Total phenolics, antioxidant and xanthine oxidase inhibitory activity of three colored onions (Allium cepaL.)

Abstract

Methanolic extracts from bulbs of three onion (Allium cepa L.) varieties: red (Pusa Red), white (Pusa White Round), and yellow (Arka Pitamber) and the CHCl 3 , Et 2 O, EtOAc, and n-BuOH fractions obtained from those extracts were investigated for their total phenolics and antioxidant activity. The antioxidant activity measurements, expressed as total antioxidant status (TAS), were 5.2-50.18, 2.2-35.6 and 3.5-42.2 mg ml −1 for red, white and yellow onion bulb extracts, respectively, as compared to trolox (IC 50 , 40.2 mg ml −1 ). The total phenolic content of the samples was 62-186, 56-156 and 68-165 mg GAE ml −1 for red, white and yellow onion bulb extracts, respectively, with all solvents. There was a positive correlation between the total phenolic content and antioxidant activity for MeOH extracts and EtOAc fractions (R 2 = 0.96, 0.8 respectively). Of the selected colored onion bulbs the red onion (IC 50 = 14.2 μg ml −1 ) revealed more potent xanthine oxidase inhibitory activity to those of yellow (IC 50 = 15.5 μg ml −1 ) and white onion (IC 50 = 17.0 μg ml −1 ) in vitro and as compared to control allopurinol (IC 50 = 10.5 μg ml −1 ). The kinetic study by xanthine oxidase revealed that the white and yellow onion extracts were non-competitive inhibitors, as K m values were constant, while V max consequently decreased with increased inhibitor concentration. In the red onion extract there was an increase in K m values while V max remained constant at all extract concentrations, thus confirming a competitive type of inhibition by the Lineweaver-Burk equation. These findings suggest that these onion varieties can be considered as potential sources of antioxidants and XO inhibitory agents.

Chemical Fingerprint of Free Polyphenols and Antioxidant Activity in Dietary Fruits and Vegetables Using a Non-Targeted Approach Based on QuEChERS Ultrasound-Assisted Extraction Combined with UHPLC-PDA

“…The TPC found in all samples ranged from 0.39 mg GAE/g fresh mass for orange carrot to 1.33 mg GAE/g fresh mass for red onion. Comparing the two onion varieties, the red onion showed the highest content, which is in agreement with the results obtained by Nile and Park [45]. In this study, the methanolic extracts from the bulbs of three onion varieties (red, white, and yellow) were analyzed, with red onion being the variety with the highest TPC, followed by the extract of yellow onion and finally the white variety.…”

Bioactives in spices, and spice oleoresins: Phytochemicals and their beneficial effects in food preservation and health promotion

“…Red onion contained the highest amount of total phenolic content and antioxidant activity followed by yellow, white, and sweet onion bulb extracts (X. Bajaj et al 1980;Prakash et al 2007;Nile and Park 2013;Onyeoziri et al 2016). Moreover, phe-nolic compounds and their antioxidant activity were determined from skin and flesh of different colored onions (pearl, yellow, red, and white); the highest content of phenolics was observed from pearl onion skins and the major compounds were quercetin, quercetin 3,4′-diglucoside, and kaempferol (Albishi et al 2013a(Albishi et al , 2013b.…”

Expression, characterization, and site-directed mutagenesis of UDP-glycosyltransferase UGT88A1 from Arabidopsis thaliana

“…Onion (Allium cepa) and related species have been widely used as flavoring vegetables, folk medicines, and so on, because of their wide range of health benefits, including antioxidant, antiplatelet, antithrombotic, antiasthmatic, and antibiotic effects [1]. In onion, flavonols have been identified as the most important bioactive components.…”