Differential Enthalpy Research Articles

Moisture desorption isotherms and thermodynamic properties of ecalyptus globulus wood

This paper aimed to analyze the moisture desorption isotherms and specific thermodynamic properties of Algerian Eucalyptus globulus wood using the static gravimetric method. The study was conducted at height temperatures and relative humidity levels ranging from 5% to 90%. The desorption isotherms exhibited a sigmoidal shape, categorized as "type II." A suitable "thermodynamic" equation was chosen to describe the desorption isotherms under controlled conditions. The Clausius-Clapeyron relationship was employed to determine the isosteric heat of desorption. The results demonstrated that, for equilibrium moisture content below 4%, the differential enthalpy and entropy decreased exponentially with increasing moisture content. Specifically, the differential enthalpy decreased from 36 kJ/mol to 5 kJ/mol, while the entropy decreased from 76 J/ (mol K) to 13 J/ (mol K). The enthalpy-entropy compensation theory in the desorption reaction was validated by the observed difference between the isokinetic temperature and the harmonic temperature. Moreover, the wood-water desorption process was spontaneous, as confirmed by the negative value of Gibbs free energy (-1690 J/mol). With increasing temperature, the spreading pressure dropped; at 40°C, it was 2.47978 J/m², and at 80°C, it was 0.82328 J/m². Conversely, the rate of increase was 0.11% J/m² per relative humidity as the water activity increased.

Synthesis and application of a perfluorinated coumarin surfactant as an antifouling coating

Perfluorinated constitute a class of non-polluting antifouling materials. The perfluorinated surfactants have been studied and used in our laboratory for biological tests. The results have shown that they have an effect that is all the faster the higher their concentration. When they are combined with coumarins, their duration of action increases, become specific and exhibit extraordinary physicochemical properties namely, flexibility, elasticity, chemical inertia ....Field tests in the port of the city of Oran (Algeria) have confirmed that soluble matrix paints formulated with this hybrid (perfluorinated coumarins) as antifouling agents have succeeded in preventing the attachment of soiling organisms. With this in mind, our objective is to study in a comparative way the properties of this new material with those of the commercial Micron Extra EU. The composition of this surfactant used is determined by nuclear magnetic resonance (1H NMR), the aggregation characteristics and the glass transition temperature of the surfactant are evaluated by Differential Enthalpy Analysis (DSC).

Effect of acetylation on wood-water interactions studied by sorption calorimetry

Sorption of water has a profound effect on the material properties of wood. The uptake of water vapour in wood and other materials releases more heat than the condensation of vapour to liquid water. This excess energy provides insights to the interactions and energy state of the absorbed water molecules. Modification of wood by acetylation is a common way of altering the wood-water interactions; however, very few data exist on how this and other types of modification affect the energy state of absorbed water in wood. This study is the first to use sorption calorimetry on modified wood to explore the effect of acetylation on wood-water interactions. Acetylation decreased the strength of the interactions between wood and water as seen from a decrease in differential enthalpy of mixing, both overall and in the dry state. It appears that acetylation removes or hinders the most-energetic interactions or bonding configurations of water in wood, perhaps because acetylation reduces the number of water-accessible hydroxyls more than it reduces the amount of absorbed water molecules.

Uncertainty quantification of exchange efficiency in membrane-based air-to-air energy exchanger cores: Repetitive manufacturing and experiments

Air-to-air membrane-energy exchangers have been widely used in green buildings as passive energy-recovery technologies for energy conservation and carbon reduction. An air-to-air membrane-energy exchanger conserves building energy by forcing the indoor exhaust air and unconditioned fresh air to exchange heat and moisture. As a critical performance indicator, the energy-exchange efficiency is primarily determined by the core. To improve energy-saving performance, many studies have been conducted to analyze and enhance the efficiency of air-to-air membrane-energy exchanger cores by manufacturing, testing, modeling, and comparing different cores. However, few studies have investigated the uncertainty introduced by the manufacturing and testing processes (most related research only studied the uncertainty of the sensible efficiency), which means that some positive results of those controlled trials are possibly owing to the manufacturing tolerance or testing errors, rather than real technical progress. This study addresses this problem by quantifying the efficiency uncertainty caused by manufacturing and testing processes. Three cores were produced using the same manufacturing process and materials, followed by identical experimental tests on their sensible, latent, and enthalpy efficiencies. Comparison results suggest that even when all variables are controlled, the differential enthalpy efficiency of two “identical” cores still vary from 0 % to 2 %. Variance of repetitive testing results of a certain core can afford an enthalpy efficiency of 4 % owing to a non-ideal experimental procedure. When manufacturing tolerances and experimental errors are considered simultaneously, the differential sensible efficiency among multiple “identical” cores is within 0–5%, whereas latent efficiency data in winter shows a significant variation of 5–10 % for “identical” cores. The contributions and conclusions of this study are as follows. The efficiency uncertainty caused by manufacturing and testing processes is non-negligible, particularly in latent efficiency. This phenomenon could alert researchers and engineers in this field to conduct repetitive manufacturing and testing while trying to modify/test/compare air-to-air membrane-energy exchanger cores. Because this study is based on a limited number of cores, the quantitative results of this study should be considered a non-universal reference, and a systematic benchmark must be established in the future.

Unraveling the influence of surface functionalities on gas Physisorption: A comprehensive study on SBA-15 nanoporous material from Monte Carlo simulation for improved Textural-Energetic characterization

In this study, we conducted experimental and Monte Carlo simulation studies in the grand canonical ensemble (GCMC) to investigate the role of molecular orientation and surface heterogeneity on the adsorption of N2 at 77 K. Our research focused on a series of ordered nanoporous materials (SBA-15) with varying degrees of oxygen functionalities. Specifically, we examined the effects of surface heterogeneity on the calculation of pore size distribution (PSD) and the Brunauer-Emmett-Teller (BET) area of porous materials. To provide a comprehensive perspective, we compared our results with three levels of surface oxidation, including a pristine case without any surface oxidation.The results from both our experimental and simulation data reveal the importance of chemical heterogeneity in determining equilibrium properties such as molecular packing within the pores, differential enthalpies of adsorption, and N2 orientation distribution. Our findings suggest that accurate characterization of surface heterogeneity is crucial for understanding gas adsorption in nanoporous materials and for developing better models for predicting their performance in various applications. Moreover, our simulations revealed substantial changes in the molecular orientation of adsorbate particles with increasing surface heterogeneity. This insight provides valuable information about the behavior of molecules within the nanoporous materials, further enhancing our understanding of the complex adsorption processes in these systems.

Water desorption isotherms and thermodynamic properties of Ora-pro-nóbis (Pereskia aculeata Miller)

Desorption isotherms of ora-pro-nóbis leaves were determined at storage (5 °C, 10 °C, 20 °C, 30 °C, and 40 °C) and drying (40 °C, 50 °C, 60 °C, 70 °C, and 80 °C) temperatures by the gravimetric static method using saturated saline solutions to obtain relative humidities ranging from 5.20% to 98.48%. The net isosteric heat of desorption and thermodynamic properties such as differential enthalpy, differential entropy, and Gibbs free energy were also estimated. The GAB model presented the best parameters of fitting and the lowest Akaike and Bayesian information criteria values. The desorption isotherm patterns presented a sigmoid shape and were categorized as BET Type II sigmoid shape. The monolayer moisture content was estimated in 0.06 kg of water/kg of dry matter using the GAB model, and it remained constant at all temperatures. The leaves presented an optimal water activity equal to 0.35 at storage temperatures. The net isosteric heat of desorption decreased with increasing Xeq, and differential entropy increased with rising equilibrium moisture content (Xeq > 0.07). The enthalpy-entropy compensation was evaluated, and the desorption process is revealed to be entropy-driven and non-spontaneous.

Thermodynamic Properties of Seeds: A Review

Study of isotherms and thermodynamic properties become essential to understand the drying and imbibition mechanisms of seeds. Among post-harvest procedures of seeds, drying is widely known and used in order to assure quality and stability during storage and shelf life. Variation of moisture content through drying is important in order to understand the interaction between water molecules and the seed components, which is the key factor for correct drying and storage. Seed viability could be maintained during long periods owing to their glass structure, as a thermodynamic unstable state, with high viscosity. Thermodynamic properties were enthalpy (Amount of energy available to do work), entropy (Amount of energy present but it not available to do work) and gibbs free energy (Differential energy between the enthalpy and entropy). Thermodynamic properties of seed water determines the reaction kinetics during seed deterioration. Thermodynamic properties showed a critical upper limit, with tolerant species having higher values then susceptible species. In general the values of critical limits of the thermodynamic parameters decreased with increasing temperature. The differential enthalpy and entropy increased in seeds with period of storage and became asymptotic as the seed lost their viability. Thermodynamics properties increased with increase in temperature, indicating that drying and water absorption do not occur spontaneously it requires external energy. A radical drop in germination follows the trend of gibbs free energy increase and enthalpy decrease, indicating intensification of endergonic reaction. Hence, it is concluded that by using thermodynamic properties of seeds the seed quality can be determined without conducting the germination test in shortest period.

Food nanostructuring of paprika capsules obtained by coacervation for improving carotenoid storage stability

In this study, paprika carotenoids were encapsulated by coacervation with a nanostructured material (NE) prepared with alginate/zeolite and another non-nanostructured (AA) made only with alginate to study the effect of nanocavities in the microstructure on the energy interactions of adsorbed water and the chemical stability of carotenoids. Capsules were characterized through fractal analysis of image, water sorption isotherms, water melting point, thermodynamic properties, and chemical stability during storage. Surface fractal dimensions were between 2.75 and 2.8 for NE and were larger than those obtained for AA, which were between 2.57 and 2.7. NE capsules showed the endothermic fusion peak at −4.42 °C, while AA capsules around 0.97 °C. Adsorbed water enthalpies calculated from adsorption isotherms of the capsules showed the maximum stability of total carotenoids at the crossing of the integral and differential enthalpy intercross (aw = 0.121 for AA and 0.443 for NE) and at the water adsorption at Langmuir-type primary sites. NE capsules improved carotenoid retention two-fold compared to AA after 63 days of storage. These results confirmed that controlling the nanoporous at the food microstructure improved the chemical stability of carotenoids during storage.

Heat capacity changes associated with G-quadruplex unfolding.

G-quadruplexes are four-stranded DNA structures that have been found in the cell and are thought to act as elements of control in genomic events. The measurements of the thermodynamic stability, ΔG, of G-quadruplexes shed light on the molecular forces involved in the stabilization of these structures. In thermodynamic studies, the differential heat capacity, ΔCP, of the folded and unfolded states of a G-quadruplex is a fundamental property that describes the temperature dependences of the differential enthalpy, ΔH, entropy, ΔS, and free energy, ΔG. Despite its recognized importance, the ΔCP of G-quadruplex unfolding has not been measured directly. Here, we use differential scanning calorimetry to evaluate changes in heat capacity, ΔCP, accompanying the unfolding transitions of G-quadruplexes formed by modified DNA sequences from the promoter regions of the c-MYC, VEGF, and Bcl-2 oncogenes. The average value of ΔCP is 0.49 ± 0.12kcal mol-1K-1. Our analysis revealed that disregarding ΔCP leads to significant errors in extrapolated values of the differential enthalpy, ΔH, and entropy, ΔS, of the folded and unfolded DNA conformations. Although the compensation between ΔH and ΔS weakens the effect of ΔCP on the differential free energy, ΔG, neglecting ΔCP may still result in relative errors in ΔG extrapolated to room temperature as great as 140%. We emphasize the importance of proper consideration of the effect of ΔCP in conformational studies of guanine-rich DNA molecules.

Sorption property, excess enthalpy, and solvatochromic parameters of choline lactate

Sorption properties, including isotherm shape, adsorption energy, maximum uptake, and cyclic hydrothermal stability, have a significant influence on the optimization of absorbents for diverse desiccant air conditioning systems. The sorption behavior of the water/choline lactate ([ch][lac]) pair was examined using a dynamic vapor sorption (DVS) analyzer. Data analysis identified type-III isotherms. The Dubinin-Astakhov (D-A) formulation, defined by a temperature-independent Polani potential, was successfully applied to the sorption equilibrium curve. The Kamlet-Taft polarity parameters were tested using solvatochromic probes with a UV/Vis spectrophotometer. Multivariate regression analysis was performed to correlate the water affinity coefficient of the D-A model with the Kamlet-Taft polarity parameters using linear solvation energy relationships (ISERs). The solvatochromic parameter of dipolarity/palarizability (π*) had a positive contribution to the water affinity coefficient of ionic liquid (IL) desiccants, and the general trend of influence was hydrogenbondacidity(α)>π*>hydrogenbondbasicity(β). Excess enthalpies were correlated well with solvatochromic parameters. The differential enthalpies and entropies, first virial coefficient (A0), and isosteric enthalpies of sorption at zero surface coverage were also discussed. The enthalpy of activation at zero surface coverage was deduced from sorption kinetics. The hydrothermal cyclic stabilities and ambient regenerabilities were determined by cycle stress tests.

Moisture Sorption Isotherms and Thermodynamic Properties of Biodegradable Polymers for Application in Food Packaging Industry.

This work aims to evaluate the influence of two starch-based materials (B16 and B20) on the moisture sorption isotherms, determined at 30, 40, and 50 °C, where B16 contains 5% (w/w) more starch than B20. Thermodynamic functions (differential enthalpy (∆Hdif), differential entropy (∆Sdif), integral enthalpy (Δhint), integral entropy (ΔSint), free Gibbs energy (∆G), and spreading pressure (φ)) were used to understand the water-binding behaviors and the energy requirements to remove the moisture content from the surface of these materials. The moisture sorption isotherms exhibited type III behavior, and the Guggenheim-Anderson-de Boer (GAB) model was the most suitable to fit the experimental moisture adsorption data. The adsorption isotherms of microparticles were enthalpy-controlled, with isokinetic temperature values of 221.45 and 279.77 K for B16 and B20, respectively, being higher than the harmonic mean temperature (312.94 K). The values of ∆G were positive (45.274 and 44.307 kJmol-1 for B16 and B20, respectively), indicating a non-spontaneous process. The spreading pressure values increased with increasing water activity (aw) for all isotherms. Higher values of ∆Hdif and ∆Sdif obtained from B16 confirmed its higher number of sorption sites available for binding with water molecules when compared to B20, making it less suitable for application in the food packaging industry.

Structure-Thermodynamic Relationship of a Polysaccharide Gel (Alginate) as a Function of Water Content and Counterion Type (Na vs Ca).

Biofilms are the predominant mode of microbial life on Earth, and so a deep understanding of microbial communities─and their impacts on environmental processes─requires a firm understanding of biofilm properties. Because of the importance of biofilms to their microbial inhabitants, microbes have evolved different ways of engineering and reconfiguring the matrix of extracellular polymeric substances (EPS) that constitute the main non-living component of biofilms. This ability makes it difficult to distinguish between the biotic and abiotic origins of biofilm properties. An important route toward establishing this distinction has been the study of simplified models of the EPS matrix. This study builds on such efforts by using atomistic simulations to predict the nanoscale (≤10 nm scale) structure of a model EPS matrix and the sensitivity of this structure to interpolymer interactions and water content. To accomplish this, we use replica exchange molecular dynamics (REMD) simulations to generate all-atom configurations of ten 3.4 kDa alginate polymers at a range of water contents and Ca-Na ratios. Simulated systems are solvated with explicitly modeled water molecules, which allows us to capture the discrete structure of the hydrating water and to examine the thermodynamic stability of water in the gels as they are progressively dehydrated. Our primary findings are that (i) the structure of the hydrogels is highly sensitive to the identity of the charge-compensating cations, (ii) the thermodynamics of water within the gels (specific enthalpy and free energy) are, surprisingly, only weakly sensitive to cation identity, and (iii) predictions of the differential enthalpy and free energy of hydration include a short-ranged enthalpic term that promotes hydration and a longer-ranged (presumably entropic) term that promotes dehydration, where short and long ranges refer to distances shorter or longer than ∼0.6 nm between alginate strands.

Thermodynamics of dual-phase compositionally complex ceramics: A case study of ultrahigh-entropy fluorite-bixbyite refractory oxides

A set of 8-, 10-, 12-, and 14-component compositionally complex refractory oxides (CCROs, containing Nb, Ta, Ti, Zr, Hf, Ce, Yb, Tm, Er, Ho, Y, Dy, Tb, and Gd) have been successfully fabricated. In addition to five single-phase high- and ultrahigh-entropy CCROs in either bixbyite or defect fluorite structure, nine dual-phase CCROs have been made with co-existing fluorite and bixbyite phases (in a thermodynamic equilibrium each other), representing a new class of dual-phase compositionally complex ceramics (DP-CCCs). A thermodynamic relation dictating the dual-phase equilibria is discovered, where the ratio of the atomic fractions in the two equilibrium phases remains roughly a constant. Interestingly, this ratio for eight different trivalent rare-earth cations linearly depends on the ionic radius (ri). A further analysis showed that the differential enthalpy of solution in the bixbyite versus fluorite phase approximately follows ΔHi (eV) = –0.80·(ri – 1.06 Å). Such thermodynamic relations are important for designing DP-CCCs.

Water sorption isotherms of different sodium alginates: Thermodynamic evaluation and influence of mannuronate‐guluronate copolymers

AbstractWater desorption isotherms of three alginates with different structural features were determined at 25, 37, and 50°C. The Halsey model was selected to fit the equilibrium water sorption data. Differential and integral enthalpy and entropy were estimated for tested alginates. Optimal storage conditions of tested alginates (moisture content from 0.15 to 0.20 kg water/kg dry solid and relative humidity from 35% to 50%) were determined from the maximum and minimum integral enthalpy and entropy values, respectively. A model was proposed to estimate the water sorption isotherms of alginates based on the alginate monomers (mannuronate, M, and guluronate, G) at low water activity (<0.4). M fraction was mainly responsible for the hygroscopicity of alginates. Alginates with similar G fraction showed different hygroscopic features by the presence of more homopolymeric G blocks that could form helical structures at low moisture content, decreasing the water affinity.Practical applicationsDetermination of water sorption isotherms is fundamental to determine the optimal storage conditions at different temperatures. Their knowledge is essential for designing drying equipment, selecting adequately drying conditions (temperature and relative humidity of air) and drying time. Mathematical models are useful to estimate equilibrium moisture content in wide ranges of water activity and temperature. The thermodynamic study also provides valuable information about energy consumption and consequently operational costs. In this case, high content of mannuronate, M, increases the hygroscopic character of alginates, but the optimal moisture content of dried alginates to achieve maximum stability during storing varies in a narrow interval (0.15–0.20 kg water/kg dry solid).

An initial evaluation of the thermodynamic or kinetic separation performance of cation-exchanged LTA zeolites for mixtures of propane and propylene

Adsorptive separation of propylene (C3H6) and propane (C3H8) may represent an energy-efficient alternative to conventional cryogenic distillation. In this perspective, a set of zeolitic adsorbents of LTA type structure (pure-silica zeolite (Si-LTA) and cation- (Na+, 33% of Li+, 50% of Mg2+ and 50% of Ca2+) containing zeolites) were prepared, then characterized using various techniques such as PXRD, gas adsorption measurement, TGA, XRF, SEM and EDX mapping. Thanks to an in-house manometric dosing setup coupled with a Tian-Calvet type microcalorimeter, the pure gas adsorption isotherms and their corresponding differential enthalpies of adsorption were measured at 303 K and for pressures up to 5 bar. To fit those adsorption data, the dual-site Langmuir was selected as the best fit model, and by using the Ideal Adsorbed Solution Theory (IAST), thermodynamic selectivities were determined. The mass transfer constants were also estimated by fitting, separately, the Linear Driving Force (LDF) and isothermal micropore diffusion models to adsorption kinetic curves, thus allowing kinetic type selectivities to be calculated. The combination of those selectivities reveals that the thermodynamic separation of C3H6 from C3H8 is highly favorable on CaNa-LTA, followed by its MgNa-LTA counterpart with IAST selectivities around 15 and 5, respectively. On the other hand, the monovalent cationic zeolites (i.e., Na- and LiNa-LTA) show a predominance of steric effects. Also, except for Si-LTA which shows a moderate kinetic separation, the studied materials are potential candidates, in the following order CaNa- > MgNa- > LiNa- > Na-LTA, for the separation of C3H6 from C3H8 by adsorption-based technologies.

Analysis of thermodynamic properties of moisture-desorption isotherms of Eucalyptus gomphocephala wood

ABSTRACT The aim of this paper was to determine the moisture desorption isotherms and certain thermodynamic properties of Eucalyptus gomphocephala wood using the static gravimetric method at five temperatures: 40°C, 50°C, 60°C, 70°C and 80°C, and relative humidity ranging from 5% to 90%. A “thermodynamic” equation was selected to describe the desorption isotherms under controlled conditions. Desorption isotherms were a “type II” sigmoid. The Clausius–Clapeyron relationship was applied to determine the isosteric heat of desorption. Results showed that for equilibrium moisture content less than 6%, the differential enthalpy and entropy decreased with increasing moisture content according to an exponential law from 26 to 0.5 kJ/mol and from 44 to 0.16 J/(mol K), respectively. The difference in isokinetic and harmonic temperature confirmed the enthalpy-entropy compensation theory of desorption reaction. The negative value of Gibbs free energy (−208.2 kJ/mol) indicated the spontaneous wood-water desorption reaction. Spreading pressure decreased with increasing temperature from 1 J/m² at 40°C to 0.16 J/m² at 80°C and increased with increasing water activity with the rate of 0.014% J/m² per relative humidity.

Hygroscopic behavior of water absorbed by capillarity and stabilization of a bio-composite building material: Clay reinforced with Chamarrops humilis fibers

The paper aims to study the hygroscopic behavior of water absorbed by capillarity of clay reinforced with Chamarrops humilis fibers as an ecologic building material strongly used in building construction in Morocco. This leads to provide a better understanding and controlling hydrothermal behavior of a building material, which integrates sorption phenomenon and its intrinsic characteristics. The static gravimetric method was used to determine sorption isotherms. Six salts were chosen so as to have a range of air relative humidity of 5.72% to 89.8%. The results showed that the water content absorbed by capillarity increases with the increasing of the air relative humidity at a given temperature, and the equilibrium water content absorbed by capillarity decreases with the increasing temperature. The sorption isotherms are of type IV, showing that the water absorption is enhanced at low humidities and a strong dominance of macropores. The differential enthalpy and entropy of sorption show that there is a strong dependence on the air relative humidity. Stabilization of clay by adding fibers indicated a strong influence on the rate of equilibrium moisture content loss, this leads to prevent cracking of earthen structures during the drying period by distributing the tensions due to shrinkage.

Modeling Differential Enthalpy of Absorption of CO2 with Piperazine as a Function of Temperature.

Temperature-dependent correlations for equilibrium constants (ln K) and heat of absorption (ΔHabs) of different reactions (i.e., deprotonation, double deprotonation, carbamate formation, protonated carbamate formation, dicarbamate formation) involved in the piperazine (PZ)/CO2/H2O system have been calculated using computational chemistry based ln K values input to the Gibbs–Helmholtz equation. This work also presents an extensive study of gaseous phase free energy and enthalpy for different reactions using composite (G3MP2B3, G3MP2, CBS-QB3, and G4MP2) and density functional theory [B3LYP/6-311++G(d,p)] methods. The explicit solvation shell (ESS) model and SM8T solvation free energy coupled with gaseous phase density functional theory calculations give temperature-dependent reaction equilibrium constants for different reactions. Calculated individual and overall reaction equilibrium constants and enthalpies of different reactions involved in CO2 absorption in piperazine solution are compared against experimental data, where available, in the temperature range 273.15–373 K. Postcombustion CO2 capture (PCC) is a temperature swing absorption–desorption process. The enthalpy of the solution directly correlates with the steam requirement of the amine regeneration step. Temperature-dependent correlations for ln K and ΔHabs calculated using computational chemistry tools can help evaluate potential PCC solvents’ thermodynamics and cost-efficiency. These correlations can also be employed in thermodynamic models (e.g., e-UNIQUAC, e-NRTL) to better understand postcombustion CO2 capture solvent chemistry.

Experimental evaluation of the partial thermal energy compensation of hydrate crystallization from cyclopentane-loaded porous activated carbon particles immersed in brine

Hydrate-based desalination (HBD) is a potential water desalination technology that has been studied over the past decades. Recently, an HBD process based on hydrate formation from cyclopentane (CP) loaded on porous activated carbon particles (PACP) was patented (“Method for crystallizing clathrate hydrates, and method for purifying an aqueous liquid using the clathrate hydrates thus crystallized”, EP3153606, 2017). It is thought that the crystallization of CP hydrates from CP adsorbed on PACP might cause partial thermal energy compensation. Actually, the heat released by the exothermic hydrate crystallization should be partially balanced by the endothermic desorption of CP from the PACP. In order to investigate this phenomenon, calorimetric and optical studies (heat flow and refractive index measurements respectively) of hydrate formation in systems consisting of CP-saturated PACP immersed in brines (3.5 wt% NaCl and 8 wt% NaCl) were performed. Comparison of the thermal energy measured directly (through the calorimetric study) - i.e. the energy produced by both hydrate crystallization and CP desorption - and the thermal energy measured indirectly (deduced from the optical study) - i.e. the energy generated by hydrate crystallization only - revealed a balanced energy ranging from 9 to 47 kJ/mol of CP. Comparison of the latter with the differential enthalpy of CP desorption from PACP suggests that the CP converted to hydrates was contained in the large pores of the PACP. It is interesting to note that salinity had no significant impact on the degree of thermal energy compensation obtained.

Addition of 1, 4-α-glucan branching enzyme during the preparation of raw dough reduces the retrogradation and increases the slowly digestible fraction of starch in cooked noodles

Consumers significantly prefer wheat noodles that offer both an acceptable texture and health benefits. To this end, a cold-active 1,4-α-glucan branching enzyme from Bifidobacterium longum (BlBE) was expressed in the generally recognized as safe (GRAS) host cell Bacillus subtilis and then used at 120, 240 or 480 U/g flour in the preparation of raw dough. The storage modulus and loss modulus of the BlBE-modified dough decreased, but the pseudo-plasticity increased. The cooked noodles' hardness, gumminess and chewiness decreased by 12.1%–45.8%, 9.7%–40.4% and 16.0%–42.4%, respectively, but both resilience and cohesiveness increased by 4.0%–14.8% and 1.8%–9.0%, respectively. Pearson analysis revealed a correlation between the noodles' textural parameters and the doughs' power law equation parameters. BlBE-modified noodles exhibited significantly (P < 0.05) lower differential scanning calorimetry retrogradation enthalpies during storage at 4 °C for 7 days and released significantly lower levels of glucose during incubation with mammalian α-glucosidase at 37 °C for 10 min–360 min. BlBE at 480 U/g flour increased the slowly digestible portion by 12.6%. BlBE decreased the molecular weight, x-ray diffraction crystallinity, and fourier transform infrared spectroscopy ratio of band's heights at 1045 cm−1 and 1022 cm−1 of starch but increased the amylopectin content and ratio of short- to long-branch chains. These structural changes in starch partially explained the reduced retrogradation and enhanced slowly digestible starch fraction in the noodles.