Extraction, Characterization And Application Of Proteins From Wheat Germ

The main objective of this research was to explore the possibility of extracting and characterizing the protein extracted from wheat germ with an improvement of nutritional and functional properties.The raw material in this study was wheat germ, a by-product obtained from a commercial mill (Fuxin Flour Mill, Shanghai, China). Normally this by-product of the wheat milling industry is used for animal feed. However, results obtained in this study showed that protein extracted could be a potential source of nutritional and functional protein for possible food applications. For the preparation of the raw material, endogenous enzymes of wheat germ were inactivated by heating for 15 min at 105C in the oven. The germ was defatted using supercritical carbon dioxide (SC-CO2), smashed and solubilized by enzymatic hydrolysis.Different treatment methods of the raw sample were used to enhance the solubilization of protein so as to increase the yield of proteins. The first method used was based on aqueous extraction followed by NaCl extraction of wheat germ protein. A two step process was developed for producing protein from defatted wheat germ. Conditions for preparation of protein were studied on a laboratory scale by orthogonal test. With the suitable conditions established, 55% of germ protein was recovered by water extraction and 22% by salt extraction. The second method was developed using the isolation of wheat germ protein by alkaline extraction. A protein isolate (90% protein) was prepared from defatted wheat germ by alkaline extraction, at pH9.5 and isoelectric precipitation at pH4.0. The third method was the enzymatic solubilization by proteases. The enzyme hydrolysate was continuously stirred under optimum conditions of hydrolysis and centrifuged. Defatted wheat germ protein hydrolysate (DWGPH) was obtained when the supernatant was spray dried. Alcalase and flavourzyme solubilized respectively, 85 and 80% of the protein, while papain, neutrase and protamex solubilized 73, 66 and 61% respectively. The functional properties of DWGPH solubilized using alcalase were as follows: nitrogen solubility, 74% at pH 6; emulsifying activity, capacity and stability were 64, 62 and 57% respectively. Water retention of DWGPH solubilized using alcalase was 232% at pH 7 and temperature of 70C.Electrophoresis (SDS- PAGE) of DWGPH was performed to obtain information on the molecular weight of DWGPH. Molecular weight distribution of DWGPH as estimated by SDS-PAGE was found to be in the range of 14.4~66.2 kDaThe thermogram of DWGPH showed broad endothermic peak with a Td of approximately 125C and enthalpy (?H) of about 68 J/g. while WEP had endothermic peak of 87.3C and enthalpy (?H) of about 1.3.The nutritional properties of DWGPH were studied and compared to that of WEP. Amino acid analysis was performed using ion exchange chromatography and was in the range of the standard reference for FAO/WHO. Oligosaccharides were identified and quantified by HPLC. Sucrose and raffinose were 8.67 and 5.39 g/100mg respectively. The analysis of glutathione (GSH) has been developed and optimized on reversed-phase HPLC column and quantified by a fluorescence detector. It was found at 85.54 mg/100g of sample. –SH was determined using UV-Vis spectrophotometer and was estimated about 312.5 mg/100g. The solubility index was determined and expressed the difference between 100% and the percentage of insoluble matter. It was found that the DWGPH was totally soluble in cold water. Carbohydrate content was determined according to the Phenol/Sulfuric Acid Assay. The absorbance of the solution was recorded at 490 nm against a reagent blank, and the carbohydrate content read from a standard glucose calibration curve was about 28.8%.The molecular weight distribution of wheat germ polysaccharide was evaluated using gel permeation chromatography on a column (1.0 x80 cm) packed with Sepharose CL-4B (Sigma Chemicals). Results of gel permeation chromatography on a column showed that extraction by enzyme decreased the molecular weight of native wh...