Study On Storage Stability And Quality Control Of Corn Germ

Corn germ is an important part of corn.The oil content of corn germ is as high as36%?47%,while the quality of corn germ only accounts for 10% of the total mass of corn.Therefore,it is one of the important oil resources in China.Corn germ oil not only rich in oleic acid and linoleic acid,but also contains a lot of nutrients such as tocopherol,retinol,and phytosterol.The germ cake,which obtained from corn germ oil preparing,owe good functional properties and rich in protein,mainly including albumin and globulin.However,as a by-product of corn starch production,corn germs are mostly obtained by wet extraction of embryos.During this process,a decrease in its storage stability with the cell structure of the germs destroyed,which limits the deep processing and utilization of the germs.At present,there are few researches on the storage performance of corn germ.Therefore,it is urgent to understand the changing regularity of corn germ quality during storage,find an effective method to improve its storage stability,and provide a basis for its further deep processing and utilization.In this study,the corn germ with wet extraction was used as raw material to investigated the lipidand protein oxidation of corn germ under different storage temperatures(15 ?,25?,35 ?).At the same time,the changes of nutrients and the microstructure of cells,and the mechanism of quality deterioration during the storage process of corn germ was explored.Results showed that the lipid rancidity in corn germ gradually intensified with the increasing of lipase and lipoxygenase activities during the storage,.It was mainly characterized by the production of bad flavor,mainly hexanoic acid and 2-pentylfuran,as well as the sharp increase of peroxide value,anisidine value and malondialdehyde content.The main manifestations are the production of undesirable flavors,2-pentylfuran,and the sharp increasing in peroxide value.At the same time,the anisidine value and the content of malondialdehyde also increase significantly.With the occurrence of oxidation reaction,tocopherols in corn germ oil are degraded and consumed as antioxidants.However,the sterol content is relatively stable.The degree of lipid oxidation between different storage temperatures also showed significant differences.Lipid oxidation in corn germ would induce changes in cell structure,leading to the increasing of cell permeability and structural collapse.The peroxide free radicals generated during lipid oxidation also promote the oxidation of proteins in corn germ.It was found that the protein of corn germ aggregated with the storage time,which is manifested as an increase in particle size,a decrease in Zeta-potential and surface hydrophobicity,an ordered state to a disordered state with the extension of storage time.With the occurrence of protein oxidative aggregation,The water retention,oil retention,foaming and foam stability,emulsification and emulsification stability of corn germ protein showed a gradual decrease with the oxidative aggregation of protein.In order to improve the storage stability of corn germ,the effects of five steady-state treatment technologies on corn germ endogenous enzyme activity,basic physical and chemical properties and nutrient content were compared and studied.After the hot air drying treatment,the corn germ color was well preserved,the water content was significantly reduced,but the endogenous enzyme activity still remained more,and the ?-tocopherol content was significantly reduced by 76.7%.Steam treatment can significantly inhibit the activities of LA and LOX,and better retain the content of tocopherol.Especially,the residual enzyme activity of LA and LOX of corn germ after high-pressure steam treatment is only30.07% and 23.28%.However,the color of maize germ became brown seriously,the moisture content increased and the peroxide value decreased significantly after steam treatment.After extrusion treatment,the endogenous enzyme activity of corn germ was inhibited;the residual enzyme activities of LA and LOX were 53.60% and 42.80%,respectively;the acid value and peroxide value were significantly reduced,whlie the color was significantly darker;the content of crude fat and tocopherol was severely lost,dropping by 8% and 31%,respectively;Microwave treatment can significantly inhibit the endogenous enzyme activity of corn germ.The residual enzyme activities of LA and LOX are 44.45%and 36.29%,respectively,and the germ color,basic components and tocopherol content are retained to the greatest extent.After comprehensive comparison,it is believed that microwave treatment has the best effect on corn germ stabilization.Microwave treatment reduces the activity of endogenous enzymes in corn germ,but the activity of endogenous enzymes will still show an upward trend with the participation of oxygen.Therefore,the storage of corn germ was studied by using microwave and air conditioning treatment.It was found that microwave treatment has a better effect of inactivating enzymes.During storage,the enzyme activity is lower than that of the untreated group,which inhibits the oxidation process of oil to a certain extent.The acid value,peroxide value,anisidine value and malondialdehyde content are all lower than the that of control group.Especially at 105 days,the peroxide value of the microwave treatment group was only 32.60% of that of the control group.Microwave and air conditioning treatment further effectively slow down the degree of oil oxidation.At the end of storage,its peroxide value content was only 80% of the microwave treatment group.At the same time,the change of protein structure during the storage of corn germ was same as and the oxidation of oil.The microwave and air conditioning treatment effectively inhibited the increase of carbonyl value,the increase and aggregation of protein particle.The degree of germ oxidation showed a trend of microwave synergistic atmosphere treatment group<microwave group<control group.At the same time,the content of erythrenone in the oil of corn germ during different storage periods was determined,and it was found that both microwave and microwave cooperating atmosphere treatment can significantly inhibit the increase of erythrenone content.Therefore,microwave synergistic atmosphere treatment can be used as an effective control method to improve the storage stability of corn germ.At present,there are few researches on the storage performance of corn germ at home and abroad,so it is urgent to understand the quality change law of corn germ during storage,and find an effective stabilization and storage method to improve its storage stability and provide a basis for its further deep processing and utilization.