Biopreservantes based timber and other extractive tannin of pine bark
and its antioxidant action: history and prospects
* Biopreservantes tannin-based wood and other extractive
* Sustainable agriculture
* Chemical composition of pine bark
* Biodegradation of wood
* Natural Durability
* The role of flavan-3-ols and proanthocyanidins in plant defense
* Antifungal activity
Antioxidants are found in many forms, and undoubtedly the best known are vitamins such as vitamin A, C and E, but these products are in the form of amino acids, phytochemicals or plant molecules “minerals and antioxidants. Are of interest from this point of view, derived from plants.
The active antioxidants plants contain phytochemicals that stimulate beneficial antioxidant enzymes in the human body and has proven to be much stronger than the same vitamin E. These plants are also known as “helpers of life”, because they help create and maintain the detoxification pathways in the human body.
The activation of oxygen, leads to the formation of reactive oxygen species (oxiradicales or products of the monovalent reduction of oxygen, between the superoxide radical (O2-) and hydroxyl (OH-) and organic radicals and peroxide (H2O2) resulting reaction with oxiradicales (Figure 4), the latter can generate the oxidation of cellular proteins, leading to its inactivation, they also rapidly react with unsaturated lipids and oxidized. This process is facilitated by transition metals such as iron and copper or blood proteins hypervalent states that quickly attack unsaturated lipids.
The organic radicals may be created by the breakdown of fatty acids and chemicals such as drugs, food additives and preservatives, cigarette smoke, pollutants, sunlight, establishment and emotional stress (Feutch & Treutter, 1999).
These compounds damage cells in the human body, generating more than 80 diseases associated with aging of human beings, we can highlight including heart disease, cancer, rheumatoid arthritis, cataracts and Alzheimer’s disease. and skin problems. Antioxidants fight free radicals and protect the human body from these diseases (Passwater, 1998).
Fig 4. Monovalent reduction of oxygen and the formation of oxiradicales.
The steps involved in the oxidation of a typical unsaturated fatty acid (eg linoleic acid) are initially forming a lipid peroxyl radical, caused by the addition of oxygen to the lipid alkyl radical intermediate, which is resulting in turn from the reaction of lipid with hydrogen peroxide or hypervalent metal. The peroxyl radical, reacts rapidly with other lipid and generates a new radical and lipid peroxyl hidroperoxidado. This reaction occurs at a constant rate of 106 moles / s represents the kinetic level suitable for the propagation of lipid peroxidation (Figure 5). The accumulation of these reactions leads to deterioration of lipids and the formation of a large amount of reactive oxygen species generated by many of the effects listed above.
Fig 5. Stages of oxidation of unsaturated fatty acid.
Antioxidants of plant origin are composed of catechin polyphenols, and are among the best known and epicatechin gallate and related compounds, as well as proanthocyanidins, all these compounds are potent antioxidant and can neutralize free radicals, suppressing the spread of lipid peroxidation also the first compounds promote the activation of macrophages, B lymphocytes and T lymphocytes in white blood cells, indirectly increasing the human immune system.
The proantocinidinas also have antimutagenic effects by inhibiting DNA mutation and have a value of “cosmetic” and that protect the collagen and elastin, while maintaining the smoothness of the skin and prevent loss of elasticity.
WOOD-BASED BIOPRESERVANTES tannins and other extracts
Currently, high consumption of wood and wood products makes this material is valuable, significant event for the field of preservation of these products, they must be treated carefully to prolong their period of service or useful life. The natural durability of wood can be effectively enhanced by chemical protection. However, the chemicals contaminate the environment and harm to humans, therefore, and to the extent possible, the use of chemical fungicides and insecticides should be minimized and should find other ways to protect the wood (Weissenfeld, 1988). Accordingly, chemical preservation of wood could be minimized and applied only when necessary (Willeitner, 1991).
This is very relevant, mainly when recent environmental restrictions limit the use of a large number of biocides for wood preservation and when standards are more demanding, changing dramatically the space where it acts to preserve wood, a phenomenon more pronounced in the developed countries. In these countries, other problems arise: the increasing problems of deposition of treated wood and that is out of service, as in the development of new, environmentally friendly control of fungal and insect attack without the period of “re-education” to assimilate and take on these changes.
This ecological approach involves the development of the “natural protection” with preservatives less harmful to the environment and humans that are selective only to organisms that destroy wood. These preservatives should be biologically degradable (Barnes, 1992).
Thus, wood preservatives based on flavonoids and phenolic extracts, mainly tannins, have attracted interest and are being developed (Lakes et al, 1988; Dirol, 1994; Pizzi & Baecker, 1996), due to its ability to form chelates insoluble with various metal ions, including copper (McDonald, et al, 1996). This type of preservatives are very advantageous to generate a low environmental impact both in preparation and during implementation, in addition, the possibility of providing greater safety to users and finally the potential social and economic benefits of these products as substitutes petroleum (Gonzales, 1996).
Tannin-metal compounds are based on the affinity of a metal hydroxyl groups in the ring – B of the flavonoid, Figure 6. The metal often used as a biocide has been copper (Pizzi, 1998). There are investigations where the metal has been replaced by zinc. The compounds thus formed are influenced by the nature of the tannin, the concentration of both of these compounds, such as copper and precipitation of this metal. (Mila, et.al., 1995). For all this, it is necessary to optimize the binding parameters of copper and zinc to achieve its insolubility in the wood, ensuring the use of these compounds as wood preservatives. (McDonald, et al, 1996).
Figure 6. Tannin-metal complex, indicating the affinity of a metal hydroxyl groups in the ring – B of the flavonoid
The reported results are acceptable, but much poorer than salt-based preservative CCA. The wood preserved with these compounds are for use outside contact with the ground and not in direct contact with the ground (Dirol, 1994). Nontoxic preservatives complex tannins with boron, using collagen proteins often are at an experimental stage (Thevenon, et.al., 1998). Unfortunately there have so far proved inadequate because they can be easily leached from the wood (Dirol, 1994). However, a new component reaction between boron and tannins, which were developed for the implementation of tannin adhesives can be used, improving the setting and retarding the leaching of boron from treated wood. (Meikleham et.al., 1994). The results indicate that can be developed preservatives containing boron and tannins for use out of contact with the ground, despite being ineffective, with the advantage that this material is not toxic to humans (Pizzi & Baecker, 1996).
Also, the insecticidal properties of extracts have been tested, in this case against subterranean termites, which have proven quite effective, however, think to diversify the methods of control to the forms of toxins, repellents, attractants, bathrooms toxic treatments in soil barriers and topical treatment of wood (Hutchins, 1997).
However, many studies still must be done before these products are commonly applied in the field of wood preservation commercially (Gonzales, 1996).
Moreover, little is known about the ability of antioxidants that can be derived from pine bark. There are no more references to it.
Sustainable agriculture can be defined as using natural resources rationally in order to meet the needs of present and future generations through the use of chemicals in plants that are resulting from primary and secondary metabolism. The first group contains the essential substances in plant form as a result of the photosynthetic process. The second group (secondary metabolites), apparently no activity in the plant, has other significant effects. These active ingredients or substances called secondary compounds are essential oils, resins, alkaloids, flavonoids, tannins, among others.
How organisms interact with variable em the various components of the environment, respond and in turn, affect them. These chemical interaccionmes have some detectable and understandable structure, which is involved em uma complex series of chemical attributes, which are called infochemicals, or secondary metabolites that mediate chemical interactions. The alkaloids, steroids and glycosides are some examples of secondary metabolites produced by plants.
In turn, there are certain substances that constitute a defense system. These substances are called chemical allele Alomone “are molecular compounds that act as signals or messengers of deterrence, causing repulsive effects, antifeedant, toxic, disrupting the physiology and / or sexual behavior or population of insects.
These natural products have multiple effects, ranging from inhibition or stimulation of growth processes of neighboring plants, to the inhibition of seed germination or prevent insects and leaf-eating animals, as well as harmful effects of bacteria, fungi and viruses.
Natural products make up an important part of the defense systems of plants with the advantage of being biodegradable. Trees and large plants produce substances that do little digestible such as tannins and lignin, while smaller plants, shorter life, they defend with toxic substances such as alkaloids. This is especially important in the tropics, where much of the lost crops consumed by pests such as insects or fungi (Vargas et al., 2002).
Reliable estimates indicate that over 5 000 secondary metabolites have been isolated from green plants and fungi, and the number of compounds isolated and identified is close to 600 000. These substances and their derivatives are a valuable source for future synthesis of herbicides, especially for weed control using natural substances less harmful to the environment.
Chemical composition of pine bark.
The chemical composition of the crust is very complex, there are many different types of chemical compounds in the bark, they are an inexhaustible source of biologically active natural products, many of which have been the model for drug formulation , poisons and insecticides (Dell, 1997). However, from the economic point of view, isolation, separation and purification of chemical compounds is not feasible for the high costs that are incurred to perform these operations (Laver, 1991).
Vazquez et al. (1987), cited by Vargas (1991), the chemical composition of the crust depends on many factors such as location, age, tree growth conditions and methods of obtaining the samples.
Crust chemically differs from the wood by the presence of polyphenols and suberin, as well as the presence of a lower percentage of polysaccharide and a higher percentage of extractives (Fengel and Wegener, 1994). The mineral content of the bark is also much higher than wood (Sjostron, 1981).
The extractive-free bark contains carbohydrates, suberin, phenolic acids, small amounts of lignin and inorganic materials (Bender, 1968). A large proportion of the crust is composed of polyphenols (Vargas, 1991) and can have large variations depending on factors such as species, age, and other growth conditions (Encinas, 1977).
The term polyphenol refers to a large number of interrelated compounds, derived mainly from flavenoid. The most common in the cortex belong to two groups of polymers, flavonoids and lignin (Vargas, 1991).
Flavonoids according to their solubility or molecular size can be classified into
1. Proanthocyanidins: Great flavonoid dimers and trimers, soluble in ethyl acetate).
2. Condensed tannins, soluble polymers acetone-water mixture.
3. Phenolic acids polymers (soluble only in dilute alkali).
In its chemical composition, the three groups have polyflavonoids character, presenting monomers with structures similar to the catechins. Regarding lignin, in general, the percentages reported for the same are actually mixtures of lignin and polyflavonoids, both phenolic polymers of high molecular weight (Cameron, 1990).
Table 1 below shows the change in chemical composition between wood and bark of conifers.
Table 1. Comparison of chemical composition of wood and bark of conifers.
Source: (Einsparh, 1976).
This term includes a wide variety of organic compounds in terms of work can be removed from the cell wall by neutral solvents (alcohol, acetone, ether, hexane, water, etc.) Or by steam distillation.
Fibrous materials are low molecular weight are not an integral part of the wall structure of the fibers (Syilvain, 1997), often dispersed and deposited in the cell lumen or impregnating the cell walls (Tsoumis, 1997 .) The extractives in general, represent 5% of the dry mass of the crust, although the amount may be subject to wide variations depending on the genetic makeup of the plant and the environment (from 2% to over 50%) ( Lombardo, 1995).
These foreign materials and classes differ significantly in chemical composition, making it difficult to establish a rigid system of classification and were grouped as organic and inorganic materials (Fengel & Wegener, 1984).
The materials consist of inorganic trace minerals such as calcium salts and silica inclusions, which are not soluble in organic solvents and represents between 0.1% to 1.0% of the dry mass of wood (Tsoumis, 1977) .
Although the extracts represent a very low percentage in weight of the wood, they contribute significantly in many of the properties of wood:
– Organoleptic properties of wood, such as the color and odor.
– Biological properties such as resistance to attack by microorganisms,
are the product of the extractives. In addition, these compounds contribute to the physical properties of wood such as hardness, specific gravity and density, both the anatomy and the presence of extractives help distinguish among the species (Young, 1991).
Biodegradation of wood:
Several external factors may cause degradation of the tree’s appearance, structure and chemical composition of wood, which can range from a simple fade into a near future useless product. This effect not only occurs in wood in service, as has been observed in standing timber, lumber and wood products (Tsoumis, 1997).
The degradation process decreases the durability of the wood over time. The overall process can be slow or fast, depending on the potential use to which it is confined to the wood, composition, surface structure and the aggressiveness of the surrounding environment and most importantly, the type of organisms that can attack . The process can be described using degradation models, which express the degradation of wood in terms of levels of degrading agents, environmental exposures and the exposure time (Odeen, 2000).
The three main areas of degradation analysis are:
* Characterization of environmental degradation.
* Mechanisms of deterioration.
* Test methods.
The most important microorganisms that degrade the wood part of a primitive group of microorganisms, better known as fungi, which have the ability to secrete enzymes through specialized structures called hyphae, which degrade organic matter, chemically modified so be used as a carbon source and nourishment. Before the fungus can colonize wood, requires four conditions:
* Supply of oxygen.
* Suitable temperature.
* Provide moisture.
* Substrate as a source of food.
The elimination of some of these requirements may prevent the attack (Smulski, 1996).
The wood decay fungi and effects, refers to a number of terms including:
* Brown rot.
* White rot.
* Soft rot.
It is produced by basidiomycetes, and they are most abundant in conifers, but may be found in other types of environments such as various soils. These fungi can attack untreated wood and wood preserved, but has a preference for woods that have not been addressed. One of the characteristic of brown rot attack is that cellulose is rapidly depolymerized, even in the earliest stages of decay and thus the loss of resistance may be very large (Singh and Kim, 1997).
During the decay carbohydrates are extensively depolymerized and removed. Furthermore, lignin may also be amended, although the lignin residues remain. The degradation of wood appears brown due to the large presence of lignin (Sing and Kim, 1997).
The fungi that cause this type of decay also belong to the basidiomycetes. They are particularly active in producing an extensive forest ecosystems in the fallen trees rotting in the forest. Hardwood species are more susceptible than conifers and untreated wood are more easily attacked than the woods preserved.
White rot fungi can degrade all cell wall components, including lignin and some species are specialized in the primary degradation of lignin with a widespread lack of attack on cellulose. They can also cause further oxidation of the sugars formed. These fungi cause “bleaching of wood.” Other species may simultaneously degrade all cell wall components, eg lignin, cellulose and hemicelulosa.La formation of erosion channels into the cell wall is the fact morphological characteristic of this type of attack (Singh, 1997).
This group includes some members of the Ascomycetes and Deuteromycetes, which are particularly active under conditions in which brown and white rot are not (timber preservatives, high moisture content).
The attack in conifers results in the formation of cavities in the secondary wall, which is observed by light microscopy as holes in a cross section of the fiber in longitudinal section these cavities are seen oriented parallel to cellulose microfibrils; in hardwoods is observed as erosion of the cell wall (Singh & Kim, 1997).
Below are presented in Table 2, a summary of the stages of attack by brown rot fungi and soft rot:
The mechanisms of action of wood decay fungi responsible for white rot and white rot are not fully understood at present, however there are several papers published on the mode of action of these microorganisms (Kerem et. Al., 1999; Mester, 1998; Bruce and Palfreyman, 1998; Barreal 1995, Eriksson 1990):
Table 2. Summary of steps in the mechanism of fungi.
As can be seen, both mechanisms of action are completely different, but have a common element of free radicals during the initial stages of colonization of wood decay fungi, so it might be probable that the free radical scavenging activity (antioxidant) of tested extract enhances the fungistatic action of it.
The wood’s natural resistance to factors that may cause degradation is called durability, and can be expressed as the time at which the wood retains its properties and characteristics under optimal conditions without the application of special protection.
Wood and wood products require a suitable biological durability for potential end use. This goal can be achieved by selecting the tree species to be used or by the introduction of synthetic biocides (Vanacker & Stevens, 2000).
Table 3. Life expectancy stakes 2 * 2 inches, in direct contact with the
soil (Findlay, 1985).
Another factor that for many authors is correlated with the resistance and the deterioration is the density of the wood. However, from a practical standpoint, many of which exhibit high density and are naturally durable, but other dense woods are rapidly degraded, so that we can deduce that the density is not indicative of natural durability, it is better correlated to the chemical composition of the extractives.
The role of flavan-3-ols and proanthocyanidins in plant defense.
Flavonols have a complex structure and are closely linked to processes of interaction of plants and the environment. In relation to plant defense, greater emphasis is given to the different responses of plants using the diversity of flavonoids. Each process of defense is the result of the combination not only biochemical but also of anatomical mechanisms. The histological reactions, including the construction of physical barriers involved in the complex regulation of resistance. The levels and location of flavonoids in the cells may determine resistance or susceptibility of the host.
Many studies have described the antioxidant status through free radical scavenging activity (AARLA) of the flavan-3-ols, which are related to vitamins, ascorbic acid, tocopherol and other phenolic compounds. Flavonols contribute to maintaining the integrity of the membranes according to Baumann et al. (1980) and Mukherjee & Choudhouri (1983), cited by Feutch & Treutter (1999).
Natural flavonols cell wall can be seen through the reagent consisting of vanillin and p-dimetilaminocinamaldehido (DMAC). The measurement of the intensity of colored product photocolorimetric at wavelengths between 500 – 640 nm, expresses the quantitative result. The concentration of soluble proanthocyanidins oligomers is determined after boiling the extract with strong mineral acid, producing the colored anthocyanidins, which are quantified photocolorimetric.
The antifungal activity of flavan-3-ols is often assumed but rarely demonstrated. The agar diffusion tests sometimes show a brown color ring around the zone of inhibition, indicating phenolic oxidation via quinone intermediates. It is speculated that these intermediaries are the current active compounds and not the flavan-3-ols original (Feutch & Treutter, 1999).
Table 4. Fungitoxicity of flavan-3-ols. (Feutch & Treutter, 1999).
The pathogenesis by fungi causing alterations in cell membranes, making them extremely permeable to store the resulting decompartmentalization of phenolic compounds.
The phenols are released to the cells in different amounts. Abscisic acid is able to induce the release of phenols into the extracellular species. In tissues invaded by pathogens, raising the levels of abscisic acid with an alteration of membrane permeability and the accumulation of flavonols was observed in the cell periphery: the dissociation of flavonoids to the cell wall reflects metabolic disorders (Feutch & Treutter, 1999).
Finally, it should be noted that in recent years, work carried out by different authors show that not only the tannin and flavonoids are substances tested as wood preservatives, but also other plant secondary metabolites such as terpenes, quinones, alkaloids, others, which play a significant role in the mechanisms of resistance to pathogens due to its antifungal properties (Singh & Kim, 1997, Rocha et al., 2001; Encinas et al, 2000, Morita et al. 2000).
The knowledge gained to date has opened new doors in this interesting field of natural products applied to agriculture and particularly to forestry, a branch of wood technology as extremely important for the preservation timber made from less aggressive to the environment, thereby allowing similar studies and apply the results in the medium and long term, since it will still be necessary to pass through stages of field evaluations required and feasible technologies develop life ecologically and economic development.
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Keywords: wood decay fungi, wood preservatives, antioxidants.