Water Activity Measurements Research Articles

Influence of meat sample geometry on dehydration dynamics during dry-aging of beef

Meat geometry may impact on the dehydration kinetics during dry-aging influencing the drying rate and, potentially, aspects of meat quality. In this study, three meat geometries (slices, steaks and sections) were prepared from three bovine Longissimuss thoracis et lumborum at 3 days post-mortem and were dry-aged at 2 °C, 75% relative humidity with an airflow of 0.5–2.0 m/s for 22 days (slices), 48 days (sections) and 49 days (steaks). Weights were recorded during dry-aging and drying curves were obtained for the three geometries, with the larger sections showing limited dehydration due to internal resistance to moisture migration from the core to the surface. Seven thin-layer equations were fitted to the dehydration data in order to model the drying kinetics during dry-aging. Thin-layer models described reliably the drying kinetics of the three geometries. In general, reduced k values (h−1) reflected the lower drying rates as thickness increased. The Midilli model provided the best fit for all geometries. Proximate analyses of the three geometries and bloomed colour of sections were measured at the start and the end of the dry-aging period. Moisture loss during dry-aging led to the concentration of protein, fat and ash contents; while no significant differences were found for L*, a* and b* values of sections before and after the dry-aging process. In addition, moisture content, water activity (aw) and LF-NMR measurements were taken at different locations within beef sections to further explore water dynamics during dry-aging.

Vapor-liquid-solid equilibria and thermodynamic study of aluminum chloride aqueous solutions at various temperatures

The vapor-liquid-solid equilibria and thermodynamics data relevant to aluminum chloride in aqueous solutions were investigated at various temperatures. The water activity measurements of AlCl3(aq) were carried out from dilution to saturated solutions at temperatures ranging from 298.15 to 353.15 K using the hygrometric method. From new experimental results, the ion interaction of Pitzer, extended ion interaction (EII) and Clegg–Pitzer–Brimblecombe (CPB) models were developed to allow the parametrization of the binary system. The interaction parameters were evaluated for the Al−Cl−H2O system and used to calculate the solute activity and osmotic coefficients form the three models. The standard approach for a 3–1 electrolyte with the ion parameters in the temperature range shows a very good agreement with osmotic coefficient data for unsaturated solutions. The solubility equilibrium of anhydrous AlCl3 in aqueous solutions was determined experimentally up to mmax=(3.383 to 3.606) mol·kg−1from (298.15 to 353.15) K respectively; then, the solubility products as LnKsp∘ of AlCl3(aq) were also given using the obtained activity coefficients at various temperatures.

On the bioprotective effects of 3-hydroxybutyrate: Thermodynamic study of binary 3HB-water systems

Microorganisms must face various inconvenient conditions; therefore, they developed several approaches for protection. Such a strategy also involves the accumulation of compatible solutes, also called osmolytes. It has been proved that the monomer unit 3-hydroxybutyrate (3HB), which is present in sufficient concentration in poly(3-hydroxybutyrate) (PHB)-accumulating cells, serves as a chemical chaperone protecting enzymes against heat and oxidative stress and as a cryoprotectant for enzymes, bacterial cells, and yeast. The stress robustness of the cells is also strongly dependent on the behavior and state of intracellular water, especially during stress exposure. For a better understanding of the protective mechanism and effect of strongly hydrophilic 3HB in solutions at a wide range of temperatures, a binary phase diagram of system sodium 3HB (Na3HB)-water in equilibrium and the state diagrams showing the glass transitions in the system were constructed. To investigate the activity of water in various compositions of the Na3HB/water system, three experimental techniques have been used (dynamic water sorption analysis, water activity measurements, and sorption calorimetry). First, Na3HB proved its hydrophilic nature, which is very comparable with known compatible solutes (trehalose). Results of differential scanning calorimetry demonstrated that Na3HB is also highly effective in depressing the freezing point and generating a large amount of nonfrozen water (1.35 g of water per gram of Na3HB). Therefore, Na3HB represents a very effective cryoprotectant that can be widely used for numerous applications.

Estimation of Albumin Denaturation Temperature in Hydrogenated Starch Hydrolysate Solutions Based on Water Activity Measurements

Estimation of Albumin Denaturation Temperature in Hydrogenated Starch Hydrolysate Solutions Based on Water Activity Measurements

Non-Conventional Time Domain (TD)-NMR Approaches for Food Quality: Case of Gelatin-Based Candies as a Model Food.

The TD-NMR technique mostly involves the use of T1 (spin-lattice) and T2 (spin-spin) relaxation times to explain the changes occurring in food systems. However, these relaxation times are affected by many factors and might not always be the best indicators to work with in food-related TD-NMR studies. In this study, the non-conventional TD-NMR approaches of Solid Echo (SE)/Magic Sandwich Echo (MSE) and Spin Diffusion in food systems were used for the first time. Soft confectionary gelatin gels were formulated and conventional (T1) and non-conventional (SE, MSE and Spin Diffusion) TD-NMR experiments were performed. Corn syrups with different glucose/fructose compositions were used to prepare the soft candies. Hardness, °Brix (°Bx), and water activity (aw) measurements were also conducted complementary to NMR experiments. Relaxation times changed (p < 0.05) with respect to syrup type with no obvious trend. SE/MSE experiments were performed to calculate the crystallinity of the samples. Samples prepared with fructose had the lowest crystallinity values (p < 0.05). Spin Diffusion experiments were performed by using Goldman–Shen pulse sequence and the interface thickness (d) was calculated. Interface thickness values showed a wide range of variation (p < 0.05). Results showed that non-conventional NMR approaches had high potential to be utilized in food systems for quality control purposes.

Application of Flory-Huggins model in experimental and theoretical study of stability of amphotericin B on nanocarrier based on functionalized carbon nanotube

• Water activities for binary and ternary systems were measured. • The interaction between species were obtained based on the Flory-Huggins parameter. • The Gibbs free energy and entropy of ternary mixtures were calculated. • The HSPs ( δ p , δ h , and δ d ) for each component were calculated by GCM. The objective of this study is to investigate the interaction between components in a novel and stable drug delivery system for delivering amphotericin B (Amb) as a model drug. A newly designed drug delivery system will be set up based on a single-wall carbon nanotube (SWCNT), which will be functionalized with a biocompatible polymer called 1,2-Distearoyl-sn-Glycerol-3-Phosphoethanolamine Polyethylene Glycol Carboxylic Acid (DSPE-PEG-COOH), and then amine groups are created on its surface by adding ethylenediamine (EDA). It is used as a novel nanocarrier vehicle for delivering Amb for treatment of potentially life threatening fungal infections. It is imperative that the conjugation of Amb to the functionalized single wall carbon nanotube (FCNT) remains stable to reach the required release profile during the drug administration process. The stabilities of conjugations are investigated through analyses of interactions and miscibility of drug delivery system components. The Flory-Huggins parameter ( χ FH ) is an important criterion that will estimate interactions between the drug delivery system (DDS) components. Each binary system has two components selected from a pool of three entities (FCNT, Amb and water), and the χ FH of each system is calculated by group contribution method (GCM) through Hansen solubility parameter (HSP) and the measurement of water activity. Calculating the χ FH for FCNT and Amb pair shows that the interactions and miscibility between them is favorable, and will provide the required stability of nanocarrier-drug conjugation in FCNT-Amb. The average absolute deviation percentages for (drug-water), (FCNT-water) and (FCNT-water-Amb) systems are 0.542, 0.549 and 0.449, respectively.

Experimental investigation and modeling on the dissociation conditions of methane hydrate in clayey silt cores

AbstractAs the majority of global natural gas hydrate reserve, the dissociation conditions of hydrate in clayey silts are of great significance for its efficient production. In this work, the dissociation conditions of methane hydrate in clayey silt cores were experimentally measured by step‐heating method at the temperature range of 280.76–289.55 K and pressure range of 8.11–15.03 MPa, respectively. Various cores including quartz powder, montmorillonite, and South China Sea sediments at the water content range of 20%–33% were used for investigation. The results showed that the dissociation temperatures of methane hydrate in clayey silt cores depressed compared to bulk hydrate. The grain size, salinity, and lithology of clayey silt cores significantly affect the dissociation conditions of hydrate. In comparison to grain size, salinity, and lithology had a more significant influence on the equilibrium temperature depression. The dissociation temperature depression of methane hydrate was considered as a consequence of the water activity depression which is caused by the effect of capillary, salt, or clay. A water activity meter was used to measure the water activity in clayey silt cores. The influence of salt component and mineral characteristics on the water activity was investigated. By combining the measured water activity data with the Chen‐Guo model, a novel water activity measurement (WAM) method for the hydrate dissociation conditions prediction was proposed. With the maximum deviation less than 12%, the predicted results are in good agreement with the experimental data. It demonstrated that the WAM method could effectively predict the dissociation conditions of methane hydrate in clayey silts with convenience and accuracy.

Measurement of Water Activity in the Presence of High Volatile Concentrations Using a Tunable Diode Laser-Single Laboratory Validation, First Action 2021.04.

Water activity is measured by equilibrating a test portion with a sealed head space and measuring the test portion temperature and the vapor density of the head space. The water activity is the ratio of head space vapor density to the saturation vapor density at test portion temperature. Headspace vapor density is typically measured using capacitance or chilled mirror sensors, but, when volatiles in significant concentration are present, these measurements may fail. Evaluate the accuracy of a tunable diode laser (TDL) for measuring the headspace vapor density and water activity of pharmaceutical preparations and food in the presence of non-aqueous volatiles. A commercial TDL water activity meter was calibrated against standards of known water activity and used to measure water activity of pharmaceutical preparations and food with high concentrations of non-aqueous volatiles. When no volatiles other than water vapor are present, this method is capable of measuring water activity with an accuracy of 0.005 or better. When high concentrations of volatiles such as ethanol, isopropanol, propylene glycol, tetrahydrofuran, or acetonitrile are present the uncertainty of the measurement increases. This is at least partly due to the uncertainty of the standards. Based on uncertainties in the water activity estimates of the water-organic mixtures, the uncertainties in water activity measurements with high concentrations of non-aqueous solvents is 0.02 or less up to mass fractions of the organic of 0.97. The theoretical background for TDL measurement of water activity is presented showing that the water vapor concentration is proportional to the area of the absorption line which is not affected by the presence of other volatiles.

Predicting Methane Hydrate Equilibrium Conditions in Ethylene Glycol and NaCl/KCl/CaCl2 Aqueous Solutions by Water Activity Measurement

Predicting Methane Hydrate Equilibrium Conditions in Ethylene Glycol and NaCl/KCl/CaCl₂ Aqueous Solutions by Water Activity Measurement

FARKLI PİŞİRME MATERYALLERİ İÇİNDE PİŞİRİLEN İSKORPİT BALIĞI (Scorpaena porcus, Linnaeus 1758) ETİNİN KALİTESİ

This study aimed to investigate the effect of different cooking materials on some physical, nutritional, and sensory characteristics of black scorpionfish (Scorpaena porcus) meat. To achieve this aim, scorpion fish fillets were divided into four groups as open-roasted (control), oven bag cooked (Group A), baking paper wrapped (Group B) and aluminum foil wrapped (Group C). All fillets were cooked in an electrical oven. The nutritional and amino acid composition, water activity and color measurements were carried out in all samples including raw fish. Sensorial properties of all cooked samples were also evaluated. On comparing the raw and cooked groups it was found that cooking materials had a considerable effect on the nutritional and amino acid composition. The protein and total amino acid contents of the Control group were higher than that of the other groups due to water loss. It was also determined that the aromatic amino acid content of the control group was higher than the other groups. The cooking losses varied according to the type of cooking material. The method of cooking in the baking paper can be said to be the most preferable method for this fish according to the sensory analysis results.

Lemongrass (Cymbopogon citratus DC. Stapf) essential oil microparticles: Development, characterization, and antioxidant potential

Maltodextrin (DE 20) and gelatin (4:1, w/w, respectively) were investigated as encapsulant materials for lemongrass (Cymbopogon citratus DC. Stapf) essential oil microencapsulation by freeze-drying. Three formulations were prepared: M1 (5% essential oil), M2 (10% essential oil), and M3 (15% essential oil), all in w/w. Microparticles were characterized by Fourier-transform infrared spectroscopy, scanning electron microscopy, water activity measurement, thermogravimetric and derivative thermogravimetric analysis, differential scanning calorimetry, and antioxidant activity analysis. Yield and microencapsulation efficiency were also determined. The results showed the promising potential of maltodextrin and gelatin as encapsulants and confirmed the feasibility of preparing C. citratus essential oil microparticles by freeze-drying. Microencapsulation improved the oil’s thermal and oxidative stability, providing protection from volatilization and environmental conditions. Scanning electron microscopic examination of M1 revealed a closed, pore-free surface. M1 had higher yield and microencapsulation efficiency, showing great commercial potential for its reduced storage, transport, and distribution costs.

Anodic alumina sensor for water activity monitoring in food materials

Water activity is a parameter that characterizes the hydration state of a particular substance and the extent of water binding therein. Many food system technology aspects are related to food system hydration, hence water activity (Aw) measurements can become widely used in technological application. However, widespread implementation of water activity monitoring is hampered by the lack of available measuring instruments. This article provides the examples of potential water activity use in food industry and proposes a method of water activity measurement with a piezoquartz sensor coated with a porous alumina layer.

Application of Dynamic Temperature-Humidity Chamber for Measuring Moisture Sorption Isotherms of Biomaterials as Compared to the Conventional Isopiestic Method

Measurement of water activity and moisture sorption isotherms of foods and biomaterials are important to determine the state of water. In this work, a dynamic temperature-humidity (DTH) controlled chamber was used to measure water sorption isotherm and compared with the conventional isopiestic method. Temperature and relative humidity of DTH chamber can be controlled in the range of -15 to 100°C and 0 to 98%, respectively; thus, measurement of water activity at any point can be measured within the above ranges. The DTH chamber method showed high reproducibility as compared with the conventional isopiestic method when measured isotherms of cellulose, lignin, and hemicellulase were compared at 30°C. Finally, isotherm data of cellulose, lignin, and hemicellulase were generated in the temperature range of 10-90°C using DTH chamber, and these were modelled by BET and GAB equations. The model parameters were correlated with the temperature.

Improving the Nutritive Value and Quality Parameters of Gluten Free Bread by Using Natural and Economical Ingredients

Absence of gluten in gluten free bread is an important technological challenge, in this study sweet whey protein powder and fresh yogurt were added individually and together at 10 and 15 %. (W/W corn flour). Different levels of yogurt and whey protein powder were incorporated into gluten-free bread formulations. Bread quality parameters i.e. chemical, physical, textural, staling rate, water activity, sensory and economical evaluation were performed to assess the nutritional and technological qualities of the free gluten bread. Results confirmed that the yogurt and whey protein addition led to a significant increase in protein, fat, ash, crude fibres, calories, Ce, Fe and Zn content in bread while significant decrease in available carbohydrates comparing with the control. Textural profile analysis showed a decrease in hardness, gumminess and chewiness when whey protein and yogurt were added to bread formula either they added individually or together. The staling rate indicated that whey protein and fresh yogurt caused retarding in the staling rate and the whey protein bread can be kept up to 3 days with good freshness. Whey protein or yogurt addition to bread formula show a significant increase in appearance, crust colour, taste, texture, layer separation and overall score. Rising levels of supplementation with whey protein and yogurt generally caused an increase in all sensory scores of free gluten bread comparing with the control, this improvement was noticed when whey protein and yogurt were added together. Water content and water activity measurements was in the allowance range, so that water activity predicted the stability and keeping safety and quality of the prepared bread. The gluten - free bread was safe for up to 3 days for consumer. Whey protein and fresh yogurt specially when they added together improving the daily diet of celiac people, so whey protein bread and yogurt bread enhanced the nutritional value of gluten free bread such as protein, Ca, Fe and Zn, also it had good efficiency of covering the recommended daily allowances (RDA %). The cost of fortified bread with whey protein and yogurt was increased by 9.84% to 44.09 % as compared with the control cost, but that increase in the cost can be adjusted to consumer by health benefits.

Prediction of Water Activity in Mam&lt;i&gt;ó&lt;/i&gt;n (&lt;i&gt;Filipino sponge&lt;/i&gt;) Cakes by near Infrared Hyperspectral Imaging

Water activity in foods can result in detrimental microbial activity during storage. The usual methods of water activity measurement involve destruction of the sample. Near infrared (NIR) hyperspectral imaging has previously been successfully used as a non-destructive method to determine various physical and chemical characteristics of a variety of foods. Therefore, this method was tested to determine whether it could be used to measure water activity of mamón cakes, a popular sponge cake developed in the Philippines. Individual samples (n = 178) were divided into a calibration set (n=119) and a prediction set (n=59). These samples were tested using NIR hyperspectral imaging (935-1720 nm) with a smoothing spectral pretreatment selected for developing the calibration model. Partial least squares regression was used to establish the model in order to predict the water activity. The results showed the accuracy of the calibration model in prediction that gave a correlation coefficient of 0.767 and the root mean square error of prediction of 0.0130. It was therefore concluded that NIR hyperspectral imaging has a potential for use and application for measuring the water activity of mamón cakes.

The Giant Nucleus Impactor (GNI)—A System for the Impaction and Automated Optical Sizing of Giant Aerosol Particles with Emphasis on Sea Salt. Part I: Basic Instrument and Algorithms

AbstractSize distributions of giant aerosol particles (dry radius larger than 0.5μm, sometimes referred to as coarse-mode aerosol particles) are not well characterized in the atmosphere. Measurements are problematic for these particles because they (i) occur in low concentrations, (ii) have difficulty in passing through air inlets, (iii) may be dry or deliquesced particles, and (iv) if sampled by impaction, typically require labor-intensive methods. In this study, a simple, high-volume impaction system called the Giant Nucleus Impactor (GNI), based on free-stream exposure of polycarbonate slides from aircraft, is described along with an automated optical microscope–based system for analysis of the impacted particles. The impaction slides are analyzed in a humidity-controlled chamber (typically 90% relative humidity) that ensures deliquescence of soluble (typically sea salt) particles. A computer-controlled optical microscope with two digital cameras is used to acquire and analyze images of the aerosol particles. At relative humidities above deliquescence (74% RH for sea salt), such particles will form near-spherical cap solution drops on the polycarbonate slides. The sea-salt mass in each giant aerosol particle is then calculated using simple geometry and published water activity measurements. The system has a sample volume of about 10 L s−1at aircraft speeds of 105 m s−1. For salt particles, the measurement range is from about 0.7μm dry radius to at least 16μm dry radius, with a size-bin resolution of 0.2μm dry radius. The sizing accuracy was tested using polystyrene latex (PSL) beads of known size.

Thermodynamic properties and solubilityof potassium fluoride in aqueous solutions at various temperatures

The experimental and calculated solubilities of potassium fluoride in aqueous solutions were investigated at various temperatures. The experimental solubility of KF in aqueous solutions was determined up to mmax = 17.50 to 25.80 mol kg−1 respectively from 298.15 to 353.15 K. The calculated solubility requires the thermodynamic properties of the binary system based on the water activity measurements. Accordingly, the water activity of KF aqueous solutions were measured from diluted to the saturated solutions, using the hygrometric method at different temperatures. The related thermodynamic properties of KF(aq) were evaluated by the development of ion interaction model. The new binary parameters (β(0)(K,F), β(1)(K,F), and Cφ(KF)) were determined at various temperatures and used to evaluate the solute activity and the osmotic coefficients ranging from 298.15 to 353.15 K. The solubility product of KF(s) (given in lnKsp°) and the standard molar Gibbs energies of dissolution ΔGdiss° were also given at different temperatures.

Measurement and modelling of water activity, density, sound velocity, refractive index and viscosity of the Na2MoO4 + poly(ethylene glycol) + H2O system in the temperature range from 313.15 to 333.15 K

Thermodynamic and physical properties of water activity, density, sound velocity, refractive index and viscosity of unsaturated solutions of Na2MoO4 + PEG 4000 + H2O system and the constituent binary systems at 313.15, 323.15 and 333.15 K were studied. The concentration range of the solutions was from 0.02 to 0.17 mass fraction of Na2MoO4 and from 0.05 to 0.30 mass fraction of poly(ethylene glycol) with an average molar mass of 4000 g/mol. Water activities were correlated with the modified Pitzer model and physical properties were correlated by the Othmer's rule, obtaining in all cases a good agreement between the experimental and correlated data. Water activity predictions for the Na2MoO4 + PEG 2000 + H2O and Na2MoO4 + PEG 4000 + H2O systems were performed with the modified Pitzer and extended UNIQUAC models, respectively, showing that both thermodynamic models can operate independently of the molar mass of the polymer used.

A review, analysis and extension of water activity data of sugars and model honey solutions

Water activity is a physical property measured in the food industry which helps predict shelf life and microbial activity. Honey normally has a water activity less than 0.6, but this can vary with the amount of crystallization in solution. The aim of this work was to obtain relationships, as fundamental as possible, that can be used to predict the water activity of solutions with compositions similar to honey. Water activity measurements of aqueous sucrose solutions have been well analysed in literature using hydration theory. The analysis based on hydration numbers was easily able to show the quality of data previously published, and hence relationships were proposed for the hydration numbers of glucose, fructose, maltose and glycerol. A model was proposed in this study, to predict the water activity of food systems containing high concentrations of sugars and some electrolytes. The model was analysed and validated using mostly literature data supplemented with new experimental data.

Kinetic study of staling in breads with high-amylose resistant starch

High-amylose resistant starch breads were long-stored (11 days) at 20 °C for kinetic analysis of different aspects of the staling process. Bread products were formulated on a French-bread recipe basis and replacing wheat flour by type II resistant starch at different levels: 0% (control), 10% (HM10), 20% (HM20) and 30% (HM30). Experiments included measurements of water activity, moisture loss, amylopectin retrogradation by DSC, crystallinity changes by X-ray diffraction, and firmness by texture analysis. In the presence of resistant starch water loss was slower, allowing amylopectin retrogradation to be more extensive. However, HM10 and HM20 had similar firming behavior to the control, likely due to the similar and adequate quality that these breads showed initially (at day 0). In contrast, samples with high resistant starch content such as HM30 presented a poor-quality and highly filled crumb that led to the highest firmness during storage.