Endothermic Transition Temperatures Research Articles

Changes in Shear Parameters, Protein Degradation and Ultrastructure of Pork Following Water Bath and Ohmic Cooking

The objective of this study was to investigate the effects of ohmic (OH) and water bath (WB) cooking on shear parameters, protein degradation and ultrastructure changes of porcine longissimus dorsi muscle at the same endpoint temperatures (EPTs; range, 20–100 °C). The cooking loss and Warner–Bratzler shear force of the OH-cooked meat were significantly lower (P < 0.05) while protein solubility, pH and endothermic transition temperature were higher than those obtained by WB cooking at the same EPTs (range, 20–80 °C). Sodium dodecyl sulphate polyacrylamide gel electrophoresis analysis showed that during OH cooking, the meat had slightly fainter protein bands than that of WB-cooked ones. Less obvious shrinkage of the sarcomere and loss in the structure of Z discs were detected especially in OH-cooked meat at EPTs (100 °C). Strong correlations among pH, cooking loss, Warner–Bratzler shear force, sarcoplasmic protein solubility, Tmax2, and Tmax3 were observed in meat following OH cooking.

Preparation and study on the structure and properties of rare-earth luminescent fiber

In order to further explain the luminous properties of rare-earth luminescent fiber and promote various-product development of the fiber, in this research, rare-earth luminescent fiber was prepared by using rare-earth strontium aluminate as the rare-earth luminescent material, fiber-forming polymer PET as the matrix. The microstructure, composition and properties of rare-earth luminescent fiber were studied systematically based on tests and analysis with luminescent fiber, rare-earth luminescent materials and polyester fiber in detail. The results showed that the crystal structure of SrAl2O4: Eu2+, Dy3+ distributed in fiber was not destroyed by the polymer matrix and that the complex manufacturing process to ensure luminous properties of fiber performed well. Meanwhile, the structure and properties of luminescent fiber with no distinct changes were similar with that of the polyester fiber. The breaking tenacity and elongation of luminescent fiber in the wet state decreased respectively compared to the dry, and the breaking tenacity of polyester fiber was higher than luminescent fiber. The endothermic melting peak and glass transition temperature of luminescent fiber were slightly higher than that of polyester fiber. Decay curves of samples were successfully fitted by the sum of three exponential components with different decay times. Characteristic decay tended to be longer in luminescent fiber, while the initial luminance intensity of SrAl2O4: Eu2+, Dy3+ was higher than that of luminescent fiber.

Site-directed mutations of thermostable direct hemolysin from Grimontia hollisae alter its arrhenius effect and biophysical properties.

Recombinant thermostable direct hemolysin from Grimontia hollisae (Gh-rTDH) exhibits paradoxical Arrhenius effect, where the hemolytic activity is inactivated by heating at 60 °C but is reactivated by additional heating above 80 °C. This study investigated individual or collective mutational effect of Tyr53, Thr59, and Ser63 positions of Gh-rTDH on hemolytic activity, Arrhenius effect, and biophysical properties. In contrast to the Gh-rTDH wild-type (Gh-rTDH(WT)) protein, a 2-fold decrease of hemolytic activity and alteration of Arrhenius effect could be detected from the Gh-rTDH(Y53H/T59I) and Gh-rTDH(T59I/S63T) double-mutants and the Gh-rTDH(Y53H/T59I/S63T) triple-mutant. Differential scanning calorimetry results showed that the Arrhenius effect-loss and -retaining mutants consistently exhibited higher and lower endothermic transition temperatures, respectively, than that of the Gh-rTDH(WT). Circular dichroism measurements of Gh-rTDH(WT) and Gh-rTDH(mut) showed a conspicuous change from a β-sheet to α-helix structure around the endothermic transition temperature. Consistent with the observation is the conformational change of the proteins from native globular form into fibrillar form, as determined by Congo red experiments and transmission electron microscopy.

Effect of succinylation on the physicochemical, rheological, thermal and retrogradation properties of red and white sorghum starches

Starches isolated from red and white sorghum were modified with succinylation. After modification proximate composition, moisture content, ash, protein and fat were reduced in percentage. Increase in swelling power was observed and did not show any significant change in solubility. Swelling and solubility were pH dependent with higher values obtained at pH 12 in both native and modified starches. At pH 4 both succinylated red and white starches had lower solubility. Rapid visco-analyser (RVA) revealed increased in peak viscosity of the succinylated starches and reduction in setback and breakdown values. There was no significant change in the pasting temperature. Gelatinization enthalpy reduced from 1.275 and 1.953 J/g in RNS (red native starch) and WNS (white native starch) respectively to 1.105 and 1.178 J/g in SUCR (succinylated red starch) and SUCW (succinylated white). Endothermic transition temperatures (T o, T p and T c) reduced and the retrogradation enthalpy increases with the storage time of gelatinized starches. Therefore retrogradation tendency was reduced by succinylation.

Gelatinization and Retrogradation Kinetics of High‐Fiber Wheat Flour Blends: A Calorimetric Approach

ABSTRACTThe impact of dietary fiber (DF) mixtures on dough thermal properties needs to be investigated when designing high‐fiber wheat bread. Effects of flour replacement at different levels (6–34%) by soluble (inuline [FN]), partially soluble (sugar beet [FX], pea cell wall [SW]), and insoluble (pea hull [EX]) DF on wheat dough thermal profiles have been investigated by simulating baking, cooling, and storage in differential scanning calorimetry (DSC) pans. In general, DF incorporation into water‐flour systems delayed endothermic transition temperatures for both gelatinization and retrogradation phenomena except for the peak temperature (Tp) of retrogradation. With some exception, the pattern of the enthalpy of amylopectin retrogradation was lower and slower (lower constant of proportion, k) over 10 days of storage in gelatinized hydrated flour‐fiber blends when compared with control without DF. FX, a partially soluble fiber, provided major effects on gelatinization (Tp decrease and ΔH increase) and retrogradation kinetics (the Avrami exponent, n, increase). Single presence of EX allowed a significant reduction in the Avrami exponent n leading to slower kinetics for amylopectin retrogradation when included in the blends.

Heat denaturation of soy glycinin: influence of pH and ionic strength on molecular structure.

The 7S/11S glycinin equilibrium as found in Lakemond et al. (J. Agric. Food Chem. 2000, 48, xxxx-xxxx) at ambient temperatures influences heat denaturation. It is found that the 7S form of glycinin denatures at a lower temperature than the 11S form, as demonstrated by a combination of calorimetric (DSC) and circular dichroism (CD) experiments. At pH 7.6, at which glycinin is mainly present in the 11S form, the disulfide bridge linking the acidic and the basic polypeptides is broken during heat denaturation. At pH 3.8, at which glycinin has dissociated partly into the 7S form, and at pH 5.2 this disruption does not take place, as demonstrated by solubility and gel electrophoretic experiments. A larger exposure of the acidic polypeptides (Lakemond et al., 2000) possibly correlates with a higher endothermic transition temperature and with the appearance of an exothermic transition as observed with DSC. Denaturation/aggregation (studied by DSC) and changes in secondary structure (studied by far-UV CD) take place simultaneously. Generally, changes in tertiary structure (studied by near-UV CD) occur at lower temperatures than changes in secondary structure.

Variation in the diffusion and release of ribonuclease through and from esterified hyaluronic acid membranes: Effect of changes in matrix characteristics

Investigations were conducted using membranes composed of esterified hyaluronic acid to determine the effect of the physical matrix properties on protein diffusion and release. Hyaluronate membranes prepared by a solvent evaporation method formed two visually distinct regions, one transparent and the other translucent. Each of the two regions were characterized by differential scanning calorimetry, Fourier transform infrared spectroscopy, and Karl Fisher titration for water content. The transparent region exhibited a higher endothermic transition temperature and lower water content than observed for the translucent region. For the transparent region, significant lag times (>50 h) were detected for the transport and release of a model protein (ribonuclease A) compared with that for the translucent region which showed no lag time. The results highlight the importance of carefully controlling matrix formation to ensure reproducible transport and release characteristics from polymer matrices.

Functional Properties and Enzymatic Digestibility of Cationic and Cross-Linked Cationic ae, wx, and Normal Maize Starch

The functional properties and enzymatic digestibility of cationic and cross-linked cationic ae, wx, and normal maize starches were studied. Cationization reduced the endothermic transition temperatures (T(o), T(p), and T(c)), however, it increased peak viscosity, swelling power, solubility, clarity, and digestibility of all the starches compared to the corresponding native starch. After cationization, the enthalpy of waxy and normal starches was little changed but ae starch showed a decrease. For gel texture, cationization increased the hardness, adhesiveness, and springiness of all the starches, except for the hardness and adhesiveness of normal starch which showed a decrease, and the springiness of waxy starch did not show much change compared to the corresponding control starch. Cross-linking of cationic starch increased the endothermic transition temperatures, as well as peak viscosity. However, it reduced the swelling power and solubility, clarity, and enzymatic digestibility of all the cationic starches.

Analysis and Characterization of Maleic Copolymers—III. Differential Scanning Calorimetry Study

Endothermic physical processes and transition temperatures below 220°C of several binary and ternary copolymers of maleic anhydride with vinyl acetate, methyl methacry-late and/or styrene were studied by differential scanning calorimetry and infrared spectroscopy. To improve resolution of differential scanning calorimetry peaks and allow correct assignment of the chemical and physical processes in the studied temperature range, multiple heating-cooling or isothermal treatments were performed. The recycliza-tion of hydrolyzed maleic acid units to maleic anhydride units, occurring around 160–190°C, was confirmed by infrared spectra.

Reactivity of mesogenic diacetylenes coupled with phase transitions between crystal and liquid crystal phases

Among mesogenic diacetylenes, N-[4-(5-hydroxypenta-1,3-diynyl)benzylidene]-4-alkoxyaniline (DA-Cn), in which n is the number of carbon atoms in the alkoxy group, DA-C8 has been found to have four phases divided by three endothermic transition temperatures. The four phases have been assigned to crystal phase I (T < 96 °C), crystal phase II (TCI–CII = 96 °C), crystal phase G (TCII–CG = 115 °C) and nematic phase (TCG–N = 123 °C), based on DCS measurements and observation under a microscope. The crystal structure of DA-C8 in phase I has been determined. Crystal data are triclinic, space group P, a = 14.580(3), b = 17.451(4), c = 10.219(3) A, α = 93.40(2), β = 103.83(2), γ = 116.85(3)° and Z = 4. Four molecules in a unit cell are hydrogen-bonded to each other at the hydroxymethyl groups and/or the imino-nitrogens of the benzylideneaniline moieties to form a checker-like structure. The phase transitions have been monitored by X-ray powder diffraction measurements. The checker-like structure in crystal I is transformed to a layered structure in crystal phase II and in crystal phase G. The structural transformation may be coupled with a change in the hydrogen-bonding scheme. Whereas crystal phase I is inactive towards the solid state polymerization, crystal phase II polymerizes with a long induction time of 50 h at 110 °C. However, the induction time of the polymerization is shortened greatly in crystal phase G, and the polymerization in the nematic phase proceeds smoothly with almost no induction time. The results are interpreted in terms of the relative orientation of diacetylene molecules in each phase.

Spin-Label Electron Spin Resonance Studies on the Dynamics of the Different Phases of N-Biotinylphosphatidylethanolamines

The chain dynamics and phase behavior of a homologous series of diacyl-N-biotinylphosphatidylethanolamines of chain lengths from C(12:0) to C(20:0) were investigated by spin-label electron spin resonance (ESR) spectroscopy using both phosphatidylcholine and N-biotinylphosphatidylethanolamine spin-label probes. Chain-melting phase transition temperatures determined from the ESR spectral measurements, for all the five lipids in the presence as well as in the absence of 1 M NaCl, correlate with the endothermic phase transition temperatures determined by differential scanning calorimetry [Swamy, M. J., Angerstein, B., & Marsh, D. (1994) Biophys. J. 66, 31-39], confirming that the latter correspond to chain-melting transitions. ESR spectra obtained in the gel phase from phosphatidylcholine probes with the spin-label near the terminal methyl of the hydrocarbon chain showed a similar degree of immobilization (as reflected by the outer hyperfine splittings) to that for spin-labels positioned close to the glycerol backbone, indicating that the biotin-lipids of chain lengths from 14 to 20 carbon atoms form interdigitated gel phases in the presence of salt, as also do those of chain lengths between 16 and 20 carbon atoms in the absence of salt. For dispersions of the C(16:0) chain length biotin-lipid in 1 M NaCl, continuous monitoring of the central ESR peak intensity as a function of temperature detects a cooperative decrease in mobility in the fluid phase at ca. 65 degrees C with a spin-label in the lipid head group and an accompanying increase in mobility at the same temperature with spin-labels positioned toward the terminal methyl of the hydrocarbon chain.(ABSTRACT TRUNCATED AT 250 WORDS)

Layered structure with side chain crystallinity in undoped poly(3-alkyl thiophenes)

The order formation of alkyl-substituted rigid polymers, like poly(3-alkyl thiophenes), is dependent on the length of the alkyl side chain. The formation of a layered structure can be observed by X-ray diffraction experiments. A linear relationship with the d-spacing for (200) plane and n has been obtained along with the observation of the endotherms for the mesophase transition by the thermal analysis. The endothermic transition temperatures observed by DSC decrease with the increasing number of carbons (n) in the alkyl side chain. Side chain crystallization becomes possible when n is larger than 10, resulting in hexagonal packing of the alkyl chains between the main chain layers.

Partitioning of some 21-alkyl esters of hydrocortisone and cortisone

The temperature dependency of the partitioning of some steroids has been determined between dimyristoyl phosphatidylcholine liposomes; isopropyl myristate and 0.9% saline (0.15 M). Partition coefficients increased as a function of temperature below the endothermic phase transition temperature (T c) of the phospholipid, but decreased above this temperature. The IPM-saline partition coefficients of the esters of hydrocortisone and cortisone decreased as a function of temperature. Free energies (ΔG w→1) for all steroids studied were negative. The transfer process was found to be entropy-dominated in both cases. Partitioning into liposomes occurs into areas slightly more hydrophilic than n-octanol and IPM. Ketones substituted on the 11-position of 21-OH steroids have greater hydrogen-bonding capability than 11-OH compounds. Esterification of the 21-hydroxyl leads to an increase in partitioning, because of a positive entropie effect and in spite of a large positive enthalpic effect. This opposing enthalpic effect is due to the increased difficulty in inserting the steroid acetate into a bilayer, due to its increased dimensions relative to the parent steroid. The negative free energy effect of steroidal side-chain lengthening per −CH 2−: group is higher than those reported for methylene group contribution of other solutes in DMPC liposome partitioning systems.

Functional group contributions to the partitioning of phenols between liposomes and water

The temperature dependency of the partitioning of p-alkylphenols and p-halophenols has been determined between dimyristoyl phosphatidylcholine liposomes and 0.15 M NaCl. Partition coefficients increased as a function of temperature below the endothermic phase transition temperature ( T c) of the phospholipid but decreased above this temperature. The transfer process was found to be entropy-dominated below and enthalpy-dominated above the T c, although large negative entropy changes were observed. Regular changes in the thermodynamic functions, partition coefficients and functional group free energies occurred as a function of the alkyl chain length or size of the halogen substituent below but not above the T c. This has tentatively been attributed to increased phenol-phospholipid interaction at the higher temperatures. The partitioning of p-fluorophenol behaved in a manner expected of fluorinated compounds, yielding relatively low partition coefficients, but it produced an additional effect of markedly lowering the T c of dimyristoyl phosphatidylcholine. Good correlations of the partition coefficients in liposomes with those in bulk organic solvents and with molecular size of the solute have been obtained.

Phase behavior of ganglioside-lecithin mixtures. Relation to dispersion of gangliosides in membranes

Ganglioside GM1 and mixed brain gangliosides were mixed with 1-stearoyl-2-oleoyl lecithin (SOPC) and examined by differential scanning calorimetry as a function of ganglioside content and temperature. Low mole fractions of ganglioside GM1 and of mixed brain gangliosides are shown to be miscible with SOPC in the gel phase up to X = 0.3, with the possible exception of a small region of immiscibility for the mixed brain gangliosides system centered around X = 0.05. Above X = 0.3, the low-temperature phases demix into a (gel) phase of composition X = 0.3 and a (micellar) phase of composition X = 1.0. Above the endothermic phase transition temperature, no phase boundaries are discerned. It is pointed out that phase structures need to be determined in each domain delineated in the phase diagrams, and that cylindrical phases may exist at higher temperatures and intermediate compositions. The effects of addition of wheat germ agglutinin, which binds to ganglioside GM1, on a ganglioside GM1-SOPC mixture (X = 0.5), are described and interpreted in terms of partial demixing of ganglioside and lecithin. Behavior of the ganglioside-SOPC system is discussed with respect to the kinetics of cholera toxin action in lymphocytes, as well as to other physiological roles of gangliosides in membranes.