Abstract: The purpose of this research was to understand the effect of citric acid on the milling characteristics of brown rice, the cadmium content during milling and the quality of parboiled rice, aiming to provide useful data for the utilization of rice contaminated by cadmium to a certain by processing it into parboiled rice. Two samples of Hunan-grown Indica rice with excessive cadmium content were selected for parboiled rice making. Brown rice derived from husking of paddy pretreated by citric acid soaking, steaming and drying was ground by a gradual milling method. The changes in cadmium content, as well as the milling characteristics and appearance quality of parboiled rice with different whitening times were measured, and the mineral composition and cooking characteristics of parboiled rice and the texture characteristics as well as the sensory evaluation of appearance and eating quality of cooked parboiled rice were determined. The results showed that after citric acid soaking, the husk of brown rice was more easily ground, and the degree of bran removal from parboiled rice per unit time was improved. However, citric acid had no significant effect on the percentage of broken kernels of parboiled rice after milling. Although citric acid made the color of parboiled brown rice more yellowish, it had no significant influence on the color of parboiled rice. The addition of citric acid promoted the migration of Cd, K, Ca and Al from endosperm to outer tissue, but had little effect on the migration of Mn and Cu. It also promoted the migration of Na, Mg, Fe and Zn from rice hull to endosperm, and increased the contents of Na, Mg and other elements. The water absorption rate, volume expansion rate, iodine blue value, pH value and hardness after cooking of parboiled rice were all significantly reduced after soaking with citric acid solution. The color of parboiled rice was significantly increased as well as taste and overall sensory score after cooking.

Key words: rice, parboiled rice, characteristics, cadmium content, mineral content, quality analysis