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Moisture sorption isotherms of dehydrated whey proteins  [cached]
Suzana Rimac Brn?i?,Vesna Lelas,Zoran Herceg,Marija Badanjak
Mljekarstvo , 2010,
Abstract: Moisture sorption isotherms describe the relation between the moisture content of the dry material (food) and relative humidity of the surrounding environment. The data obtained are important in modelling of drying process conditions, packaging and shelf-life stability of food that will provide maximum retaining of aroma, colour and texture as well as nutritive and biological value. The objective of this research was to establish the equilibrium moisture content and water activity, as well as monolayer value of two commercial powdered whey protein isolates before and after tribomechanical micronisation and enzymatic hydrolysis, respectively. At the same time it was necessary to evaluate the best moisture sorption isotherm equation to fit the experimental data. The equilibrium moisture contents in investigated samples were determined using standard gravimetric method at 20 °C. The range of water activities was 0.11 to 0.75. The monolayer moisture content was estimated from sorption data using Brunauer-Emmett-Teller (BET) and Guggenheim-Anderson-de Boer (GAB) models. The results have shown that tribomechanically treated whey protein isolates as well as protein hydrolizates had lower monolayer moisture content values as well as higher corresponding water activity. Therefore, in spite of the fact that they have lower moisture content, they can be storage at higher relative humidity compared to untreated samples. BET model gave better fit to experimental sorption data for a water activity range from 0.11-0.54, while GAB model gave the closest fit for a water activity to 0.75.
Thermodynamic Properties and Moisture Sorption Isotherms of Argania spinosa and Zygophyllum gaetulum  [PDF]
A. Idlimam,A. Lamharrar,N. Abdenouri,S. Akkad
Journal of Agronomy , 2008,
Abstract: Almond of Argania spinosa and Zygophyllum gaetulum moisture sorption isotherms were determined within the range of 0.1-0.9 water activity at three temperatures (30, 40 and 50°C), using saturated salt solutions dynamic method. Sorption isotherms of Argania spinosa and Zygophyllum gaetulum have, respectively a sigmoid shape (Type 2) and (Type 5). The GAB, modified Oswin, modified Henderson, Peleg, modified BET and modified Halsey models were tested to fit the experimental data. In relation to the isotherm models the best models were, GAB, modified Oswin and Peleg obtaining minor values of % mean relative errors and higher correlation coefficient. Isosteric heats of sorption were calculated through direct use of moisture isotherms by applying the Clausius-Clapeyron equation. The differential enthalpy and entropy decreased with increasing moisture content and were adequately characterized by polynomial function. A plot of differential heat versus entropy satisfied the enthalpy-entropy compensation theory. The comparison between the sorption isotherms and thermodynamic properties of A. spinosa almond and Z. gaetulum was studied.
Moisture sorption isotherms and isosteric heat determination in Chilean papaya (Vasconcellea pubescens)
Vega-Gálvez, Antonio;Palacios, Marlene;Lemus-Mondaca, Roberto;Passaro, Catarina;
Química Nova , 2008, DOI: 10.1590/S0100-40422008000600026
Abstract: the moisture sorption isotherms of chilean papaya were determined at 5, 20, and 45 oc, over a relative humidity range of 10-95%. the gab, bet, oswin, halsey, henderson, smith, caurie and iglesias-chirife models were applied to the sorption experimental data. the goodness of fit of the mathematical models was statistically evaluated by means of the determination coefficient, mean relative percentage deviation, sum square error, root-mean-square error, and chi-square values. the gab, oswin and halsey models were found to be the most suitable for the description of the sorption data. the sorption heats calculated using the clausius-clapeyron equation were 57.35 and 59.98 kj·mol-1, for adsorption and desorption isotherms, respectively.
Moisture sorption isotherms of fresh and blanched pumpkin (Cucurbita moschata)
Molina Filho, Lucídio;Gon?alves, Ana Karla Rebes;Mauro, Maria Aparecida;Frascareli, Elen Cristina;
Ciência e Tecnologia de Alimentos , 2011, DOI: 10.1590/S0101-20612011000300025
Abstract: moisture desorption isotherms of fresh and heat blanched pumpkins (cucurbita moschata) were determined at three temperatures (30, 50 and 70 °c), using the standard, static-gravimetric method. the gab, oswin, bet, halsey, and henderson models were tested and, with the exception of the henderson model, showed satisfactory fits to the experimental data. the gab model was used to analyze the fitting ability to describe the isotherm type. the shape of the desorption isotherms of fresh and blanched pumpkin at 30 and 50 °c was intermediate to types ii and iii, and at 70 °c it was of type ii for the blanched pumpkin and close to type ii for the fresh sample. the influence of blanching on the decrease in equilibrium moisture was very small compared to the fresh samples and it was related to the loss of soluble solids during the pre-treatment. the isosteric heat of sorption measures indicated that a larger amount of heat was required to remove the water from the fresh samples than from the blanched ones.
Relationship between Solubility, Moisture Sorption Isotherms and Morphology of Chitosan/methylcellulose Films with Different Carbendazim Content  [cached]
Dang Thi Mong Quyen,Joomwong Adisak,Pornchai Rachtanapun
Journal of Agricultural Science , 2012, DOI: 10.5539/jas.v4n6p187
Abstract: Chitosan and methylcellulose are popular biopolymer materials that are used in films and as coatings for food products. The addition of carbendazim which is an antimicrobial agent to these biopolymers can lead to changes in solubility, moisture sorption isotherm and the morphology of the chitosan/methylcellulose films (C/MC) at various carbendazim contents (0.8; 1.6; 3.2 and 4.8 g/100 g of solid C/MC). C/MC films with carbendazim had lower solubility values than control films. The moisture sorption isotherms of C/MC films incorporated with carbendazim were examined for water activities in the range of 0.11-0.86 at 25±0.5oC. These isotherms showed that carbendazim content affected the equilibrium moisture content (%EMC) of the films and the %EMC of all films dramatically increased above aw=0.66. The C/MC films incorporated with carbendazim exhibited lower %EMC than that of the control films under all relative humidity conditions. The changes of the moisture sorption isotherms of the C/MC films at different carbendazim contents can be related to changes in cross-section morphology of these films. By understanding the behavior of the sorption isotherms, it is possible to predict the moisture sorption properties of C/MC films via moisture sorption empirical models. The Guggenheim–Anderson–deB er (GAB), Brunauer-Emett-Teller (BET) and Oswin sorption models were used to fit the experimental data. Our results show that the GAB model was the best-fit model for C/MC films incorporated with carbendazim at 25±0.5oC.
Moisture Sorption Isotherms of Pigeonpea (Cajanas cajan) Grain and its Dehulled Splits (Dhal)
R.K. Vishwakarma,R.K. Goyal,V.K. Bhargav
American Journal of Food Technology , 2007,
Abstract: Moisture sorption isotherms of pigeonpea grain (Cajanas cajan) and dehulled splits of pigeonpea (dhal) at 10, 20, 30, 40 and 50°C were derived. The sorption data were treated according to many well-known sorption isotherm equations. The goodness of fit was evaluated on the basis of criteria such as the residual sum of squares, standard errors of estimates and mean relative deviation. It was found that the modified Chung-Pfost equation was the most satisfactory model for representation of the EMC data for pigeonpea grain up to 80% ERH. Modified Henderson equation was the most satisfactory model for representation of the EMC data for pigeonpea dhal.
Kinetics of Moisture Uptake of Osmo-Foam-Mat Dried Mango Powders and Application of Sorption Isotherms to Shelf-Life Prediction
J.S. Alakali,C.C. Ariahu,E.I. Kucha
American Journal of Food Technology , 2009,
Abstract: The kinetics of moisture uptake by foam-mat dried powder from mango pulp was evaluated at four temperatures (10, 20, 30 and 40°C) and two relative humidities (55 and 80%), while moisture sorption data for shelf life prediction was determined at the same temperatures and eight water activities ranging from 0.032-0.925. Result show that the rate of moisture uptake was highly in the first 2 to 4 h at any given storage temperature and relative humidity. Moisture uptake generally decreased with increase in storage temperature but did not show a defined trend after the first few hours. The rate of moisture uptake was higher at 55 than at 80% storage relative humidities. Effective diffusivities of samples incorporated with foam stabilizes were higher due to high porosity. Moisture uptake obeyed the penetration theory indicating that the process was Fickan. Predicted shelf-life of the powders generally decreased with increased storage relative humidity and temperature. The predicted shelf-life of the powders was generally above 365 days. The shelf life of powders incorporated with foam stabilizers was generally shorter as they had lower equilibrium moisture content. Predicted shelf life of the powders was longer in packaging materials of low permeability to thickness ratio.
MODELS OF SORPTION ISOTHERMS FOR FOOD: USES AND LIMITATIONS
ANDRADE P,Ricardo D; LEMUS M,Roberto; PéREZ C,Carmen E;
Vitae , 2011,
Abstract: moisture sorption isotherms describe the relationship between moisture content and water activity in food. this work presents basic concepts related to the sorption thermodynamics of water, the classification of isotherms, ''uses and limitations of the models'', and measurement of sorption isotherms for food materials. the most commonly used models in food are brunauer-emmett-teller and guggenheim-anderson-de boer. the success of the brunauer-emmett-teller model is rather qualitative, considering that almost all cases are linear only in a limited rank of water activity from 0.05 to 0.45, as its main applicability is the estimation of surface areas. and, the use of the guggenheim-anderson-de boer model is generalized by its theoretical bases, mathematical simplicity, and ease to interpret; but it is not frequently used when the water activity greater than 0.93.
Sorption Isotherms of Some Nigerian Dry Condiment Powders
V.N. Enujiugha,S.O. Iyiola,M.O. Oluwamukomi,S. Gbadamosi,I.B. Oluwalana,L.O. Lalude
Journal of Food Technology , 2013,
Abstract: The moisture sorption isotherms of dehydrated flours of four commonly consumed Nigerian condiments (namely, ugba, okpeye, ogiri and iru) were determined. The dry milled products were kept at three separate temperatures (10, 30 and 40 C) and at four different relative humilities using saturated salt solutions (RH 20, 30, 50, and 70%) for a period of 21 days. Both the initial and equilibrium moisture contents were determined on the products and the data obtained were used to construct moisture sorption isotherm curves. The results reveal that higher storage temperature gave lower sorption capacities for the condiment powders. Also, the rate of moisture absorption increased at the monolayer at all the storage temperatures considered. At ambient and higher storage temperatures, ogiri had the relatively longest shelf life, followed by okpeye, then iru and finally ugba.
Sorption Isotherms and Isosteric Heats for Algerian Dates Deglet Nour  [PDF]
A. Ferradji,M.A.A. Matallah
American Journal of Food Technology , 2012,
Abstract: The stability of organoleptic quality of dates Deglet Nour during storage is affected by the water activity (aw). The purpose of this study is to determine the optimal moisture in order to preserve the quality of dates using the technique of sorption isotherms. Moisture sorption isotherms of the date "Deglet Nour" were determined at 25, 30 and 40°C by balancing the atmosphere with relative humidity fixed by dilute solutions of sulphuric acid. The isotherms were fitted to Guggenheim-Andderson-Boer (GAB) and BET sorption equations. The GAB and BET equations provided a good fit to experimental data (<6% RMS). Monolayer moisture contents for date Deglet Nour was 10.07%. The enthalpy of sorption of the monolayer at 25°C was 113.03 kJ mol-1. Heat of desorption estimated using the Clausius-Clapeyron equation was 75 kJ mol-1.
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