Small-scale induction of postharvest yellowing of rice endosperm

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 degrees 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 degrees 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.