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Small-Scale Induction of Postharvest Yellowing of Rice Endosperm

¹USDA-ARS, Dale Bumpers National Rice Research Center, 2890 Hwy 130 E, P.O. Box 1090, Stuttgart, AR 72160. Names are necessary to report factually on available data; however, the USDA neither guarantees nor warrants the standard of the product, and the use of the name by the USDA implies no approval of the product to the exclusion of others that may also be suitable. ²Corresponding author. Phone: 870-672-9300. E-mail: hmiller@spa.ars.usda.gov ³Univ. of Arkansas, Rice Research and Extension Center, Stuttgart, AR 72160.

Rice endosperm often develop a yellow discoloration during commercial storage in conditions of high temperature and moisture, thereby reducing the value of the grain. This postharvest yellowing (PHY) appears to be coincidental with fungal presence. To study the yellowing process in a controlled manner, we developed a technique to induce PHY on a small, laboratory scale. Milled rice kernels were rinsed with water and incubated in clear test tubes or microfuge tubes at 65–80°C. This allowed direct observation of the color change and measurement using a colorimeter. Every rice cultivar tested (long and medium grain japonicas and indicas) showed some level of PHY, which increased with temperature yielding a maximum color change at 79°C. Most color change occurred within one day. The moisture parameters required for yellowing to occur were measured. Using sterilization and culture techniques, we found no indications of direct fungal involvement in the yellowing process.