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

Figures & data

Table 1 The TAC of white-skinned (Albion), yellow-skinned (Rijnsburger), red-skinned (variety Red Baron), and spring onion species, extracted with water or EtOH, and determined with CERAC, CUPRAC, and Folin-Ciocalteau methods

Onion sample	Aqueous extract (mmol quercetin/g onion)	Ethanol extract (mmol quercetin/g onion)	Method of determination
White-skinned	2.36 × 10^−3	3.38 × 10^−3	CERAC
Yellow-skinned	3.93 × 10^−3	3.42 × 10^−3
Red-skinned	3.87 × 10^−3	4.54 × 10^−3
Spring onion (leaf)	2.66 × 10^−3	2.26 × 10^−3
Spring onion (root)	3.57 × 10^−3	2.70 × 10^−3
White-skinned	1.84 × 10^−4	2.20 × 10^−4	CUPRAC
Yellow-skinned	2.79 × 10^−4	3.83 × 10^−4
Red-skinned	5.40 × 10^−4	6.25 × 10^−4
Spring onion (leaf)	8.54 × 10^−4	7.06 × 10^−4
Spring onion (root)	3.26 × 10^−4	1.10 × 10^−3
White-skinned	2.05 × 10^−3	1.17 × 10^−3	Folin-Ciocalteau
Yellow-skinned	2.06 × 10^−3	2.14 × 10^−3
Red-skinned	2.35 × 10^−3	3.26 × 10^−3
Spring onion (leaf)	3.01 × 10^−3	2.24 × 10^−3
Spring onion (root)	2.86 × 10^−3	3.21 × 10^−3

Figure 2 The change of absorbance at 320 nm—due to Ce(IV)—with the volume of alcoholic onion extract as a result of the reaction of EtOH extracts (of onion varieties) with 2.0 × 10⁻⁴ M Ce(IV) solution in the CERAC method.

Figure 1 The change of absorbance at 320 nm—due to Ce(IV)—with the volume of aqueous onion extract as a result of the reaction of aqueous extracts (of onion varieties) with 2.0 × 10⁻⁴ M Ce(IV) solution in the CERAC method.

Table 2 The percentage of weight loss of heating process for microwave- and oven-heated onions

Heating process	Heating period	Yellow-skinned onion (%)	Red-skinned onion (%)	White-skinned onion (%)	Spring onion, leaf (%)	Spring onion, root (%)
Microwave 90 W power	1 min	13.40	6.20	5.60	10.20	8.40
	2 min	19.8	25.4	24.0	32.0	25.6
	4 min	45.6	49.6	47.4	58.0	51.0
Oven 50°C	1 h	22.2	30.0	30.6	22.4	29.2
	2 h	45.6	41.0	54.0	47.4	40.8
	4 h	77.0	65.4	70.0	79.2	69.0

Table 3 The TAC changes of microwave-heated onions at 90 W power as a function of time (heating periods 1, 2, and 4 min)

		Method of TAC determination (mmol quercetin/g fresh-weight onion)
Sample	Heating time (min)	CERAC method	CUPRAC method	Folin method
Yellow-skinned onion	1	3.91 × 10^−3	2.52 × 10^−4	2.42 × 10^−3
	2	3.88 × 10^−3	2.40 × 10^−4	2.41 × 10^−3
	4	3.04 × 10^−3	1.77 × 10^−4	2.34 × 10^−3
Red-skinned onion	1	3.87 × 10^−3	5.79 × 10^−4	3.67 × 10^−3
	2	3.75 × 10^−3	5.72 × 10^−4	3.41 × 10^−3
	4	3.63 × 10^−3	4.82 × 10^−4	2.37 × 10^−3
White-skinned onion	1	1.82 × 10^−3	1.69 × 10^−4	1.97 × 10^−3
	2	1.62 × 10^−3	1.34 × 10^−4	1.94 × 10^−3
	4	1.50 × 10^−3	1.15 × 10^−4	1.72 × 10^−3
Spring onion, leaf	1	2.86 × 10^−3	6.63 × 10^−4	2.29 × 10^−3
	2	2.34 × 10^−3	6.59 × 10^−4	2.19 × 10^−3
	4	2.35 × 10^−3	6.55 × 10^−4	2.16 × 10^−3
Spring onion, root	1	2.77 × 10^−3	1.86 × 10^−4	2.39 × 10^−3
	2	2.76 × 10^−3	1.22 × 10^−4	2.34 × 10^−3
	4	2.61 × 10^−3	1.15 × 10^−4	1.77 × 10^−3

Table 4 The TAC changes of oven-heated onions (at 50°C) as a function of time (heating periods 1, 2, and 4 h)

		Method of TAC determination (mmol quercetin/g fresh-weight onion)
Sample	Heating time (h)	CERAC method	CUPRAC method	Folin method
Yellow-skinned onion	1	2.67 × 10^−3	1.54 × 10^−4	2.79 × 10^−3
	2	2.00 × 10^−3	1.21 × 10^−4	2.25 × 10^−3
	4	1.83 × 10^−3	1.05 × 10^−4	2.09 × 10^−3
Red-skinned onion	1	3.86 × 10^−3	5.67 × 10^−4	3.67 × 10^−3
	2	3.72 × 10^−3	4.90 × 10^−4	3.45 × 10^−3
	4	3.33 × 10^−3	3.18 × 10^−4	2.88 × 10^−3
White-skinned onion	1	2.14 × 10^−3	1.32 × 10^−4	2.14 × 10^−3
	2	2.13 × 10^−3	1.09 × 10^−4	2.05 × 10^−3
	4	2.05 × 10^−3	1.12 × 10^−4	1.93 × 10^−3
Spring onion, leaf	1	2.35 × 10^−3	6.88 × 10^−4	2.56 × 10^−3
	2	2.38 × 10^−3	6.45 × 10^−4	2.57 × 10^−3
	4	2.76 × 10^−3	7.82 × 10^−4	3.14 × 10^−3
Spring onion, root	1	3.21 × 10^−3	2.56 × 10^−4	2.12 × 10^−3
	2	2.54 × 10^−3	2.34 × 10^−4	1.95 × 10^−3
	4	2.57 × 10^−3	1.45 × 10^−4	1.77 × 10^−3