Off-flavor removal from soy-protein isolate by using liquid and supercritical carbon dioxide

The efficacy of liquid carbon dioxide (L-CO₂), supercritical carbon dioxide (SC-CO₂), and SC-CO₂ containing 5% ethanol in the removal of off-flavors from soybean protein isolate was studied. Medium-chain aldehydes:n-butanal,n-pentanal, andn-hexanal; ketones: 2-butanone, 2-pentanone, and 2-hexanone; and alcohols: 1-butanol and 2-butanol; were the major compounds extracted. The extractions were performed at a constant fluid density of 901 kg/m³ with 100, 500, and 1000 standard liter of carbon dioxide. None of the treatments had a detrimental effect on soy-protein functionality. Headspace gas chromatography (GC) and sensory analysis of the treated samples were compared with the untreated soy isolate (control). In general, L-CO₂ was the least effective, and SC-CO₂ was the most effective in removing the off-flavor volatiles. Addition of ethanol as an entrainer did not improve the efficiency of off-flavor removal by SC-CO₂. The results of sensory analysis correlated well with the GC analysis. Sensory analysis of a 33% (wt/vol) slurry of treated soy-protein isolate had more off-flavor notes than the dry soy isolate. Dry and slurried treated soy-protein isolates had significantly less off-flavors and significantly more acceptability than the untreated control.