Effect of Oven and Microwave Heating on the Total Antioxidant Capacity of Dietary Onions Grown in Turkey

Abstract

The active components of largely consumed dietary onions (Allium species) in Turkey were extracted with water and ethanol, separately heated in a drying oven (at 50 • C, for 1-4 h) and in a microwave oven (at 90 W, for 1-4 min), and their total antioxidant capacity was determined with different electron transfer-based assays. Five different onion species/aerial parts, namely yellow, red, white, fresh green leaf, and fresh green root, were measured for total antioxidant capacity with different methods, the hierarchic order in aqueous extracts being: CERAC: yellow-skinned > red-skinned > spring-root > spring-leaf > whiteskinned onion; CUPRAC: spring-leaf > red-skinned > spring-root > yellow-skinned > white-skinned onion; Folin-Ciocalteau method: spring-leaf > spring-root > red-skinned > yellow-skinned > white-skinned onion. Using all three methods, white onion, showed the lowest total antioxidant capacity, while with respect to two methods (i.e., CUPRAC and Folin-Ciocalteau), spring onion-leaf showed the highest value. In ethanolic extracts, white onion exhibited the lowest total antioxidant capacity using two methods (CUPRAC and Folin-Ciocalteau). Of the heat-processed onions, the highest CERAC and Folin-Ciocalteau total antioxidant capacity values were obtained for red-skinned onions, while the highest CUPRAC value was for spring onion leaves. All three assays marked white-skinned onion as the lowest total antioxidant capacity content of heat-processed products. The change in total antioxidant capacity caused by both heating processes was not drastic; spring onion leaves essentially maintained its total antioxidant capacity level after 4 min microwave or 4 h drying oven heating. Onion processing by heat treatment did not cause a drastic loss in antioxidant values, favourable for traditional cooking practices.

Effect of Domestic Cooking Methods on Antioxidant Capacity of Fresh and Frozen Kale

“…[11,25] When comparing different studies, it is worth remembering that the effect of cooking likely depends on the vegetable structure, cooking procedures, extraction solvents, and antioxidant assays. [26] Our results revealed that the type of vegetables (fresh or frozen) should be taken into consideration.…”

Identification of Antioxidants in Aged Garlic Extract by Gas Chromatography-Mass Spectrometry and Liquid Chromatography-Mass Spectrometry

“…Therefore, GC-MS was performed to analyze the volatile components of the ethyl acetate fraction, which showed the highest antioxidant activity in AGE. A total of 23 compounds (Table 1) Organosulfur compounds found in garlic have been shown to exert diverse biological effects such as antioxidant effects, anti-inflammatory properties, inhibition of platelet aggregation, reduction of systolic blood pressure, and reduction of cholesterol levels [17,18]. The spectrum of these sulfur-containing compounds depends considerably upon the methods of extraction of the original garlic bulbs, as well as upon the solvent conditions of processing [19].…”

Quantitative Evaluation of the Pyruvic Acid Content in Onion Samples with a Fully Validated High-Performance Liquid Chromatography Method

“…The recent literature is rich in both in vivo and in vitro studies reporting the anti-thrombotic-, [1] hypolipidemic-, [2,3] anti-diabetic-, [4,5] anti-obesity-, [6] antioxidant-, [7][8][9] anti-inflammatory-, [10] cancer chemopreventive-, [11] and antiparasitic- [12,13] properties of onion extracts. Moreover, some epidemiological studies suggest that a diet rich in onions may have a favorable effect on the risk of acute myocardial infarction [14] and benign prostatic hyperplasia.…”