Effects of the Domestic Cooking on Elemental Chemical Composition of Beans Species (Phaseolus vulgaris L.)

Cooking is imperative for beans owing to the presence of compounds that can negatively affect nutritional value. Additionally, the heating of beans can increase protein digestibility and induce desirable sensory properties. However, cooking also causes considerable changes in the composition of numerous chemical constituents, including amino acids, vitamins, and minerals. For this, effects of domestic cooking on the essential element concentrations in various beans species (Phaseolus vulgaris L.) were investigated using jalo, fradinho, rajado, rosinha, bolinha, black, and common species. Elemental determination was made with flame atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry after sample digestion in a closed-vessel microwave oven using a diluted oxidant mixture. Analytical methods were evaluated with an addition and recovery test and analysis of certified reference materials (apple and citrus leaves). Ca, Cu, K, and Mg were present mainly in rajado, Cu in jalo, Fe in black, S and Zn in fradinho, and P in rosinha species. Thermal treatment did not affect Cu, Fe, S, and Zn concentrations, but it increased Ca, K, Mg, P, and Zn concentrations in jalo and black species. Ca concentration decreased in fradinho and rajado species, as did Fe concentration in jalo and rajado species. 1. Introduction Brazil is the largest worldwide producer (2.2–2.5 million tons on approximately 5 million hectares cultivated) and consumer (around 16？kg per capita) of beans [1–3]. The Brazilian food pyramid shows beans in a group of their own, and the Food Guide for the Brazilian Population recommends the consumption of at least one portion of beans per day [4]. Beans are one of the main protein sources for Brazilians [1–3]. There are several typical Brazilian Phaseolus species, including jalo, rosinha, fradinho, rajado, bolinha, common (“carioca”), and black. In general, these species are good sources of vitamins, minerals (K, Ca, Mg, P, and Fe salts), protein (20–25%), and complex carbohydrates (50–60%) [2, 5, 6]. Besides being nutritionally important, beans serve as rich sources of bioactive compounds such as enzyme inhibitors, lectins, phytates, oligosaccharides, and phenolic compounds with potential health implications [7]. Importantly, the elemental chemical composition of beans varies with species, geographic origin (soil, water, pesticides, insecticides, and fertilizers), and climate [8]. Given the nutritional importance of beans, differences in the elemental chemical composition of Phaseolus species should be evaluated in