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ARS Home » Southeast Area » Stuttgart, Arkansas » Dale Bumpers National Rice Research Center » Research » Publications at this Location » Publication #173360
Title: SMALL-SCALE INDUCTION OF POSTHARVEST YELLOWING OF RICE ENDOSPERM

Author
item Miller, Helen
item KAY, MARK - UA RREC
item LEE, FLEET - UA RREC

Submitted to: Cereal Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2005
Publication Date: 10/1/2005
Citation: Miller, H.B., Kay, M., Lee, F.N. 2005. Small-scale induction of postharvest yellowing of rice endosperm. Cereal Chemistry. 82(6):721-726.

Interpretive Summary: Rice may yellow during commercial storage. Yellowing can occur whenever rice is harvested too wet or if the stored grain becomes wet from rain, from leaks around storage bin door seals, etc. The problem can occur in large storage bins and trucks as well as in relatively small piles or containers. The portion of the pile of rice that is wet gets hot and has a distinct moldy smell. The yellowing has been associated with fungus. Rice containing discolored kernels has a lower commercial grade and value. We developed a technique to induce yellowing on a small, laboratory scale. Milled rice kernels were rinsed with water and kept in clear test tubes at 65-70C for several days. This allowed direct visualization and measurement of the color change using a colorimeter. Every rice cultivar tested showed some level of yellowing. Yellowing increased with temperature with a maximum color change occurring at 79C. Most of the color change occurred in one day. The amounts of water needed for yellowing to occur were measured. Using sterilization and culturing, we found no indications of direct fungal involvement in the yellowing process. Understanding the control of yellowing may provide the means to reduce its incidence.

Technical Abstract: Rice endosperm may yellow during commercial storage in conditions of high temperature and moisture, thereby reducing the value of the grain. In order to study the process in a controlled manner, we developed a technique to induce this postharvest yellowing on a small, laboratory scale. Milled rice kernels were rinsed with water and incubated in clear test tubes or microfuge tubes at 65-70C. This allowed direct visualization and measurement of the color change using a colorimeter. Every rice cultivar tested, which included long and medium grain as well as japonicas and indicas, showed some level of yellowing. Yellowing increased with temperature with a maximum color change occurring at 79C. Most of the color change occurred in one day. The amounts of water needed for yellowing to occur were measured as well as the changes in relative water contents during yellowing. Using sterilization and culturing, we found no indications of direct fungal involvement in the yellowing process.