Comparative study of heating processes for full-fat soybeans
2004
Wiriyaumpaiwong, S. | Soponronnarit, S. | Prachayawarakorn, S.
Heating is very important to inactivate anti-nutritional factors and enhance quality of soybean products. Four heating techniques i.e. extrusion, fluidized bed, spouted bed and infrared radiation have been investigated along with their performances, regarding moisture reduction, urease inactivation, protein solubility and lysine. The rate of moisture diffusion for soybean kernel in the spouted bed and infrared dryer was described by a semi-empirical drying equation for which the drying constant was determined using non-linear regression. The experimental results have shown that the water mobility is more rapidly accelerated by infrared radiation. Every technique has a potential to reduce the urease activity to the standard range, with the quantity of remaining lysine being insignificantly different (p<0.05) under the testing conditions. The extent of urease inactivation in each technique depends on the moisture content, time and temperature, the latter being the most important factor. High moisture content induces rapid urease inactivation for the soybeans treated by the convection and radiation-type equipments. Conversely, inhibited inactivation is encountered with the extruded soybeans due to the strong cohesive forces amongst ground soybeans at a higher moisture content of 24% d.b., inducing poor mixing behaviour in the barrel. The results from the lab- and commercial-scale equipment are shown to have higher soluble protein content in 0.2% KOH for the infrared-treated soybeans, comparing to the other techniques. Extrusion consumed the largest quantity of energy followed by the fluidized bed with no recycled air and the micronizer becomes the most effective energy utilization.
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