Macauba ( Acrocomia aculeata ) pulp oil quality is negatively affected by drying fruits at 60 ºC

Simone Palma Favaro Crissia Fernanda Tapeti Cesar Heraclides Behling Miranda Gabrielly Ciaconini Maria Amélia M Miyahira Renato Roscoe About the authors

ABSTRACT

This study aimed to determine if the quality of macauba pulp oil is affected by drying the whole fruits at 60 ºC. Mature fruits were collected at every five days on the ground under 10 palm trees. A mixed batch of 3 kg of whole fruits, with three replications each, was dried in an oven with air circulation for 0, 12, 24, 36 and 48 h at 60 ºC. After every drying time, dried fruits were pulped using an automated device, followed by oil extraction with hexane. Moisture and oil content were determined in the pulp, and the pulp oil quality was analyzed for fatty acid composition, free fatty acids content, peroxide value, molar absorptivity at 232 and 270 nm, refractive index, and total carotene content. The tested temperature was sufficient to decrease moisture to a range suitable for automated pulping, with the best combination and easier pulping being reached after 24 h of drying. In the first 12 h there was an apparent synthesis of unsaturated fatty acids and carotenes. The tested temperature was insufficient to avoid the enhancement of acidity since the beginning and throughout the drying period, nor the degradation of polyunsaturated fatty acids. Thus, it is concluded that drying of fresh fruits of macauba palm at 60 ºC is not appropriate to obtain an overall good quality pulp oil for industrial purposes.

Key words:
macauba palm; high oleic; pulping; pulp oil; vegetable oil oxidation; vegetable oil acidity

INTRODUCTION

Brazilian public politics regarding biofuel production, such as biodiesel11 Brasil. Ministério das Minas e Energia. Programa Nacional de Produção e Uso de Biodiesel, 2005. Accessed in 2015 sep 29. Available from: http://www.mme.gov.br/programas/biodiesel.
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and aviation biokerosene22 Minas. Plataforma Mineira de Bioquerosene. 2014. Accessed in 2015 oct 11. Available from: http://www.sede.mg.gov.br/pt/transparencia/page/1877-plataforma-mineira-de-bioquerosene.
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, and the encouragement for mitigation of climate change by low carbon agriculture33 Brasil. Ministério da Agricultura, Pecuária e Abastecimento. Plano setorial de mitigação e de adaptação às mudanças climáticas para a consolidação de uma economia de baixa emissão de carbono na agricultura: plano ABC (Agricultura de Baixa Emissão de Carbono) / Ministério da Agricultura, Pecuária e Abastecimento, Ministério do Desenvolvimento Agrário, coordenação da Casa Civil da Presidência da República. In: Ministério da Agricultura PeA, editor. Brasília2012. p. 173., among others, have increased the interest in the tropical macauba palm (Acrocomia aculeata (Jacq.) Lodd). This species provides a high pulp oil yield, close and even higher than oil palm44 Pires TP, Souza ED, Kuki KN, Motoike SY. Ecophysiological traits of the macaw palm: A contribution towards the domestication of a novel oil crop. Ind Crop Prod. 2013;44:200-10.,55 Motoike SY, Kuki KN. The potential of macaw palm (Acrocomia aculeata) as source of biodiesel in Brazil. Int Rev Chem Eng. 2009;1:632-5., with suitable features for oil-based products besides a large amount of useful coproducts66 Cesar AS, Almeida FA, de Souza RP, Silva GC, Atabani AE. The prospects of using Acrocomia aculeata (macauba) a non-edible biodiesel feedstock in Brazil. Renew Sust Energ Rev. 2015;49:1213-20.,77 Evaristo AB, Grossi JAS, Carneiro ADO, Pimentel LD, Motoike SY, Kuki KN. Actual and putative potentials of macauba palm as feedstock for solid biofuel production from residues. Biomass Bioenerg. 2016;85:18-24.. However, the development to obtain high quality macauba pulp oil is still in the beginning.

Macauba fresh fruits present elevated moisture content at ripening. For example, in a study with wild groves in either wet and dry areas, moisture of ripe fruits ranged from 50 to 63%88 Ciconini G, Favaro SP, Roscoe R, Miranda CHB, Tapeti CF, Miyahira MAM, et al. Biometry and oil contents of Acrocomia aculeata fruits from the Cerrados and Pantanal biomes in Mato Grosso do Sul, Brazil. Ind Crop Prod. 2013;45:208-14.. Fresh fruit pulp also has got a strong stickness, which paired with moisture hinder automated pulping and further mechanical oil extraction by expeller pressing. Practice has shown that automated pulping and pressing is facilitated when moisture is reduced to around 20%.

Currently, fruits are mostly gathered by extractive activity from wild groves, after naturally dropping from the bunch as they mature. Then, the fruits are allowed to dry for months under room conditions in the industry quarters. The fruits processing takes place when a suitable moisture is reached. Such approach results in pulp oil with high acidity, originated from hydrolysis reactions of triglycerides, which may be caused by microbial activity99 Cavalcanti-Oliveira ED, Silva PR, Rosa TS, Moura NML, Santos BCP, Carvalho DB, et al. Methods to prevent acidification of Macauba (Acrocomia aculeata) fruit pulp oil: A promising oil for producing biodiesel. Ind. Crop Prod. 2015;77:703-7. and/or endogenous metabolism1010 Tilahum WW. Postharvest treatment of macauba palm (Acrocomia aculeata) fruit: storage period, gamma radiation and drying temperature. Viçosa: Universidade Federal de Viçosa; 2015, 110p., academic thesis. Accessed in 2016 feb 10. Available from: http://www.locus.ufv.br/bitstream/handle/123456789/6965/texto%20completo.pdf?sequence=1&isAllowed=y.. It has been demonstrated that macauba oil with high acidity can be successfully converted to biodiesel and biokerosene in lab conditions1111 Silva LN, Fortes ICP, Sousa FP, Pasa VMD. Biokerosene and green diesel from macauba oils via catalytic deoxygenation over Pd/C. Fuel. 2016;164:329-38.,1212 Souza GK, Scheufele FB, Pasa TLB, Arroyo PA, Pereira NC. Synthesis of ethyl esters from crude macauba oil (Acrocomia aculeata) for biodiesel production. Fuel. 2016;165:360-6.. However, in Brazil the current industrial processes to convert vegetable oil into biodiesel are mostly based in alkaline-transesterification, which is limited by oil acidity1313 Kusdiana D, Saka S. Methyl esterification of free fatty acids of rapeseed oil as treated in supercritical methanol. J Chem Eng Japn. 2001;34(3):383-7.. Therefore, low acid oil is still required by biofuel and other industrial purposes.

The quality of vegetable oils may also be compromised by oxidative reactions during storage and processing, which are influenced by temperature, light irradiation, metals, endogenous and exogenous enzymatic reactions, and their fatty acid composition1414 Choe E, Min DB. Mechanisms and factors for edible oil oxidation. Compr Rev Food Sci F. 2006;5(4):169-86.,1515 Hwang H. NMR spectroscopy for assessing lipid oxidation. Lipid Tech. 2015:187-9.. Macauba pulp oil presents characteristics that possibly imply a good oxidative stability. It is composed predominantly of monounsaturated fatty acids (47.05-81.32% oleic acid), followed by saturated acids (13.42-30.60% palmitic acid), with lower contents of polyunsaturated (1.40-24.71%)1616 Nunes AA, Favaro SP, Galvani F, Miranda CHB. Good practices of harvest and processing provide high quality Macauba pulp oil. Eur J Lipid Sci Tech. 2015;117(12):2036-43.,1717 Ciconini G. Caracterização de frutos e óleo de polpa de macaúba dos biomas Cerrado e Pantanal do estado de Mato Grosso do Sul, Brasil [academic]. Campo Grande: Catholic University Dom Bosco (UCDB); 2012, academic thesis. Accessed in 2016 jan 10. Available from: http://site.ucdb.br/public/md-dissertacoes/8212-caracterizacao-de-frutos-e-oleo-de-polpa-de-macauba-dos-biomas-cerrado-e-pantanal-do-estado-de-mato-grosso-do-sul-brasil.pdf.
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,1818 Hiane PA, Filho MMR, Ramos MIL, Macedo LR. Bocaiúva (Acrocomia aculeata [Jacq.] Lodd.) pulp and kernel oils: characterization and fatty acid composition. Braz J Food Tech. 2005;8:256-9.. Rich polyunsaturated lipids oxidize at a faster rate than mono and saturated ones1919 Kerrihard AL, Nagy K, Craft BD, Beggio M, Pegg RB. Oxidative Stability of Commodity Fats and Oils: Modeling Based on Fatty Acid Composition. J Am Oil Chem Soc. 2015;92(8):1153-63.. Also, it has got a significative amount of carotenoids, mostly β-carotene2020 Ramos MIL, Ramos MM, Hiane PA, Neto JAB, Siqueira EMD. Nutritional quality of the pulp of bocaiuva Acrocomia aculeata (Jacq.) Lodd. Ciencia Tecnol Alime. 2008;28:90-4.,2121 Coimbra MC, Jorge N. Fatty acids and bioactive compounds of the pulps and kernels of Brazilian palm species, guariroba (Syagrus oleracea), jeriva (Syagrus romanzoffiana) and macauba (Acrocomia aculeata). J Sci Food Agric. 2012;92:679-84., that play an important role to prevent the oil oxidation.

For the optimization of obtaining high quality macauba pulp oil is necessary to devise an efficient method of drying the fruits that could prevent acidification and oxidation, as well as to facilitate the mechanical processing of fruits. Drying fruits usually aims to maintain original color and vitamin contents. There is a wide range of temperatures and methods of drying fruits. However, it is usual to find data on fruit drying in the range of 50 to 80 ° C, more usually at 60 °C2222 Fernandes FAN, Rodrigues S, Law CL, Mujumdar AS. Drying of Exotic Tropical Fruits: A Comprehensive Review. Food Bioprocess Tech. 2011;4(2):163-85.. There is scarce information on whether accelerated drying processes of oil bearing fruits induce undesirable quality changes on the extracted oil or not, with reports going in both directions2323 Gutierrez L-F, Ratti C, Belkacemi K. Effects of drying method on the extraction yields and quality of oils from quebec sea buckthorn (Hippophae rhamnoides L.) seeds and pulp. Food Chem. 2008;106(3):896-904.,2424 Santana I, dos Reis LMF, Torres AG, Cabral LMC, Freitas SP. Avocado (Persea americana Mill.) oil produced by microwave drying and expeller pressing exhibits low acidity and high oxidative stability. Eur J Lipid Sci Tech. 2015;117(7):999-1007.. Regarding macauba palm it was reported that pulp oil acidity development, during long term storage, may be prevented by pre-treatment that controls lipolytic microorganisms, followed by drying at 60 °C during 15 days99 Cavalcanti-Oliveira ED, Silva PR, Rosa TS, Moura NML, Santos BCP, Carvalho DB, et al. Methods to prevent acidification of Macauba (Acrocomia aculeata) fruit pulp oil: A promising oil for producing biodiesel. Ind. Crop Prod. 2015;77:703-7.. This approach may be expensive and time consuming, especially for large scale processing.

This paper reports the results of a trial devised to determine if macauba fruit pulp oil quality is compromised by drying at 60 ºC until moisture content is reduced to a range that facilitates automated pulping.

MATERIAL AND METHODS

Raw Materials

Ripened fruits of macauba were collected from native palm trees growing in a central Brazil area under typical savanna-like vegetation called Cerrados, in the Campo Grande Municipality, Mato Grosso do Sul State. The minimum average temperature is 19 °C and maximum is 30 °C; the average relative humidity is 68% and annual precipitation is 1400 mm. The ground under the ten macauba palm trees was cleaned, and dropped fruits were collected every five days from January to March, being stored at -18 °C until processing. The fruit collection mimics what is usually done in the actual exploitation of macauba palm. Ten fruits from every sampled palm were randomly selected for fruit mass and size measurements. On average, the transversal external diameter was 35.6 ± 5.3 mm, and the mass of whole fruit was 27.5 ± 6.2 g.

Drying and pulping

Whole unfrozen fruits were grouped randomly into batches of 3 kg each. Three replications were directly pulped, while another three replications were pulped after 12, 24, 36, and 48 hours of drying at 60 ºC. The drier was a convective oven (Marconi, model MA035, Brazil), with air circulation and renovation. Pulping was made with the help of an automated pulper, specifically designed for macauba palm fruits (RM Ltda, Brazil), allowing to process batches of fruits up to 5 kg. The device makes an easy separation and recollection of husk, pulp, and the shell + kernel.

Determination of pulp moisture and lipid content

The moisture content of fresh and dried fruit pulp in each sampling was determined by drying at 105 °C until constant weight2525 AOAC. Association of Official Analytical Chemists. Official Methods of Analysis of AOAC International. 18 ed. Gaithersburg, Maryland, USA, 2005.. The total content of lipids was determined according to AOAC standard2525 AOAC. Association of Official Analytical Chemists. Official Methods of Analysis of AOAC International. 18 ed. Gaithersburg, Maryland, USA, 2005., using a Soxhlet apparatus and hexane as solvent.

Physicochemical analysis of pulp oil

Physicochemical analysis were performed using the oil extracted with hexane by refluxing in a Soxhlet apparatus, with further removal of the organic solvent in a rotary evaporator working at 40 °C. The following parameters were analysed: free fatty acid (FFA, expressed as percentage of oleic acid, according to method Ca5a-402626 AOCS. American Oil Chemists' Society. Official Methods and Recommended Practices of the AOCS. Champaign, Illinois, USA: AOCS Press; 2004.; peroxide value (PV), according to method Cd8-532626 AOCS. American Oil Chemists' Society. Official Methods and Recommended Practices of the AOCS. Champaign, Illinois, USA: AOCS Press; 2004.; molar absorptivity at 232 nm (K232) and 270 nm (K270), respectively, to check the eventual formation of any dimers and trimers that could result from oxidation reactions, according to method Ch5-912626 AOCS. American Oil Chemists' Society. Official Methods and Recommended Practices of the AOCS. Champaign, Illinois, USA: AOCS Press; 2004.; refractive index (RI) by refractometry at 20 oC, according to method Cc7-252626 AOCS. American Oil Chemists' Society. Official Methods and Recommended Practices of the AOCS. Champaign, Illinois, USA: AOCS Press; 2004.; and total carotene content by absorbance at 446 nm (spectrometer Aquamate, v model. 4.), using petroleum ether as organic solvent2727 PORIM. Palm Oil Research Institute of Malaysia. Determination of carotene content. Kuala Lumpur, Malaysia1990. 2-6 p..

In the sequence, the fatty acid profile was determined after the lipids were converted to fatty acid methyl esters (FAME). FAME was obtained by the addition of 2 mL of 7% Boron Fluoride (BF3) methanolic solution, plus 1 mL of toluene, followed by heating at 100 °C for 45 minutes, and cooling to room temperature with further addition of 5 mL of water, 3 mL of hexane, and 300 mg of sodium sulphate, all mixed by stirring. The top layer was collected and injected into a GC (Agilent 6890N, California, USA) equipped with a flame ionization detector (FID) and a polar capillary column (HP88, 0.25 mm internal diameter, 100 m length and 0.25 mm film thickness), to obtain individual peaks. Injector temperature was 225 °C and detector temperature was 285 °C. The initial column temperature was held at 160 °C for 3 minutes and then increased to 190 °C at 3 °C/minutes for 6 minutes, followed by an increase to 230 °C at 6 °C/minutes and then held for 12 minutes. Total run time was 37.67 minutes. FAME peaks were identified comparing their relative retention times with individual standards (Supelco C8-C22, USA), spiking the samples with methyl undecanoate. Data were analyzed using Agilent Technologies Chemstation A09.01 Software. The relative percentage of a given fatty acid was calculated comparing its individual peak with the total peak area of all fatty acids in the oil sample.

Experimental Design

An entirely randomized experimental design was applied, encompassing five drying times as the independent variable, with three replications of the drying time. Analytical procedures were done in triplicate for every sample. The results were submitted to analysis of variance and regression, using GraphPad InStat software.

RESULTS AND DISCUSSION

Drying effects upon macauba pulp moisture, lipid content, and pulping

The pooled macauba fruits showed pulp with an initial moisture content averaging 390 g kg-1, which was reduced to 370, 220, 180, and 130 g kg- 1 after drying at 60 °C during 12, 24, 36, and 48 hours, respectively, following a significant (P<0.001) linear pattern of moisture decrease (Fig. 1). As water was removed from the pulp, there was a parallel concentration in oil amount, whose content raised from 68 to 184 g kg-1 (Fig. 1). As expected, both trends were significantly correlated (Pearson Correlation 0.94, P<0.001). Only 5% of the water content was lost in the first 12 h of drying, suggesting a period of adjustment for the heated water inside the fruit to move from the inner parts through the lignocellulosic epicarp and out to the environment. Such long period under a range of temperature and moisture that might enhance some metabolic activities, may lead to either synthesis or degradation of fruit compounds.

Figure 1
Moisture and oil content of macauba pulp fruit along drying at 60 oC.

The pulp moisture dropped after 24 h to a value close to that commonly practiced to macauba fruit processing of drying, around 20%. With such moisture content, automated pulping was easily performed, being necessary only a single step operation of 2.5 minutes to pulp a batch of 3 kg fruits. When fruits had a moisture content higher than 220 g kg-1, at least three steps were needed for a complete pulping, with interruptions to disperse the jammed pulp in the machine, taking more than 10 minutes each batch.

Effects of drying on the composition of macauba pulp oil fatty acid composition

Monounsaturated fatty acids were predominant in the extracted macauba pulp oil (Table 1), with oleic acid encompassing 70% of the total composition. Palmitic acid was predominant within the saturated fatty acid fraction, accounting for 17% of the total. Polyunsaturated fatty acids corresponded to only 2.6% of the total. Overall, there were amounts higher in oleic acid, almost similar to those of palmitic acid, and lower in linoleic acid than reported in other studies99 Cavalcanti-Oliveira ED, Silva PR, Rosa TS, Moura NML, Santos BCP, Carvalho DB, et al. Methods to prevent acidification of Macauba (Acrocomia aculeata) fruit pulp oil: A promising oil for producing biodiesel. Ind. Crop Prod. 2015;77:703-7.,1818 Hiane PA, Filho MMR, Ramos MIL, Macedo LR. Bocaiúva (Acrocomia aculeata [Jacq.] Lodd.) pulp and kernel oils: characterization and fatty acid composition. Braz J Food Tech. 2005;8:256-9.,2121 Coimbra MC, Jorge N. Fatty acids and bioactive compounds of the pulps and kernels of Brazilian palm species, guariroba (Syagrus oleracea), jeriva (Syagrus romanzoffiana) and macauba (Acrocomia aculeata). J Sci Food Agric. 2012;92:679-84., although within the range determined for a large number of wild genotypes1717 Ciconini G. Caracterização de frutos e óleo de polpa de macaúba dos biomas Cerrado e Pantanal do estado de Mato Grosso do Sul, Brasil [academic]. Campo Grande: Catholic University Dom Bosco (UCDB); 2012, academic thesis. Accessed in 2016 jan 10. Available from: http://site.ucdb.br/public/md-dissertacoes/8212-caracterizacao-de-frutos-e-oleo-de-polpa-de-macauba-dos-biomas-cerrado-e-pantanal-do-estado-de-mato-grosso-do-sul-brasil.pdf.
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. Oleic and palmitic acids contents are the traits related to the profile of fatty acids which most contributed to the total divergence and differentiation of macauba genotypes2828 da Conceição LDHCS, Antoniassi R, Junqueira NTV, Braga MF, Machado AFF, Rogério JB, et al. Genetic diversity of macauba from natural populations of Brazil. BMC Res Notes. 2015;8:406-14..

Table 1:
Fatty acid profile of macauba pulp oil over fruit drying at 60 ºC.

The fatty acid composition of macauba palm oil showed some changes along the 48 h drying period (Table 1). Oleic acid content increased by around 5%, while the palmitic acid content decreased in the same proportion. These changes suggest that there were ongoing metabolic activities during the drying, with the biosynthesis of monounsaturated fatty acids. It seems that palmitic acid was converted into oleic acid by lipid chain elongation reaction in macauba pulp fruit under the drying conditions, following the normal pathway of lipid synthesis. Lipids biosynthesis begins with a source of carbon, Acetil CoA, which is converted to palmitato by a sequence of enzymes activity, is further elongated and desaturated to build up unsaturated fatty acids2929 Nelson DL, Cox MM. Lehninger Principles of Biochemistry. 5 ed. New Yourk: W. H. Freeman; 2008.. On the other hand, changes were also observed in polyunsaturated fraction, which increased in the first 12 h of drying, but was strongly reduced afterwards, remaining only 68% of its initial content after 48 h of drying (Table 1), probably because of oxidative reactions on the double bonds of those fatty acids. A similar pattern of decrease in polyunsaturated fatty acid content was also reported when macauba fruits were dried at the same temperature for 15 days99 Cavalcanti-Oliveira ED, Silva PR, Rosa TS, Moura NML, Santos BCP, Carvalho DB, et al. Methods to prevent acidification of Macauba (Acrocomia aculeata) fruit pulp oil: A promising oil for producing biodiesel. Ind. Crop Prod. 2015;77:703-7..

Effects of drying on the macauba pulp oil quality

The overall quality of a given vegetable oil is expressed in terms of its acidity (FFA, as oleic acid) and oxidative indexes such as K232, K270, PV, RI and minor components like pigments, among others. All these were measured in this study, at every sampling time along the drying period.

A superior limit for vegetable crude oil of 5.0% FFA is established by international3030 Alimentarius C. Standards for Fats and Oils from Vegetable Sources -CODEX ALIMENTARIUS, Section 2 -Codex Alimentarius Standards for Named Vegetable Oils - Stan 210, 1999. as well as by Brazilian regulations3131 ANVISA. National Agency of Sanitary Surveilliance. Resolution #482, of September 23rd, 1999. Technical rules for identification and quality of vegetable oils and fats, 1999., although the industry looks for oils with lower than 3% FFA to make feasible the further processing. In this study, the initial FFA of the extracted oil was 4.8%, as oleic acid, that jumped to 5.3% during the first 12 h of drying, with a faster release of fatty acids afterwards, reaching 30.2% after 48 h. The best fit of the data is a first order equation (Fig. 2A), and its pattern indicates that the temperature of 60 oC was not suitable to prevent hydrolitic reactions upon tryacylglicerides of the oil. It is usually assumed that macauba oil has got high acidity, although reports in the literature show variable results, with values as low as 0.8%1818 Hiane PA, Filho MMR, Ramos MIL, Macedo LR. Bocaiúva (Acrocomia aculeata [Jacq.] Lodd.) pulp and kernel oils: characterization and fatty acid composition. Braz J Food Tech. 2005;8:256-9. and as high as 65%3232 Navarro-Diaz HJ, Gonzalez SL, Irigaray B, Vieitez I, Jachmanian I, Hense H, et al. Macauba oil as an alternative feedstock for biodiesel: Characterization and ester conversion by the supercritical method. J Supercrit Fluid. 2014;93:130-7.. Acidity development in the macauba pulp oil seems to be dependent on how the fruits are collected, stored3333 Evaristo AB, Grossi JAS, Pimentel LD, Goulart SM, Martins AD, Santos VL, Motoike S. Harvest and post-harvest conditions influencing macauba (Acrocomia aculeata) oil quality attributes. Ind Crop Prod. (2016); 85:63-73.,3434 Del Río JC, Evaristo AB, Marques G, Martín-Ramos P, Martín-Gil J, Gutiérrez A. Chemical composition and thermal behavior of the pulp and kernel oils from macauba palm (Acrocomia aculeata) fruit. Ind Crop Prod. 2016;84:294-304., and samples are prepared for analytical procedures3535 Trentini CP, Oliveira DM, Zanette CM, Silva Cd. Low-pressure solvent extraction of oil from macauba (Acrocomia aculeata) pulp: characterization of oil and defatted meal. Cienc Rural. 2016;46(4):725-31.,3636 Lescano, CH, Oliveira IP, Silva, LR, Baldivia DS, Sanjinez-Argandoña EJ, Arruda, EJ, Moraes ICF, Lima F F. Nutrients content, characterization and oil extraction from Acrocomia aculeata (Jacq.) Lodd. Fruits. Afr J Food Sci. 2015;9:113-119.. It is commonly accepted that fruits should be collected from the bunch and processed as soon as possible to render low acidification, but there is not enough support in the literature for such a claim. Acidity of macauba pulp oil lower than 1% was reported in fruits kept on the ground during seven days after abscision3333 Evaristo AB, Grossi JAS, Pimentel LD, Goulart SM, Martins AD, Santos VL, Motoike S. Harvest and post-harvest conditions influencing macauba (Acrocomia aculeata) oil quality attributes. Ind Crop Prod. (2016); 85:63-73., while a 5.6% acidity was registered in oil obtained from fruits collected directly from the bunch3434 Del Río JC, Evaristo AB, Marques G, Martín-Ramos P, Martín-Gil J, Gutiérrez A. Chemical composition and thermal behavior of the pulp and kernel oils from macauba palm (Acrocomia aculeata) fruit. Ind Crop Prod. 2016;84:294-304..

Figure 2
Physicochemical characteristics of macauba pulp oil along the fruit drying at 60 ºC. (bars indicate standard deviation and different letters means significative difference at P<0.01 by Tukey test).

The actual agents of tryacilglycerides hydrolysis in macauba fruits are not yet properly known. Lipases produced by microorganisms that contaminate the fruits have been suggested to be responsible for the development of acidity during oil storage99 Cavalcanti-Oliveira ED, Silva PR, Rosa TS, Moura NML, Santos BCP, Carvalho DB, et al. Methods to prevent acidification of Macauba (Acrocomia aculeata) fruit pulp oil: A promising oil for producing biodiesel. Ind. Crop Prod. 2015;77:703-7.. Lipase activity was detected in macauba fruit without isolation of endogenous or exogenous sources up to forty days, and it was, also, correlated to the decay index1010 Tilahum WW. Postharvest treatment of macauba palm (Acrocomia aculeata) fruit: storage period, gamma radiation and drying temperature. Viçosa: Universidade Federal de Viçosa; 2015, 110p., academic thesis. Accessed in 2016 feb 10. Available from: http://www.locus.ufv.br/bitstream/handle/123456789/6965/texto%20completo.pdf?sequence=1&isAllowed=y.. On the other hand, a study on lipases in macauba pulp carried out in our laboratory (data not published), employing the methodology described by Iaderoza and Baldini3737 Iaderoza M, Baldini VLS. A importância da análise enzímica em alimentos. Ênzimos e a qualidade de vegetais processados. Campinas: ITAL; 1991., indicated the occurrence of endogenous lipolytic activity in fruits lying on the ground up to 30 days. The peak of activity was within a 40 to 70 °C temperature range. Therefore, acidification could have been further favored by drying temperature.

Besides the acidification, polyunsaturated lipid oxidation also seems to have taken place on the macauba pulp oil during the drying, as indicated by significant (P<0.001) increases measured in the K232 and K270 values (Fig. 2B). Increases of K232 values are related to the formation of primary compounds of polyunsaturated lipid degradation, indicating the beginning of the oxidative process, while increase of K270 results from further stages, are related to stable substances like conjugated trienes3838 Shahidi F, Zhong Y. Lipid oxidation: measurement methods. In: Shahidi F, editor. Bailey's industrial oil and fat products. 5th ed. New York: John Wiley; 2005. p. 357-385.. Changes in the polyunsaturated fatty acids are shown by the decrease in the amount of linoleic acid over drying process (Table 1). The slope of the best fit of the data measured along the drying period suggests distinct states of oxidative evolution into the analyzed samples. There were increases in K232 since the beginning of drying, measured at 12 h, while K270 value was significantly altered after 12 h of drying.

Although it is important to know the possible changes that could affect macauba pulp oil quality during the drying process, these measured variations in K232 and K270 cannot be assumed as constrain to determine its usage or not in the oleochemical industry, because there is not yet a regulation for this oil source. Further investigations should address this issue and contribute to set legal ranges for quality indexes of macauba pulp oil.

On the other hand, the monounsaturated lipid fraction of the macauba pulp oil does not seem to be affected by oxidation, since there were no peroxides measured as PV, neither there were increases in RI over the whole drying period (Fig. 2C),which is related to oxidative reactions upon lipids. The initial macauba pulp oil RI was 1.4675 (Fig. 2C), higher than that reported in other works, such as 1.4661616 Nunes AA, Favaro SP, Galvani F, Miranda CHB. Good practices of harvest and processing provide high quality Macauba pulp oil. Eur J Lipid Sci Tech. 2015;117(12):2036-43., 1.4643939 Ferrari RA, Azevedo Filho JA. Macauba as promising substrate for crude oil and biodiesel production. J Agric Sci Technol. 2012;B2:1119-26., and 1.4434040 Bora PS, Rocha RVM. Macaiba palm: fatty and amino acids composition of fruits. Cienc Tecnol Aliment. 2004;4:158-62.. These variations are probably caused by sampling of different wild groves of macauba palm, Mato Grosso do Sul State (Southwest), São Paulo State (Southeast) and Paraíba State (Northeast) of Brazil, respectively to the citations. During the first 36 h of drying, RI decreased slightly, but it decreased significantly (P<0.05) by the next evaluation (Fig. 2C). Together with no detection of peroxides, RI results suggest that the bulk of macauba pulp oil shows some extent of oxidative stability under those drying conditions, probably confered by the well known stability of oleic acid1919 Kerrihard AL, Nagy K, Craft BD, Beggio M, Pegg RB. Oxidative Stability of Commodity Fats and Oils: Modeling Based on Fatty Acid Composition. J Am Oil Chem Soc. 2015;92(8):1153-63., which accounts fo a high proportion of macauba pulp oil. This oil has got a crosslinked structure, due to its diglycerides content3333 Evaristo AB, Grossi JAS, Pimentel LD, Goulart SM, Martins AD, Santos VL, Motoike S. Harvest and post-harvest conditions influencing macauba (Acrocomia aculeata) oil quality attributes. Ind Crop Prod. (2016); 85:63-73., which, added to its degree of monounsaturation, confers the high thermal stability observed in this study.

The oxidative stability may also be helped by the carotene content of the macauba pulp oil, which averaged 179.88 mg kg-1 in fresh fruits (Fig. 2D). There was a significant (P<0.05) increment during the first 12 hours of drying, to 221.31 mg kg-1, suggesting a possible synthesis of carotenes, as observed for the fruits of Lycium barbarum dried at 55 ºC4141 Wen-ping MA, Zhi-jing NI, L.I. H, Chen M. Changes of the main carotenoid pigment contents during the drying processes of the different harvest stage fruits of Lycium barbarum L. Agric Sci China. 2008;7:363-9.. In the sequence of drying, carotene content dropped to a final content of 89.11 mg kg-1 after 48 h of drying. Such a pattern is usually observed when processing temperatures are higher than the environmental conditions, in the presence of oxygen4242 Daood HG, Kapitany J, Biacs P, Albrecht K. Drying temperature, endogenous antioxidants and capsaicinoids affect carotenoid stability in paprika (red pepper spice). J Sci Food Agr. 2006;86(14):2450-7..

Overall, results suggest that drying macauba fruits at 60 ºC is not a suitable procedure to obtain a final oil with a quality acceptable for most industrial purposes. The reduction of moisture to a water content that facilitates pulping, around 20%, was reached after 24 h of drying (Fig. 1), a period of time long enough to allow some important degradation processes to happen, despite the occurrence of synthesis of interesting components as well. The main constraint was the development of acidity. Actually, the acidity of the fresh fruits was at the limit for a suitable vegetable oil, and it was enhanced by the drying process, increasing more than twofold after 24 h (Fig. 2A). Perhaps this temperature of drying would be suitable for fresh fruits with lower acidity, resulting in dried fruits that would be easily pulped before acidity reaches the standard industrial limit. Furthermore, oxidation reactions in the macauba pulp oil were observed to a small extent during the first 24 h of drying, which can be an effect of its fatty acid composition (Table 1) and carotene content (Fig. 2D). Thus, it would be worthy to carry out further studies with higher temperatures of drying, searching for a combination of temperature and time that would provide a reduction of moisture to around 20%, without allowing lipids degradation reactions.

CONCLUSIONS

Accelerated drying of fresh fruits of macauba palm at 60 °C is not suitable to obtain an overall good quality pulp oil for industrial purposes, because it allows the development of undesirable acidity, although keeping its intrinsic oxidative stability.

ACKNOWLEDGEMENTS

The authors gratefully acknowledge funding from Institute Euvaldo Lodi, Biocom - Biofuels Co., and National Council for Scientific and Technological Development (CNPq).

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Publication Dates

  • Publication in this collection
    2017

History

  • Received
    03 Feb 2016
  • Accepted
    14 July 2016
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