Rice protein is rich lysine, which is the first limiting essential amino acid. In an earlier study, the genetic properties of rice protein, the environmental conditions that affected the protein content, and the correlation between protein content and grain quality have been reported. The protein content of rice can be the result of interaction between environmental forces and genetic properties of the individual. From 1970–1990, several institutions, such as Chinese academy of agriculture science began a screening and identifying program to research the quality and protein content from the China’s germplasm collections. To our knowledge, there are few studies concerning the distribution, classification of all the rice varieties. In this paper, the distribution, classification and related quality of protein content of 5 323 varieties (times) rice in China were studied. Of these, 3 805 are indica varieties (times) and 1 518 are japonica varieties (times).
Results showed that there was a normal distribution for protein content of rice varieties in general. The protein content was 8%–11% for most rice varieties, although a broad range from 6.0%–15.7% was found in this study. There were some differences for indica and japonica rice on distribution curve of protein content. The protein content ranged from 6.3% to 15.7%，in indicas, and 6.0% to 13.6% in japonicas(Fig.1). Classifying the rice protein content into high (11%), middle (8%–11%) and low (8%) groups, 73% of rice varieties belonged to middle group, 14% to high, and 13% to low. Among them, the percent of varieties with high protein content for indica rice was 5 times more than that for japonica rice, but that with low protein content, for indica rice, was one third of that for japonica (Fig.2). Either indica or japonica rice, the rate of superior varieties with low or middle protein contents was significantly higher than that with high protein content, Due to the negative effect of protein content on chalkiness, translucency and amylose content of rice.
The protein contents among paddy rice, brown rice and hull were compared, and their correlation and regression analyses were also made in this study. Mean protein content is 9.55% for brown rice, 8.34% for paddy rice, and 3.18% for hull (Table 1), and the ratio of protein content in above three parts was 3.0:2.6:1. The protein content of paddy in indica rice often exceeded that in japonica, there was a same case for hull and brown- rice protein content. For indica rice, the protein content was negatively correlated to Gel consistence (GC) and amylose content with a significant coefficient r of －0.093 and －0.17, respectively, and positively related to translucency (grade) with a significant coefficient r of 0.154. For japonica rice, the protein content was negatively correlated to GC and amylose content with a significant coefficient r of －0.233 and －0.0258, respectively, and positively related to translucency (grade) with a significant coefficient r of 0.219. High-protein rice was usually preferred over poor translucency, hard GC and low amylose content.
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