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Moisture Sorption Isotherms for Mungbean (vigna Radiata L)

M.M.I. Chowdhury
Department of Farm Mechanization, Patuakhali Science and Technology University, Patuakhali 8600, Bangladesh

M.D. Huda
Farm Machinery and Post Harvest Technology Division, Bangladesh Rice Research Institute, Gazipur 1701, Bangladesh

M.A. Hossain
Machinery Repair and Maintenance Division, Bangladesh Agricultural Research Institute, Gazipur 1701, Bangladesh

M.S. Hassan
Machinery Repair and Maintenance Division, Bangladesh Agricultural Research Institute, Gazipur 1701, Bangladesh

Abstract/ Executive Summary:

Adsorption equilibrium moisture contents of mungbean were determined by standard gravimetric method at the temperature of 20, 30, 40 and 50 C and the relative humidity range of 11–97%. The effects of temperature were found to be significant and all the isotherms were found sigmoid in shape. Five widely used three parameters sorption isotherms equations such as modified Henderson, modified Chung–Pfost, modified Oswin, modified Halsey and GAB were used to fit the experimental data. The modified Chung–Pfost and modified Oswin equations have the ability to describe well the EMC/ERH relationship selected range of the relative humidity and temperature. The modified Chung–Pfost equation is the most suitable in M = f(rh,T) form while the modified Oswin equation is the most suitable in rh = f(M,T) form. 2005 Elsevier Ltd. All rights reserved.

Keywords: Moisture sorption isotherms, Mungbean, Modified Chung–Pfost and modified Oswin equations

Location: Patuakhali Science and Technology University, Patuakhali

Start Date:

End Date:

Program Area: Postharvest and Agro-processing

Commodity: Mungbean

Objectives:

To determine the sorption isotherms of mungbean experimentally and then fitting these data in most commonly used isotherm equations in both M = f(rh,T) and rh = f(M,T) forms.

Methodology:

The standard gravimetric method was used to determine the adsorption isotherms of mungbean. An air tight cylindrical plastic container, 115 mm diameter and 135 mm height, containing saturated salt solutions was placed at an environment of constant temperature in an incubator. The equilibrium relative humidities of the saturated salt solutions were checked with a humidity/ temperature sensor (model HT-3003, Philips). A digital temperature controller (model XMTJ) provided the desired temperature (accuracy ±1 C). A mini fan of 60 mm diameter (3 V, 0.25 A) was fitted inside the plastic container to provide continuous circulation of the air. Values for relative humidity of saturated salt solutions were obtained from the works of Wexler and Hasegawa (1954) and Young (1967) and are listed . The samples of 5 g dry mungbean of variety BARI-1 were weighed into a cylindrical nylon box (50 mm diameter and 40 mm height) and suspended over the saturated salt solutions in the container. The container was made air tight with a plastic lid. The container was then placed in the oven maintained at the desired constant temperature and allowed to equilibrate. The selected temperatures were 20, 30, 40 and 50 C with ±1 C variation. The weight of each sample was checked with an electronic balance (sensitivity = 0.01 g) initially after 12 h and then at 6 h intervals until the weight became constant. For adsorption equilibrium moisture content about 2–3 days were required to reach the equilibrium of the sample with the environment maintained by saturated salt solutions. The moisture content of each sample was then determined by drying the sample in a ventilated air-circulated oven at 105 C for 24 h. The procedure was repeated for all the15 samples at five different relative humidity and three replications. The criteria used to select the most appropriate sorption model were the degree of fit to the experimental data and the simplicity of the model. Therefore, five widely used empirical equations (the modified Henderson, modified Chung–Pfost, modified Halsey, modified Oswin and GAB equations) were chosen to fit the experimental data to evaluate their utility for mungbean. They were also chosen because they could all be written explicitly in the rh = f(M,T) and M = f(rh, T) forms. A non-linear multiple regression analysis (SPSS 10.0) was used to fit the experimental data in the above models as shown in Table 2 with description of the functional forms. The package was based on minimizing the residual sum of squares (RSS) between the predicted and measured data. The sum of square error (SEE) was used to measure the accuracy of the model and the coefficient of determination (R²) to show the variability between the predicted and measured data. In a good mathematical model, the coefficient of determination should be closed to 1 (one) and sum of square errors should be closed to 0 (zero). The suitability of the equations was evaluated and compared using residual sum of square (RSS), standard error of estimate (SEE) and coefficient of determination (R²). The equation giving the smallest RSS and SEE and highest R² values was considered to be the best fitted equation.

Source of Information: Journal of Food Engineering 74 (2006) 462–467

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The methodology and equipment used allowquicker collection of EMC data than conventional gravimetric method over the full range of relative humidity. The significant temperature effects were found and all the isotherms were sigmoid in shape. Among the sorption isotherm equations were used to fit the experimental data of mungbean, both the modified Chung–Pfost and modified Oswin equations have the ability to accurately describe the EMC/ERH relationship for mungbean over a broad range of the relative humidity and temperature (Figs. 4 and 5). The modified Chung–Pfost equation is the most suitable in M = f(rh,T) form while the modified Oswin equation is the most suitable in rh = f(M,T) form.

Knowledge Management: Journal