Effect Of Microwave Treatment On Physicochemical Properties Of Brown Rice And Its Mechanism

As a raw material of whole grain,brown rice has high edible value and development prospect.On account of the surface of brown rice contains a lot of cellulose and pectin,the water absorption rate is lower.The relatively dense bran and testa also affect the texture and the taste of brown rice directly,which makes it difficult to eat as staple food directly.This paper mainly focuses on the improvement of cooking and eating property on brown rice through microwave treatment and keeping the nutritional property of brown rice.Optimize microwave processing parameters and analyze the changes of storage property.The main contents and conclusions are as follows:1.The results indicated that positive influence was occurred by microwave radiation.The pasting temperature,viscosity value,breakdown and setback were increased and the hardness,springiness,gumminess and chewiness of steamed brown rice were decreased while the adhesiveness was increased.These were all benefit to raise the taste of brown rice.Under the process conditions of microwave radiation 4.0 kW·kg-1 and microwave working time 60 s,the effectiveness was relatively optimal.The peak viscosity,breakdown and adhesiveness were increased by 23.1%,16.0%and 95.1%while the hardness was decreased by 13.5%.The results showed that the section of brown rice kernel was cracked and pearl starch were increased after microwave radiation.The arrangement of starch granules was loose and rough,the morphology was changed,the micropores and pits were occurred and the swelling of starch granules was increased after the microwave radiation.The pasting properties and texture properties of brown rice kernel were improved.2.The microwave radiation dose and microwave working time had significant effects on the content of brown rice polyphenol,total flavonoids and antioxidant activity(P<0.05).And the content of brown rice polyphenol was significantly correlated with total flavonoids after microwave treatment(P<0.01).The increase of microwave radiation dose was consistent with the trend of extending microwave working time.Along with the increasing of microwave radiation dose or the extension of working time,the DPPH radical scavenging activity and ferric ion reducing antioxidant power of brown rice were reduced.The brown rice DPPH radical scavenging activity was significantly correlated with ferric ion reducing antioxidant power(P<0.01).The brown rice was treated with 60 s under the microwave radiation dose of 4.0 kW kg-1 and the content of polyphenols and total flavonoids in brown rice were the highest.Under the microwave treatment,the contents of polyphenol and total flavonoids were more than 50%of the original brown rice and the antioxidant activity and reduction ability were all kept high level.3.Box-Behnken response surface experimental design based on three-factor-three-level was applied in this work to optimize microwave processing technology of brown rice.The results showed that pasting properties,water absorption and iodine blue value increased with microwave treatment time,microwave power and initial moisture content increasing,while hardness and head rice rate decreased.The Box-Behnken response surface analysis was used to obtain the best technological conditions and the best process parameters for the microwave treatment of brown rice was established:microwave power,2400 W;microwave time,50 s;initial moisture content,14.5%.The maximum value of this desirability function was 0.67 and no significant difference was seen between the experimental data and model prediction(P>0.05).The cooking property and edible quality of brown rice were improved obviously.4.During storage,the variation tendency of storage property of brown rice samples with microwave treatment and original brown rice samples were basically the same.The moisture content,germination rate,taste value,freshness,polyphenol oxidase activity and peroxidase activity of brown rice were all on a declining curve and the higher the temperature during storage,the faster the decline rate.The moisture content of brown rice samples with microwave treatment was basically consistent with that of original brown rice samples during storage.In the same storage temperature and time,the descent rate of taste value,freshness,polyphenol oxidase activity and peroxidase activity of brown rice was lower than that of original brown rice,while the descent rate of germination rate was higher.During storage,the variation tendency of peak viscosity and breakdown of brown rice samples with microwave treatment and original brown rice samples were basically the same.The peak viscosity and breakdown increased in 30 days and began to decline after 30 days.In the same storage temperature and time,the peak viscosity and breakdown of brown rice samples with microwave treatment were lower than that of original brown rice samples.The variation tendency of minimum viscosity,final viscosity and setback of brown rice samples with microwave treatment and original brown rice samples were basically the same during storage.Under the storage condition of high temperature,the minimum viscosity,final viscosity and setback were on the rise.While under the storage conditions of normal temperature and low temperature,the minimum viscosity,final viscosity and setback were on the decline as a whole.