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Agrociencia
versión On-line ISSN 2521-9766versión impresa ISSN 1405-3195
Agrociencia vol.52 no.5 Texcoco jul./ago. 2018
Natural renewable resources
Inhibition of lipid oxidation and related phenolic constituents in the wood and bark of three oak species (Quercus candicans, Q. laurina, and Q. rugosa)
1 Facultad de Ingeniería en Tecnología de la Madera, Universidad Michoacana de San Nicolás de Hidalgo. 58040. Avenida Francisco. J. Mugica s/n, Edificio D, planta alta, Ciudad Universitaria, Colonia Felicitas del Rio, Morelia, Michoacán, México. (rutiaga@umich.mx)
2 Departamento de Investigación en Alimentos, Facultad de Ciencias Químicas, Universidad Autónoma de Coahuila. 25280. Boulevard Venustiano Carranza y José Cárdenas V. Colonia República, Saltillo, Coahuila, México.
An increasing number of researches have focused on phenols with antioxidant capacities that can fight diseases caused by free radicals. Those phenols can be found in various plants, fruits, and other structures. These substances were also detected in the wood of conifers and some oak species. However, there are few studies about this kind of wood, even though they could be a source of these phenols. Therefore, the objective of this study was to determine the antioxidant capacity and the phenolic profile of the methanolic and aqueous extracts from the sapwood, heartwood, and bark of three oaks (Quercus candicans, Q. laurina, and Q. rugosa). The extracts were obtained by successive extraction with solvents of increasing polarity (cyclohexane, acetone, and methanol) in a Soxhlet equipment, and they were finally subject to hot water with reflux. The antioxidant activity was analyzed through the inhibition of the lipid oxidation, while the phenolic composition of the extracts was analyzed through a HPLC analysis. Higher outputs were obtained from the total extracts with methanol taken from bark. The inhibition of the lipid oxidation was higher when the methanolic extract was taken from the sapwood of Q. rugosa (antioxidant activity: 94.09 %), while the methanolic extract taken from the sapwood of Q. laurina was lower (42.54 %). The phenolic compounds most frequently found in the extracts taken from the three oaks were chlorogenic acid, resorcinol, catechin, and gallic acid. Methanolic and aqueous extracts taken from the wood and bark of three oaks are rich in phenolic compounds with potent antioxidant activity and they are an alternative source of biomolecules.
Key words: extractives; sapwood; heartwood; Quercus spp.; antioxidant activity; phenols
La búsqueda de fenoles con capacidad antioxidante presentes en diferentes plantas, frutos y otras estructuras para combatir enfermedades que ocasionan los radicales libres va en aumento. Estas sustancias también se han detectado en maderas de coníferas y en algunas especies de encinos, pero hay pocos estudios con maderas de este género y que puedan ser fuente de estos fenoles. Por ello, el objetivo de este estudio fue determinar la capacidad antioxidante y el perfil fenólico de extractos metanólicos y acuosos en albura, duramen y corteza de tres encinos (Quercus candicans, Q. laurina y Q. rugosa). Los extractos se obtuvieron por extracción sucesiva con disolventes de polaridad creciente (ciclohexano, acetona, metanol) en equipo Soxhlet y al final con reflujo de agua caliente. La actividad antioxidante se analizó mediante la inhibición de la oxidación de lípidos y la composición fenólica de los extractos por análisis HPLC. Los rendimientos mayores se obtuvieron en los extractos totales con metanol de las cortezas. La inhibición de la oxidación de lípidos fue mayor con el extracto metanólico de la albura de Q. rugosa (94.09 % de actividad antioxidante), en contraste el extracto metanólico de la albura de Q. laurina fue el menor (42.54 %). Los compuestos fenólicos más frecuentes en los extractos de los tres encinos fueron el ácido clorogénico, resorcinol, catequina y ácido gálico. Los extractos metanólicos y acuosos de madera y corteza de los tres encinos son ricos en compuestos fenólicos con actividad antioxidante potente y son una alternativa como fuente de biomoléculas.
Palabras clave: extraíbles; albura; duramen; Quercus spp.; actividad antioxidante; fenoles
Introduction
There are several studies about the antioxidant capacity and chemical analysis of the extracts of various plants and fruits. Some of their compounds were approved for medicinal treatments. The antioxidant activity of the plants is caused by non-nutritional compounds with high biological activity, such as polyphenols, vitamins, and minerals (Khalaf et al., 2008; Chemah et al., 2010). The following polyphenols found in plants or trees stand out: flavonoids, isoflavones, flavones, quercetin, catechin, gallic acid, and resorcinol (Cai et al., 2010; Ruiz-Martínez et al., 2011; Rosales-Castro et al., 2012; Huang et al., 2015).
Plants have a very important antioxidant activity that can help and improve the well-being of the people who consume them, as well as fight diseases caused by free radicals (Ruiz-Martínez et al., 2011). Free radicals -molecules or groups of molecules with an unpaired electron- cause cellular oxidation. They are highly reactive and they contribute to a chain reaction that damages the organism and causes the oxidative stress associated with Alzheimer, cancer, diabetes, and cardiovascular diseases (associated with lipid peroxidation mechanisms), as well as damage to DNA and proteins (Butera et al., 2002; Nuengchamnong et al., 2004).
The chemical composition of extractives is complex (Fengel and Wegener, 1984) and separating each antioxidant compound and studying it individually is costly and inefficient (Kalia et al., 2008; Wong-Paz et al., 2015a). Some available systems can evaluate the antioxidant activity of plants, such as the DPPH free radical (1,1-diphenyl, -1-picril hydrazine) and ABTS cation (2,29-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid). Other methods suggest more accurate information about the antioxidant capacity of biological systems such as the inhibition of lipid oxidation (Huang et al., 2005). This antioxidant capacity has been detected in compounds found in fruits, vegetables, and parts of lower plants, as well as in conifers (Rosales-Castro et al., 2009) and some oaks (Kim et al., 2008; Rocha-Guzmán et al., 2009; Rosales-Castro et al., 2012). Oaks -trees that belong to the Quercus genus- are the second most important group for Mexican economy and about 250 species are distributed in the country’s various regions (Martínez, 1951). Their wood is rich in extractives and their heartwood and sapwood have different output; there is also a high concentration of extractives in their bark (Fengel and Wegener, 1984).
There are few studies about the antioxidant activity of extractives taken from wood of the Quercus genus. These extractives could be a source of phenols with antioxidant properties. Therefore, the aim of this study was to evaluate their antioxidant capacity -through the inhibition of lipid oxidation- and to obtain their phenolic profile -through an HPLC analysis of the methanolic and aqueous extracts of the wood (sapwood and hardwood) and the bark of three oak species (Quercus candicans Née, Q. laurina Humb. & Bonpl., and Q. rugosa Née).
Materials and Methods
Collecting the material
The materials studied were wood and bark samples from the forest use of the indigenous community at Nuevo San Juan Parangaricutiro, Michoacan, Mexico (19° 21’ 00” and 19° 34’ 45”, 102° 08’ 15” and 102° 17’ 30”). Sapwood and heartwood were separated from the wood. Sapwood, heartwood, and bark samples from the three oak species were dried outside in the shade. Afterwards, the material was crushed using a Wiley mill (TAPPI, 2000), it was sieved with a 40 mesh (420 mμ), and the wood dust obtained was used to carry out this study.
Reagents
Chemical solvents with analytical degree were used during the Soxhlet extraction process. They were obtained from J. T. Baker (Mexico). All the reagents used to determine the antioxidant capacity and the standards used in the HPLC analysis were obtained from Sigma-Aldrich (Mexico).
Extractive content
The extractives were obtained through a successive 6 h extraction using solvents with increasing polarity (cyclohexane, acetone, methanol) in a Soxhlet equipment, before subjecting to hot water under reflux (Mejía-Díaz and Rutiaga-Quiñones, 2008). Organic solvents were recovered in a rotary evaporator (using vacuum), while the aqueous extracts were recovered using a lyophilization equipment. For this study, only the methanolic and aqueous extracts were studied, as explained below.
Inhibition of lipid oxidation test
This test was carried out using the method described by Huang et al. (2005) and the antioxidant activity percentage was calculated using the following equation:
% of the reduction of lipid peroxidation = (Ac - Am)/Ac *100
where Ac is the witness’ absorbance (distilled water) and Am is the sample’s absorbance (Ruiz-Martínez et al., 2011).
HPLC (high pressure liquid chromatography)
The phenolic profile of the methanolic and aqueous extracts -taken from the wood and bark of the three oaks used in the antioxidant activity- was evaluated according to the methodology proposed by Ruiz-Martínez et al. (2011), using a HPLC equipment (Varian Pro-Star 330, model 0128). The 10-μL samples were injected into a varian pursuit Xrs C18 column (150 x 4.6 mm). The standard solutions were cinnamic acid, chlorogenic acid, coumaric acid, hydrocinnamic acid, catechin, gallic acid, methyl gallate, quercetin, pyrogallol, and resorcinol.
Results and Discussion
Content of extractives
The total content of compounds extracted from the tree oak species was classified in ascending order as follows: sapwood > heartwood > bark. Their values varied from 8.72 % (sapwood, Q. candicans) to 19.39 % (bark, Q. rugosa) (Table 1). According to Fengel and Wegener (1984), bark had a great content of extractives and their concentration in heartwood is greater than in sapwood. The findings of our study match those results. With regard to the solvents used, methanol had the highest solubility; polyphenolic substances are extracted with high polarity solvents (such as alcohols and water), and these phenolic compounds show good antioxidant activity (Salazar et al., 2008; Wong-Paz et al., 2015a). The overall quantity of compounds extracted from the heartwood of Q. candicans is similar to the percentage (10.2 %) obtained from the same species by Rutiaga et al. (2000). The overall output of extractives in Q. laurina in this study was higher than the percentage reported for sapwood (5.29 %) and heartwood (5.35 %), while bark had a slightly lower percentage than the one reported for the inner bark (14.9 %) of the same oak species (Ruiz-Aquino et al., 2015). The overall content of compounds extracted from Q. laurina in this study was higher than the content obtained from the sapwood (4.91 %) and heartwood (5.02 %) of the same oak species, at the State of Puebla, by Honorato and Hernández (1998). The variation of extract percentage in timber-yielding species does not only depend on the solvents that are used, but also on the species itself. Additionally, environmental and genetic factors, the age of the tree, weather conditions, available nutrients, and the time when the cut is made can influence the result (Hillis, 1971).
Table 1 Output of sapwood, heartwood, and bark extracts from oak species (%).
Extractos | Q. candicans | Q. laurina | Q. rugosa | ||||||||
Al | Du | Co | Al | Du | Co | Al | Du | Co | |||
Ciclohexano | 0.29± 0.12 | 0.42± 0.04 | 0.26± 0.15 | 0.53± 0.24 | 0.56± 0.13 | 0.60± 0.02 | 0.17± 0.02 | 0.53± 0.01 | 2.02± 0.18 | ||
Acetona | 4.81± 1.49 | 1.68± 0.07 | 3.87± 1.17 | 3.17± 0.57 | 4.08± 0.51 | 3.52± 0.30 | 3.81± 0.25 | 7.65± 1.61 | 4.93± 0.19 | ||
Metanol | 2.24± 0.04 | 4.56± 1.28 | 6.16± 0.03 | 4.49± 2.15 | 2.77± 0.75 | 5.86± 0.69 | 2.62± 0.07 | 5.47± 0.31 | 6.45± 0.69 | ||
Agua caliente | 1.44± 0.08 | 2.92± 0.12 | 2.89± 0.26 | 1.39± 0.25 | 2.15± 0.34 | 2.81± 0.27 | 2.88± 0.79 | 4.62± 0.35 | 5.99± 0.29 | ||
Extractos totales | 8.72± 1.64 | 9.58± 1.42 | 13.18± 0.71 | 8.26± 1.12 | 9.57± 0.71 | 12.80± 0.14 | 9.47± 0.44 | 18.27± 1.55 | 19.39± 0.39 |
sapwood (Al), heartwood (Du), bark (Co).
Inhibition of lipid oxidation
Inhibiting the extracts against the perodixation of the linoleic acid caused by FeCl2 did not modify the antioxidant activity of any of the tissues of the three oaks, regardless of the solvent used to extract them (Table 2). The methanolic extract taken from the sapwood of Q. rugosa had the highest percentage of antioxidant activity (94.09 %). In contrast, the methanolic extract taken from the sapwood of Q. laurina had the lowest percentage (42.54 %). The inhibition against the peroxidation of the linoleic acid from the methanolic extract taken from the sapwood of Q. rugosa had a similar activity to gallic acid (95 %), when the same technique was applied (Sánchez-Aldama et al., 2013). The antioxidant activity of the aqueous extracts taken from the sapwood and bark of the three oaks studied in our research is greater than the 65 % (average) obtained from ethanol-aqueous extracts of plants located in semiarid regions of Mexico (Flourensia cernua, Eucalyptus camaldulensis, and Turnera diffusa), when the same methodology is used (Wong-Paz et al., 2015a). The inhibition values of the methanolic extracts taken from the bark of Q. laurina and from the sapwood of Q. rugosa are higher than the 76.86 % of the ethanolic extract taken from Laurus nobilis (Muñiz-Márquez et al., 2014). The number of phenolic compounds in the extracts correlates with their antioxidant activity (Wong-Paz et al., 2015b) which confirms that the variation of antioxidant activity depends on the polarity of the solvents used and on the phenolic compounds that contain the extracts from each plant.
Table 2 Inhibition of the lipid oxidation (%) of the methanolic and aqueous extracts taken from sapwood, heartwood, and bark of the oak species.
Inhibición de la
oxidación lipídica |
Q. candicans | Q. laurina | Q. rugosa | ||||||||
Al | Du | Co | Al | Du | Co | Al | Du | Co | |||
Metanol | 68.36± 5.75 | 50.69± 15.52 | 48.01± 8.03 | 42.54±10.5 | 72.33±3.38 | 89.92±4.72 | 94.09±1.50 | 74.76±15.89 | 68.91±4.05 | ||
Agua caliente | 53.96± 2.38 | 68.30± 8.28 | 82.01±24.58 | 60.39±26.7 | 87.67±17.71 | 67.05±23.34 | 73.05±32.2 | 68.30±28.80 | 87.17±9.95 |
sapwood (Al), heartwood (Du), bark (Co).
HPLC analysis
The compounds identified by the qualitative HPLC analysis of the methanolic and aqueous extracts are shown in Table 3. The compound most frequently found in the sapwood, heartwood, and bark of the three oaks was chlorogenic acid which is a powerful antioxidant compound (Kamiyama et al., 2015). Additionally, it is the main component of the methanolic and ethanolic extracts found in the plants used in traditional Chinese medicine (Wu, 2007). Methanolic extracts taken from the sapwood of Q. laurina and Q. rugosa have the highest content of phenolic compounds (six compounds each); resorcinol was frequently found in the methanolic extracts taken from heartwood of the three oak species (Table 3), and it is used as a chemical intermediate for the synthesis of pharmaceutical products (Ruiz-Martínez et al., 2011). Gallic acid -a chemical compound with powerful antioxidant, antiviral, antibacterial, and anticarcinogenic properties- was identified in the wood of Q. rugosa (Lekha and Lonsane, 1997; Shahrzard et al., 2001; Ruiz-Martínez et al., 2011). Catechin contributes to the antimicrobial and antioxidant properties which are important to prevent such pathologies as diabetes (Ruiz-Martínez et al., 2011; Alam et al., 2014; Huang et al., 2015). This compound was detected in the methanolic extract taken from the bark of Q. candicans, as well as from the sapwood and bark of Q. laurina. Studies about other oak species have identified gallic acid and catechin in the acetone-aqueous extract (70 %) taken from the bark of Quercus sideroxyla (Rosales-Castro et al., 2012), while coumaric acid, gallic acid, catechin, and chlorogenic acid have been identified in infusions made from the leaves of Q. resinosa (Rocha-Guzmán et al., 2009). In both cases, they were detected through a HPLC analysis.
Table 3 Phenolic compounds detected by means of HPLC in methanolic and aqueous extracts taken from the sapwood, heartwood, and bark of the oak species.
EST | TR | Q. candicans | Q. laurina | Q. rugosa | |||||||||||||||||
Al | Du | Co | Al | Du | Co | Al | Du | Co | |||||||||||||
M | A | M | A | M | A | M | A | M | A | M | A | M | A | M | A | M | A | ||||
PG | 6.5 | - | + | - | - | - | - | - | - | + | - | - | - | - | - | - | - | - | - | ||
ACG | 4.40 | - | - | - | - | - | - | - | - | - | - | - | - | + | + | + | - | - | - | ||
RES | 9.57 | - | - | + | - | + | - | - | - | + | + | - | - | + | + | + | - | - | - | ||
ACL | 11.11 | + | - | + | + | + | + | + | + | + | + | + | + | + | + | + | + | - | + | ||
ACU | 15.14 | - | - | - | - | - | + | - | - | - | - | - | - | - | - | - | - | - | - | ||
CAT | 15.77 | - | - | - | - | + | - | - | - | + | + | - | + | - | - | - | - | - | - | ||
ACH | 17.75 | - | - | - | - | - | - | - | - | + | - | - | - | - | - | + | - | - | - | ||
MEG | 12.92 | - | - | - | - | - | - | - | - | + | - | - | + | - | - | - | - | - | - | ||
QUE | 20.06 | - | - | - | - | - | - | - | - | - | - | - | - | - | - | + | - | - | - | ||
ACI | 21.04 | - | - | - | - | + | - | - | - | - | - | - | - | - | - | + | - | - | - |
Standard (EST), retention period (TR), methanol (M), water (A), sapwood (Al), heartwood (Du), bark (Co), pyrogallol (PG), gallic acid (ACG), resorcinol (RES), chlorogenic acid (ACL), coumaric acid (ACU), catechin (CAT), hydrocinnamic acid (ACH), methyl gallate (MEG), quercetin (QUE), cinnamic acid (ACI), presence (+), and absence (-).
Methyl gallate was identified in the sapwood and bark of Q. laurina and this compound has a strong antimicrobial and antioxidant activity (Choi et al., 2009; Cheng et al., 2009). Quercetin is a powerful antioxidant, antihistamine, anti-inflammatory, and antidiabetic agent (Ruiz-Martínez et al., 2011; Alam et al., 2014). This phenol was found in the methanolic extract taken from the heartwood of Q. rugosa. Using an IR analysis, Kim et al. (2008) found methyl gallate and quercetin in the methanolic extract taken from the trunk of this species. Cinnamic acid was identified in the methanolic extracts taken from the bark of Q. candicans and from the heartwood of Q. rugosa; this phenol is a powerful antimicrobial agent, it inhibits certain fungi species and is responsible for antitubercular activity (Guzmán, 2014). Based on this discussion, wood and bark extracts from the three oaks are certainly rich in phenolic compounds with a powerful antioxidant activity; besides, they might prevent and inhibit certain human pathologies. Nevertheless, further studies are necessary to determine conditions for a better use.
Conclusions
The highest output of the extracts was found in the bark and they were more soluble in methanol. Methanolic and aqueous extracts taken from the three oak species inhibited the peroxidation of linoleic acid, which correlates with the antioxidant activity that could have been mainly caused by the phenolic compounds that were detected: chlorogenic acid, resorcinol, catechin, and gallic acid. The methanolic extracts taken from the wood and bark of the three oaks have a high content of phenolic compounds with a powerful antioxidant activity.
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Received: October 2017; Accepted: June 2018