Preparation And Characterization Of Functional Soy Protein Combined With Subcritical Extraction Technology

Soy protein is a kind of vegetable protein with high nutritional value and good functional properties which is widely used in food industry. Defatted soy meal is the main raw material for extracting soy protein, which is mainly produced by hexane extraction. But hexane has certain neurotoxicity and can accumulate in the body, meanwhile it needs high temperature to be removed from plant materials thus denaturation of protein happens. These disadvantages make people eager to find an alternative method to hexane extraction. Subcritical extraction is a new separation technology and its biggest advantage is the low temperature process. In addition, subcritical extraction has a wide choice of solvents and can use entrainers so it has good selectivity for the target extraction substance. Taking advantage of new technologies is of great practical significance to promote the rapid development of soy industry. Combined with subcritical extraction, the study aims to prepare soy protein which is lowly denatured, rich in nutrients, with health care function and has superior functional properties. The results were showed as followed:(1) Defatted soy meal was prepared by subcritical butane extraction. By investigating extraction temperature and time, the final conditions were selected as 55 °C, 40 min and 3 times for good comprehensive effect. Compared with industrial white flakes, soy protein isolate(SPI) from defatted soy meal prepared by subcritical butane extraction had lower thermal denaturation temperature, worse solubility and digestibility and easier to be oxidized.(2) Soy flour was defatted by n-hexane extraction and subcritical butane extraction, obtaining defatted soy flour-hexane(DSF-H) and defatted soy flour-butane(DSF-B) respectively. DSF-H and DSF-B, along with SPIs from them were analyzed and compared systematically. The results showed that: compared with DSF-H, nitrogen solubility index(NSI) and protein yield of DSF-B were higher, the total amount of residual polar lipids was lower while phospholipid content was higher(mainly PC), protein from DSF-B was easier to be oxidized during defatted soy flour storage; SPI from DSF-B exhibits higher lipids content, deeper colour, better emulsification and similar thermal properties.(3) Defatted soy meal was extracted by subcritical butane with ethanol of different concentrations as an entrainer, then composition and properties of both meals and proteins were analyzed. The results showed that: effects of this extraction with ethanol on defatted soy meal included that the content of residual polar lipids was decreased, NSI dropped from 87% to 50%~66% and with the concentration of ethanol increased the content of residual polar lipids was decreased gradually and its composition changed; as for SPI, the content of residual polar lipids and turbidity were decreased, solubility together with flavor, color and emulsification were improved significantly, while there was no obvious difference between the effects of ethanol concentration on properties of protein.