Evaluation Of Wheat Germ Oil Extracted By Supercritical CO₂and Modification Of Wheat Germ Protein

Wheat germ is the life source of wheat kernel. Although it makes up about1.4%-3.9%of wheatkernel, it contains highly concentrated nutrients and is considered as “treasure house of naturalnutrition for human”. The total production of wheat kernel in China is the highest in the world andits yield is up to280-420million tons every year. However, the development of wheat germ is late inour country. For a long time, only a small amount of wheat germ is used to product wheat germ oil,while the majority of defatted wheat germ is used for animal feed, because of the wheat bran mixed.Up to now, wheat germ is still in a high quality resource low utilization condition.The purpose of this study is to enhance the utilization value of wheat germ. We not only focuseson the production and evaluation of wheat germ oil with highly activity components by supercriticalCO₂extraction technology, but also pay attention to the use of defatted wheat germ. In order toexplore new method to modify wheat germ protein, Maillard reaction and fermentation technologywere applied. The main results and conclusions obtained are as follows.1. The supercritical CO₂extraction technology was applied to extract wheat germ oil. Theoptimal extract condition was obtained through single factor experiments and a Box-Behnken designcombined with response surface methodology. The maximal oil yield of10.38%was achieved underthis optimal condition of wheat germ particle size60-80mesh, water content4.37%, extractionpressure30MPa, extraction temperature40℃, extraction time1.7h, separation pressure5MPa andseparation temperature50℃. The VEcontent was3.19mg/g under this condition. Data showed that apositive correlation was found between oil yield and VEcontent, but the correlation was notsignificant. The extraction condition may be selected according to the aim of extraction.2. Different extraction methods showed greater impact on the content of activitycomponents （such as VEand total phenols） in wheat germ oil. The oil obtained by supercritical CO₂extraction owned higher content of activity components, such as VE, so the oil showed strongerDPPH radical scavenging ability at different concentration. However, different extraction methodsshowed no impact on the composition of fatty acids and amino acids.3. The oil obtained by supercritical CO₂extraction showed better quality than the oilobtained by solvent extraction in appearance, physical and chemical index, oxidation stability and soon. The oil obtained was rich in polyunsaturated fatty acid （69.73%）, especially in linoleic acid（64.82%）. The mainly fatty acids distributed in Sn-2were unsaturated fatty acids, such as oleic acidand linoleic acid （80%）. The oil has a unique smell of wheat germ,44volatile compounds wereisolated and identified by HS-SPME-GC-MS. The content of unsaponifiable matters in oil was4.16%, and5compounds were identified by GC-MS. The main content of unsaponifiable matterswas sterol, especially β-sitosterol （64.64%）. In addition, the residual oil of defatted wheat germobtained supercritical CO₂extraction was only0.96%and the water content was0.47%. Thedefatted meal was lower denaturation and the content of protein was high （34.3%）. The compositionof amino acid was balance and the essential amino acids were abundant.4. The intakes of wheat germ oil had no significant effect on the normal growth and theheart, spleen and kidney index, but significantly reduced the liver index. Compared with the Controlgroup, in a simple high-fat model, the TC, TG and AI of serum were not significantly increased bythe intakes of wheat germ oil （p＜0.05）. However, the TC, TG and HDL-C of liver lipid were significantly increased （p＜0.05）. Moreover, the intakes of wheat germ oil can significantlyimproved the concentration of GSH, the activities of SOD and CAT, and reduced the concentrationof MDA in the two different models （p＜0.05）.5.“Enzyme hydrolysis+alkali-soluble and acid precipitation” technology was applied toextract protein from defatted wheat germ. The purity of protein was88.26%, and albumin was19.5%, globulin was27.37%, glutelin was21.24%, prolamine was2.94%. The distribution ofamino acid was balance and the amount of essential amino acids reached40.67%. Compared withsoy protein isolate, although foam properties and oil absorption capacity of wheat germ proteinwere better, its solubility, emulsifying and emulsion stability, as well as water absorption capacitywere poorer.6. Wheat germ protein was modified by Maillard reaction with Dextran. The optimumcondition was obtained through single factor experiments and orthogonal optimization experiments.Under the condition（substrate concentration of2%, protein: dextran=1:1, pH11.0, temperature110℃, time20min）, the DS reached12.05%and NSI was85.34%. After modification, the isoelectricpoint of the product moved to lower pH. The functional properties of conjugates, such as solubility,emulsification activity and emulsification stablility were improved greatly. The conjugates have thestrongest florescence intensity when emission was347nm and excitation was422nm, which inaccordance with the fluorescence characteristics of Maillard reaction product. The amino acidanalysis showed that the content of Lys and Arg was decreased by glycation. In addition, thenumber of α-helix structure was significantly increased in MRPs. Because the introduction ofhydroxy, the intermolecular steric effect was increased and thermal stability was enhanced slightly.7. Wheat germ peptides were prepared by fermentation with Bacillus Subtilis B1. Thefermentation condition was optimized through single factor experiments and a Box-Behnkendesign combined with response surface methodology. A maximal yield of peptides was achieved8.69mg/mL under optimal conditions: wheat germ particle size60-80mesh, pH6.5, inoculum size8%, fermentation temperature31°C and time48h. A positive correlation （R2=0.9911） was foundbetween the concentration of peptides and total antioxidant capacity. The peptides presented asignificant does-dependent on scavenging activities of DPPH, hydroxyl and superoxide anionradicals, especially on scavenging activities of DPPH in the molecular weight distribution ofpeptides between500-1000Da and180-500Da.