Kaolin mined from the Ipixuna deposit of Pará Pigmentos S.A. in the Capim river area of northern Brazil has been studied at various stages of beneficiation to determine the behaviour of Fe- and Ti-bearing minerals which can reduce the brightness of the product. X-ray diffraction and Mössbauer spectroscopy showed the principal pigmenting minerals to be hematite and goethite, with chemical analyses showing a distinct decrease of both the total Fe and Ti contents in the course of processing. The Ti contents were primarily reduced due to the removal of anatase during particle size fractionation and dithionite reduction. While the Fe content of the final product is structurally bound in kaolinite, Raman spectroscopy indicates the remnant Ti to be bound both structurally in kaolinite and in remnant anatase.

The aim of the present study was to compare Fe absorption from industrially-manufactured and home-cooked cereal foods. Fe absorption was measured using the radiolabelled Fe extrinsic tag technique in thirty-nine adult human subjects from cereal porridges manufactured by extrusion cooking or roller-drying, and from the same cereal flours after home cooking to produce pancakes, chappattis or bread. One series of cereal porridges was amylase-treated in addition before roller-drying. Fe absorption was relatively low from all products, ranging from 1·8–5·5% for rice, 2·5–3·5% for maize, 4·9–13·6 % for low-extraction wheat, and <1% for high-extraction wheat foods. The phytic acid content remained high after drying of the cereal porridges being about 1·20, 1·70, 3·20, 3·30 mg/g in low-extraction wheat, rice, high-extraction wheat and maize products respectively, and could explain the low Fe absorption. There were little or no differences in Fe absorption between the extruded and roller-dried cereals, although amylase pre-treatment increased Fe absorption from the roller-dried rice cereal 3-fold. This was not due to phytate degradation but possibly because of the more liquid nature of the cereal meal as fed. There were similarly few or no differences in Fe absorption between the industrially-processed cereals and home-cooked cereals made into pancakes or chappattis. Bread-making, however, degraded phytic acid to zero in the low-extraction wheat flour and Fe absorption increased to 13·6%, the greatest from all cereal foods tested. It is concluded that Fe absorption from extruded, roller-dried or home-cooked cereal foods is similarly low and that only those cooking procedures such as bread-making, which extensively degrades phytic acid, or amylase pre-treatment, which substantially liquifies cereal porridges, improve Fe absorption.