The Micronization And Properties Of Rice Bran And Its Application In Steamed Brown Rice Cake

Brown rice has high nutritional value,but has a poor mouthfeel.Improving the processing method of brown rice is conductive for the quality of brown rice food.In this study,rice bran and white rice of brown rice were treated separately.Extrusion and ball milling technology were used to superfine grind rice bran,white rice was ground appropriately,and then they were mixed to prepare reconstituted brown rice flour,which was made into steamed brown rice cakes.The effects of extrusion and ball milling on the processing properties,nutritional properties,and microstructure properties of superfine rice bran powder were investigated.The differences in gelatinization properties and thermal characteristics of the obtained reconstituted brown rice flour,directly ground brown rice flour,and rice flour were compared,as well as the differences in the quality of steamed cakes.Firstly,different superfine rice bran powders were obtained through single ball milling and extrusion-ball milling.It was found that the ball milling could effectively reduce the particle size of rice bran,the superfine rice bran powder with particle size of D₅₀=18.90μm was obtained.Extrusion technology was beneficial to shorten the ball milling duration of rice bran,when the particle size was close to D₅₀=18.90μm,the milling time was shortened by75%.Simultaneously,the physical properties of different superfine rice bran powders were explored,such as powder characteristics and hydration properties.Results showed that as the particle size decreasing,the bulk and tap density of the superfine rice bran powder increased,the repose and slide angle increased first and then decreased,the water holding capacity,swelling capacity,and oil holding capacity decreased first and then increased,the water solubility index increased,and compared with the swelling capacity of rice bran powder with particle size of 203.33μm,that of superfine rice bran powder with particle size of 18.90μm increased by 37.36%.Compared with the dry-ball milling rice bran as the control sample,the bulk density of extrusion-ball milling rice bran powder reduced,the tap density increased,the repose and slide angle had no obvious differences,the water solubility index reduced,the water holding capacity and swelling capacity increased by 26.98%and 94.93%,respectively.In addition,the mild extrusion treatment（extrusion temperature 90℃,moisture content 40%）prior to ball milling was more conducive to the enhancement of the water holding capacity,swelling capacity and water solubility index of the obtained superfine rice bran powder.Secondly,the nutritional properties of different superfine rice bran powders were explored,such as antioxidant properties,total phenols,total flavonoids,γ-aminobutyric acid,andγ-oryzanol.The results showed that when rice bran was modified by single ball milling,with the decrease of particle size,the IC₅₀ value of DPPH and ABTS radical scavenging ability of rice bran powder decreased,compared with rice bran powder with particle size of D₅₀=203.33μm,that of the superfine rice bran powder with particle size of D₅₀=18.90μm decreased by 13.31%and 11.96%respectively,ball milling was conductive to the dissolution of effective ingredients such as total phenol,γ-aminobutyric acid andγ-oryzanol,thereby making the content of total phenol increased by 11.01%,the contents ofγ-aminobutyric acid andγ-oryzanol increased by 23.68%and 6.06%respectively,and the content of insoluble dietary fiber decreased,the content of soluble dietary fiber increased by 35.82%.Compared with the dry-ball milled rice bran superfine powder as control sample,the extrusion-ball milling rice bran superfine powder had a lower IC₅₀ value of DPPH and ABTS radical scavenging ability,which decreased by 30.77%and 24.74%respectively,extrusion was beneficial to the release of effective ingredients such as total phenols,total flavonoids,andγ-oryzanol,which led to the increased total phenols,total flavonoids,andγ-oryzanol contents,and reduced insoluble dietary fiber content,increased soluble dietary fiber content,but the total dietary fiber content did not change significantly.In addition,the moderate extrusion treatment（extrusion temperature 120℃,moisture content 25%）before ball milling was more conducive to the enhancement of the antioxidant properties,the easier release of total phenols andγ-oryzanol of superfine rice bran powder,while the severe extrusion treatment（extrusion temperature 160℃,moisture content 18%）was more conducive to the reduction of the insoluble dietary fiber and the increase of soluble dietary fiber in superfine rice bran powder.Then,the microstructure properties of different superfine rice bran powders were explored,such as pore size distribution,SEM,FTIR,XRD.The results showed that when rice bran was modified by single ball milling,as the particle size decreased,the total pore volume of rice bran powder first decreased and then did not change significantly,the porosity and average pore diameter decreased,the total pore area increased,and the rice bran structure gradually changed from large blocks into granules,the hydrophilic groups such as O-H were exposed,and the crystal structures of cellulose as well as starch were destroyed.These might be the reason of the changes in the powder characteristics,hydration properties and nutritional properties of superfine rice bran powder.Compared with the dry-ball milling rice bran powder as the control sample,the total pore volume and total pore area of the extrusion-ball milling rice bran powder increased,the average pore size reduced,the rice bran structure was looser,and the hydrogen bonding was stronger,the starch-lipid complex was formed.Finally,the differences of gelatinization properties,thermal characteristics in different reconstituted brown rice flours,directly ground brown rice flour,and white rice flour were explored,as well as the differences of the quality in the prepared steamed cakes.The results showed that compared with that of the directly ground brown rice flour,the final viscosity and through viscosity of the reconstituted brown rice flour composed of extrusion-ball milling superfine rice bran powder increased,the break down value decreased.The specific volume of steamed brown rice cake made by reconstituted brown rice flour which was composed of extrusion-ball milling superfine rice bran powder increased by 21.71%,it had stronger springiness and resilience,decreased hardness,and higher total sensory evaluation score.In summary,the rice bran modified by extrusion and ball milling had effectively reduced particle size,improved physical properties such as powder properties and hydration properties,and enhanced release of nutritional properties including total phenols,γ-aminobutyric acid,γ-oryzanol and dietary fiber.The obtained superfine rice bran powder and the white rice flour were mixed to form the reconstituted brown rice flour with enhanced heat resistance and shear resistance,and the prepared steamed brown rice cake had better specific volume,texture characteristics and sensory quality.