Volume and density of whole soybean products during hot-air thermal treatment in fluidised bed

Abstract

Soybeans contribute to healthy nutrition because of the high proportion and quality of proteins. Its oil content is considerably lower than in peanuts, restricting energy intake. To produce a whole soybean snack, four type of samples were processed by first increasing the water content and then reducing it by hot-air fluidisation: moistened–dried at 60 °C (MD), soaked–dried at 60 °C (SD), soaked and dried–toasted at 140 °C (SDT) and soaked–cooked and dried–toasted at 140 °C (SCDT). A semi-theoretical model was proposed to describe volume and density as a function of moisture during fluidisation. An equilibrium shrinkage coefficient a was determined. Volume expansion achieved by increasing the moisture content was not totally lost during fluidisation, allowing for lighter products, whose density decreased with the reduction in moisture. As the overall treatment was more severe (SCDT > SDT > SD > MD), shrinkage coefficients increased, up to 0.75. The SCDT sample became crispy and glassy after cooling.