鸡胸肉肌原纤维蛋白的提取及凝胶特性的研究

研究从鸡胸肉中提取肌原纤维蛋白，探讨不同pH值对肌原纤维蛋白含量的影响。研究结果：在pH7．0时，蛋白含量最大为69．74％，通过SDS—PAGE凝胶电泳分析表明，其主要成分为肌球蛋白、肌动蛋白和肌动球蛋白及其他一些小分子肌原纤维蛋白碎片；在离子强度0．6、pH7．0时提取的肌原纤维蛋白所制备的凝胶的保水性、硬度、胶粘性最大。     

EFFECT OF MICROBIAL GROWTH UPON MYOFIBRILLAR PROTEINS

SUMMARY— Aseptic samples from pig and rabbit muscles were inoculated with Achromobacter liquefaciens, Micrococcus luteus, Pediococcus cerevisiae, Pseudomonas fluorescens, Streptococcus faecal is end a mixed culture obtained from commercial hamburger. Some difficulty was encountered in getting the organisms to grow, and good growth was achieved only with A. liquefaciens end mixed culture from commercial meat. Both inoculated and uninoculated control samples were incubated at 3 and 10°C for 0, 8 and 20 days. The salt soluble proteins were extracted with Weber-Edsall solution and subjected to sucrose density gradient centrifugation, gel filtration and disc gel electrophoresis. The microorganisms utilized in this study had no measurable effect upon the myofibrillar proteins from either pig or rabbit muscle. However, bacterial growth decreased the amount of certain non-protein ultra-violet absorbing components in the ultracentrifugal pattern of Weber-Edsall extract. These components did not appear to be of myofibrillar origin. Disc gel patterns of Weber-Edsall extracts from pig muscle produced a more intensely staining band than those from rabbit muscle at R_m, = 0.59.     

RHEOLOGICAL AND INTERFACIAL BEHAVIOUR OF SOME WHEAT PROTEIN FRACTIONS 1

Gluten from the wheat variety Monopol was fractionated by successive extractions with dilute HCl (0.625–1.5 mM). The first two fractions, obtained at the highest pH values, contained a high proportion of low molecular weight proteins, they spread quickly at the air/water interface and when added to a wheat flour dough they increased the phase angle of the dough. The three following fractions contained a high proportion of high molecular weight proteins, they spread very slowly at the air/water interface and they caused the wheat flour dough to become stiffer (the storage modulus increased) and more elastic (the phase angle δ decreased). The last fractions obtained in amounts enough for investigation were in between the other fractions in the molecular weight distribution and interfacial behaviour, and they hardly affected the rheological properties of the dough.     

SOME PROPERTIES OF MYOFIBRILLAR PROTEINS OBTAINED FROM LOW IONIC STRENGTH EXTRACTS OF WASHED MYOFIBRILS FROM PRE- AND POST-RIGOR CHICKEN PECTORAL MUSCLE

SUMMARY— Changes in extractability of the proteins associated with the fragmentation phenomenon of myofibrils in chicken pectoral muscle were studied. The results indicate that the protein fractions extracted by neutralized water from muscle residue. from which water-soluble proteins have been washed out, increase in post-rigor muscle. The extracts from pre- and post-rigor muscle were fractionated with ammonium sulfate into two fractions: the fraction precipitated by 1.7 M ammonium sulfate (Fr.1) and the supernatant (Fr. 2). Depressing effect on the onset of ATP-induced superprecipitation of trypsin-treated myosin 6 which was initially present in Fr. 2 from pre-rigor muscle decreased to a great extent in that from post-rigor muscle, whereas promotive effect on gelation of F-actin and superprecipitation of the myosin 6 which was little in Fr. 1 from pre-rigor muscle appeared in that from post-rigor muscle. It is proposed that an increasing amount of protein which indicates α-actinin activity is released along with the destruction and final dissolution of the Z-line structure during postmortem storage of chicken pectoral muscle.     

COATING CHARACTERISTICS OF FRIED CHICKEN BREASTS PREPARED WITH DIFFERENT PARTICLE SIZE BREADING

Characteristics of coatings formed from breading of different particle sizes were investigated in breaded, fried chicken breasts. Breading was divided into three categories namely, small (particle size ≤ U.S. No. 60 mesh), medium (particle size between U.S. No. 20 and U.S. No. 60 mesh) and large (particle size > U.S. No. 20 mesh). Chicken breasts were battered, breaded and deep-fat fried for 240 s at 160C. Smaller breading particle size produced smoother and more uniform coatings. Compressive force at 80% strain was 14.3, 85.6 and 130.5 N for small medium and large particle size breading, respectively. With larger breading particle size, L* and a* color values increased, while b* values showed no significant change. Acoustical data taken during compression of coatings did not show any significant differences due to different breading particle sizes.     

CATHEPSIN D AND ITS EFFECTS ON MYOFIBRILLAR PROTEINS: A REVIEW1

The molecular and enzymatic properties of the extensively studied enzyme cathepsin D are reviewed and additional information concerning its activity presented. Cathepsin D at pH 5.5 (37°C) degraded several myofibrillar proteins. The most rapidly hydrolyzed included titin and perhaps nebulin, myosin heavy chain, and M and C-proteins. The effects of cathepsin D on myofibrillar structure under these conditions included reduction in A band width, cleared central region in the A band, and dislocation of the Z line. Temperature was found to exert a strong influence on activity of cathepsin D and maximum activity was observed at 45°C with both muscle and hemoglobin substrates. Activity was evident at even higher temperatures and approximately 49% remained at 55°C (hemoglobin assay). Low temperature (i.e., < 15°C) however, has been observed to result in almost complete inactivity of the enzyme. The implications of this information for involvement of cathepsin D in postmortem proteolysis and tenderization were discussed.     

RELATIONSHIPS BETWEEN BINDING QUALITY OF MEAT AND MYOFIBRILLAR PROTEINS

The binding quality of the heat set gel increased when F-actin was present in an appropriate ratio to myosin A. It increased further when tropomyosin was added to the myosin A/F-actin model system. The water holding capacity was increased by tropomyosin only. Thus, the contribution of not only myosin A but also of native tropomyosin and actin should be controlled in sausage manufacture. The presence of 0.6 M NaCl or KCl in the sol was necessary to produce high binding quality and high water holding capacity of heated myosin B gels. NaCl is preferred because of the taste effect on the meat product. Heating temperature (65, 80, or 90°CC) affected the physical properties of heated myosin B gels. The water holding capacity and the maximum relaxation time decreased with increasing temperature. In the manufacture of meat products, the heating temperature should be selected in accordance with the desired properties in the finished product.     

A COMPARISON OF THE FARINOGRAPH AND A MODIFIED SHEAR-PRESS FOR MEASURING THE RHEOLOGICAL PROPERTIES OF DOUGH AND ITS FINISHED PRODUCTS1

The development of a single texture testing instrument for determining the complicated properties of dough and the textural characteristics of the final product of dough will eliminate the need for a series of specialized instruments. The farinograph and a modified shear-press were used to determine the rheological properties of doughs made from 15 mixtures of all purpose wheat flour, hard wheat flour and 6% soy fortified wheat flour adjusted with 54.7, 58.0, 61.1, 64.6 and 67.9% water absorptions. The shear-press was also used to determine the textural characteristics of the finished products. The shear-press was found to be equal to the farinograph in providing information on certain rheological properties of dough, and high correlations were obtained between these ‘texturegrams’ and farinogram parameters. For instance, the correlation between “viscoelasticity” per texturegram and “maximum consistency” per farinogram was 0.982; between “viscoelasticity” per texturegram and “elasticity” per farinogram was 0.969; and the correlation between “stability of viscoelasticity” per texturegram and “twenty minute drop” per farinogram was 0.941. The adhesive and cohesive properties of dough obtained from shear-press texturegrams explained 88.4% of the variance of the hardness of the end-products. The consistency and elasticity of dough obtained from farinograms explained 90.6% of the variance of the hardness of the end-products. If the method of water absorption and mixing of flour could be standardized, the shear-press could be utilized both for predicting rheological properties of bakery products from determinations on doughs as well as direct evaluations of the finished products.     

THE STRUCTURE AND PROPERTIES OF MYOFIBRILLAR PROTEINS IN BEEF, POULTRY, AND FISH

The myofibrillar proteins myosin, actin, tropomyosin, and troponin are involved in the contraction of muscle. They are also an integral part of the unique, highly organized structure of muscle tissue. The chemistry and biochemistry of these proteins has been studied both in vivo and in vitro by scientists from many different fields. The same proteins are of great importance to food scientists because of their role in meat and meat products. This review summarizes some of the important physicochemical and biochemical properties of these proteins that may be important for food scientists.     

干酪质地及流变学特性的研究进展

介绍了有关干酪的成分及工艺过程对质地和流变学特性影响的研究。在干酪成分中，蛋白质是影响产品流变学特性的主要因素，酪蛋白空间形成的网状结构构成了干酪流变学的基础。在加工过程中，pH、温度、钙浓度、蛋白水解等所有对干酪成分分子产生变化的因素都可能使干酪的流变学特性和质地发生变化。因此，干酪流变学特性的研究对更好地控制质地，生产出质优价廉的干酪，具有重要的意义。最后，研究状况进行了展望。     

THE EFFECT OF SOME MEAT PROTEINS ON THE RHEOLOGICAL PROPERTIES OF PECTATE AND ALGINATE GELS

The viscosity of 1% sodium alginate and 1% sodium pectate solutions containing low levels of calcium chloride were investigated using cone and plate viscometers. The level of calcium required to initiate partial gelation was significantly lower for pectate compared with alginate. With increasing calcium chloride concentration the solutions became more pseudoplastic and eventually showed thixotropy.
One percent bovine serum albumin or 1% myoglobin was incorporated into the polysaccharide solutions together with sufficient calcium to cause incipient gelation in the absence of the protein. Myoglobin inhibited the formation of an alginate gel, the effect being greatest at a pH of about 6.3. Bovine serum albumin also inhibited alginate formation, the effect increasing with increasing pH. In contrast the addition of both myoglobin and bovine serum albumin caused gel formation in the presence of pectate below pH 6.0.
The results are discussed in terms of the protein/polysaccharide interactions and the polymer/ion interactions that can take place in these systems. The relevance of this work to the use of these polysaccharides as thickeners and gelling agents in canned meat products is considered.     

THE DEGRADATION OF MYOFIBRILLAR PROTEINS IN BEEF AND LAMB USING DENATURING ELECTROPHORESIS - AN OVERVIEW

Degradation of specific myofibrillar proteins has been followed in many studies using SDS-PAGE (denaturing) electrophoresis and these have shown that proteins such as titin, nebulin, troponin-T, desmin, filamin and vinculin are degraded at different rates during postmortem storage of meat. Although informative, electrophoresis is usually restricted to qualitative interpretation of the gels and there have been few studies that have quantitatively linked the degradation of specific proteins to changes in toughness. Improved quantitative methods (including scanning densitometry, image analysis, and modeling approaches) will be necessary to determine the protein and/or protein alterations that cause postmortem tenderization. This approach is complementary to other measurements of proteolysis where the objective is to more adequately explain the variation in toughness.     

COMPARISON OF DIFFERENT MALT ANALYSES

The results of applying three types of analytical mashing procedure—Institute of Brewing, European Brewery Convention, and Tepral systems—to the same malts are examined. Statistical correlations of the results are made. It is concluded that the main difference between the results of the Tepral method and the other two procedures is that the first gives much lower extracts when applied to malts which would be likely to be troublesome in the brewery, and is thus more discriminatory for these. The advantages of including sparging in an analytical method are pointed out.