Abstract
ABSTRACT ‘Okara’ is the insoluble part obtained after the aqueous extraction of soybeans, generated in large quantities as a by-product of the ‘tofu’ industry or soybean water-soluble extract. This work aimed to study ‘okara’ convective drying kinetics, determine the effective diffusion coefficient, and obtain activation energy and thermodynamic properties under different drying conditions. The by-product ‘okara’ was obtained from the processing of BRS 257 soybean water-soluble extract, homogenized and dried in a forced-air oven at temperatures of 40, 50, 60 and 70 °C until constant weight. Among the analysed models, Wang & Singh was selected to represent the drying phenomenon. Effective diffusion coefficient increased with the temperature rise, and the activation energy for the net diffusion in the drying was 28.15 kJ mol-1. Enthalpy and Gibbs free energy increased with the elevation of drying temperature.
Highlights
‘Okara’ is the by-product of the ‘tofu’ production process or soybean water-soluble extract, and is the insoluble part left after aqueous extraction from soybeans (Mateos-Aparicio et al, 2010)
Drying processes are widely used as methods of conservation in the food industry, because they reduce moisture content in foods and limit the deterioration rate
Mathematical modeling depends on the drying conditions, such as time, temperature and type of equipment used
Summary
‘Okara’ is the by-product of the ‘tofu’ production process or soybean water-soluble extract, and is the insoluble part left after aqueous extraction from soybeans (Mateos-Aparicio et al, 2010). Due to its high moisture content, ‘okara’ is very perishable; when dry (in the form of flour), it has rich nutritional composition and yet is normally undervalued by the food industry and widely used as animal feed (Vong et al, 2016). Drying processes are widely used as methods of conservation in the food industry, because they reduce moisture content in foods and limit the deterioration rate. To obtain the desired final product with the lowest energy demand possible, it is necessary to study product characteristics and drying conditions. In this context, mathematical modeling stands out, and dried ‘okara’ can be conserved for a longer time and added as ingredient in various foods (Perussello et al, 2012). Mathematical modeling depends on the drying conditions, such as time, temperature and type of equipment used. Perussello et al (2012) have already studied other ‘okara’ drying processes using devices such as spray-dryer adapted with pneumatic pipe (130, 150 and 170 °C), rotary drum (50, 60 and 70 °C) and fixed-bed dryer (130, 150 and 170 oC), but the diffusion coefficient and thermodynamic properties were not investigated by these authors
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