Table 3.

Oxidation products of soybean oil during frying process by ¹H NMR (mmol/mol oil).

		Primary oxidation products				Secondary oxidation products
	Time/h	E, E conjugated	Z, E conjugated	(E)-2-alkenals	(E, E)-2,4-alkadienals	n-alkanals	4-hydroxy-(E)-2-alkenals + 4-hydroperoxy-(E)-2-alkenals	4,5-epoxy-(E)-2-alkenals	4-oxoalkanals
BF	0	ND	ND	ND	ND	ND	ND	ND	ND
	6	6.38 ± 0.20Bd	ND	1.78 ± 0.01Cd	3.10 ± 0.07Bc	1.96 ± 0.04Bd	0.75 ± 0.09Bc	0.27 ± 0.14Bc	ND
	12	11.07 ± 0.19Ac	ND	3.44 ± 0.12Bc	4.80 ± 0.29ABb	3.78 ± 0.15Bc	0.87 ± 0.03Bbc	0.47 ± 0.12Abc	0.24 ± 0.02Ab
	18	13.15 ± 0.97Ab	2.34 ± 0.02Ab	5.15 ± 0.49Ab	6.41 ± 0.81A a	5.66 ± 0.64Bb	1.07 ± 0.16Bab	0.58 ± 0.13Ab	0.40 ± 0.05Ab
	24	14.36 ± 0.43Aa	2.71 ± 0.20Aa	6.78 ± 0.58Aa	6.26 ± 0.32Aa	8.32 ± 0.00Aa	1.12 ± 0.11Ba	0.82 ± 0.07Aa	0.83 ± 0.27Aa
AF	0	ND	ND	ND	ND	ND	ND	ND	ND
	6	6.54 ± 0.53Bc	ND	1.99 ± 0.04Bd	3.23 ± 0.15Bb	1.98 ± 0.05Bd	0.59 ± 0.05Cb	0.52 ± 0.06Aa	ND
	12	10.79 ± 0.97Ab	ND	4.23 ± 0.45Ac	4.04 ± 0.96Bb	3.62 ± 0.13Bc	1.22 ± 0.28Aa	0.55 ± 0.12Aa	0.21 ± 0.00Ac
	18	11.23 ± 1.29Bb	1.11 ± 0.00Bb	5.41 ± 0.43Ab	6.01 ± 0.68Aa	6.46 ± 0.03Ab	1.06 ± 0.11Ba	0.53 ± 0.02Aa	0.30 ± 0.03Bb
	24	15.66 ± 2.16Aa	1.97 ± 0.05ABa	7.12 ± 0.78Aa	6.09 ± 0.43Aa	8.18 ± 0.00Aa	1.09 ± 0.13Ba	0.61 ± 0.07Ba	0.56 ± 0.03Aa
CK	0	ND	ND	ND	ND	ND	ND	ND	ND
	6	7.67 ± 0.04Ac	ND	2.11 ± 0.02Ad	3.71 ± 0.19Ac	2.24 ± 0.20Ad	0.93 ± 0.06Ac	0.18 ± 0.10Bb	ND
	12	9.83 ± 0.77Ab	0.55 ± 0.13Ab	3.06 ± 0.30Bc	5.80 ± 0.08Ab	4.84 ± 0.04Ac	1.47 ± 0.11Ab	0.22 ± 0.00Bb	0.11 ± 0.04Bc
	18	14.52 ± 0.24Aa	2.24 ± 0.36Aa	5.25 ± 0.13Ab	6.17 ± 0.28Aab	6.37 ± 0.14ABb	1.80 ± 0.04Aa	0.26 ± 0.01Bb	0.33 ± 0.04ABb
	24	14.91 ± 0.34Aa	1.55 ± 0.78Bab	6.71 ± 0.04Aa	6.50 ± 0.55Aa	7.21 ± 0.49Ba	1.94 ± 0.16Aa	0.36 ± 0.04Ca	0.67 ± 0.03Aa

Note: Different lowercase letters indicated significant differences among samples with frying time, where different capital letters indicated significant differences among BF, AF and CK. BF – before frying, AF – after frying, CK – control.