Page Banner

United States Department of Agriculture

Agricultural Research Service

Research Project: Bioproducts from Agricultural Feedstocks

Location: Bioproduct Chemistry and Engineering Research

Title: Use of microscopy to assess bran removal patterns of rice milling

Authors
item Wood, Delilah
item Siebenmorgen, Terry -
item Williams, Tina
item Orts, William
item Glenn, Gregory

Submitted to: Journal of Cereal Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 8, 2012
Publication Date: May 28, 2012
Citation: Wood, D.F., Siebenmorgen, T.J., Williams, T.G., Orts, W.J., Glenn, G.M. 2012. Use of microscopy to assess bran removal patterns of rice milling. Journal of Cereal Science. 60:6960-6965. DOI: 10.1021/jf301263s.

Interpretive Summary: Rice milling entails removal of the outer layers (bran and germ) of the kernel and results in a product having improved functionality, shelf-life and appearance. However, extensive milling reduces the yield of rice so milling quality, the degree of milling, needs to be monitored. Current standards of measuring the degree of milling used by the Federal Grain Inspection Service involve visual comparison of milled samples to standard line samples. This method is subject to error since it is a visual method and is highly dependent on operator and lighting conditions. Thus, new standards of measure are needed that ensure repeatibility. Bran and germ components of rice contain large amounts of lipid so the analysis of lipid content provides a valuable tool for measuring the degree of milling. In this study, we use microscopy and specific staining of lipid to compare three rice varieties grown in three locations each milled to four different milling times. Our work showed that less lipid remains with increasing milling times and that the location of the remaining lipid occurs in the natural depressions of the rice grain.

Technical Abstract: Since the bran and germ are successively removed during rice milling and those tissue components contain large quantities of lipid, the remaining surface lipid content may be used as an alternative method of determining milling quality. Bulk samples of rice pureline varieties and a hybrid were milled for 0, 10, 20, 30 and 40 sec. Scanning electron microscopy revealed that brown rice kernels had large contours of linear protuberances and depressions running lengthwise along the kernel surface. The protuberances were abraded successively during milling and left material in the depressions. Light microscopy combined with lipid-specific probes, Nile Blue A or Sudan Black B, showed that the material in the depressions noted in the scanning electron micrographs was lipid. Sections of whole, milled rice kernels, were prepared using a modified sectioning technique were stained with Nile Blue A and showed that portions of the embryo remain after milling and that the lipid is located on or near the surface of the kernel. Differences in lipid quantity and distribution as milling duration increased was observed to indicate the manner in which the bran and embryo components were removed during milling. During rice milling, the bran and germ are successively removed from the caryopsis. Because bran and germ contain large quantities of lipid, the amount of lipid remaining on the grain surface may be used as an alternative method of determining milling quality. Bulk samples of rice pureline varieties and an experimental hybrid were milled for 0, 10, 20, 30 and 40 sec. Scanning electron microscopy (SEM) revealed that brown rice kernels had large contours of linear protuberances and depressions running lengthwise along the kernel surface. The protuberances were abraded successively during milling, but varying amounts of material remained in the depressions. Light microscopy combined with the lipid-specific probes Nile Blue A or Sudan Black B, demonstrated that the material in the depressions observed with SEM was lipid. Sections of whole, milled rice kernels, prepared using a modified sectioning technique and stained with Nile Blue A showed that portions of the embryo remain after milling and that the lipid is located on or near the surface of the kernel. Differences in quantity and distribution of residual lipid as milling duration increased were documented to indicate the extent to which the bran and embryo components were removed during milling.

Last Modified: 8/21/2014
Footer Content Back to Top of Page