Components Analysis And Recovery Of Proteins From Okara In SPI Processing

Large amounts of byproducts-okrara were produced in the processing of tofu, soymilk,and soy proteins. Okara contains about15%～20%proteins. The paper studies thecomponents of okara proteins by Sodium Dodecyl Sulfate-Polyacrylamide GelElectrophoresis (SDS-PAGE) and the optimal prparation conditions of okara proteis as well asits functional properties measurement. Finally,enzymatic modification was studied.The results showed that, when compared with Soy Protein Isolates (SPI), okara proteinscontained three characteristic protein bands, whose molecule weight (MW) were respectively27.21,16.00and23.38kDa. By MALDI-TOF/TOF-MS, the27.21and16.00kDa proteinwere identified as subunits of basic7S globulin (Bg7S), while the23.38kDa protein wereidentified as oleosin isoform. The oleosin isoform was firstly reported to be found in okarasystem and its isoelectric point (pI) was determined to be about pH7.80by isoelectrofocusing(IEF). Research results of reducing, non-reducing electrophoresis and diagonalelectrophoresis showed that there were two proteins which were linked by subunits throughdisulfide bond, and they are identified as Bg7S and11S globulin. The comparative contentsof remaining storage proteins (7S and11S), Bg7S and oleosin were determined to be about57%,31%,12%, respectively.Alkaline extraction temperature and time had little effect on extraction rate of okaraproteins, while it was significantly improved by increase of pH. With the increase of pH,soluble protein aggregates were formed and its content went up, leading to the increase ofextraction rate of okara proteins. The pI of proteins in alkali extraction supernatants wasdetermined to be4.5. Therefore, the best conditions for preparing okara proteins were listed asfollows: the quality ratios of solids to solvents1:30, pH12.6, room temperature25℃, time1h, pH used to precipitate proteins4.5. Then the fuctional properties of okara proteins obtainedat the best conditions were measured and compared with those of SPI. The results show that,its foaming stability, emulsion stability and amino acid analysis were similar with SPI, whilethe solubility, foaming and emulsifying ability of okara proteins were comparatively worsethan SPI. After trypsin modification, the solubility of okara proteins was significantlyimproved, and its emulsifying and foaming ability also showed increasing trend, whileemulsion and foaming stability decreased slightly.