Determination of macro-, micro-element and heavy metal contents localized in different parts of three different colored onions

Abstract

The element found at the highest amount in onion samples was sulfur, and followed by K, Ca, P, Na, and Mg in decreasing order. While K contents of white onion parts are determined between 1406.31 (outer most edible) and 1758.72 mg/kg (inner most edible), K contents of the parts of brown onions were measured between 1779.79 (head) and 2495.89 mg/kg (inner most edible). Also, K amounts of purple onions were detected between 2248.73 (shell) and 3064.64 mg/kg (middle edible). In addition, in general, the highest P, S, and K were detected in the middle edible and inner most edible parts of the edible onion samples. While the highest Ca content was localized in brown and purple onion roots, it was most localized in the shell part of white onions. In edible white and brown onions, the highest Na content was found in the inner most edible part. Fe amounts of white and brown onion samples were identified between 7.94 (head) and 20.41 mg/kg (root) to 9.56 (middle edible) and 23.67 mg/kg (head), respectively. Also, Fe contents of the parts of purple onions varied between 13.04 (shell) and 20.61 mg/kg (inner most edible). While the highest Fe and Zn are determined in the middle edible part in edible white onions, the highest Fe and Zn were determined in the outer most edible part in brown onions. In general, the most heavy metals were localized in the bark, head, and root parts of the onions. This had a positive effect on the safe edibility of onions. The heavy metal detected in the highest amount in onion samples was arsenic, followed by Cr, Al, Ni, Se, Ba, Pb, Mo, Co, and Cd in descending order. Generally, purple onion type showed maximum values. Therefore, results of the present study seen to be beneficial in the way that it allowed us to selected some varieties with nutrition value that could be interesting to introduce in gastronomy.