Air drying of macauba fruits: maintaining oil quality for biodiesel production

Macauba fruits are oil-rich drupes with high moisture content at harvest. This feature can affect the chemical properties of the oil and increase the costs of biodiesel production. Therefore, it is necessary to adopt postharvest strategies to ensure oil quality. The aim of this work was to evaluate the effect of drying macauba fruit on the quality of the pulp oil. Husked and dehusked fruits were dried at 60°C and then stored. At 0, 15, 45, 100, and 180 days after storage, fruit samples were retrieved, and the oil from the pulp was evaluated for physicochemical parameters. The removal of the husk from the fruits considerably reduced the drying time compared to that of the husked fruits. Drying prevented deterioration of the fruit even after 180 days of storage, regardless of the presence of the husk. The drying process allowed for efficient storage of the macauba fruit while maintaining low levels of oil acidity. Furthermore, the oxidative stability of the pulp oil from the dehusked dried fruits lasted longer than that from the husked dried fruits. Therefore, drying is a viable alternative for the postharvest of macauba fruits to maintain the quality of the oil for biodiesel production.

Keywords:
Acrocomia aculeata; postharvest; storage; bioenergy

Authorship

Gutierres Nelson Silva ^**Author for correspondence. E-mail: gutierres.silva@ifma.edu.br

Instituto Federal de Educação, Ciência e Tecnologia do Maranhão, Povoado Poraquê, s/n., 65400-000, Codó, Maranhão, Brazil. Instituto Federal de EducaçãoBrazilCodó, Maranhão, BrazilInstituto Federal de Educação, Ciência e Tecnologia do Maranhão, Povoado Poraquê, s/n., 65400-000, Codó, Maranhão, Brazil.

http://orcid.org/0000-0002-4272-0634

José Antonio Saraiva Grossi

Departamento de Fitotecnia, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil. Universidade Federal de ViçosaBrazilViçosa, Minas Gerais, BrazilDepartamento de Fitotecnia, Universidade Federal de Viçosa, Viçosa, Minas Gerais, Brazil.

Marcela Silva Carvalho

Kacilda Naomi Kuki

Samuel de Melo Goulart

Leonardo Duarte Pimentel

*Author for correspondence. E-mail: gutierres.silva@ifma.edu.br

SCIMAGO INSTITUTIONS RANKINGS

Figures | Tables | Formulas

Figures (2)
Tables (5)
Formulas (16)

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Figure 1
Visual changes in the macauba fruits submitted to the drying temperature treatments and throughout the storage period at 25°C. Treatments: C-HU: 25°C (control) - husked fruits; D-HU: 60°C (drying) - husked fruits; C-DH: 25°C (control) - dehusked fruits; D-DH: 60°C (drying) - dehusked fruits.

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Figure 2
Response of the macauba pulp oil variables throughout the storage period: Oil content (A); Free fatty acid content (B); Oxidative stability; (C); and Water content (D). Treatments: Fruit category - husked (HU) and dehusked (DH); Drying temperature/treatment - 25 (control-C) and 60°C (drying-D).

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Table 1
Average moisture content of the freshly harvested macauba fruits (PH₀) and after the 20-day resting period (PH₂₀) and the time required for the husked and dehusked fruits to reach a 10% moisture content at 60°C (M10% - Drying time).

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Table 2
The results of the pulp oil analysis of the freshly harvested macauba fruits (PH₀) and the fruits after the 20-day resting period (PH₂₀).

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Table 3
Adjusted regression equations and their respective regression and probability coefficients for macauba fruit pulp oil content (OC) and related variables: free fatty acid content (FFA), oxidative stability (OS) and water content (WCO).

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Table 4
Macauba fruit pulp oil content (OC) and related variables: free fatty acid content (FFA), oxidative stability (OS) and water content (WCO).

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Table 5
Fatty acid profile (%) from the pulp oil of freshly harvested (IC) macauba fruits and after 0 and 180 days of storage following treatments.

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Figure 1 Visual changes in the macauba fruits submitted to the drying temperature treatments and throughout the storage period at 25°C. Treatments: C-HU: 25°C (control) - husked fruits; D-HU: 60°C (drying) - husked fruits; C-DH: 25°C (control) - dehusked fruits; D-DH: 60°C (drying) - dehusked fruits.

Figure 2 Response of the macauba pulp oil variables throughout the storage period: Oil content (A); Free fatty acid content (B); Oxidative stability; (C); and Water content (D). Treatments: Fruit category - husked (HU) and dehusked (DH); Drying temperature/treatment - 25 (control-C) and 60°C (drying-D).

Table 1 Average moisture content of the freshly harvested macauba fruits (PH₀) and after the 20-day resting period (PH₂₀) and the time required for the husked and dehusked fruits to reach a 10% moisture content at 60°C (M10% - Drying time).

Fruit category	Moisture content (%)^*		M_10% - Drying time (60°C)
Fruit category	PH₀	PH₂₀	(hour)
Husked	43.3 ± 0.82^**	35.8 ± 2.73	60
Dehusked	38.7 ± 0.70	29.4 ± 0.78	22

*During the entire resting period, the fruits were kept intact (husked fruit). However, the fruit moisture evaluations were performed on intact fruit (husked) and after husk removal (dehusked). **mean ± SE.

Table 2 The results of the pulp oil analysis of the freshly harvested macauba fruits (PH₀) and the fruits after the 20-day resting period (PH₂₀).

Variables	Sampling time
Variables	PH₀	PH₂₀
Oil content (% db)^*	47.12 ± 0.66^**	58.15 ± 0.41
Free fatty acids in the oil (% oleic acid)	0.8 ± 0.02	2.22 ± 0.59
Oxidative stability of the oil (h)	18.8 ± 0.30	14.85 ± 1.19
Water content in the oil (%)	0.16 ± 0.01	0.05 ± 0.01

*db - dry basis. **mean ± SE.

Table 3 Adjusted regression equations and their respective regression and probability coefficients for macauba fruit pulp oil content (OC) and related variables: free fatty acid content (FFA), oxidative stability (OS) and water content (WCO).

Variable	Treatment^*	Adjusted equations	R^2**	p^***
OC (% db)	D-HU	$ŷ = 60.7626 + 0.0555 x - 0.0003 x^{2}$	0.83	0.05
D-DH	$ŷ = 60.1900$	-	-
C-HU	$ŷ = 58.3936 + 0.0656 x - 0.0003 x^{2}$	0.83	0.05
C-DH	$ŷ = 61.0284 + 0.0364 x - 0.0002 x^{2}$	0.99	0.05
FFA (% oleic acid)	D-HU	$ŷ = 0.9845 + 0.0251 x$	0.91	0.01
D-DH	$ŷ = 1.0101 + 0.0385 x$	0.89	0.01
C-HU	$ŷ = 6.1719 + 0.4973 x - 0.0016 x^{2}$	0.95	0.05
C-DH	$ŷ = 2.0067 + 0.3377 x - 7.9568 x^{1 / 2}$	0.98	0.05
OS (h)	D-HU	$ŷ = 5.9638 + 0.0651 x - 1.2930 x^{1 / 2}$	0.98	0.01
D-DH	$ŷ = 12.3833 + 0.0903 x - 2.1376 x^{1 / 2}$	0.99	0.01
C-HU	$ŷ = 15.1860 + 0.1262 x - 2.8000 x^{1 / 2}$	0.96	0.05
C-DH	$ŷ = 12.3430 + 0.1556 x - {2.9396 x}^{1 / 2}$	0.92	0.05
WCO (%)	D-HU	$ŷ = 0.0562 + 0.0006 x$	0.97	0.01
D-DH	$ŷ = 0.0470 + 8.8914 x 10^{- 5} x + 1.8953 x 10^{- 6} x^{2}$	0.99	0.05
C-HU	$ŷ = 0.0428 + 0.0030 x - 9.3660 x 10^{- 6} x^{2}$	0.95	0.05
C-DH	$ŷ = 0.0728 + 0.0002 x - 9.6884 x 10^{- 6} x^{2}$	0.95	0.05

*Treatments - Fruit category: Fruit category - husked (HU) and dehusked (DH); Drying temperature/treatment - 25 (control-C) and 60°C (drying-D). **Coefficient of determination. ***Probability by t test.

Table 4 Macauba fruit pulp oil content (OC) and related variables: free fatty acid content (FFA), oxidative stability (OS) and water content (WCO).

Variable	Storage period	0		15		45		100		180
Variable	Treatment^*	HU	DH	HU	DH	HU	DH	HU	DH	HU	DH
OC (% db)	Drying	61.01Aa^**	60.37Aa	60.05Aa	61.99Aa	58.10Ab	59.13Aa	59.56Aa	59.56Aa	59.68Aa	59.92Aa
OC (% db)	Control	58.15Aa	60.99Aa	59.13Aa	60.60Aa	61.61Aa	59.75Aa	61.19Aa	59.51Aa	60.21Aa	61.29Aa
FFA (% oleic acid)	Drying	1.21Aa	0.93Aa	1.11Ab	1.72Ab	1.59Ab	1.76Ab	4.36Ab	6.41Ab	5.17Ab	7.31Ab
FFA (% oleic acid)	Control	2.22Aa	1.73Aa	16.64Ba	27.20Aa	28.55Ba	43.34Aa	36.52Ba	44.25Aa	45.04Aa	49.20Aa
OS (hour)	Drying	6.13Bb	12.15Aa	1.59Bb	6.22Aa	0.08Ba	1.44Aa	0.08Aa	0.08Aa	0.09Aa	0.04Aa
OS (hour)	Control	14.85Aa	13.23Ba	7.66Aa	0.98Bb	0.30Aa	0.30Ab	0.61Aa	0.11Aa	0.22Aa	0.04Aa
WCO (%)	Drying	0.05Aa	0.05Aa	0.06Aa	0.05Ab	0.08Aa	0.05Ab	0.12Ab	0.07Ab	0.15Ab	0.12Ab
Control	0.05Aa	0.05Aa	0.09Ba	0.14Aa	0.12Ba	0.17Aa	0.27Aa	0.24Aa	0.28Aa	0.25Aa

*Treatments - Fruit category: husked (HU) and dehusked (DH) - Drying temperature/treatment: 25 (control) and 60°C (drying). **Means followed by the same capital letter in each row or by the same lowercase letter in each column for each storage period do not differ according to Tukey’s test at a 5% significance level.

Table 5 Fatty acid profile (%) from the pulp oil of freshly harvested (IC) macauba fruits and after 0 and 180 days of storage following treatments.

Fatty acid profile (%)	Sampling occasion
	IC	0 day of storage				180 day of storage
	IC	D-HU	C-HU	D-DH	C-DH	D-HU	C-HU	D-DH	C-DH
Palmitic acid (16:0)	17.12 ± 1.27^*	20.29 ± 0.44	22.58 ± 1.31	19.37 ± 0.16	21.57 ± 0.93	21.24 ± 1.59	19.43 ± 0.14	21.35 ± 1.31	19.66 ± 0.88
Palmitoleic acid (16:1)	1.42 ± 0.38	1.98 ± 0.16	2.58 ± 0.25	1.95 ± 0.06	2.39 ± 0.16	1.65 ± 0.07	1.56 ± 0.05	1.95 ± 0.02	1.61 ± 0.12
Stearic acid (18:0)	6.74 ± 0.50	6.25 ± 0.39	5.09 ± 0.34	6.04 ± 0.13	6.22 ± 0.27	7.79 ± 0.31	6.61 ± 0.02	6.58 ± 0.27	6.32 ± 0.43
Oleic acid (18:1)	61.53 ± 2.00	58.56 ± 1.27	60.90 ± 2.17	58.76 ± 0.23	58.26 ± 0.99	62.51 ± 0.99	64.86 ± 0.29	61.57 ± 0.64	65.51 ± 0.88
Linoleic acid (18:2)	10.70 ± 1.67	9.72 ± 0.55	6.86 ± 1.02	10.66 ± 0.19	8.11 ± 0.27	5.67 ± 1.00	6.66 ± 0.09	7.21 ± 1.02	6.11 ± 0.50
Linoleic acid (18:3)	1.32 ± 0.19	1.03 ± 0.19	0.90 ± 0.09	1.14 ± 0.03	0.96 ± 0.02	0.69 ± 0.11	0.69 ± 0.01	0.70 ± 0.13	0.65 ± 0.01
Docosadienoic acid (22:2)	1.14 ± 0.49	2.13 ± 0.64	1.06 ± 0.30	2.05 ± 0.24	2.45 ± 0.12	0.42 ± 0.09	0.17 ± 0.03	0.60 ± 0.06	0.10 ± 0.01

Treatments: C-HU: 25°C (control) - husked fruits; D-HU: 60°C (drying) - husked fruits; C-DH: 25°C (control) - dehusked fruits; D-DH: 60°C (drying) - dehusked fruits. ^*mean ± SE.

ŷ = 60.7626 + 0.0555 x - 0.0003 x^{2}

ŷ = 60.1900

ŷ = 58.3936 + 0.0656 x - 0.0003 x^{2}

ŷ = 61.0284 + 0.0364 x - 0.0002 x^{2}

ŷ = 0.9845 + 0.0251 x

ŷ = 1.0101 + 0.0385 x

ŷ = 6.1719 + 0.4973 x - 0.0016 x^{2}

ŷ = 2.0067 + 0.3377 x - 7.9568 x^{1 / 2}

ŷ = 5.9638 + 0.0651 x - 1.2930 x^{1 / 2}

ŷ = 12.3833 + 0.0903 x - 2.1376 x^{1 / 2}

ŷ = 15.1860 + 0.1262 x - 2.8000 x^{1 / 2}

ŷ = 12.3430 + 0.1556 x - {2.9396 x}^{1 / 2}

ŷ = 0.0562 + 0.0006 x

ŷ = 0.0470 + 8.8914 x 10^{- 5} x + 1.8953 x 10^{- 6} x^{2}

ŷ = 0.0428 + 0.0030 x - 9.3660 x 10^{- 6} x^{2}

ŷ = 0.0728 + 0.0002 x - 9.6884 x 10^{- 6} x^{2}

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Air drying of macauba fruits: maintaining oil quality for biodiesel production

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[1] *Author for correspondence. E-mail: gutierres.silva@ifma.edu.br