Response of Striated Muscle to Electrical Stimulation

SUMMARY— The response of striated muscle to electrical stimulation was studied in 30 Duroc pigs at two weights; and in 14 Poland China, 11 Yorkshire and 8 Yorkshire-Duroc crossbred pigs of market weight. The Duroc pigs in the heavyweight group were more responsive to electrical stimulation, had a slower rate of post-mortem pH decline and higher color-morphology ratings than the light weight group of Durocs.
The sex of the animal had only a slight effect on the response of the muscle to electrical stimulation. Muscles with a slow rate of glycolysis were significantly more responsive to electrical stimulation than those with an intermediate rate of glycolysis.
The initial lactic acid concentration, unless present in excessive quantities, appeared to have little influence on the responsiveness of the muscle to electrical stimulation. Lactic acid increased significantly, accompanied by a lowering of pH, during the electrical stimulation of the muscle.
Stimulation of the spinal cord caused a significantly lower color-morphology rating and pH in the Poland China and Yorkshire, but not in the Duroc animals. Electrical stimulation in animals other than Poland China did not produce pale, soft, exudative (PSE) musculature.
The electrical stimulatory response of red and white muscle was not significantly (P > .05) different; however, the data indicate that white muscle and PSE muscle do not respond in a similar manner to electrical stimulation.     

Influence of Reconstituted Dark and Light Chicken Muscle Myosin Filaments on the Morphology and Strength of Heat-Induced Gels

The morphological characteristics and heat-induced gel properties of filaments reconstituted from dark and light chicken muscle myosin by dialysis (slow filamentogenesis) and dilution (fast filamentogenesis) methods were studied. The solubility/turbidity properties of myosin isolated from dark and light muscles were quite similar at different pH values and temperatures, but the morphological characteristics of reconstituted filaments of dark and light myosin varied markedly, depending upon whether they were formed by dialysis or dilution.     

Factors Influencing Color of Dark Cutting Beef Muscle

Color of dark cutting beef rib muscle was measured as affected by treatment with rotenone or chilling in an oxygen rich atmosphere. Samples homogenized with the mitochondrial inhibitor, rotenone, or pH 5.0 buffer remained red for up to 1 hr. Control samples blended with water remained red when chilled but turned dark when held at room temperature. Thin slices of dark cutting beef muscle would turn red when chilled in air or oxygen to 3°C, or when chilled in oxygen to 14°C, but would turn dark when transferred from oxygen at 3°C to air at room temperature. Thus, dark cutting beef muscle will turn red if mitochondrial respiration is inhibited, allowing myoglobin at muscle surfaces to remain oxygenated.     

Lipid Hydrolysis and Oxidation Related to Astaxanthin Content in Light and Dark Muscle of Frozen Stored Rainbow Trout (Oncorbynchus mykiss)

Astaxanthin decreased significantly during frozen storage in both light and dark muscle of farmed rainbow trout (Oncorhynchus mykiss). Astaxanthin sunolementation did not affect lipid hydrolysis and oxidation during frozen storage of fish muscle. Deposition of astaxanthin was higher in dark muscle than in light muscle. Astaxanthin decreased in both supplemented and nonsupplemented fish. The sum of trans-astaxanthin and its cis-isomers decreased during frozen storage, indicating mechanisms other than trans-cis isomerization were causes. α-Tocopherol decreased to the same extent in both light and dark muscle for both diets.     

Properties of Dark and Light Tissue from Horse Mackerel (Trachurus murphyi)

Mechanical and physical properties of light and dark tissues from horse mackerel (Trachurus murphyi) were determined for tissue separation. Raw dark tissue was 1.8 times harder than raw white (1.4 and 0.79 kg-f/g, respectively). Hardness after heating to 20°C decreased slightly but it increased sharply to a value of about 2.4 kg-f/ g at 40°C. Tensile strength of the skin was highest at 30°C and a large reduction in the shearing force of the interfibrillar matrix (connective tissue) was also attained at that temperature. Pieces of light muscle were denser (d =1.082) than those of dark tissue (d = 1.059) and relative separation was attained based on terminal velocities. Heating at 30°C appeared adequate to implement future mechanical disruption processes.     

Pattern of Muscle Proteolytic and Lipolytic Enzymes from Light and Heavy Pigs

Samples of muscle Semimembranosus were removed from light and heavy pork hams 3 days after slaughtering and analysed for chemical composition and proteolytic and lipolytic enzyme activity. Light hams were higher in moisture content and cathepsin (B and B+L) activity, and lower in peptidase (pyroglutamyl and dipetidyl IV) activity; the absence of further differences in proteolytic and in lipolytic enzymes could be due to large variation coefficients found within both ham classes. The use of principal components analysis displayed distinct patterns for light and heavy samples, with the latter being mainly characterised by greater peptidase-to-proteinase ratio and, to a lesser extent, by higher lipase activity. It was concluded that different chemical and enzyme patterns in fresh meat might be the cause of the wide variations in protein and lipid breakdown mechanisms that are often encountered in dry-cured pork derivatives.     

Effect of Postmortem Storage on Titin and Nebulin in Pork and Poultry Light and Dark Muscles

Purified myofibrils were prepared from samples of chicken breast and thigh muscles and from light and dark portions of pork semitendinosus muscle at death and after storage at 4° and 22°C for 1, 3, and 7 days postmortem. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) was used to examine the effect of postmortem storage of muscle on titin and nebulin. Results indicated that titin and nebulin were more rapidly degraded in light than in dark chicken muscle. In contrast, titin and nebulin were more rapidly degraded in dark than in light pork muscle.     

两类显示器色光性能的对比测试

为了明晰高端应用的CRT和LCD显示器的色光特性,测试分析了两类各一个显示屏幕在暗室和明室环境中色光的位置均匀性、光亮度和色度、CIE_xy色品域,及其随水平观测角度的变化等特性。实验结果表明：两个显示器在暗室环境中,7个不同色光在屏幕9个位置面法线方向的颜色标准偏差在1.8以内,明室中会增大为3.0以内。明室、暗室中,色光的性能随水平观测角而变化;面法线方向上,LCD显示器的光亮度及色品域均大于CRT显示器;随着观测方向与屏幕面法线方向夹角的增加,均表现为光亮度减小、颜色变化增大,在可接受的颜色差异内,CRT显示器形成面法线水平方向两侧约±25°角的可视范围,而LCD的情况降低为±20°左右;此外,该可视角度内,两个显示器各自的色品域几乎保持不变。     

Physical and Sensory Properties of Chicken Patties Made with Varying Proportions of White and Dark Spent Fowl Muscle

Spent fowl was flaked and formulated to include: (1) 100% dark meat; (2) 75% dark meat, 25% white meat; (3) 50% dark meat, 50% white meat; (4) 25% dark meat, 75% white meat; and (5) 100% white meat. Patties were made and half from each formulation were coated with calcium alginate. Proximate analysis of patties before and after cooking, calculation of cooking loss, and evaluations for textual properties and sensory attributes were performed. As the proportion of white meat increased, the samples contained less fat, had less cooking loss and shrinkage, and received higher sensory preference scores. Patties coated with calcium alginate were more desirable in texture, flavor, juiciness, and overall palatability as compared to the controls.     

Role of Light Chains In Heat-Induced Gelation of Skeletal Muscle Myosin

More than 60% of alkali light chains were released from rabbit skeletal myosin during heating to form gel. The removal of about 1 mol of regulatory light chain (LC2)/mol of myosin (LC2-deficient myosin) resulted in major decrease of gel strength at low ionic strength. The F-actin concentration required to attain maximum gel strength of the LC2-deficient myosin was greater than that of control myosin. These changes in functional characteristics of myosin induced by removal of LC2 were restored by reassociation of LC2 to the LC2-deficient myosin. Results showed skeletal myosin LC2 has an important role in its heat-induced gelation.     

Light-induced Flavour Deterioration. Exposure of Potato Crisps to Light and its Effect on Subsequent Storage in the Dark

The flavour changes and extent of oxidation in crisps that had been exposed to light were studied by flavour difference assessment and peroxide value. When the crisps were examined immediately after illumination, both mean flavour difference ratings and peroxide values increased with the duration of exposure. When the crisps were stored for different periods after a fixed duration of exposure, an increase of flavour difference was observed without concomitant increase in peroxide value. The observation that the storage in the dark after illumination is different to exposure to light alone is significant because actual conditions of storage of food products usually involve both light and dark periods.     

Lipid Peroxidation by Microsomal Fractions Isolated from Light and Dark Muscles of Herring (Clupea harengus)

Enzymic lipid peroxidation by light and dark muscle microsomes of herring (Clupea harengus) required ATP or ADP, NADH and Fe. NADPH could not effectively replace NADH. Inhibition was observed at high concentrations of ADP and NADH but not Fe. The optimal pH for the reaction of both types of microsomes was between 6 and 7. The average peroxidation rate was 362 and 1143 nmoles MDA per mg protein per hr at 6°C for the light and dark muscle microsomes, respectively. The energy of activation for the light and dark muscle microsomes was similar. The light muscle microsomes lost activity faster than the dark muscle microsomes when exposed to 35°C. Ferrous ion stimulated enzymic lipid peroxidation of light and dark muscle microsomes over that observed with ferric ion.     

Relative Roles of the Head and Tail Portions of the Molecule in Heat-Induced Gelation of Myosin

Myosin molecules are cleaved by chymotrypsin digestion into two fragments: subfragment 1, which originates from the globular heads of myosin, and the myosin rod, which originates from the helical tail of the myosin molecule. The heat-induced gelation of these subfragments was compared to that of intact myosin by measuring rigidity, turbidity, and other physico-chemical characteristics of each system. Two features of the heat-induced gelation of myosin, aggregation and three-dimensional network formation were found to be imparted by the subfragment 1 and the rod, respectively. The former involves disulfide exchange and the latter relates to conformational changes arising from a partially irreversible helix-coil transition during heating. Possible relationships are suggested between these physicochemical changes of the myosin head and tail regions upon heating and the heat-induced gelation of myosin.     

Comparison of Methods Used for Measuring pH in Muscle Tissue

Two methods widely accepted for measuring muscle/meat pH are: (1) homogenizing muscle tissue in 5 mM iodoacetate and (2) spear-tip penetrating probe electrode. These two methods were compared with a third method to evaluate the precision of these methods for measuring muscle pH. The third method involved homogenizing tissue in deionized water and measuring pH within 3–5 set of homogenization. It was verified that pH values measured within 3–5 set of homogenization using deionized water were statistically equivalent (P>0.O5) to those measured using the iodoacetate procedure or a spear-tip probe electrode.     

羊奶异军突起,欲分羹乳品市场

<正>在历经波折的乳业市场,众多厂家为重塑形象而努力的同时,一种“另类”乳产品——山羊奶,已经悄然加入了这场市场争夺战。虽然与牛奶市场相比,羊奶市场仍犹如新生婴儿,但经过几年的培育,各种品牌和产品已经粉墨登场。除了羊奶粉、羊奶片外,一些企业已开始研制和生产液态羊奶制品。     

Lipid Extraction from Channel Catfish Muscle: Comparison of Solvent Systems

During extraction of lipids from catfish minced muscle using 9 solvent systems, phospholipid and triacylglycerol recoveries were similar when tissue was mixed on a vortex (under nitrogen) with about 20 vol of chloroform:methanol (2:1), hexane:isopropanol (3:2), chloroform :isopropanol (7:11), dichloromethane:methanol (2:l) or chloro-form:methanol:water (2:2:1). Only a few minutes were required to extract a tissue sample by these methods as compared to a few hours for a Soxhlet extraction (petroleum ether) or for extraction by a dry column procedure (dichloromethane:methanol, 9:l). The time available for interaction of the muscle tissue with the dichlorome-thane:methanol (9:l) system was critical in extraction of lipids, particularly phospholipids.     

Comparison of Methods for Quantifying Fiber Types in Skeletal Muscle Tissue

Measurements obtained using three bundle fiber sizes were compared with the template (4.7 cm² in area) method and the actual fiber population present in the entire photomicrograph. Longissimus muscles from lamb, beef, and pork were evaluated. Muscle fiber populations measured by the template or by selecting a minimum number of fibers to be counted (e.g., based on bundle size) were statistically equivalent (p>0.01) to those measured using the entire micrograph and counting all the fibers present. Small bundles or a template designed to quantitate approximately 20% of the photomicrograph are recommended as the methods of choice for quantifying fiber populations because they would be less labor intense and would, therefore, result in a savings in time.