Influence of Bran Layer Characteristics on Rice Milling Quality

Authors: SIAW, MICHELLE - University Of Arkansas; McClung, Anna; MAUROMOUSTAKOS, ANDY - University Of Arkansas; WANG, YA-JANE - University Of Arkansas

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/2/2023
Publication Date: 8/7/2023
Citation: Siaw, M., McClung, A.M., Mauromoustakos, A., Wang, Y. 2023. Influence of Bran Layer Characteristics on Rice Milling Quality. Cereal Chemistry. 100(6):1234-1249.

Interpretive Summary: Most rice is consumed after milling which removes the outer bran layer. The bran layer contains many nutritional compounds including protein, lipids, minerals, and vitamins and can vary in thickness depending upon the rice variety. The value of the rice crop is partly dependent upon of the amount of whole grain produced after milling and removal of the broken grains. This study investigated bran thickness and bran chemical composition as factors that influence bran removal and rice milling yield. Nine rice varieties were evaluated following milling the rice in short intervals to achieve the same degree of milling. At each interval the bran was collected and then analyzed for chemical composition. Surprisingly, bran chemical composition had a greater relationship to milling yields than bran thickness. Arabinoxylan content in the bran, a compound which forms structural components of plant cells, was positively associated with milling yield. There was also a significant interaction between arabinoxylan and protein contents which affected milling yield and bran yield suggesting the occurrence of crosslinking of these components. Bran lipid content also had a significant effect on milling yield. These results signify that rice milling characteristics are influenced by the amount of bran removed during milling, which is determined by the chemical composition of the bran and the interactions of these components, rather than physical properties of the grain. This indicates that improving rice milling quality may be enhanced through bran composition.

Technical Abstract: Rice milling involves applying forces to remove bran from brown rice to produce milled rice. The physical and chemical properties of a rice kernel may affect both the amount of bran removed during milling and the amount of head rice yield (HRY) produced, which is a determinant of crop value. This study investigated bran thickness and bran chemical composition as factors that influence bran removal and HRY as a result of milling. Findings: The results showed that brown rice kernels with initial higher surface lipid contents (SLCs) required longer milling times to achieve 0.4% SLC, but the longer milling times did not translate into lower HRYs or higher bran yields. Bran chemical composition had a more significant impact on the milling characteristics than bran thickness. Arabinoxylans had the greatest impact on HRY, followed by lipids and proteins. In conclusion, bran thickness did not have a significant impact on the milling time, bran yield, or HRY. There was significant interaction between arabinoxylans and proteins on HRY and bran yield, which indicates the probability of crosslinking between proteins and arabinoxylans. Instead of grain physical properties, this study demonstrates the importance of rice bran chemical components and their interactions on rice milling quality.