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Moisture Sorption Isotherms for Lentil (lens Culinaris L)

M.D. Hudar
Farnr Machinery and Postharvest Technology Division, Bangladesh Rice Research Institute, Gazipur-1701.

M.M. Islams
Planning and Evaluation Division, Bangladesh Rice Research Institute, Gazipur-1701.

M.S. Alama
Plant Breeding Division, Bangladesh Rice Research Institute,.Gazipur-1701.

M.A. Hossain
Farm Machinery and postharvest Process Engineering Division, Banglidesh Agricultural Research Institute, Gazipur-1701.

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

Abstract/ Executive Summary:

Adsorption equilibrium moisture contents of lentil were determined at four different temperature of 20, 30, 40 and 50^oC and the relative humidity range of ll to 97% using gravimetric dynamic method. 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 Oswin equation has the ability to describe well the EMC/ERH relationship at selected rage of the relative humidity and temperature. The modified Oswin equation is the most suitable in both M - f (rh,T) and rh = f (M, T) form. The agreement between experimental and calculated values was found to be satisfactory.

Keywords: Lentil, Sorption isotherms, Moisture

Location: Bangladesh Institute of Nuclear Agriculture.

Start Date: 01-05-2006

End Date: 30-08-2007

Program Area: Postharvest and Agro-processing

Commodity: Lentil

Objectives:

To determine the sorption isotherms of lentil 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 lentil seeds of the BINA-I variety grown in 2006-07 year (collected from the Bangladesh Institute of Nuclear Agriculture) were used for this experiment. The collected freshly harvested seeds was sun dried below at moisture content l0 (% d.b.) and stored at ambient temperature up to use (e.g. 2 months) of these seed for the experiment. Experimental procedure: The adsorption isotherms of lentil were determined by a standard dynamic gravimetric method, using an air tight cylindrical plastic container having 115 mm diameter and 135 mm height, containing saturated salt solutions was placed at an environment of constant temperature and relative humidity in an incubator. Six saturated salt solutions were used to maintain constant water activities at four temperatures, 20, 30, 40 and 50⁰C. 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 equilibrium relative humidities of the saturated salt solutions were checked with a humidity and temperature sensor. A digital temperature controller (model XMTJ) provided the desired temperature (accuracy +1⁰C) is used. 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. The samples of 5 g dry lentil 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 50⁰C with +l^oC variation. The weight of each sample was checked at 6 hour intervals until the weight became constant. For adsorption equilibrium moisture content about 2 to 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 ⁰C for 24 hours . The procedure was repeated three times for all the 18 samples at six different relative humidity. Isotherm equation and fitting method: 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 lentil. 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 11.5) was used to fit the experimental data with the above mentioned 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 I (one) and sum of square errors should be closed to 0 (zero).

Source of Information: The institution of Engineers Bangladesh,Vol-38/AE, No-1,June 2000.

Article Link (Online Journal):

Funding Source:

Total Budget (Tk.) :

Achievement/Findings:

The dynamic gravimetric method was used allow quicker collection of EMC data than static 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 lentil, the modified modified Oswin equations have the ability to accurately describe the EMC/ERH relationship for lentil over a broad range of the relative humidity and temperature in both form of M =f (rh,T) and rh =-f (M, T) form and the modified Halsey equation was the second best sorption equation.

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