Study On The Extraction Of Oil And Protein From Maize Germ By Reverse Micelles

China is the second largest country products maize in the world, the yearly capacity of maize is nearly 10 million tons. Maize germ has a relatively high content of nutritious protein and oil. Traditionally, the maize germ is used to product corn germ oil. However, the maize germ protein (MGP) would denaturated because of the high temperature in the maize germ oil production. Moreover, MGP has been done by alkaline extraction and isoelectric precipitation in the industry, but this method has some defects: a great deal of wastewater is produced which causes serious environmental pollution and it is high consumption of acid and alkali. Reverse micelles could extract oil and protein at the same time, and has some advantages: simple process, saving water, low cost, less pollution, mild conditions and high quality product. Reverse micelles had been used in the extraction of vegetable protein and oil because of its advantages, such as no loss of native function/activity, low interfacial tension, ease of scale up, and potential for continuous operation .There are two steps about the process of protein and oil extraction from vegetables by reverse micelles: a forward extraction and a backward extraction. Protein was solubilized into polar core of the reverse micellar in the forward extraction, then the solubilized protein was recovered from the polar core to aqueous phase. When material was mixed with the reverse micelles, protein would diffuse from the material to the reverse micellar core because of the electrostatic, steric, and hydrophobic interactions between protein and reverse micelles. The experimental results lead to the conclusion that the highest forward extraction efficiency of MGP and maize germ oil(MGO) was reached at the sulphosuccinic acid bis (2-ethylhexyl) ester sodium salt (AOT) concentration 0.06g/ml, pH 7.0, KCl concentration 0.1mol/L, time 60min, the amounts of MG 0.500g, W0 25 and temperature 40℃. Under these conditions, the forward extraction efficiency of MGP and MGO achieved 45.61% and 85.49% respectively. The influences of pH, KCl concentration, the volume ratio between KCl solution and supernatant of the forward extraction (VRSS), ultrasonic power, ultrasonic time and intermittent mode on the backward extraction efficiency were studied on the study of the backward extraction. The effects of ultrasonic power, ultrasonic time and intermittent mode were investigated using response surface methodology (RSM) base on the single-factor experiments. By analyzing the response surface contour plots and single-factor experiments, the optimal extraction conditions of MGP were determined: pH 6.0, KCl concentration 1.00 mol/L, VRSS 1:1, work time 3.06 min, ultrasonic power 457W, intermittent mode 1.5s:2.0s. When those parameters ran under optimized conditions, the backward extraction efficiency of MGP achieved 62.97%.The fat acid of MGO extracted by reverse micelles and the aqueous enzymatic extraction technology and n-hexane extraction were roughly the same, the conent of UFA(unsaturated fatty acids) is more then 82%,and the conent of linoleic acid is about 50%. The ratio of MUFA (mono-unsaturated fatty acid) and PUFA (poly-unsaturated fatty acids) is about 1:1.48;The acid value of MGO extracted by reverse micelles (5.4 mg KOH/g) was markedly lower than extraction by the aqueous enzymatic extraction technology (32.7 mg KOH/g), and was a little higher than extraction by n-hexane (3.7 mg KOH/g). The iodine value of MGO extracted by three methods were roughly the same. They are 83 gI/100g, 98 gI/100g and 112 gI/100g respectively. The peroxide number(POV) of MGO extracted by reverse micelles (17meq/kg) was markedly lower than extraction by n-hexane (72meq/kg), and was a little higher than extraction by the aqueous enzymatic extraction technology (11 meq/kg).Protein isolates were prepared from MG by there different methods, i.e. by traditional salt solubilization-alkaline extraction-isoelectric precipitation (MGPI) and by reverse micelles (MGRMPI) and by aqueous enzymatic extraction (MGAEPI). The yield of MGRMPI (28.23%) was higher than DWGPI (16.63%) and MGAEPI (22.01), and the purity of DWGRMPI (96.21%) was also higher than DWGPI (72.97%) and MGAEPI (12.94%). The contens of Lys, Met, Phe, His, Thr, Asp, Cys, Glu, Gly, Tyr and Pro in MGRMPI were relative higher compared to those in MGP. DSC showed that the denaturation temperature of MGPI, MGRMPI and MGAEPI were 67.776℃, 73.287℃and 72.847℃, andΔH of MGPI, MGRMPI and MGAEPI were 0.298J/g, 0.451 J/g and 2.606J/g. CD spectra indicated that the secondary structure of MGPI was mainly random coil (54%), followed byβ-sheet (30%), having a smaller amount ofα-helix (16%); MGRMPI hadβ-sheet (27%), random coil (45%) andα-helix (28%).