Determinação da concentração total e da fração bioacessível de metais em amostras de casca de uva das cultivares Tannat e Cabernet Sauvignon por MIP OES

Abstract

Every year in the world millions of tons of waste are generated from the most diverse agribusiness crops, many of which are not used and are eventually disposed of incorrectly, which causes environmental damages. The use of these residues, such as those from wineries, whose main residue is grape skin, has increased the interest of the food and cosmetic industries in the extraction of compounds that have important biological properties. These residues contain water, proteins, lipids, carbohydrates, vitamins, phenolic compounds and minerals, which are dependent on the type of residue generated, the cultivar, as well as the climatic and cultivation conditions. Thus, the elementary characterization of these samples becomes necessary, which helps to the best form of destination of these. The objective of the present work was the development of a simple and safe sample preparation methodology with the use of the reflux system for subsequent determination of the total concentration and the bioaccessible fraction of metals (essential and potentially toxic metals such as Ba, Bi, Ca , Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Pb and Zn) in grape peel samples of cultivars Cabernet Sauvignon and Tannat by means of the microwave induced plasma optical emission spectrometry (MIP OES) with multimode system for introduction of samples. To determine the total concentration of the elements of interest, the samples were prepared in a digester block by acid decomposition in cold reflux with HNO3 and H2O2 as the oxidizing medium. The accuracy of the method was performed by analytical addition and recovery tests, obtaining adequate recoveries, which were in the range of 82 to 118%, as well as through a comparative method of sample preparation in a closed system. According to the results of the total concentration, the elements Cd and Bi were below the limit of detection of the method (LODm) in both samples and Cr for the cultivar Tannat. In order to determine the bioacessible fraction, the gastrointestinal system was simulated in vitro. The accuracy of the method was evaluated by adding the bioaccessible (supernatant) fraction to the non-bioaccessible fraction, which should be close to the total concentration, the results were between 81 and 120%. The bioaccessible fraction of the elements Zn, Cu, Ba, Pb, Mn were in the range of 13.5 to 52.8%. However, the Fe that despite being present in the samples in considerable concentrations, had its bioaccessible fraction below the LODm. It is important to point out that Pb, which is considered a non-essential and potentially toxic element, showed high bioaccessibility, which highlights the need to monitor essential and potentially toxic elements in these samples, which helps to the destination of these residues.