Chemical and Functional Characterization of Soy Protein Concentrate Produced by an Ultrasound-Assisted Ethanol Washing Process

In this study, soy protein concentrate (SPC) was produced from defatted soybean meal using ultrasound-assisted ethanol extraction, and the chemical composition and functional properties of the resulting product were investigated. The effects of reaction time (2-4 h), solid-to-liquid ratio (1:4-1:12), and ethanol concentration (65-85%) were evaluated using a 2³ full factorial screening design. The highest protein increase ratio (29.70%) was obtained in the screening run at 4 h, a 1:12 solid-to-liquid ratio, and 65% ethanol. Subsequent USPC and K-SPC samples were prepared under this selected condition; USPC contained 62.87±0.40% protein (wet basis; approximately 65.89% on a dry-matter basis). Ultrasound did not significantly increase total protein versus the control; it improved foaming capacity and short- to medium-term foam stability, with a more limited positive effect on the emulsion activity index. No marked improvement occurred in protein solubility, water-holding capacity, emulsion stability, or gelation. The results indicate that, under the selected processing conditions, ultrasound treatment mainly enhanced foaming behavior and the emulsion activity index, whereas its influence on protein enrichment and most other functional properties was limited; therefore, process conditions should be further optimized in terms of functional performance.