Experimental study and modelling of water sorption/desorption isotherms on two agricultural products: Apple and carrot (original) (raw)
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Sorption isotherms and isosteric heat of sorption for grapes, apricots, apples and potatoes
Lebensmittel Wissenschaft Und Technologie, 2004
Moisture sorption isotherms of grapes, apricots, apples and potatoes were determined at 30 C, 45 C, and 60 C using the standard, static-gravimetric method. Six two-parameter and five three-parameter sorption models were tested to fit the experimental data. A nonlinear regression analysis method was used to evaluate the constants of the sorption equations. The Halsey equation gave the best fit to the experimental sorption data for all materials tested over the range of temperatures and water activities investigated. The GAB model gave also the closest fit to the sorption data for potatoes and grapes. The agreement between experimental and predicted values of these models was found to be satisfactory. The isosteric heat of desorption and adsorption of water determined from the equilibrium data using the Clausius-Clapeyron equation.
Drying characteristics and sorption isotherm of tomato slices
Journal of food engineering, 2006
The drying behaviour of tomato slices was investigated at 45, 60 and 75 °C. Three falling rate periods were observed with diffusion coefficients in the range 3.72–12.27 × 10−9 m2 s−1. The water vapour sorption isotherm of dehydrated tomato slices in the water activity (aw) range of 0.08–0.85 was also determined at three temperature levels, i.e., 25, 30 and 40 °C. Five sorption models were fitted with the adsorption data generated from the gravimetric method. GAB and Oswin models describe the adsorption characteristics of dehydrated tomato at 25 °C better than other models with GAB model being the best applicable model. The isosteric heat of adsorption decreases with increasing moisture.
Sorption isotherms and moisture sorption hysteresis of intermediate moisture content banana
Journal of Food Engineering, 2008
Sorption isotherms of dried or intermediate moisture content (IMC) products are most important to model moisture uptake during storage and distribution. Working isotherms of IMC bananas were determined at five different temperatures (10, 15, 20, 30 and 40°C). Desorption and adsorption isotherms were determined at 10 and 40°C. All the sorption curves were found to be Type II, with non-zero moisture content (approximately 3-9% db for different temperatures) when the water activity was zero. Different models were fitted to the data and it was found that the best results were obtained with a modified Freundlich equation (valid from 0.06 to 0.76 water activity). The dependence of the models constants on temperature was investigated and the secondary models were built accounting for the effect of a w and temperature on the samples moisture content (R 2 = 99%). Hysteresis was observed at 10°C and 40°C, but the effect was greater at 10°C. The net isosteric heat of sorption (working isotherms) varied from 0.85 kJ g À1 mol À1 to 7.67 kJ g À1 mol À1 , decreasing with increasing moisture content. This effect was well described by an exponential function (R 2 > 99%). These results provide reliable experimental data on sorption isotherms which is important for designing an optimized packaging system.
Moisture Sorption Isotherms and Thermodynamic Properties of Carrot
International Journal of Food Engineering, 2011
Urtica dioica is a Moroccon endemic plant of used for its virtues in traditional medicine. Thus, it is necessary to study the effect of preservation processes on the storage conditions of the plant. The static gravimetric method was used to determine sorption isotherms of Urtica dioica leaves at three temperatures (40, 50 and 60 °C) and in the range of water activity (w a) ranging from 0.0572 to 0.898. Six mathematical models were used to fit the experimental data. The Enderby and Peleg models were found to be the most suitable for describing the sorption curves. The optimal water activity for conservation of Urtica dioica leaves was determined. Isosteric heats of desorption and adsorption were calculated by applying the Clausius-Clapeyron equation to the sorption isotherms at different temperatures; it decreased with increasing moisture content. A linear relation exists between the enthalpy and entropy of the sorption reaction.
Moisture Sorption Isotherms and Isosteric Heats of Sorption of Tomato Slices
2015
The adsorption and desorption isotherms of tomato were determined by static gravimetric method at different temperatures, in the range from 30°C to 60°C and relative humidities of 5%–85%. The curves obtained can be considered as type II according to the Brunauer–Emmett–Teller classification. Equilibrium moisture content data were correlated by different mathematical models usually applied to foodstuffs (GAB, Peleg, Smith, Caurie, Oswin...). A non-linear least square regression analysis was used to evaluate the models constants. The best fit of the experimental data was obtained with GAB and Peleg models. The Chung-Pfost model was the least adequate. Hysteresis was also observed at all temperatures investigated. The isosteric heat of sorption was determined using the Claussius–Clapeyron equation, and it decreases with increasing moisture content at the average temperatures investigated.
Desorption isotherms of fresh and osmotically dehydrated apples (Golden delicious)
Revue des énergies …, 2009
The each year larger apples national production, as well as, the higher demand of the food industry for such pre-treated dried fruits, has conducted researchers to better investigate this field. Osmotic dehydration is a partial dehydration through an osmosis process which involves immersing fruits for a given period of time in a hypertonic solution, here a sugar solution. Sugar impregnation allows an inhibition of polyphenoloxydase and prevents the loss of volatile compounds during the dehydration process. It is also used as a pretreatment process to improve the sensory quality of dried products. This work is divided in two main parts. First, an experimental determination of the desorption isotherms of fresh and osmotically dehydrated apples at different sugar concentrations (0 %, 30 % and 40 % w/w) was conducted. A static gravimetric method, based on the use of 9 saturated salts solutions was used to determine the sorption isotherms of fresh apple and apple subjected to osmo-dehydration processes in sucrose syrup solution at 30 % and 40 % concentration and at three different temperatures: 30, 40 and 50 °C. The fresh apple isotherms showed a type III sigmoid shape, with a decrease of the equilibrium moisture content with increasing temperature at constant relative humidity. However, in the water activity below 0.6, temperature effect seems to be negligible. Several models were adjusted to the experimental sorption data and the GAB equation gave the best fit. Sorption isotherms curves of osmotically dehydrated apples showed the same shape and for a constant water activity the equilibrium water content decreased with increasing sugar concentration. Thus, for 40 %, sucrose solution, the equilibrium water content is lower for the same equilibrium RH. Finally, Mathematical prediction of the experimental isotherms of sucrose treated apples may be satisfactorily done using the GAB model.
Sorption in 2020s
Moisture sorption characteristics of agricultural and food products play important roles in such technological processes as drying, handling, packaging, storage, mixing, freeze-drying and other processes that require the prediction of food stability, shelf life, glass transition and estimation of drying time and texture and prevention of deteriorative reactions. They are useful in the computation of thermodynamic energies of moisture in the products. An understanding of moisture sorption phenomena in products, moisture sorption isotherm (MSI) determination techniques and moisture sorption isotherm model evaluation procedures would be useful in the development or selection, modeling and controlling as well as optimization of appropriate processes to make for enhanced efficiency. The phenomena addressed in this chapter are equilibrium moisture content (EMC)-water activity (a w) relationships and MSI types, temperature influence on isotherms and occurrence of moisture sorption hysteresis. MSI measurement techniques highlighted are the gravimetric, vapor pressure manometric (VPM), hygrometric and inverse gas chromatographic and the use of AquaLab equipment. Commonly used moisture sorption isotherm models (BET, GAB, modified GAB, Hailwood-Horrobin, modified Hailwood-Horrobin, modified Halsey, modified Henderson, modified Chung-Pfost and modified Oswin) were selected, and their evaluation procedures using moisture sorption data were outlined. Static gravimetric technique involving the use of saturated salt solution appears to be the most widely used and recommended method of determining the EMC of agricultural and food products. Most of the MSI models can be fitted to moisture sorption data thorough linearization by logarithmic transformation, while others can be solved using such expression as second-order polynomial. Model goodness of fit can be determined using standard (SE) error of estimate, coefficient of determination (R 2), mean relative percentage deviation (P) and fraction explained variation (FEV). The acceptance of a model depends on the nature of its residual plots. A model is considered acceptable if the residual plots show uniform scatter around the horizontal value of zero showing no systemic tendency towards a clear pattern. A model is better than another model if it has lower SE, lower P, higher R 2 and higher FEV. Although it appears as if a generalized MSI model is yet to exist, it is recommended that the Ngoddy-Bakker-Arkema (NBA) model should be given thorough going and extensive testing on the MSI of different categories of food as it could prove true to its generalized model posture due to the fundamental nature of its derivation.
Journal of Horticultural Science & Biotechnology, 2009
The aim of our work was to measure sorption isotherms on freeze-dried and convectively-dried fruits (apple cv. Idared; sour cherry cv. English Morello; blackcurrant cv. Tiben), previously osmotically dehydrated in fructooligosaccharide solution, or concentrated apple juice. Isotherms were fitted using the Guggenheim-Anderson-de Boer Model. In none of the cases studied was isotherm non-continuity in the vicinity of the initial value of a w observed. All isotherms, classified as type III, demonstrated an increase in the equilibrium water content, along with an increase in water activity. A higher water content was observed in lyophilised material compared to material dried by convection. The water content in the monolayer (100 g-1 dry matter) ranged from 12.0 g for dried apple, to 17.0 g for dried sour cherry. These values can be considered as optimal in order to ensure safe storage conditions. The dried fruits should therefore be kept in a water activity range of 0.45-0.54 for lyophilised, and 0.46-0.63 for convectively-dried material.
Sorption Isotherm Behavior of Osmoconvectively Dehydrated Carrot Cubes
Journal of Food Processing and Preservation, 2006
Carrot cubes, osmotically pretreated with aqueous sodium chloride (10%, w/v), sucrose syrup (55°Brix), and mixture of sucrose and sodium chloride (50°Brix + 10%, w/v), were convectively dehydrated at 65C temperature up to final moisture content of 4-5% (wet basis). To study their equilibrium moisture content (EMC) behavior, the dehydrated carrot cubes were stored at temperature ranging from 10 to 50C and relative humidity ranging from 15-95% using static desiccator technique. Five isotherm equations, viz, Chung-Pfost, modified Henderson, modified Halsey, modified Oswin and modified exponential were applied to examine the data. Among the applied models, modified Oswin model was best fit for control (untreated) and salttreated samples, modified Hesley model for sucrose-treated samples and twoterm exponential model for mixture of sucrose-salt treatment over the entire range of relative humidity and temperature. The EMC values of cubes osmotically pretreated with sodium chloride solution were highest among all pretreatments, and were lowest for control (unosmosed) samples.