Study On The Technology Of Wheat Germ By Microwave Coupled Chitosan Coating

Wheat germ(WG)which accounts for 2.5~3.0% of grain quality,is the life source of wheat grain.However,it has poor storage stability owing to the presence of large amount of nutrients and endogenous enzymes.In order to improve the utilization value of wheat germ,the stabilization technologies of wheat germ were studied in this thesis.The main research procedures and conclusions of this thesis were as follows:With fresh wheat germ as raw material,the acid value(AV)and peroxide value(POV)were selected as the evaluation index of the degree of wheat embryo metamorphism.In order to explore the possible reasons of the rancidity of wheat germ,different treatments which include vacuum pumping,inhibition of enzyme,vacuum joint inhibition of enzyme and so on were applied to wheat germ.Every two days the AV and POV of the treated wheat germs were determined and compared with the control group.The results showed that the rancidity of wheat germ was related to the endogenous enzymes and oxygen.From the standpoint of oxygen barrier,chitosan solution was sprayed on 150 g wheat germ surface.A layer of polymer film was formed on the surface of wheat germ after drying and it can prevent the oxygen from entering.The effects of wheat germ AV and POV of chitosan solution concentration and addition amount were studied in the factorial design experiment.The results indicated that the concentration and addition amount of chitosan solution had a significant effect on wheat germ AV and POV.The stability of wheat germ was the best when the initial water content of wheat germ at 9%~10%,concentration of chitosan solution was 1.0% and the addition amount of chitosan solution was 15 mL.Under this condition,the AV of wheat germ is 8.11 mg/g and the POV is 2.54 meq/kg.Starting from the angle of enzyme inactivation,effects of wheat germ initial water content,microwave power and heating time on AV and POV of wheat germ were investigated by the orthogonal method.The optimum condition was initial water content at15%,additive content at 150 g,microwave power of 581 W and heating time for 5 min.Under this condition,the AV of wheat germ is 7.78 mg/g and the POV is 1.49 meq/kg.Due to the stabilization effect of chitosan film is not significant compared with other methods,microwave coupled chitosan coating was applied to wheat germ stabilization to impro-ve the stabilization effect.The indepentent variables of this experiment were the initial water content of wheat germ,microwave heating time and the addition of chitosan solution while the dependent variables were the AV and POV of wheat germ.Response surface methodology(RSM)was applied to optimize the processing conditions of wheat germ treated by microwave coupled chitosan coating.Design-Expert 8 software was used to simulate two quadratic polynomial regression model to determine the stability of wheat germ.The optimum conditions were that wheat germ initial moisture content at 15.86%,additive content at 150 g,microwave power at 462 W,microwave heating time at 5 min,concentration of chitosan solution at 1.3%,chitosan solution addition at 15 m L.According to the Arrhenius empirical formula,40 ? storage one day is equivalent to20?storage for 4 days.To do the 40?accelerated storage test,150 g wheat germ treated by different methods respectively were put in a constant temperature incubator,and the AV and POV of wheat germ during 30 days were measured.The results showed that the stabilizing effect of microwave coupled chitosan coating was better than any single method and the AV and POV increased slowly while the control group and chitosan film group increased rapidly.The AV and POV of fresh wheat germ were respectively increased from 8.51 mg/g and 2.81meq/kg to 23.80 mg/g and 21.17 meq/kg on the 12 th day.According to the hygienic standard of edible vegetable oil in China(GB 2716-2005,POV?19.7 meq/kg),the wheat germ oil has been rancidity seriously so that it couldn't be used as edible oil.On the 12 th day,the indexes of other stabilization methods did not exceed the standard;the growth speed of the wheat germ AV and POV which had been treated by microwave coupled chitosan film was the slowest in several methods whose AV and POV were only 9.11 mg/g and 4.67 meq/kg.The pros and cons order of wheat germ storage stability of those methods was: microwave coupled chitosan coating > microwave treatment > heat-moisture treatment > drying process >chitosan film > the control group.