Study On The Milling Performance Of Rice Based On The Three-Dimensional Characterization Method Of Bran Degree

Grain saving and loss reduction are of great importance at present.Strengthening the uniform milling of rice and reducing endosperm damage are the main ways to reduce grain loss in processing.The precise detection of the milling degree of rice is an important prerequisite and means for moderate rice processing.In this paper,the brown rice of Daohuaxiang with geographical representation and grain type representation was selected as raw material,and the bran degree of rice was accurately characterized by non-destructive whole grain three-dimensional images.And simple and overall characterization methods of bran degree were created,including powder homogeneous spectrophotometry and powder homogeneous color difference method.Based on the three-dimensional information of rice bran,the change of surface bran during rice processing was studied,and the best technology of uniform whitening was explored.This will provid data support and theoretical basis for moderate and precise processing of rice.The main research contents and results were as follows:At first,rice with different milling degrees（bran degree of 99.48%～0.42%）was milled with emery roller and iron roller.Using a rice appearance detector and a stereomicroscope to capture two-dimensional images to characterize the bran degree,and using an X-ray electron computed tomography（Micro-CT）to perform a three-dimensional image method to characterize the bran degree.The two-dimensional image method showed that when the bran degree was greater than 7.0%,the bran of the rice grain gradually wears off,but the proportion of rice kernels with no bran did not exceed 7%.For reasonably well milled rice,the rice kernels with no bran increased significantly,but the contribution to the overall bran degree was only less than half.The increase of rice kernels with no bran mainly led to the decrease of the overall bran degree for the well milled rice.The milling process of rice grain bran was as follows:the front,reverse,ventral and dorsolateral bran of rice grain were ground first,followed by most of the four longitudinal groove bran of rice grain front and reverse,until the dorsal of rice grain and the top bran of longitudinal groove near the dorsal remain after well-milling.In the process of rice whitening,the relationship of rice bran area of each part was always as follows:the area of dorsal and dorsolateral bran>the area of ventral and ventrilateral bran>the area of front bran≈the area of reverse bran.But when the bran degree was 0.70%,the areas of front and reverse bran（0.26%、0.25%）were larger than the areas of dorsal and ventral bran（0.07%、0.11%）.Micro-CT images showed that the thickness of bran reflected the three-dimensional structure of bran.And the dorsal bran of rice grains was thicker than the ventral bran as a whole.And from the changes of bran thickness in different parts of rice,it can be seen that the effective work of rice whitening was only to gradually remove the dorsal and dorsolateral bran.Secondly,two simple and easy-to-operate three-dimensional methods to characterize bran degree were established:powder homogeneous color difference method and powder homogeneous spectrophotometry method.The relationship equations between bran degree and the measured results by two new methods were as follows:Y_L*=-0.08（log₂X）²-0.50（log₂X）+92.37,R²=0.9971;Y_a*=0.01（log₂X）²+0.14（log₂X）+0.57,R²=0.9470;Y_b*=0.43（log₂X）²+0.32（log₂X）+4.38,R²=0.9986;Y _{absorbance value}=0.01（log₂X）²+0.02（log₂X）+0.24,R²=0.9970.Methodological investigation of the two methods showed that the results of powder homogeneous color difference method had good precision,and the results of powder homogeneous spectrophotometry had high accuracy and good precision.The variation trends of powder homogenization photometry and color difference method（a^*,b^*）were similar.The color difference L^*,a^*,b^*values on the surface of rice grains did not increase significantly（P>0.05）for reasonably well milled,but the L^*value of rice powder was still changing significantly（P<0.05）for reasonably well milled.The L^*value of rice powder was better than the L^*value of rice grain to distinguish rice with different bran degree.In the range of reasonably well milling and well milling,the powder homogeneous photometry and color difference method were more sensitive to the characterization of bran degree than the rice appearance detector.Finally,based on the bran degree characterized by the rice appearance detector,the rice was milled to the same milling degree with different milling technology.The residual bran of the rice was characterized by the powder homogeneous spectrophotometry method to find the best milling technology and achieve uniform milling.The results showed that in CBS550AS（2）iron roller,when the flow rate was 3-scale,the weight loss rate was minimum（7.54%,8.85%,9.85%）,accordingly the absorbance value of methylene blue complexes with bran degree of 5.00～5.50%,3.00～3.50%and 0.65～0.75%was minimum（0.290,0.273,0.228）,respectively.And the fissure ratio（4.25%、4.38%、4.75%）、the broken rice rate（9.46%,15.29%,18.34%）were the smallest,and the head rice rate（90.42%,84.60%,81.52%）and the proportion of whole kernel（85.78%,77.46%、70.65%）were the highest.In CBS550AS（2）iron roller,when the flow scale was 3 scales,and the pressure gears were 1.25,1.75 and 2.75 respectively,the iron roller flows were 37 kg/h,31 kg/h and 24 kg/h respectively,which was the most beneficial to realize the uniform milling of rice.