| In 2017,China's rice production was approximately 2.08 billion tons.The total amount of rice bran production in China is very large,but due to the limitation of rice bran is very easy to rancidity and rice processing enterprises scattered conditions,resulting in the effective utilization rate of less than 20%of rice bran.During its processing,it produced approximately 120 million tons of rice bran.At present,heat treatment,enzyme and chemical method are used to prolonge the storage period of rice bran,among which heat treatment has the advantages of simple treatment and no chemical residue.But during the current heat treatment,such as extrusion,microwave and infrared,rice bran keeps in contact with oxygen at a relatively high temperature,the oxidation of reactive substances that are easily oxidized in rice bran are destroyed.Superheated steam(SS)has the advantages of oxygen-free,high thermal efficiency and fast speed of inactiving enzymes.Anaerobic characteristics of SS can effectively reduce the loss of readily oxidizable nutrients in rice bran when the rice bran is stabilized.In this thesis,the rice bran was treated with SS at 120,130,140,150 and160°C for 1-5 min with lipase activity as index to obtain the least passivation time of rice bran at 120,130,140,150 and 160°C.The rice bran at the passivation point best was selected and named as rice bran at the best passivation point.These,nutritional,physicochemical and stability properties of original rice bran(BR)were investigated and compared.The main conclusions are as follows:(1)The lipase activity of rice bran did not significantly change after SS at 120°C for 4 min,130°C for 4 min,140°C for 3 min,150°C for 3 min and 160°C for 2 min.Therefore,rice bran treated at these condititions were rice bran atthe best passivation point and was named as BR-120(SS),BR-130(SS),BR-140(SS),BR-150(SS),and BR-160(SS)for short.Their lipase residual activity was 30.99%,19.80%,16.07%,14.45%and 13.41%,respectively.There was no significant difference in the content of protein,fat,total starch and total dietary fiber between rice bran at the best passivation point and BR.The extraction rate of total phenol content of BR-120(SS),BR-130(SS),BR-140(SS),BR-150(SS),and BR-160(SS)increased significantly by 6.08%,5.57%,3.28%,3.27%,and 2.93%,represetively.The total antioxidant capacity increased significantly,and the change trend was the same to that of the total phenol content.The extraction rate of total phenolic acid(free+binding)increased by10.31%,7.86%,4.32%,2.99%,and 2.31%,represetively,and the extraction rate of ferulic acid was improved;SS treatment did not destroy alpha-tocopherol and gamma-glutamin of rice bran.(2)Compared with BR,the surface of the rice bran at the best passivation point was much rougher.There were no significant difference in color and volume density between rice bran at the best passivation point and BR.However,after ss treatment,the water solubility index and the water holding capacity significantly increased,but the oil holding rate significantly decreased.Because SS treatment significantly reduced the water soluble protein content of rice bran,its foaming and foaming stability also significantly decreased.(3)After 6-month storage,the fatty acid values of rice bran at the best passivation point were 36.0%,27.6%,23.6%,22.9%,21.9%,respectively,and the peroxide values were 50.0%,47.1%,46.7%,46.2%,and 44.3%,respectively.In addition,carbonyl values were 30.3%,26.1%,24.6%,22.5%,and 22.1%,respectively.During the storage period,the fatty acid value,peroxide value and carbonyl value of rice bran at the best passivation point were significantly lower than those of the original rice bran.Considering the rice bran nutrition,physicochemical and storage properties,BR-130(SS)samples were the best,that is,rice bran treated at 130 ~oC for 4 min. |
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