Milling characteristics and distribution of phytic acid and zinc in long-, medium- and short-grain rice

Abstract

Milling and polishing are important operations during the production of white rice. The degree of milling and polishing has a significant effect on the nutritional aspects of white rice, especially on minerals, due to a non-uniform distribution of nutrients in the kernel. Information on the distribution of nutrients in rice will greatly help to understand the effect of milling and aid in designing procedures that improve technological and sensory properties of rice while retaining its essential nutrients as much as possible. In this study, three kernel shapes (short-, medium-and long-grain) of rice were selected for the study of milling characteristics and distribution of zinc (Zn) and phytic acid using abrasive milling and X-ray fluorescent microscope imaging approaches. Milling characteristics differed with kernel shapes and cultivars. Mass loss (y, %) correlated well with milling duration (x, s) and was fitted using a polynomial equation of y = ax 2 +bx+c (R 2 =0.99). Different kernel shapes of rice resulted in different patterns. Breakage in milling increased with longer duration of milling. The relation between breakage (y, %) and milling duration (x, s) fitted the exponential equation y = ae bx. Levels of phytic acid, as well as Zn decreased with prolonged milling. Phytic acid decreased at a higher rate than Zn. The analysis of different milling runs showed that the concentration of phytic acid decreased from the surface region inward, whereas X-ray fluorescent images indicated that the highest concentration of phosphorus was at the interface of embryo and perisperm. Our results help to understand the milling characteristics of different rice cultivars. Understanding these characteristics offers opportunities to optimize milling procedures for maximum phytate removal, at minimum mineral losses and yield loss.

Changes in the zinc content of selected bangladeshi rice varieties through modified parboiling and milling methods

“…10%) zinc content was reduced by half. While some previous studies had observed a negligible (Doesthale et al, 1979) or relatively modest decline (Liang et al, 2008) in zinc content of rice with 10-12% degree of milling, the magnitude of decrease observed in this study of 10 Bangladeshi rice varieties is consistent with the range observed in other studies. A 10-12% degree of milling resulted in retention of zinc of 73% (Villareal et al, 1991) and 55% (Pedersen and Eggum, 1983) compared to brown rice.…”

Zinc-enriched fertilisers as a potential public health intervention in Africa

“…Thus, milling and processing generally reduce the concentration of Zn in the edible product (Bityutskii et al 2002;Ozturk et al 2006;Liang et al 2008;Cakmak et al 2010;Joy et al 2015). Many of the studies included in the metaanalysis only reported Zn concentrations in whole grain, with and without application of Zn.…”

Preliminary Study on the Visualization and Quantification of Elemental Compositions in Individual Microdroplets using Solidification and Synchrotron Radiation Techniques

“…Self-absorption of primary X-rays and emitted X-ray fluorescence may be caused by the relative thickness of a fixed droplet (from several tens to several hundreds of μm). However, Liang et al (2008) successfully visualized X-ray fluorescence images of K, Ca and Fe at different depths (200, 400, and 500 μm) in a kernel of rice grain. The samples in the present study were quite thin (50 μm) compared to a rice grain, and homogenous elemental distribution were less affected by the selfabsorption of X-rays.…”