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Biomedical subjects

D A Ledward

Publications and source records attributed to D A Ledward.

At least 19 recordsLinked to original sources
PubMed2005

Microstructure and thermal characteristics of Thai indigenous and broiler chicken muscles.

The microstructure and thermal characteristics of Thai indigenous (Gallus domesticus) and broiler chicken (commercial line CP707) biceps femoris and pectoralis muscles were determined. Perimysium thicknesses were 14.2 microm for biceps femoris muscle and 7.10 microm for pectoralis muscle of indigenous chicken muscles, thicker than those of broiler muscles, which were 9.93 microm for biceps femoris muscle and 3.87 microm for pectoralis muscle (P < 0.05). Five endothermic peaks with peak transition temperatures (Tp) of 54.9, 61.7, 65.4, 70.6, and 76.1 degrees C were obtained for broiler pectoralis muscle, whereas only 3 endothermic peaks (Tp of 56.6, 62.6, and 74.9 degrees C) were obtained for broiler biceps femoris muscle. Thai indigenous biceps femoris and pectoralis muscles had endothermic peaks with Tp ranges of 53.5 to 54.8, 60.7 to 61.9, and 75.9 to 76.9 degrees C. The fiber diameters of Thai indigenous chicken muscles were greater (P < 0.05) than those of the broiler, 31.7 vs. 20.4 microm for biceps femoris muscle and 28.9 vs. 26.6 microm for pectoralis muscle, respectively. After cooking at 80 degrees C for 10 min, the fiber diameter of indigenous chicken muscles significantly decreased while those of the broiler significantly increased. The mean of sarcomere lengths of the raw muscles ranged from 1.56 to 1.64 microm and decreased to 0.92 to 1.32 microm (P < 0.001) for broiler muscles and 1.22 to 1.35 microm (P < 0.001) for indigenous chicken muscles after cooking. The perimysium and endomysium of broiler muscles melted after cooking at 80 degrees C, however, only slight disintegration was observed in these tissues in the indigenous chicken muscles.

Animals↗
PubMed2004

Composition, color, and texture of Thai indigenous and broiler chicken muscles.

Chemical compositions and physical properties of mixed-sex Thai indigenous (Gallus domesticus) and broiler (commercial breed, CP707) chicken biceps femoris and pectoralis muscles were determined. Indigenous chicken muscles contained higher protein contents but lower fat and ash contents compared to broiler muscles (P < 0.001). The amino acid profile of the indigenous chicken muscles was similar to that of the broiler muscles except they were slightly richer in glutamic acid (P < 0.05). The indigenous chicken muscles contained more saturated and less polyunsaturated fatty acids than the broiler muscles. There were no differences in the monounsaturated fatty acid contents between the breeds. The total collagen contents of indigenous pectoralis and biceps femoris muscles were 5.09 and 12.85 mg/g, respectively, which were higher than those found in broiler pectoralis (3.86 mg/g) and biceps femoris muscles (8.70 mg/g) (P < 0.001). Soluble collagen contents were lower for indigenous pectoralis and biceps femoris muscles, 22.16 vs. 31.38% and 26.06 vs. 33.87%, respectively. The CIE system values of lightness (L*), redness (a*), and yellowness (b*) of indigenous chicken muscles were higher than those of broiler muscles. The shear values of indigenous chicken muscles either raw or cooked were higher than those of broiler muscles (P < 0.05). After cooking, the shear values decreased for broiler biceps femoris and pectoralis muscles (P < 0.05), whereas no change was observed for indigenous chicken biceps femoris muscle (P > 0.05). Shear values increased for indigenous chicken pectoralis muscle (P < 0.05).

Amino Acids↗
PubMed2000

Effect of high-pressure treatment on the texture of cherry tomato.

The effect of high-pressure treatment (200-600 MPa for 20 min) on the texture of cherry tomatoes and on the key softening enzymes (pectinmethylesterase and polygalacturonase) was investigated. When subjected to high-pressure treatment whole cherry tomatoes showed increasing textural damage with increasing pressures up to 400 MPa. However, treatment at pressures above 400 MPa (500-600 MPa) led to less apparent damage than treatment at 300 and 400 MPa; the tomatoes appearing more like the untreated samples. These visual changes were reflected in the texture (firmness) and amount of cell rupture in the tomatoes, with the least firmness and the most cell rupture being seen after treatment at 400 MPa. Light and scanning electron microscopy supported these observations. Although a sample of purified commercial pectinmethylesterase was partially inactivated at pressures above 200 MPa, irrespective of pH (4-9), in the whole cherry tomatoes no significant inactivation was seen even after treatment at 600 MPa, presumably because other components in the tomato offered protection or the isoenzymes were different. Polygalacturonase was more susceptible to pressure, being almost totally inactivated after treatment at 500 MPa. It is concluded that the textural changes in tomato induced by pressure involve at least two related phenomena. Initially, damage is caused by the greater compressibilty of the gaseous phase (air) compared to liquid-solid components, giving rise to a compact structure which, on pressure release, is damaged as the air rapidly expands, leading to increases in membrane permeability. This permits egress of water, and the damage also enables enzymatic action to increase, causing further cell damage and softening. The major enzyme involved in the further softening is polygalacturonase, which is inactivated at 500 MPa and above, and not pectinmethylesterase, which in the whole fruit, is barotolerant.

Solanum lycopersicum↗
PubMed2000

Effect of high-pressure treatment on lipoxygenase activity.

Solutions of commercial soybean lipoxygenase (100 microgram/ML in 0.2 M citrate-phosphate and 0.2 M Tris buffer were subjected to pressures of 0.1, 200, 400, and 600 MPa for 20 mm. The enzyme was stable at atmospheric pressure (0.1 MPa) over a wide pH range (5-9). In citrate phosphate buffer, the enzyme had maximum stability over the pH range 58 in untreated samples and after treatment at 200 MPa, but with increasing pressure, the pH stability range become narrower and centered around pH 78. The enzyme was more sensitive to acid than alkali, and at pH 9, it lost virtually all activity after pressurization at 600 MPa for 20 mm in both buffers. The activity of the crude enzyme extracted from tomatoes treated at 200 and 300 MPa for 10 mm was not significantly different from that of the untreated tomatoes, while a pressure of 400 MPa for 10 mm caused a significant decrease in activity and treatment at 600 MPa led to complete and irreversible activity loss. Compared to unpressurized tomatoes, treatment at 600 MPa gave significantly reduced levels of hexanal, cis-3-hexenal, and trans-2-hexenal, which are important contributors to "fresh" tomato flavor, and this was attributed to the inactivation of lipoxygenase.

Electrophoresis, Polyacrylamide Gel↗
PubMed1999

Effects of high pressure on the myofibrillar proteins of cod and turkey muscle.

When turkey breast muscle and isolated myofibrillar protein and myosin of cod or turkey (pH approximately 7) were subjected to pressures up to 800 MPa for 20 min, DSC and electrophoresis (SDS-PAGE) indicated that high pressure-induced denaturation of myosin led to the formation of structures that contained hydrogen bonds and were additionally stabilized by disulfide bonds. Disulfide bonds were also important in heat-induced myosin gels. Hardness of whole cod muscle, estimated by texture profile analysis, showed pressure-treated samples (400 MPa) to be harder than cooked (50 degrees C) or cooked and then pressure-treated or pressure-treated and then cooked samples, supporting the suggestion that pressure induces the formation of heat labile hydrogen-bonded structures while heat treatment gives rise to structures that are primarily stabilized by disulfide bonds and hydrophobic interactions. As expected, turkey myosin is more stable than that of cod; however, it seems their pressure-induced gelation mechanisms are similar.

Animals↗
PubMed1999

Effect of high hydrostatic pressure on the volatile components of a glucose-lysine model system.

An aqueous glucose-lysine model system (initial pH 10.1) was incubated at 60 degrees C and atmospheric pressure (system A) or 600 MPa (system B) to the same absorbance value at 420 nm. Volatile reaction products were isolated by solvent extraction and analyzed by gas chromatography/mass spectrometry. Thirty-two compounds were identified; most contained nitrogen, and pyrazines predominated. Yields of all compounds were suppressed at 600 MPa. Further incubation, at either atmospheric pressure (system C) or 600 MPa (system D), of system A, resulted in lower yields of many compounds at 600 MPa, compared to prolonged incubation at atmospheric pressure. Many of the compounds reported may be formed by, or subsequently react via, aldol condensation. The observed differences among the systems in the profiles and yields of volatile compounds suggest that aldol condensations increase in rate in the systems under pressure.

Furans↗
PubMed1998

Factors affecting the heat resistance of Escherichia coli O157:H7.

Escherichia coli O157:H7 has been reported as being not particularly heat resistant. However, several factors which might increase its heat resistance have been investigated in this study using five strains. Increase in growth temperature to 40 degrees C, as found in the cow gut, heat-shock at sub-lethal temperatures of 42, 45, 48 and 50 degrees C, and variable heating rate (1 degree C min-1 to 23 degrees C min-1) had no dramatic effect on heat resistance. Growth phase had a marked impact on heat resistance; late stationary phase cells were more heat-resistant than were log phase cells. The difference in heat resistance between the two phases of growth became more pronounced when cells were resuspended in fresh nutrient broth; heat resistance of late stationary phase cells increased dramatically whereas no such effect was observed with log phase cells. The addition of polyphosphates to the heating medium did not increase heat resistance. A reduction in water activity of the heating medium from 0.995 to levels between 0.980 and 0.960 also resulted in a marked increase in heat resistance. This effect was more pronounced under conditions of extremely low water activity created by resuspending late stationary phase cells in sunflower oil. Survivors were detected even after a heat treatment at 60 degrees C for 1 h or 70 degrees C for 5 min. It can be confirmed that this serotype has no unusual heat resistance and that the heating environment markedly affects resistance.

Animals↗
PubMed1995

Differential scanning calorimetry of lupin and soy proteins.

Differential scanning calorimetry (DSC) was used to study the 7S and 11S globulin fractions extracted from lupin seed (Lupinus luteus) flour. In agreement with previous work on other lupin species, the isolate showed three denaturation peaks compared to the two observed with soy. By comparison with the isolated globulin fractions, the denaturation peaks at the two higher temperatures in the lupin isolate were assigned to the 11S and 7S globulins. The denaturation temperature of the lupin 7S globulin was about 10 K higher than that for the corresponding soy globulin, whereas the values for the 11S globulin were similar. All globulins displayed increasing thermal stability with decreasing moisture contents. Possible reasons for the differences in behaviour of soy and lupin protein isolates are discussed.

Calorimetry, Differential Scanning↗
PubMed1989

Effects of dietary iron deficiency and tungsten supplementation on 59Fe absorption and gastric retention from 59Fe compounds in rats.

1. In vivo 59Fe absorption from intrinsically labelled Fe-containing fractions of liver and blood were measured in rats by intragastric dosing. All rats were fed on a low-Fe diet for 3 d before dosing in order to standardize the Fe status of the intestinal mucosal cells. 2. An increase in digestion time from 2 to 12 h increased 59Fe absorption (P less than 0.01) from all fractions except ferritin. 3. Fe-deficient rats when compared with essentially Fe-replete rats showed decreased gastric retention for all fractions, but increased 59Fe absorption over 2 h only from ferritin. Ferritin showed several unusual absorption characteristics. 4. Dietary tungsten supplementation of Fe-deficient rats reduced the ferroxidase activity of intestinal mucosal xanthine oxidase. In addition, gastric retention and 59Fe absorption (P less than 0.05) from all fractions were increased.

Animals↗
PubMed1984

Conformational stability of the myosin rod.

Chymotryptic cleavage patterns of myosin rods from pig stomach, chicken gizzard, and rabbit skeletal muscle indicate that short (approximately 45 nm) heavy meromyosin subfragment 2 (SF2) is a consistent product of all three rods, whereas long (approximately 60 nm) SF2 is derived only from skeletal muscle myosin. Differential scanning calorimetry was used to follow the thermally induced melting transition of the rods and certain of their subfragments. In 0.12 M KCl, sodium phosphate buffer, pH 6.2-7.6, the light meromyosin (LMM) and SF2 domains of each rod had essentially identical conformational stabilities. Temperature midpoints for the melting transitions were 54-56 degrees C for the two smooth muscle myosin rods and 50-53 degrees C for the skeletal muscle myosin rod. In 0.6 M K Cl buffer, melting transitions for the smooth muscle myosin rods were essentially unchanged, but skeletal muscle myosin rods showed multiphase melting, with major transitions at 43 degrees C and 52 degrees C. The first of these was tentatively attributed to LMM, and the second to SF2. In 0.12 M K Cl buffer, the LMM transition was stabilised so that it superimposed on that of SF2. No melting was observed in any of the rods at physiological temperature. These results indicate that, excluding a possible but only narrow hinge region, the entire myosin rod has essentially uniform conformational stability at physiological pH and ionic strength, and thus that the contractile and elastic properties of the cross-bridge exist in the heavy meromyosin subfragment 1 (SF1) domains of the molecule.

Animals↗
PubMed1983

Availability of iron from chicken meat and liver given to rats.

The concentration and distribution of iron in 59Fe-labelled chicken leg and breast meat and liver were determined by gel filtration. In all samples approximately 50% of the Fe was insoluble (haemosiderin) and the haemoproteins (haemoglobin and myoglobin) constituted from 15% (liver) to 25% (leg meat) of the total Fe. Ferritin accounted for from 12% (leg meat) to 27% (liver) of the total Fe. A technique was developed which enabled the time-course of the passage of 59Fe-labelled whole and fractionated meat and liver through the gastrointestinal tract of Fe-replete and Fe-deficient rats to be followed and it was found that the rate of stomach emptying appeared to be a function of the viscosity of the meal. In Fe-replete rats approximately 71% of a meal of raw chicken meat had left the stomach within 1 h of administration and by 2 h the stomach was almost empty and much of the unabsorbed 59Fe was in the ileum. By 4 h the ileum and colon contained almost equal amounts of 59Fe. Between different test meals there were only slight differences in gastrointestinal distribution and these reflected the different rates of stomach emptying. Stomach emptying was slower in Fe-deficient compared with Fe-replete rats. In Fe-replete, but not Fe-deficient, rats it was found that the amount of 59Fe lost (absorbed) from the gastrointestinal tract 2 h after administration of a test meal was not significantly different from the value found using a 7 d faecal collection technique. Comparison of the 2 h absorption values for several test meals indicated that 59Fe absorption from raw whole meat was significantly higher than from the soluble extract and the residue after extraction (haemosiderin). Heat treatment caused a significant decrease in the absorption of Fe in whole meat and the soluble meat extract but a significant increase in the liver absorption values. It is suggested that denatured haemoproteins are less available for absorption than their native forms but that heating increases the availability of the Fe of haemosiderin or ferritin or both. Isolated muscle ferritin was poorly absorbed but on the addition of excess bovine serum albumin the absorption of the Fe was markedly increased. It is concluded that, to estimate the Fe availability of a food such as chicken meat or liver one must not only take account of the concentration and type of each Fe-containing compound present but also such factors as their possible synergistic effects, the presence of chelating agents, the extent of cooking and the concentration and type of proteinaceous digestion products.

Animals↗
PubMed1978

Iron availability from meat.

1. The distribution of radioactive iron in 59Fe-labelled rat muscle extract was determined using gel filtration. This showed that most (approximately 70%) of the radioactivity was associated with the heamatin compounds; myoglobin and haemoglobin. 2. Raw beef and freeze-dried rat muscle were digested in vitro, under simulated physiological conditions, and after centrifugation the supernatants fractionated by gel filtration. The soluble products were haematin Fe complexes of molecular weight above 10,000 and non-haematin Fe compounds of molecular weight below 6000, the major products being the non-haematin Fe complexes. The soluble compounds were also separated by dialysis and, in rat muscle, it was found that the low-molecular-weight non-haematin compounds accounted for more than 80% of the total soluble iron. 3. In vivo absorption studies with rats showed the Fe in a digested muscle dialysate to be more readily absorbed than that from an aqueous muscle extract which itself was more readily absorbed than the Fe from whole blood. 4. It may not, therefore, be the haemoproteins per se which are responsible for the high availability of Fe in meat, but rather the nature of their degradation products, formed by digestion within the meat environment.

Animals↗
PubMed1978

Protein quality and iron availability of intermediate moisture beef stored at 38 degrees C.

The longissimus dorsi of a bull and steer were cut into cubes 1.5 cm3 and processed to a water activity (aw) 0.85 by canning in a solution of 9.5 p. 100 sodium chloride, 0.5 p. 100 potassium sorbate and a pre-determined amount of glycerol and water for sixteen hours with continuous tumbling on an end over shaker. After partial drying the intermediate moisture (i.m.) meat pieces were stored at 38 degrees C for periods up to 24 weeks and then freeze-dried before milling and incorporation into test diets fed to rats. Protein quality of fresh cooked beef and i.m. meat stored at 38 degrees C was measured in terms of net protein utilisation (NPU). There was no significant difference in NPU between cooked beef and freshly processed i.m. beef. There were no changes in NPU of i.m. meat from bull up to 9 weeks of storage. After 3 weeks of storage of the meat from the steer however, the NPU fell to 53.0, a level characteristic of cereal protein. This fall in NPU was associated with a decrease in the levels of all essential amino acids (in the protein hydrolysate). Valine and threonine being first and second limiting amino acids. Further storage of i.m. beef after 3 weeks produced a slower rate of decrease in NPU, the value at 24 weeks being 32.1 (61 p. 100 fall). Available lysine decreased by only 15 p. 100 after twenty-four weeks, this measurement under-estimating the fall in protein quality. The decrease in solubility of the meat in SDS/beta-mercaptoethanol on storage was of similar magnitude to that of NPU. Iron availability of i.m. meat, measured by haemoglobin regeneration in rats, showed improved iron availability compared to freshly cooked beef, even though marked changes had occurred in the meat heamatin complexes.

Animals↗
PubMed1976

Enthalphy changes associated with the denaturation of collagens of different imino acid content.

The enthalpy changes associated with the denaturation of acid-soluble and insoluble collagens prepared from sheep, cod, halibut and pike skin were determined by differential scanning calorimetry. The enthalpy change associated with the soluble collagens decreased with decreasing imino acid content (from 1420 cal/mol for sheep to 736 cal/mol for cod) while the value for insoluble collagens was approximately constant at 1360 cal/mol. A possible explanation for these values in terms of the nautre of the bonds present in collagen is discussed.

Collagen↗
PubMed1975

Structural and functional determinants of Mucor miehei protease. V. Enthalpy changes upon thermal denaturation in solution of varying pH.

The thermal denaturation of Mucor meihei protease was studied as a function of pH by differential scanning calorimetry. In both citric acid-Na2HPO4 and in acetic acid-sodium acetate buffers, maximum thermal stability was at pH 4.0-4.2. However, the maximum enthalpy changes associated with the denaturation process were buffer-dependent and occurred between pH values of 4.7 and 5.7.

Calorimetry↗