Study On The Extraction Of Protein From Wheat Germ By Reverse Micelles

China is one of countries with the major wheat-production and the total production is the highest in the world. Wheat germ is one of the main by-products of wheat-milling industry and annually its yield is about 2.8 ~ 4.2 million tons in China. Wheat germ has a relatively high content of nutritious protein. Traditionally, the separation of defatted wheat germ protein (DWGP) has been done by alkaline extraction and isoelectric precipitation. However, this method has some fatal defects: a great deal of wastewater is produced which causes serious environmental pollution and it is high consumption of acid and alkali. Moreover, it is easy to cause protein denaturation. The extraction of protein by reverse micelles has the advantage of simple process, saving water, low cost, less pollution, mild conditions and high quality product. Therefore, DWGP was extracted by an alternative extraction approach--reverse micelles and the properties and secondary structures of DWGP were also studied in this work. The purpose of this study was to provide an alternative effective approach for deep processing of defatted wheat germ (DWG), and develop some high value-added products for human consumption.The procedure of protein extraction from DWG by reverse micelles consisted of two steps: a forward extraction and a backward extraction. On the study of the forward extraction, the optimum extraction was achieved by response surface methodology. The experimental results lead to the conclusion that the highest forward extraction efficiency of DWGP was reached at the sulphosuccinic acid bis (2-ethylhexyl) ester sodium salt (AOT) concentration 0.06mol/L, pH 8.0, KCl concentration 0.1mol/L, time 60min, the amounts of DWG 0.500g, W0 25 and temperature 36℃. Under these conditions, the forward extraction efficiency of DWGP achieved 34.55%. On the study of the backward extraction, the optimum extraction was reached at KCl concentration 0.61mol/L, the amount of KCl solution 1.0mL and pH 9.47 and the backward extraction efficiency of DWGP achieved 80.07%. Thus, the yield of DWGP by reverse micelles was 27.66%。Tween-60, sucrose ester and lecithin were added to the AOT-isooctane reverse micellar systems as cosurfactant, and analysis showed that all of the three cosurfactant could increase the forward extraction efficiency of DWGP and sucrose ester was best, followed by lecithin and Tween-60. Adding alcohol as cosolvent can also increase the forward extraction efficiency of DWGP, moreover, long chain alcohol was better and could increase the forward extraction efficiency of DWGP to 41.14%. On the basis of the definitely optimum forward extraction conditions, combining with ultrasound assisted extraction and reverse micelles can increase the forward extraction efficiency of DWGP from 34.55% to 58.27%, and the optimum extraction was reached at ultrasonic output power 363W, ultrasonic time 24min and pulse mode 2.4s on and 2s off. In this case, the yield of DWGP by reverse micelles was 46.66%。Protein isolates were prepared from DWG by two distinct methods, i.e. by traditional salt solubilization-alkaline extraction-isoelectric precipitation (DWGPI) and by reverse micelles (DWGRMPI). The yield of DWGRMPI (46.66%) was higher than DWGPI (32.08%) and the purity of DWGRMPI (98.38%) was also higher than DWGPI (81.63%). The contens of Lys, Thr, His, Ala, Arg, Gly, Ser, Cys-s and Pro in DWGRMPI were relative higher compared to those in DWGPI. DSC showed that the denaturation temperature of DWGPI and DWGRMPI were 64.148℃and 68.818℃andΔH of DWGPI and DWGRMPI were 0.724J/g and 1.091J/g. DWGRMPI had good solubility, fat absorption capacity, foaming capacity, foaming stability and emulsifying stability compared to DWGPI, while had relative low water holding capacity, surface hydrophobicity and emulsifying activity.Raman and CD spectra indicated that the secondary structure of DWGPI was mainlyβ-sheet (50.1%), followed by random coil (42.7%), having only a small amount ofα-helix (3.3%) andβ-turn (3.9%); DWGRMPI hadβ-sheet (43.0%), random coil (34.2%),α-helix (20.6%) andβ-turn (2.2%). FT-IR spectra showed that the secondary structures of DWGPI and DWGRMPI dissolved in heavy water were also mainlyβ-sheet, while the amount of random coil decreased andβ-turn increased.