Optimization of Solvent Extraction and Direct Transmethylation Methods for the Analysis of Egg Yolk Lipids

Figures & data

Table 1 Lipid content of egg lipids obtained from 2 different extraction methods (% lipid/yolk).

Replicates	OBD ^a	MBD
1	30.76	34.64
2	31.41	33.72
3	32.55	35.52
4	32.55	35.59
Mean ^b	31.82	34.87
SD	0.89	0.88
^aOBD = original Bligh and Dyer procedure; MBD = modified Bligh and Dyer procedure using a 15x excess of solvent; ^bValues differ (P < 0.01).

Table 2 Fatty acid content of egg yolk lipids after applying different extraction methods (mg/g yolk, means ± standard deviation) ^a .

	OBD ^b	MBD	DM
	(n = 4)
C14:0	0.76 ± 0.01	0.76 ± 0.07	0.75 ± 0.02
C14:1n5	0.13 ± 0.01	0.15 ± 0.01	0.13 ± 0.01
C16:0	60.37 ± 1.26	63.16 ± 2.74	60.52 ± 1.95
C16:1n9	1.55 ± 0.10	1.61 ± 0.15	1.59 ± 0.06
C16:n7	6.91 ± 0.20	7.41 ± 0.44	6.89 ± 0.19
C18:0	21.11 ± 0.55	20.98 ± 0.89	20.60 ± 0.41
C18:1n9	113.92 ± 3.49	110.81 ± 5.26	107.55 ± 3.31
C18:1n7	5.41 ± 0.39	5.30 ± 0.27	5.07 ± 0.13
C18:2n6	35.43 ± 0.94	36.20 ± 1.87	35.42 ± 0.84
C18:3n3	0.73 ± 0.02	0.75 ± 0.02	0.73 ± 0.03
C20:1n9	0.63 ± 0.04	0.60 ± 0.04	0.57 ± 0.03
C20:2n6	0.38 ± 0.02	0.35 ± 0.01	0.35 ± 0.02
C20:3n6	0.34 ± 0.04	0.36 ± 0.04	0.38 ± 0.04
C20:4n6	5.30 ± 0.17	5.26 ± 0.32	5.44 ± 0.17
C22:4n6	0.48 ± 0.04	0.43 ± 0.07	0.42 ± 0.04
C22:5n6	1.50 ± 0.12	1.38 ± 0.02	1.36 ± 0.04
C22:5n3	0.15 ± 0.02	0.14 ± 0.09	0.18 ± 0.02
C22:6n3	1.71 ± 0.06	1.68 ± 0.07	1.63 ± 0.05
Σ fatty acids	256.10 ± 2.01	257.31 ± 12.10	249.60 ± 7.27
^aNone of the values measured differed (P > 0.05);^bOBD = original Bligh and Dyer procedure, MBD = modified Bligh and Dyer procedure using a 15x excess of solvent, DM = direct method (one-step extraction/transmethylation).

Figure 1 Recovery of fatty acids after addition of water to the tramsmethylation reaction ^a . ^a The crossmark represents the recovery of directly transmethylated fresh (liquid) yolk.

Table 3 Recovery of individual fatty acids after addition of water to the transesterification mixture

	mg water/mg dry yolk
	0.0	0.1	0.5	1.0	2.0	4.0	10.0
	Recovery (%) ^a
C16:0	98.0	102.4	102.8	98.8	98.4	99.0	34.4
C18:0	98.2	102.2	104.6	109.2	101.9	102.2	58.5
C18:1n9	97.6	102.1	104.2	109.2	101.8	100.8	28.6
C18:2n6	98.7	102.4	104.9	109.6	102.2	101.6	36.4
C18:3n3	88.4	100.3	104.2	99.6	101.8	99.9	0.0
C20:4n6	99.1	101.7	107.4	110.8	103.4	104.0	87.9
C22:6n3	96.7	99.7	96.7	101.6	103.7	99.1	99.9
^aRecovery calculated versus the mean of a duplicate control sample, which was transmethylated from freeze-dried egg yolk and internal standard added prior to transmethylation.

Table 4 Fatty acid content of egg yolk after direct transmethylation of fresh egg yolk

	Fatty acids (mg/g yolk)
	Mean ± SD (n = 4)
C14:0	0.58 ± 0.03
C14:1n5	0.11 ± 0.01
C16:0	63.72 ± 0.67
C16:1n9	1.53 ± 0.15
C16:1n7	6.80 ± 0.17
C18:0	22.59 ± 0.32
C18:1n9	108.33 ± 1.26
C18:1n7	4.95 ± 0.05
C18:2n6	33.40 ± 0.41
C18:3n3	0.62 ± 0.04
C20:1n9	0.46 ± 0.01
C20:2n6	0.29 ± 0.02
C20:3n6	0.34 ± 0.04
C20:4n6	5.90 ± 0.13
C22:4n6	0.39 ± 0.07
C22:5n6	1.40 ± 0.05
C22:6n3	1.45 ± 0.05
Σ fatty acids	252.98 ± 2.52