Onion skin (Allium cepa L.) of three landrace varieties produced in Uruguay: minerals and fatty acids composition, phytochemical compounds, in vitro antioxidant and anti-inflammatory properties

Abstract

The onion skin powder (OSP) of three Uruguayan varieties, namely Arber (yellow), Pantanoso (yellow) and Naqué (red) were studied regarding chemical composition, phenolic content, antioxidant capacity and anti-inflammatory activity. The samples were obtained from local producers, were collected after drying in the field and passed through a crusher to obtain OSP. Dietary fiber ranging 69.76–71.57 g/100 g dry matter (DM), and mineral content, particularly Calcium (19.4–22.5 g/kg DM), Mg (1.2–1.7 g/kg DM) and potassium (K; 3.6–8.6 g/kg DM), make these three OSP important sources of these nutrients for human and animal health. The Naqué variety was particularly rich in K, magnesium and protein content, while Arber and Pantanoso had more copper. The three varieties proved to be a source of phenolic compounds, with Arber variety showing the higher content of total polyphenols (72.90 mg GAE/g DM) and flavonoids (29.50 mg QE/g DM), among which the quercetin content was the most represented (11.38 mg/g DM). The antioxidant potential of OSP was determined by DPPH and ABTS assay, the three varieties shows a high percentage of inhibition, ranging from 75.31 to 87.46 and 84.74–90.99 % inhibition, respectively. The anti-inflammatory activity was determined as a function of the percentage of inhibition of protein denaturation, which ranged from 59.88 to 77.33 %. The results of the present investigation show interesting compounds and properties of OSP of the varieties studied and could help Uruguayan onion producers to value and promote the use of their by-products as a potential food supplement.