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Modeling of Moisture Adsorption Isotherm of Selected Commercial Flours of Bangladesh

Md. Wadud Ahmed
Department of Agricultural Engineering, Sher-e-Bangla Agricultural University, Dhaka-1207, Bangladesh

Mohammad Gulzarul Aziz
Department of Food Technology and Rural Industries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Md. Nazrul Islam
Department of Food Technology and Rural Industries, Bangladesh Agricultural University, Mymensingh-2202, Bangladesh

Abstract/ Executive Summary:

The moisture adsorption behavior is a fundamental knowledge in the processing and storage of food materials. In this paper, the experimental adsorption behavior of wheat, rice and corn flours were compared with five widely recommended adsorption models (BET, GAB, Oswin, Smith and Halsey) in the literature. From the sorption data, monolayer moisture content of wheat, rice and corn flours were estimated as per BET and GAB models. For all flours, GAB model gave higher monolayer moisture content compare to the BET model. Linear regression analysis was done to determine the model constants where all models were compared using regression coefficient and standard error of the estimate. It was observed that there is no single model that could describe accurately the sorption isotherm over the whole range of water activity (a_w) and for all types of flours. BET model was found as the best model for the prediction of equilibrium moisture content (EMC) of the most stable region (i.e. EMC corresponding to a_w range below 0.52) but it was not suitable at a_w above 0.52. The GAB model was found to be the most suitable to predict the EMC for wide range of water activity (0.11 to 0.93).

Keywords: Wheat flour, Rice flour, Corn flour, Sorption isotherm, Equilibrium moisture content

Location: Bangladesh Agricultural University campus, Mymensingh

Start Date:

End Date:

Program Area: Food Safety and Security

Commodity: Flour

Objectives:

i). Modeling of moisture adsorption data employed by different model equations.

ii). Finding the best model based on the validity of the models by experimental data.

Methodology:

Locally available commercial wheat flour (Bosundhora atta), corn flour (Noor-Nobi) and milled rice flour (BRRI-28 variety) purchased from the local market of Bangladesh Agricultural University campus, were used in this study. Moisture contents (As per AOAC, 1990) of raw samples were 0.1383 kg.kg^-1(d.b) for wheat flour, 0.138 kg.kg^-1(d.b) for rice flour and 0.1286 kg.kg^-1(d.b) for corn flour. The EMC of selected flours at different humid condition was determined by the static gravimetric method at temperature 30 °C. Each flour, with a triplicate sample, were put into the ceramic crucible and placed inside the glass desiccator. The saturated salt solutions were used to maintain a specific water activity inside the desiccator. The saturated salt solution of LiCl, KC₂H₃O₃, MgCl₂6H₂O, K₂CO₃, Mg(NO₃) 2.6 H₂O, CaCl₂, NaCl₂, KCl and KNO₃ were used to maintain a specific of 0.11, 0.2, 0.33, 0.44, 0.52, 0.68, 0.75, 0.85 and 0.93 respectively. The Genlab Incubator (Model M75CPD) was used to maintain desiccator temperature 30°C with deviation ±1°C. When the constant weight of the sample was reached, within maximum 4 weeks, the equilibrium moisture content (EMC) of the samples was determined by AOAC (1990) method.

Source of Information: The Agriculturists 16 (2): 35-42 (2018)

Article Link (Online Journal): DOI: http://dx.doi.org/ 10.3329/agric.v16i02.40341

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The five sorption models (BET, GAB, Oswin, Smith and Halsey) were used to predict the equilibrium moisture content at different water activities. From the moisture sorption isotherm data, the monolayer moisture content was estimated by BET and GAB model. It was found that the GAB equation gave much higher value of monolayer moisture content compared to those for all flour types obtained from BET equation. No single equation describes accurately the sorption isotherms over the whole range of relative humidity for all types of flours. However, based on the study the GAB model was found to be more appropriate to predict the EMC according to statistical parameters for the wide range of water activity.

Knowledge Management: Journal