicability of a commercial tensiometer. When tensiometer measurements were compared to 48 h drip loss, the results indicated the tensiometer could accurately detect the variations in free fluids expressed in muscle and that the procedure could be applied quickly and invasively without altering the commercial value of the product. However, particles (primarily protein and fat) in the muscle fluid became imbedded in the pores of the tensiometer ceramic tip, thus impairing the repeated use of the instrument. A plastic filter was developed to prevent clogging, but it could not be molded adequately to permit rapid insertion and removal for on-line measurements of WHC. Therefore, despite the various desirable features of the tensiometer, it failed to meet some requirements considered essential for further testing as a potential commercial, on-line procedure. First, the clogging problem must be resolved The study also indicated that the filter paper test would be more appropriate than the tensiometer for use in field tests to predict WHC when limited numbers of samples were to be tested.     

宰后肌肉蛋白质变化对冷却猪肉持水性的影响

对正常肉和PSE肉的蛋白质进行溶解性测定、DSC分析和SDS-PAGE电泳分析,结果显示,宰后1hPSE肉的肌浆蛋白和肌球蛋白的变性焓较低,宰后24h不同品质肉样间肌浆蛋白+肌球蛋白的变性焓、总蛋白变性焓和蛋白质溶解性存在明显差异。PSE肉的肌浆中45,40和22kDa蛋白质低于正常肉,而肌原纤维中100,25和24kDa蛋白质高于正常肉,225和16.6kDa低于正常肉。PSE肉的严重汁液流失是肌浆蛋白和肌球蛋白变性的结果,而宰后早期（6h前）的低pH是蛋白质变性的主要诱因;PSE肉蛋白质降解程度较高并和其严重的汁液流失有一定的关系。      

Use of electrical conductivity to predict water-holding capacity in post-rigor pork

This study was designed to re-examine the interrelationships among ultimate pH (pH_u), electrical conductivity (EC) and water-holding capacity (WHC), and to test if EC, using one of two EC instruments, and pH_u can be used to predict WHC. The % drip (PD) was used as measure of WHC. Forty-seven pork loins were classified either as PSE (pale, soft, exudative), RSE (reddish-pink, soft, exudative), RFN (reddish-pink, firm, non-exudative) or DFD (dark, firm, dry), based on L* values, PD and pH_u. The measurement of EC, conducted using the instrument developed at the University of Wisconsin-Madison (UW-EC) was highly correlated to PD at 24 h post mortem (CD=66%), but the pH (NWK) measure of EC was not as highly related to WHC as UW-EC. The predictive value of pH_u and EC for WHC were similar. When 47 samples were divided into three different groups, such as low (< 2% drip), medium (2–6% drip) and high (> 6% drip) drip loss, UW-EC alone grouped 80% of the samples correctly. Thus, EC seemed to be an accurate predictor of WHC in pork muscle when measured at 24 h post mortem. It is conceivable that EC can be used independently, or with even better success in combination with pH_u, to classify WHC of pork carcasses.     

The effect of ageing on the water-holding capacity of pork: role of cytoskeletal proteins

The water-holding capacity (WHC) of pork decreases post-mortem but has been shown to increase during subsequent ageing. In order to test a hypothesis that water-holding capacity increases during ageing due to degradation of the cytoskeleton, WHC was followed 10 days post-mortem and related to the extent of proteolysis of cytoskeletal proteins. A fast method for measuring WHC in small meat samples was developed by the use of centrifugation. The WHC of fresh pork decreases in the first part of post-mortem storage after which it increases to the level of 1 day PM. No changes in total water content of the meat were observed which could explain changes in WHC during ageing. Vinculin and desmin degrade gradually during ageing while talin degrades rapidly. These observations are consistent with the hypothesis that degradation of the cytoskeleton slowly removes the linkage between lateral shrinkage of myofibrils and shrinkage of entire muscle fibres, so removing the force that causes flow into the extracellular space. Inflow of previously expelled water is then possible, so increasing WHC as observed in later periods of storage.     

Effects of high-pressure-modified soy 11S globulin on the gel properties and water-holding capacity of pork batter

The effects of high-pressure-modified soy 11S globulin (0.1, 200, and 400 MPa) on the gel properties, water-holding capacity, and water mobility of pork batter were investigated. The high-pressure-modified soy 11S globulin significantly increased (P < 0.05) the emulsion stability, cooking yield, hardness, springiness, chewiness, resilience, cohesiveness, the a^* and b^* values, and the G′ and G′′ values of pork batter at 80 °C, compared with those of 0.1 MPa-modified globulin. In contrast, the centrifugal loss and initial relaxation time of T_2b, T₂₁, and T₂₂ significantly decreased (P < 0.05). Meanwhile, the microstructure was denser, and the voids were smaller and more uniform compared with those of 0.1 MPa-modified globulin. In addition, the sample with 11S globulin modified at 400 MPa had the best water-holding capacity, gel structure, and gel properties among the samples. Overall, the use of high-pressure-modified soy 11S globulin improved the gel properties and water-holding capacity of pork batter, especially under 400 MPa.     

Centrifugal drip is an accessible source for protein indicators of pork ageing and water-holding capacity

Achieving an improvement in water-holding capacity (WHC) of pork and a reduction in the incidence of pale, soft and exudative (PSE)- and dark, firm and dry (DFD)-like meat is a major challenge for the swine industry. Using proteomics, we sought to identify proteins associated with WHC and to monitor postmortem protein degradation. Twenty longissimus samples were categorised into WHC phenotypes. The centrifugal drip was subjected to SDS-PAGE and mass-spectrometry. Forty-four proteins were identified in the centrifugal drip proteome. Changes occurred in volume of five bands across the ageing period, with most significant changes representing increases between day 3 and day 7. Seven proteins were identified in these bands, most with functions in glycolysis. One band significantly differed in abundance across WHC phenotypes. Peptide signatures of the heat shock protein family were identified in this band.     

Rate and extent of pH decline affect proteolysis of cytoskeletal proteins and water-holding capacity in pork

The objective of this study was to determine the extent to which early postmortem (PM) pH decline influences proteolysis of the intermediate filament protein desmin, the costameric proteins vinculin and talin and autolysis of μ-calpain in the longissimus muscle (LM) of pigs from two genetic lines. Based on the LM 3 h pH (H = 3 h pH of LM > 6.0; L = 3 h pH of LM pH < 5.7) PM, 10 carcasses per line and pH group were selected. The average 3 h pH within pH group was 6.23 (H) and 5.44 (L). The LM samples were collected 24, 48, 72, and 120 h PM and percent drip loss was measured after 1, 2, and 4 d of storage. Samples collected at 24, 48, 72, and 120 h PM were used to monitor desmin, vinculin, and talin degradation and samples collected at 24 h PM were used to determine the extent of μ-calpain autolysis by immunoblotting. Higher (P < 0.01) pH values at 45 min, 6 h, and 24 h PM and lower (P < 0.01) drip losses after 1, 2, and 4 d of storage were recorded in the H-compared to the L-group. Abundance of the 76 kDa μ-calpain autolysis product was greater (P < 0.01), proteolysis of talin at all measured time points and proteolysis of desmin after 24 and 48 h PM was greater (P ? 0.03) in the H-group than in the L-group. The current findings indicate activation rate of μ-calpain may be associated with proteolysis of desmin and talin and could play a role in the development of drip loss. The rate of early PM pH decline can partly explain the variation of desmin and talin degradation by affecting the activation of μ-calpain.     

复合变性淀粉提高鸡胸肉保水率的研究

报道了利用复合变性淀粉提高鸡胸肉保水率的研究。通过单因素实验，分别研究了磷酸酯玉米淀粉、磷酸酯木薯淀粉、交联马铃薯淀粉、交联木薯淀粉、醋酸酯玉米淀粉添加量对胸肉的吸水率和失水率的影响。根据单因素实验结果，进行了正交实验，验证得出最优配方为磷酸酯玉米淀粉为0．4％，磷酸酯木薯淀粉为0．8％，交联马铃薯淀粉为0．5％，交联木薯淀粉为0．6％及醋酸酯玉米淀粉为0．06％。经过验证实验所得到的吸水率和失水率的数据分别为7．9％和13．8％。     

复合食品添加剂在猪肉保水及保鲜中的应用

研究将焦磷酸钠、三聚磷酸钠、壳聚糖3种不同功能的食品添加剂复合在一起,并应用在猪肉保水、保鲜实验中。结果确定,当复合食品添加剂焦磷酸钠(SAP)、三聚磷酸钠(STP)、壳聚糖的最佳配比为0.15%∶0.1%∶1%,最适添加量为2%,此时的保水保鲜效果为最佳。     

Antioxidant activity and water-holding capacity of canola protein hydrolysates

Canola protein hydrolysates were prepared using commercial enzymes, namely Alcalase, an endo-peptidase and Flavourzyme with both endo- and exo-peptidase activities. The hydrolysates so prepared were effective as antioxidants in model systems, mainly by scavenging of free radicals and acting as reducing agents. This effect was concentration-dependent and also influenced by the type of enzyme employed in the process. The hydrolysate prepared using flavourzyme showed the highest antioxidant activity among all samples, whereas the hydrolysates prepared by combination of Alcalase and Flavourzyme did not differ significantly (P > 0.05) in antioxidant effectiveness from that produced by Alcalase alone. The hydrolysates were also found to be effective in enhancing water-holding capacity and cooking yield in a meat model system. Their capability in improving the cooking yield of meat was in the order of Flavourzyme hydrolysates > combination hydrolysates > Alcalase hydrolysates. These results suggest that canola protein hydrolysates can be useful in terms of their functionality and as functional food ingredients and that their composition determines their functional properties and thus their potential application in the food and feed industries.     

生鲜肉品持水性的核磁共振研究

低场核磁共振(LF-NMR)技术在地矿、石油及粮油食品等领域已得到了广泛的应用,但在肉品特别是宰后生鲜肉品水分研究中的应用国内还很少.本文主要介绍低场核磁共振的基本原理及近年来国外利用其在宰后生鲜肉品持水性方面的研究进展.     

提高肉制品保水性方法的研究进展

肉制品的保水性是衡量肉制品品质和经济价值的重要指标之一,如何提高肉制品的保水性具有重要意义。本文对影响肉制品保水性的因素和提高肉制品保水性的方法进行了综述,希望为肉制品的生产加工提供参考。      

转谷氨酰胺酶对碎牛肉保水性和微观结构的影响

为提高碎牛肉的利用率,将碎牛肉制成牛肉肠经转谷氨酰胺酶处理,在单因素实验的基础上,通过响应面分析得到转谷氨酰胺酶降低牛肉肠蒸煮损失率的最适条件为酶量0.3%、反应时间20min、反应温度30℃,提高牛肉肠保水性的最适处理条件为酶量0.4%、反应时间20min、反应温度30℃,且经该条件(酶量0.4%、反应时间20min、反应温度30℃)处理后的牛肉肠各项指标明显优于对照组,微观结构也更加规则有序。由此可知:适当的转谷氨酰胺酶处理可以有效改善碎牛肉的保水性能和微观结构,具有较好的应用前景。      

不同解冻方法对鸡肉保水性的影响

分别采用不饱和湿空气解冻和静水解冻在5、10、15、20、25℃下对冻鸡胸肉进行解冻,并研究其保水性的变化。结果显示:样品的解冻时间随温度升高而缩短,相同温度时静水解冻所需时间较短;解冻损失随着温度的升高而降低,静水解冻时的解冻损失显著低于不饱和湿空气;加压损失、蒸煮损失在两种解冻方式中随着温度的升高变化很小,静水解冻均优于不饱和湿空气解冻;总可溶蛋白、肌浆蛋白、肌原纤维蛋白溶解度均随温度的升高不断降低,不饱和湿空气解冻的蛋白质溶解度高于静水解冻;两种解冻方法的P2%和T2值在两种解冻方式和不同温度之间差异很小。因此,静水解冻比不饱和湿空气解冻更适合鸡肉解冻,在保证解冻用水卫生安全的前提下,15℃时最佳。      

挤压组织化对脱脂花生蛋白粉持水性和持油性的影响

采用挤压组织化方法加工花生脱脂蛋白粉,分析挤压组织化前后花生蛋白持水性和持油性的变化,探讨了挤压组织化对花生蛋白在不同蒸煮温度和蒸煮时间下持水性和持油性的影响规律。结果发现,挤压组织化前后花生蛋白粉的持水性随蒸煮温度的升高而增大,随蒸煮时间的延长先增大后减小,在40min时达到最大值;而持油性受蒸煮温度和蒸煮时间的影响不显著;挤压组织化对花生蛋白粉在各蒸煮条件下的持水性和持油性均影响显著(P<0.01)。     

食品添加剂对低温脱脂豆粉保水保油性的影响

通过卡拉胶、酪蛋白、德惠3号胶和黄原胶四种食品添加剂提高低温脱脂豆粉保水性和保油性,在单因素实验基础上采用混料设计对四种食品添加剂提高低温脱脂豆粉保水性、保油性进行复配实验。综合考虑,复配时最佳配比为：卡拉胶20%、酪蛋白15%、德惠3号胶38%、黄原胶27%,总添加量为3%。此时混合添加剂对低温脱脂豆粉的保水性保油性分别为6.728g·g-1和4.351mL·g-1。