Analytical Method Development for Fatty Acid Direct Methylation in Fruits

Santos, Patrícia D. S.; Silveira, Roberta da; Reis, Natália V.; Visentainer, Jesuí V.; Santos, Oscar O.

doi:10.21577/0103-5053.20180036

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Articles • J. Braz. Chem. Soc. 29 (8) • Aug 2018 • https://doi.org/10.21577/0103-5053.20180036 copy

Analytical Method Development for Fatty Acid Direct Methylation in Fruits

Authorship SCIMAGO INSTITUTIONS RANKINGS

Due to the amount of pigments, sugars and fibers found in fruits, the fatty acid quantification process leads to errors, such as its amount underestimation in the matrix. Therefore, the proposed method allows performing experiments in shorter time with reduced amount of sample and reagent. Design Expert software was used to find the validated time for alkaline and acidic reactions, which were six and eight minutes, respectively, and both concentration was 0.5 mol L^-1. The validation was made for avocado pulp and different fruits were used for application of the method, such as: apple, mango, coconut and another avocado variety. Accuracy values ranged from 89.05 to 100.21%, being in accordance with acceptable values. Also the relative standard deviation (RSD)_intra-day (0.30 to 1.30%) and the RSD_inter-day values (0.32 to 1.44%) confirmed that the proposed method for fatty acid derivatization has good precision.

Keywords:
lipids; direct derivatization; ultrasound

Experiment		Reaction time of NaOH in methanol		Reaction time of H₂SO₄ in methanol		Concentration of H₂SO₄ in methanol		Concentration of NaOH in methanol		Sum of FA / (mg g^-1 of sample)
Experiment		Real / min	Coded	Real / min	Coded	Real / min	Coded	Real / min	Coded	Sum of FA / (mg g^-1 of sample)
Full factorial design	1	6.0	-1	8.0	-1	0.2	-1	0.2	-1	14.6
	2	11.0	+1	8.0	-1	0.2	+1	0.2	-1	14.4
	3	6.0	-1	15.0	+1	0.2	-1	0.2	+1	19.2
	4	11.0	+1	15.0	+1	0.2	+1	0.2	+1	17.1
	5	6.0	-1	8.0	-1	0.5	-1	0.2	-1	18.1
	6	11.0	+1	8.0	-1	0.5	+1	0.2	-1	10.2
	7	6.0	-1	15.0	+1	0.5	-1	0.2	+1	17.2
	8	11.0	+1	15.0	+1	0.5	+1	0.2	+1	11.6
	9	6.0	-1	8.0	-1	0.2	-1	0.5	-1	14.8
	10	11.0	+1	8.0	-1	0.2	+1	0.5	-1	16.7
	11	6.0	-1	15.0	+1	0.2	-1	0.5	+1	14.7
	12	11.0	+1	15.0	+1	0.2	+1	0.5	+1	17.5
	13	6.0	-1	8.0	-1	0.5	-1	0.5	-1	22.1
	14	11.0	+1	8.0	-1	0.5	+1	0.5	-1	11.8
	15	6.0	-1	15.0	+1	0.5	-1	0.5	+1	16.3
	16	11.0	+1	15.0	+1	0.5	+1	0.5	+1	13.5
Axial point	17	3.50	-a	11.5	0	0.35	-a	0.35	+1	12.5
	18	13.5	+a	11.5	0	0.35	+a	0.35	+1	12.0
	19	8.5	0	4.5	-a	0.35	0	0.35	-a	10.3
	20	8.5	0	18.5	+a	0.35	0	0.35	+a	18.3
Central point	21	8.5	0	11.5	0	0.05	0	0.35	0	17.1
	22	8.5	0	11.5	0	0.65	0	0.35	0	17.1
	23	8.5	0	11.5	0	0.35	0	0.05	0	15.3
	24	8.5	0	11.5	0	0.35	0	0.65	0	18.9
	25	8.5	0	11.5	0	0.35	0	0.35	0	18.9
	26	8.5	0	11.5	0	0.35	0	0.35	0	18.5
	27	8.5	0	11.5	0	0.35	0	0.35	0	20.1
	28	8.5	0	11.5	0	0.35	0	0.35	0	16.9
	29	8.5	0	11.5	0	0.35	0	0.35	0	19.3

	Square sum	LD^a a LD: degree of freedom;	Square average	F-value	Prob > F^b b Prob > F: probability value associated with F value;
Model	171.83	6	28.64	6.96	0.0003	S^h h S: significant;
A^c c A: reaction time of NaOH;	26.46	1	26.46	6.43	0.0188	-
B^d d B: reaction time of H2SO4;	17.34	1	17.34	4.21	0.0522	-
AC^e e C: concentration of NaOH; ,^f f AC: interaction between reaction time of NaOH and concentration of NaOH;	52.56	1	52.56	12.77	0.0017	-
A²	57.55	1	57.55	13.98	0.0011	-
B²	23.94	1	23.94	5.82	0.0246	-
Residue	90.53	22	4.12	-	-	-
Lack of adjustment	84.90	18	4.72	3.35	0.1249	NSⁱ i NS: non-significant.
Pure error	5.63	4	1.41	-	-	-
Total color^g g Total color: total squares sum corrected to mean;	262.67	28	-	-	-	-

CN/BD	Avocado / (mg g^-1 of sample)
CN/BD	TM	PM
16:0	7.65^a ± 1.75	6.68^a ± 1.62
16:1n-7	0.85^a ± 2.30	1.13^a ± 1.55
18:0	0.17^a ± 1.30	0.21^a ± 1.51
18:1n-9	8.3^a ± 1.1	7.50^a ± 0.11
18:1n-7	0.75^a ± 2.1	1.03^a ± 2.50
18:2n-6	3.23^b ± 4.4	5.30^c ± 3.86
18:3n-3	0.32^a ± 1.2	0.31^a ± 1.50
SFA	7.82^a ± 3.05	6.89^a ± 3.13
MUFA	9.9^a ± 5.5	9.65^a ± 4.16
PUFA	3.55^b ± 5.6	5.61^c ± 5.36
n-6	3.23^b ± 4.4	5.30^c ± 3.86
n-3	0.32^a ± 1.2	0.31^a ± 1.50
n-6/n-3	10.10^a ± 3.67	16.99^a ± 2.57
PUFA/SFA	0.45^a ± 1.84	0.81^a ± 3.0
ΣFA	21.27^a ± 5.84	22.16^a ± 5.80

CN/DB	FA / (mg g^-1 of sample)
	Apple		Banana		Mango		Coconut		Backyard avocado
	TM	PM	TM	PM	TM	PM	TM	PM	TM	PM
8:0	-	-	-	-	-	-	2.23^e ± 3.2	4.0^f ± 3.1	-	-
10:0	-	-	0.042^a ± 1.3	0.085^a ± 1.7	0.30^c ± 1.5	0.097^b ± 2.0	8.42^e ± 3.5	4.3^f ± 3.1	-	-
12:0	-	-	-	-	-	-	32.31^e ± 4.3	48.9^f ± 2.1	-	-
14:0	-	-	0.020^a ± 1.4	-	-	-	13.82^e ± 2.1	24.0^f ± 2.9	-	-
16:0	0.08^b ± 3.8	0.04^b ± 4.0	0.61^a ± 2.5	0.075^a ± 3.0	0.34^c ± 1.2	0.2^b ± 2.7	8.58^e ± 3.8	14.3^f ± 4.1	9.8^m ± 1.3	12.9^m ± 1.6
16:1n-7	-	-	0.046^a ± 1.2	-	0.07^d ± 0.9	-	-	-	0.90^m ± 0.4	2.7^m ± 0.5
18:0	0.014^a ± 1.4	-	0.024^a ± 1.8	0.40^a ± 2.0	0.03^d ± 1.8	-	2.21^e ± 3.3	4.2^f ± 3.0	0.25^m ± 1.6	0.32^m ± 0.9
18:1n-9	0.099^c ± 2.3	-	0.26^a ± 1.1	0.25^a ± 1.5	0.35^c ± 0.7	0.22^b ± 0.8	8.84^e ± 4.2	13.2^f ± 4.5	14.4^m ± 0.7	13.8^m ± 0.5
18:1n-7	-	-	0.32^a ± 1.0	0.002^a ± 2.2	0.25^c ± 1.9	0.12^b ± 0.9	1.59^e ± 2.6	3.4^f ± 2.5	0.46^m ± 1.3	0.53^m ± 1.5
18:3n-3	-	-	-	-	-	-	-	-	0.06^m ± 0.7	0.35^m ± 0.4
18:2n-6	0.020^b ± 1.1	0.083^b ± 0.9	-	-	-	-	-	-	5.49^m ± 1.3	6.80^m ± 0.9
ΣFA	0.213^b ± 8.6	0.12^b ± 4.9	1.32^a ± 10.3	0.812^a ± 9.8	1.34^c ± 8.0	0.637^b ± 6.5	78.0^e ± 27.0	116.3^t ± 25.3	31.4^m ± 7.5	37.4^m ± 7.5

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