Variations in the appearance quality of brown rice during the four stages of milling

Abstract The milling of rice plays a key role in determining rice quality, and the evaluation of the appearance quality is an efficient method to distinguish the degree of milling (DOM). The appearance and morphological characteristics in Japonica rice with different milling times were analyzed by scanning electron microscopy (SEM), white light interference, the bran degree, as well as whiteness and color parameters. Based on the changes in the appearance and morphology of rice, the milling process could be divided into four stages: the brown rice stage (DOM=0.00%), the seed coat crushing stage (0.00%＜DOM≤4.56%), the aleurone layer grinding stage (4.98%≤DOM≤8.72%), and the endosperm polishing stage (DOM≥9.13%). The surface cortex on both sides of the rice grain was easily milled while the abdomen and back of the rice grain were more difficult. The root mean square height (Sq) value of the sample increased initially with the bran degree（DOM≤6.56）and decreased with further milling, the whiteness, transmittance, and L-value of the samples showed gradual increases, the MMID DOM increased from 0% to 102%, and the a and b values gradually decreased to 180% and 58%, respectively. Based on the appearance and morphological characteristics, the Stage III (Aleurone layer grinding stage, 4.98%≤DOM≤8.72%) gave the best quality during milling.