Composition and estimate of daily mineral intake from samples of Brazilian rice

Rice is one of the most produced and consumed cereals in the world, making the control of its chemical composition, especially of minerals, important. A method of rice digestion using nitric acid and hydrogen peroxide to determine metals (Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, Pb and Zn) using Inductively Coupled Plasma Optical Emission Spectrometry (ICP OES) was developed. The optimized conditions were established using a factorial design 23, obtaining the following digestion conditions as the most adequate: digestion time (20min), concentration of HNO3 (8molL−1) and H2O2 volume (2.5mL). Recovery values ranging from 80 to 120% with RSD<5.1% were obtained for most elements of interest and limits of detection of the method were in the range of 0.02mgkg−1 (Mn) to 5.6mgkg−1 (Ca). A table of metal composition for the different types of processed rice (white, parboiled and brown) was established through an analysis of 54 rice samples. Brown rice contributed significantly to the Recommended Dietary Allowances (RDA) of Mn (61%) and Mg (20%), parboiled rice with Cu (45%) and white rice with Mn (14%). In addition, the daily intake estimated through rice consumption, for all detected metals, was much lower than the Tolerable Upper Intake Level. The rice samples could be differentiated by their type of processing, based on their mineral composition using Principal Component Analysis (PCA).