Refunctionalization of extruded-expelled soybean meals

Soybean meals produced by extruding-expelling (EE) have poor functional properties due to heat denaturation of the proteins, which limits their utilization in foods. Hydrothermal cooking (HTC), a treatment in which steam (150degreesC) and high shear are applied to a slurry of soybean meal, was used to refunctionalize EE protein meals. Two EE samples with protein dispersibility indexes (PDI) of 35 and 60 were used, along with solvent-extracted white flakes and full-fat whole soy meal as controls. Two HTC methods were explored: One method used a treatment temperature of 154degreesC and seven different residence times, controlled by varying the holding tube length; the other involved flashing the treated slurry directly into the atmosphere without any back-pressure regulation or holding. Effects of residence time on functional properties of the samples were investigated. The maximum effect of HTC conducted with the use of holding tubes (with-holding-tube HTC) was also compared with that of flash-out HTC. Solid dispersibility, protein dispersibility, and emulsification capacity of both EE meals were significantly improved by both types of HTC treatments. The flash-out HTC showed more benefits than the with-holding-tube HTC in refunctionalizing heat-denatured EE protein. For example, the solid dispersibility, protein dispersibility, and emulsification capacity of EE meal with PDI of 35 were improved 2.0, 4.4, and 2.1 times, respectively, by flash-out HTC treatment. Therefore, the HTC refunctionalization was proved effective in partially restoring the functional properties of the heat-denatured soy proteins.