Accumulation and distribution of 14 elements in rice grains during the main and ratoon seasons

Rice is an important food crop in China. The edible part of rice is the endosperm in the grain, and the content and distribution of nutrients and toxic elements in different parts of the grain are the key factors determining the nutritional and hygienic quality of rice. Comprehensively considered the influence of various factors such as environment and variety, 18 rice varieties of main season and ratoon season form three ecological conditions were used as test materials. By measuring the content, distribution, accumulation and transport coefficient of 14 elements in different parts of the rice grain in the main and ratoon seasons, the common and differential rules of element accumulation and distribution in the main and ratoon seasons were summarized and clarified. The results showed that the 14 elements could be divided into two categories. The first category included six elements: Mg, Zn, As, Cu, Se and Cd, which had the highest content in the bran. Among them, the proportion of Mg, Cu and As in the bran was 10.1% to 45.7%, and the proportion of Zn and Cd in the endosperm was 50.3% to 78.9%. The second category included eight elements: Si, Fe, Mn, Ca, Cr, Ni, Pb and Co, which had the highest content in the husk and showed a decreasing trend layer by layer towards the interior of the grain. The accumulation proportion of these elements in the husk was as high as 59.1% to 99.95%. In terms of different rice seasons, the total accumulation of Si, Mg and Ca was higher in the ratoon season, while the total accumulation of Mn, Cr, Cu, Ni, Co and Zn was higher in the main season. The content of Mg, Si, Mn and Zn in the husk varied greatly among different ecological conditions and rice seasons, while the content of other elements varied greatly in the endosperm. The content difference of elements in different parts was closely related to their transport ability. The transport coefficient indicated that the transport ability of Ni among different parts was stronger in the ratoon season, and the transport ability of Mg, Cu, Zn, As and Cd from husk to bran was stronger. Moreover, the main season rice could more effectively transport and retain Cd in the endosperm. The principal component analysis results also showed that Mg, Zn and Cu in the bran, Ca, Si, Mn, Fe and Cr in the husk, and the harmful elements Pb and Ni were positively correlated with each other. In conclusion, most elements had similar distribution patterns in different rice seasons, ecological conditions and different parts of the rice grain. While, the main season had a greater impact on the content and accumulation of elements in different parts than the ratoon season. The bran is rich in toxic (As, Cd) and beneficial (Mg, Zn, Cu, Se) elements. The transport of elements from the husk to the bran and the processing accuracy of rice are the key factors determining the content of elements in the edible parts of rice. It is recommended to consume more brown rice in daily diet to increase the intake of trace elements needed by the human body, while in areas with heavy metal pollution, it is advisable to consume more polished rice with higher processing accuracy to reduce the intake of heavy metals and ensure human health and safety..