The concentration of minerals and physicochemical contaminants in conventional and organic vegetables

•The conventional vegetables exhibited higher values of all physical parameters when compared to the organic samples.•Higher values of total dietary fibre were found in the organic vegetables.•Contamination by pesticide residues was found in organic tomatoes and conventional peppers.

In this study, we performed a comparative analysis of the physical-chemical composition and pesticide residue content of lettuce, peppers, and tomatoes that were grown in organic and conventional systems. The vegetables were purchased at the Food Supply Centre of Pernambuco [Centro de Abastecimento Alimentar de Pernambuco – CEASA/PE], Pernambuco state, Brazil. The physical-chemical composition of the vegetables was determined according to the analytical procedures of the Association of Official Analytical Chemist. The minerals (Cu, Cr, Fe, K, Mn, Mg, Na, and Zn) and the heavy metals (Cd, Ni, and Pb) were assessed using atomic absorption spectrometry, and the pesticide residues were determined using a multi-residue analysis. The results were compared by means of a Student's t-test. Principal component analysis was performed to investigate the correlations between the minerals and the heavy metals. The measurements of weight, length, and width of all three of the vegetables that were assessed were higher in the conventional group. There were significant differences (p < 0.05) in the proximate composition of conventional and organic lettuces (moisture, ash and protein) and in all the parameters of conventional and organic peppers. To tomatoes there wasn't significant difference (p > 0.05). All three of the organic vegetables were higher in total dietary fibre. The composition of the minerals and heavy metals varied between all three vegetables. Contamination by pesticide residues was found in conventional peppers and organic tomatoes.