Vapour pressures of CaCl2–NaCl–H2O and MgCl2–NaCl–H2O at 25 °C. Prediction of the water activity of supersaturated NaCl solutions

1978 ◽  
Vol 56 (14) ◽  
pp. 1853-1855 ◽  
Author(s):  
Doan Thi An ◽  
Tjoon Tow Teng ◽  
James Malcolm Sangster
Keyword(s):  
Water Activity ◽  
Static Method ◽  
Polynomial Form ◽  
Concentrated Solutions

Vapour pressures of concentrated solutions (up to I = 14) of the Systems CaCl2 + NaCl + H2O and MgCl2 + NaCl + H2O have been measured at 25 °C by the static method. By means of reverse application of the Reilly–Wood–Robinson and Zdanovskii–Stokes–Robinson equations to these data, water activities of supersaturated NaCl solutions up to ∼15 m have been deduced, and are represented in polynomial form.

scholarly journals Sorption isotherms of Brazil nuts

2019 ◽  
Vol 23 (10) ◽  
pp. 776-781 ◽  
Author(s):  
Fernando M. Botelho ◽  
Nilso J. Boschiroli Neto ◽  
Silvia de C. C. Botelho ◽  
Gabriel H. H. de Oliveira ◽  
Michele R. Hauth
Keyword(s):  
Moisture Content ◽  
Equilibrium Moisture Content ◽  
Water Activity ◽  
Sorption Isotherms ◽  
Static Method ◽  
Acid Solutions ◽  
Brazil Nut ◽  
Brazil Nuts ◽  
Abstract Knowledge ◽  
Sorption Phenomenon

ABSTRACT Knowledge of the water sorption phenomenon in Brazil nut seeds will allow proper handling of this product, especially with regard to adequate conditions for safe storage. Thus, the present study aimed to determine the sorption isotherms (desorption and adsorption) of Brazil nuts, fitting different mathematical models to the experimental data, as well as to examine the hysteresis effect. To obtain the sorption isotherms, the static method was employed at temperatures of 25, 35, 45 and 55 °C and air relative humidities varying from 10 to 80%. The psychrometric conditions of the air were acquired with the aid of acid solutions and specific saturated saline left inside desiccators with the samples. It was verified that for a given isotherm, the equilibrium moisture content of Brazil nuts increases with water activity increment. In addition, at a constant water activity, equilibrium moisture content decreases with temperature increase. The Copace, Henderson and Oswin are the models that best describe the hygroscopicity of the Brazil nut seed for both the adsorption and desorption processes. Hysteresis was more pronounced at lower temperatures and higher values of water activity. The moisture content value for storage at temperatures less than 55 °C, without the risk of fungal development, must be lower than 8.2% (d.b.).

Desorption Isotherm of Mango Soy Fortified Yoghurt

2005 ◽  
Vol 1 (5) ◽  
Author(s):  
Pradyuman Kumar ◽  
H. N. Mishra
Keyword(s):  
Water Activity ◽  
Goodness Of Fit ◽  
Static Method ◽  
Desorption Isotherm ◽  
Percentage Error ◽  
Typical Type ◽  
Sigmoid Curve ◽  
Relative Percentage Error ◽  
Desorption Isotherms ◽  
Residual Plots

Desorption isotherms of three yoghurt samples viz. plain yoghurt, mango soy fortified yoghurt (MSFY) and MSFY containing 0.4 % gelatin stabilizer (MSFYG) were determined by gravimetric static method at 20, 30, 40 and 50 °C in the range of 0.11 – 0.81 water activity. It was found that desorption isotherm of yoghurt samples follow a typical type III sigmoid curve. Experimental data were fitted to five mathematical models i. e. modified Henderson, modified Chung Pfost, Oswin, Smith and Guggenheim-Anderson-deBoer (GAB). Equations were developed for the prediction of the GAB constants as a function of temperature and these equations were used during modeling. Standard error of estimate (SE), mean relative percentage error (P), percent root mean square (% RMS) and trend of residual plots were used to compare the goodness of fit. It was found that the GAB models were acceptable in describing equilibrium moisture content – water activity relationships for yoghurt samples over the entire experimental temperature range.

Solvation properties in iso-acidic media involving phosphoric acid

1988 ◽  
Vol 66 (9) ◽  
pp. 2422-2427 ◽  
Author(s):  
C. Louis ◽  
A. Bebba ◽  
J. Bessière
Keyword(s):  
Carbon Tetrachloride ◽  
Phosphoric Acid ◽  
Water Activity ◽  
Ionic Species ◽  
Concentrated Solutions ◽  
Acidic Media ◽  
Acidic Solutions ◽  
Mineral Acids ◽  
Acidity Level ◽  
Silver Extraction

Concentrated solutions of mineral acids (phosphoric, hydrochloric, perchloric, sulfuric) are characterized, for an equal value of their water activity, by an equal R0(H) acidity level (iso-acidic solutions). By mixing them, we prepare what we call iso-acidic mixtures which keep the same acidity level as the constitutive solutions whatever the proportions; their redox and solvating properties depend both on the nature and on the ratio of the constitutive solutions. Reactivity variations for ionic species: Cl−, Br−,I−, diethyldithiophosphate (LET−), Si(W3Ol0)44−, Si(W3O10)45−, Cu2+, Cu+, Pb2+, Sn2+, Cd2+, Zn2+, Ag+, Fe3+, Fe2+, UO22+, U4+ in the iso-acidic mixtures are characterized by their ƒ solvation-transfer activity coefficients. Relations between ƒ coefficient values and complexation properties are established and it is shown that phosphoric acid has comparatively weak solvating properties toward most species. The possibility for anticipating reaction changes with the iso-acidic mixture composition by using the ƒ coefficients is demonstrated in the case of cadmium ionic flotation with diethyldithiophosphate and silver extraction with dithizone in carbon tetrachloride.

scholarly journals Desorption isotherms and isosteric heat of 'cajuzinho-do-cerrado' achenes

2016 ◽  
Vol 20 (5) ◽  
pp. 481-486 ◽  
Author(s):  
Karine F. Barbosa ◽  
Juliana de F. Sales ◽  
Osvaldo Resende ◽  
Daniel E. C. de Oliveira ◽  
Jacson Zuchi ◽  
...  
Keyword(s):  
Moisture Content ◽  
Water Activity ◽  
National Park ◽  
Linear Regression Analysis ◽  
Isosteric Heat ◽  
Static Method ◽  
Different Temperatures ◽  
Desorption Isotherms ◽  
The One ◽  
Content Range

ABSTRACT The objective of this study was to determine the desorption isotherms of 'cajuzinho-do-cerrado' achenes (Anacardium humile St. Hil.) in various conditions of temperature and water activity, as well as to select the one that best represents the phenomenon and to determine the isosteric heat of desorption. The fruits were collected at the Emas National Park, in the municipality of Mineiros-GO, Brazil, pulped and then subjected to drying in silica gel at temperature of 25 ± 2 °C until the moisture contents of 17.6, 13.6, 11.1, 8.7 and 5.3 (d.b.%). After drying, the desorption isotherms were determined by the indirect static method. The water activity (Aw) was determined at different temperatures, and the achenes were placed in a B.O.D. chamber, regulated at 10, 20, 30 and 40 °C. Data of hygroscopic equilibrium moisture content were fitted to different mathematical models through non-linear regression analysis, using the Gauss-Newton method. The Copace model was the one that best represented the hygroscopicity of 'cajuzinho-do-cerrado' achenes, while the integral isosteric heat of desorption of 'cajuzinho-do-cerrado' achenes for the moisture content range of 4.51 to 13.40 (% d.b.) varied from 2,734.82 to 2,548.49 kJ kg-1.

Acidity level in concentrated mineral acid mixtures. Iso-acidic media

1987 ◽  
Vol 65 (6) ◽  
pp. 1353-1355 ◽  
Author(s):  
C. Louis ◽  
A. Bebba ◽  
J. Bessiere
Keyword(s):  
Water Activity ◽  
Mineral Acid ◽  
Acidity Function ◽  
Concentrated Solutions ◽  
Acidic Media ◽  
Comparison System ◽  
Acidic Solutions ◽  
Complexing Properties ◽  
The Relationship ◽  
Acidity Level

Assuming the relationship between the R0(H) acidity function and the water activity in mineral acid concentrated solutions, iso-acidic solutions are prepared by mixing in all proportion two or three of the acids: H3PO4, HCl, HClO4, H2SO4, H2SiF6. These solutions are characterized by an equal R0(H) acidity level and different redox and complexing properties. Their R0(H) acidity level is determined from potential measurements involving o-chloranil as an H+ indicating system and ferricinium/ferrocene as a comparison system.

Vapour pressures of aqueous solutions of AgNO3 + TlNO3 by the static method at 98.5 °C

1977 ◽  
Vol 55 (10) ◽  
pp. 1713-1719 ◽  
Author(s):  
Marie-Christine Trudelle ◽  
Maurice Abraham ◽  
James Sangster
Keyword(s):  
Free Energy ◽  
Aqueous Solutions ◽  
Water Activity ◽  
Mole Fraction ◽  
Vapour Pressure ◽  
Excess Free Energy ◽  
Static Method ◽  
Present System ◽  
Activity Data ◽  
Bet Isotherm

Vapour pressures of the system (Ag,Tl)NO3 + H2O have been measured at 98.5 °C by the static method over the complete concentration range for Ag/Tl mole ratio = 1.14. The water activity data can be represented by a modified BET isotherm in the range 0.1 < aw < 0.7. The derived BET constants indicate that the salts in this system are very weakly hydrated, probably less so than (for example) CsNO3. The linearity of vapour pressure with water mole ratio RH, found previously by Tripp and Braunstein for (Li,K)NO3 + H2O, is absent in the present system. The Henry's law constant for water dissolved in molten (Ag,Tl)NO3 has been deduced. The excess free energy of the system is positive at all concentrations and shows a maximum of 117 cal/mol at water mole fraction 0.66.

scholarly journals Evaluation of Norrish’s Equation for Correlating the Water Activity of Highly Concentrated Solutions of Sugars, Polyols, and Polyethylene Glycols

2008 ◽  
Vol 3 (1) ◽  
pp. 87-92 ◽  
Author(s):  
Rosa Baeza ◽  
Adriana Pérez ◽  
Virginia Sánchez ◽  
María C. Zamora ◽  
Jorge Chirife
Keyword(s):  
Water Activity ◽  
Polyethylene Glycols ◽  
Concentrated Solutions

Obtaining and Characterisation of Starch-Based Edible Films Incorporating Honey, Propolis and Bee Bread

2019 ◽  
Vol 23 (2) ◽  
pp. 193-198
Author(s):  
Monica Mironescu ◽  
Laura Fratila ◽  
Alexandru Hupert ◽  
Ion Dan Mironescu
Keyword(s):  
Water Activity ◽  
Mechanical Characteristics ◽  
Edible Films ◽  
Ash Content ◽  
Colour Intensity ◽  
Sensorial Analysis ◽  
Physical Chemical ◽  
Control Film ◽  
Bee Bread

Abstract This research investigates the physical-chemical, sensorial and mechanical characteristics of starch-based edible films incorporating three types of bee hive products: honey, propolis and bee bread, in concentrations varying from 1% to 3%, reported to starch. The results indicates an increasing of films moisture, water activity, ash content and acidity, in the order: honey<propolis<bee bread, all values increasing with the increasing of hive products percentage into the control film; aw is remaining at very low values, under 0.4. Sensorial analysis indicated honey as the better suited for improving taste and flavour and bee bread for increasing colour intensity of the films; the sensorial characteristics are maintained during 30 days of films storage, in all cases. Compared with the control starch-based film (which is elastic, brittle and hard), the films containing 2% bee hive products are elasto-plastic and more resistant to penetration, the resistance increasing in the order: bee bread<propolis<honey.

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