Abstract
The recovery of proteins using ultrafiltration (UF) process is an attractive alternative compared to conventional acid precipitation method. The mild processing condition, which leads to less protein denaturation, may be one of major virtues of this method. This research was directed to identify such assumptions of the products. Three soy protein concentrates were obtained in this study. Full-fat soybean flour and hexane-defatted soybean flour were dispersed into distilled water (1:8) at 60⁰C, respectively. A series of operations including pH adjustment (8.0), agitation (250 rpm, 30 min), sonication (40 dB, 20 min), homogenization (3 min), and centrifugation (3,000 x g, 15 min) were followed. For the membrane processing, the ultrafiltration cartridge used molecular weight cut-off 100,000 daltons. Acid-precipitated protein (at pH 4.5) was produced from hexane-defatted soybean flour following the identical procedures as above. Protein content of the membrane-processed product from full-fat soybean flour was 63.5% and that of the acid precipitated product was 71.9%. All samples were comparable in their functional properties. Nitrogen solubility at pH 7.0 was exhibited better in the protein produced by membrane filtration than the protein produced by acid precipitation due to protein denaturation. Also the membrane-processed soy protein showed good heat coagulation, emulsifying stability, and foaming stability. Amino acid patterns were similar to the typical one of soy proteins. However, relatively low lysine, threonine and valine contents in the acid-precipitated protein were noteworthy. The sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) patterns were almost comparable among samples. In appearance, the acid-precipitated protein was light and slightly greenish tint.
Kim, Hyun Jung (2003). Comparison of soy protein concentrates produced by membrane filtration and acid precipitation. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -2003 -THESIS -K49.