Fatty Acid Determination in Fermented Milk Samples Employing Direct Esterification and Gas Chromatography

The developed method (DM) allows to perform experiments in shorter time with reduced amount of sample and reagent for fatty acids (FA) determination in fermented milk samples. Design Expert software was employed to discover the greatest sonication time (7 and 20 min) and concentration for alkaline and acidic reactions (0.70 and 1.5 mol L^-1). Validation procedures were applied in yogurt samples with diverse fat content, ranging from 1.22 to 2.83%, being in agreement with acceptable values. Besides, the intraday relative standard deviation (RSD) (1.86%) and interday RSD (4.23%) values confirmed the good accuracy of the proposed method for FA derivatization.

Keywords:
fermented milk; design expert; derivatization; gas chromatography

Authorship

Angélica F. B. Piccioli

Programa de Pós-Graduação em Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, BrazilUniversidade Estadual de MaringáBrazilMaringá, PR, BrazilPrograma de Pós-Graduação em Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, Brazil

Departamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, BrazilUniversidade Estadual de MaringáBrazilMaringá, PR, BrazilDepartamento de Química, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, Brazil

https://orcid.org/0000-0002-3315-8731

Patrícia D. S. Santos

Roberta da Silveira

Programa de Pós-Graduação em Ciência dos Alimentos, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, BrazilUniversidade Estadual de MaringáBrazilMaringá, PR, BrazilPrograma de Pós-Graduação em Ciência dos Alimentos, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, Brazil

Departamento de Ciência dos Alimentos, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, BrazilUniversidade Estadual de MaringáBrazilMaringá, PR, BrazilDepartamento de Ciência dos Alimentos, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900 Maringá-PR, Brazil

Elton Bonafé

Jesuí V. Visentainer

Oscar O. Santos ^** e-mail: oliveirasantos.oscardeoliveira@gmail.com

https://orcid.org/0000-0002-9631-8480

* e-mail: oliveirasantos.oscardeoliveira@gmail.com

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables | Formulas

Figures (2)
Tables (4)
Formulas (1)

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Figure 1
3D graph of the response surface obtained for the interactions between the variables A (alkaline concentration) and B (acid concentration) in the responses as sum of FA concentration.

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Figure 2
Lipid profile by ESI(+)-MS of the (a) derivatization of the conventional method and (b) derivatization developed in this work, focused on mass ranges of m/z 100-1200.

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Table 1
ANOVA parameter models for develop methodology (DM) in fermented milk

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Table 2
Factors, levels and FA sum for each procedure of the experimental design

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Table 3
Fatty acids quantification by conventional extraction, esterification and transesterification methodology (CM) in comparison to developed methodology (DM) (n = 3, mean ± standard error)

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Table 4
Fatty acid composition of fermented milk by develop methodology (DM) (n = 3, mean ± standard error)

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(1)

Figure 1 3D graph of the response surface obtained for the interactions between the variables A (alkaline concentration) and B (acid concentration) in the responses as sum of FA concentration.

Figure 2 Lipid profile by ESI(+)-MS of the (a) derivatization of the conventional method and (b) derivatization developed in this work, focused on mass ranges of m/z 100-1200.

Table 1 ANOVA parameter models for develop methodology (DM) in fermented milk

	Square sum	LD^a a LD: freedon degree;	Square	F value	Prob > F^b b Prob > F: probability value associated with F value;
Model	82.36	22	3.74	7.35	0.0100	S^f f S: significant;
A^c c A: NaOH concentration;	12.29	1	12.29	24.13	0.0027	-
B^d d B: H2SO4 concentration;	12.62	1	12.62	24.77	0.0025	-
ACD^e e ACD: interaction between NaOH concentration (A), NaOH retention time (C) and H2SO4 retention time (D);	3.53	1	3.53	6.93	0.0390	-
Residue	3.06	6	0.51	-	-	-
Absence of adjustment	1.71	2	0.85	2.54	0.1941	NS^g g NS: non-significant.
Pure error	1.35	4	0.34	-	-	-
Total core	85.42	28	-	-	-	-

^a
LD: freedon degree;
^b
Prob > F: probability value associated with F value;
^c
A: NaOH concentration;
^d
B: H₂SO₄ concentration;
^e
ACD: interaction between NaOH concentration (A), NaOH retention time (C) and H₂SO₄ retention time (D);
^f
S: significant;
^g
NS: non-significant.

Table 2 Factors, levels and FA sum for each procedure of the experimental design

	Experiment	Concentration of NaOH in methanol		Concentration of H₂SO₄ in methanol		Sonication time of NaOH in methanol		Sonication time of H₂SO₄ in methanol		FA sum / (mg g^-1 of sample)
	Experiment	Real / (mol L^-1)	Coded	Real / (mol L^-1)	Coded	Real / min	Coded	Real / min	Coded	FA sum / (mg g^-1 of sample)
Full factorial design	1	0.70	-	0.70	-	7.00	-	7.00	-	3.03
	2	1.50	+	0.70	-	7.00	-	7.00	-	2.38
	3	0.70	-	1.50	+	7.00	-	7.00	-	6.68
	4	1.50	+	1.50	+	7.00	-	7.00	-	5.89
	5	0.70	-	0.70	-	20.00	+	7.00	-	5.00
	6	1.50	+	0.70	-	20.00	+	7.00	-	2.13
	7	0.70	-	1.50	+	20.00	+	7.00	-	7.04
	8	1.50	+	1.50	+	20.00	+	7.00	-	2.86
	9	0.70	-	0.70	-	7.00	-	20.00	+	4.51
	10	1.50	+	0.70	-	7.00	-	20.00	+	2.03
	11	0.70	-	1.50	+	7.00	-	20.00	+	7.37
	12	1.50	+	1.50	+	7.00	-	20.00	+	4.94
	13	0.70	-	0.70	-	20.00	+	20.00	+	4.57
	14	1.50	+	0.70	-	20.00	+	20.00	+	1.94
	15	0.70	-	1.50	+	20.00	+	20.00	+	5.52
	16	1.50	+	1.50	+	20.00	+	20.00	+	5.14
Axial point	17	0.30	-α	1.10	0	13.50	0	13.50	0	6.95
	18	1.90	+α	1.10	0	13.50	0	13.50	0	1.98
	19	1.10	0	0.30	-α	13.50	0	13.50	0	1.94
	20	1.10	0	1.90	+α	13.50	0	13.50	0	6.96
	21	1.10	0	1.10	0	0.50	-α	13.50	0	3.00
	22	1.10	0	1.10	0	26.50	+α	13.50	0	3.81
	23	1.10	0	1.10	0	13.50	0	0.50	-α	2.50
	24	1.10	0	1.10	0	13.50	0	26.50	+α	4.82
Central point	25	1.10	0	1.10	0	13.50	0	13.50	0	2.60
	26	1.10	0	1.10	0	13.50	0	13.50	0	3.39
	27	1.10	0	1.10	0	13.50	0	13.50	0	3.39
	28	1.10	0	1.10	0	13.50	0	13.50	0	4.05
	29	1.10	0	1.10	0	13.50	0	13.50	0	3.96

FA: fatty acid; ±1: factor points; ± α: axial points; 0: central points.

Table 3 Fatty acids quantification by conventional extraction, esterification and transesterification methodology (CM) in comparison to developed methodology (DM) (n = 3, mean ± standard error)

Carbon number	FA^a a FA: fatty acid; / (mg g^-1 of sample)
Carbon number	CM^b b CM: conventional methodology;	DM^c c DM: developed methodology;
14:0	0.48 ± 0.36	0.90 ± 0.14
16:0	1.22 ± 2.70	2.33 ± 0.08
18:0	0.49 ± 2.08	1.03 ± 0.15
18:1n-9	1.13 ± 2.09	1.79 ± 0.19
18:2n-6c	0.16 ± 2.41	0.42 ± 0.07
ΣFA^d d ΣFA: sum of fatty acid.	3.48 ± 1.52	6.47 ± 0.27

^a
FA: fatty acid;
^b
CM: conventional methodology;
^c
DM: developed methodology;
^d
ΣFA: sum of fatty acid.

Table 4 Fatty acid composition of fermented milk by develop methodology (DM) (n = 3, mean ± standard error)

Carbon number	FA^a a FA: fatty acid; / (mg g^-1 of sample)
Carbon number	Y1	Y2	Y3	Y4	Y5
12:0	0.28 ± 0.02	0.29 ± 0.06	0.27 ± 0.15	0.48 ± 0.13	-
14:0	1.12 ± 0.04	1.07 ± 0.09	0.84 ± 0.06	1.40 ± 0.08	0.84 ± 0.07
16:0	3.44 ± 0.09	2.96 ± 0.42	2.30 ± 0.28	3.90 ± 0.30	2.14 ± 0.19
16:1	0.18 ± 0.03	0.12 ± 0.03	-	0.26 ± 0.07	-
18:0	1.29 ± 0.05	1.04 ± 0.05	0.84 ± 0.06	1.44 ± 0.12	0.86 ± 0.09
18:1n-9	2.11 ± 0.05	1.98 ± 0.18	1.51 ± 0.22	2.68 ± 0.19	1.48 ± 0.08
18:1n-6	-	0.19 ± 0.07	-	0.45 ± 0.04	-
ΣFA^b b ΣFA: sum of fatty acid.	8.42 ± 0.13	7.65 ± 0.77	5.76 ± 0.77	10.61 ± 0.66	5.32 ± 0.11

^a
FA: fatty acid;
^b
ΣFA: sum of fatty acid.
Y1-Y5: yogurt samples.

(1)

FA Sum = + 3.48 - 1.24 (A) + 1.26 (B) + 0.47 (ACD)

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Fatty Acid Determination in Fermented Milk Samples Employing Direct Esterification and Gas Chromatography

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[1] * e-mail: oliveirasantos.oscardeoliveira@gmail.com