Bioacessibility of Fe and Zn (associated to proteins) in cashew nut

Abstract

A series of experiments were carried out as part of the current study with the overall aim of quantifying the contribution of metal associated to proteins to the overall bioaccessible portion of Fe and Zn present in cashew nut. Concentrations of Fe, Zn, and proteins in cashew nut were experimentally determined to be 55.0 ± 1.2 mg kg−1, 41.0 ± 0.1 mg kg−1 and 22.1 ± 0.3%, respectively. Considering these results, an investigation of Zn and Fe bioaccessibility was carried out, demonstrating that approximately 36% and 32% of total Fe and Zn concentrations, respectively, become bioaccessible to humans upon digestion. Aiming to investigate the percentages of total concentration amounts of Fe and Zn that are bound to groups of protein present in cashew nut, ground samples were submitted to a sequential extraction procedure for extraction of albumins, globulins, glutelins, and prolamins. The results showed that 16% of the total Fe concentration present in cashew nut is associated to albumins, 37% to globulins, and only 8.4% to glutelins. In turn, 21.5% of the total Zn concentration was found to be associated to albumins, 11.71% associated to globulins, and 4.73% to glutelins. Of note, no significant amounts of Fe and Zn were found in prolamin extraction solutions. A precipitation step was carried out in protein solutions, and an in vitro digestion assay undertaken on the isolated raw protein content for the purpose of evaluating the bioaccessibility of Fe and Zn in this sample. The results showed that only one third of Fe and Zn associated to proteins in cashew nut becomes bioaccessible to humans upon digestion. As such, the findings of this study indicate that the global bioaccessibility of Fe and Zn in cashew nut cannot be not solely attributed to associations between metals and proteins.