Cork: science, environment & pharmacological potential

Highlights:

• The cellular structure and the chemical composition of cork are the basis of its low density, impermeability to liquids, elasticity, resilience, heat and acoustic insulation proprieties and resistance to chemical and microbial attack.
• Cork production is closely related to the maintenance of biodiversity which is at the heart of sustainable development.
• Friedelin and related compounds also present in cork have been studied and reported to show antioxidant, antihistaminic, antiulcer, anti-inflammatory or even anticancer effects.
• Cork’s fatty acid content and low cost is what makes it a promising biosorbent for oils and heavy metals such as copper, zinc, chromium and nichel.  

Contents of this article:

1) Cork, nothing more than the bark of the oak

2) Cork natural proprieties

3) Cork & the environment

4) Pharmacological potential

5) Cork sorpion capacity

6) Support us & References

Cork is nothing more than the bark of the oak (Quercus suber L.). Yes, that simple!

Quercus suber, commonly called the cork oak, is a long-lived (up to 200 years or more), slow growing, evergreen oak that flourishes only when a unique combination of lot of sunlight, low rainfall and high humidity occurs. [1] ; [2]

Cork stoppers are the main cork application, having the highest added-value and largest market

Today, most of the world production is concentrated in Europe, especially Portugal where approximately 25 thousand tons per year of cork stoppers are produced. [3]

The bark is periodically harvested, usually every 9-12 years, after the trees reach at least 25 cm in diameter. After the harvest, the trees are left to regrow their bark, which will take about another 9 years. [1]

The tree produces three qualities of cork during its life cycle:

• virgin cork (irregular in structure, thickness and density)
• reproduction cork from the second stripping
• reproduction cork from subsequent strips [4]

While all types of cork can be used for agglomerates for its insulation proprieties, the best quality for cork stopper comes from the second reproduction cork onward. [1]

Cork natural proprieties

The cellular structure and the chemical composition of cork are the basis of its low density, impermeability to liquids, elasticity, resilience, heat and acoustic insulation proprieties and resistance to chemical and microbial attack.

This remarkable set of properties is the central reason for its use as a barrier against liquid, heat and sound.

Structure of cork as observed by scanning electron microscopy in the three main sections: (left) tangential section, perpendicular to the tree’s radial direction; (middle) transverse section, perpendicular to the tree’s axial direction; and (right) radial section, the tree’s radial section

Cork specialized cellular structure and chemical composition is naturally designed to protect the tree against temperature variation, water loss, fire, and biological attacks. Its major chemical component and cork’s fingerprint is suberin (a waterproofing waxy substance), accounting for approximately 40% of the material. [5] ; [6]

This combination of properties provides cork with characteristics hard to match with other materials: excellent sealing ability and ease of removal, thermal insulation at very low temperatures and thermal comfort and damping for walking, among others. [1]

Quercus suber & the environment

Cork production is closely related to the maintenance of biodiversity which is at the heart of sustainable
development.

Mediterranean cork oak forests, are ecosystems of high socioeconomic and conservation value. Such forests, characterised by sparse tree cover, are habitat for many plants and animal species, some endangered like the Iberian lynx which is on the Red List of Threatened Species.

Today, such ecosystems require active management and responsible use by humans to ensure their continued existence. [2]

Decline and abandon of the land, are considered by researchers and phytopathologists as ones of the major causes of the regression of cork oak forests. In fact, this brings about an embrittlement of the populations that becomes home of predilection for different antagonistic agents. [7]

Cork is extracted manually every 9–12 years

Beside forest production and activities associated with the extraction of cork, other activities such as beekeeping, livestock (the acorns of cork oak are used as feed for free-ranging autochthonous Iberian pigs), harvesting of mushrooms, herbs and medicinal plants have a great social and economic importance in regions where the cork oak grows. [8] ; [9] ; [10]

Cork production is also closely related to the reduction of emissions and sequestration of carbon dioxide (CO2), aspect that is both environmentally and economically very important today.

When the bark of the tree is harvested for cork, the tree produces rapidly new bark for protection. This mechanism enables the long-living cork oaks to increase their cork production between 250% and 400% during their lifespan, thus increasing the fixation of CO2. Therefore, the consumption of cork products promotes the formation of more cork and thus more CO2 is sequestered. In addition, such products are reusable, long-life products retaining the carbon during their useful life and being “carbon neutral” at the time of decomposition. [8]

All this process, happens without cutting one single tree!

Future Developments

To date, the cork industry and general public have viewed cork mainly in terms of stoppers. However, innovation is increasingly occurring in this traditional industry.

Pharmacological potential

The pharmacological potential of cork lies in its low molecular weight components, but to date, only its friedelin and friedelin derivatives have been studied. Friedelin is a terpene also commonly found in cannabis roots and it has been reported, together with related compounds, to show antioxidant, anti-histaminic, antiulcer, anti-inflammatory and even anticancer effects. [1 ; 12]

It also contains sterols, flavonoids and other simple phenolic compounds with well known biological activity. For example, sterols may reduce cholesterol problems or influence cancer proliferation. Flavonoids have been studied for their cancer chemoprevention and also their antioxidant activity. [1, 13]

In addition, it has been shown that leaves and acorns from cork oak are a potential source of biomolecules useful for alleviating symptoms associated with Alzheimer’s Disease and other neurodegenerative disorders, as well as diabetes. [10] ; [11]

In 2013 a Portuguese study examined the antioxidant potential and inhibitory activity of leaf and acorn extracts of cork oak on key enzymes relevant for hyperglycemia (amylase and glucosidase) and neurodegenerative diseases (AChE and BuChE).

Their search for cholinesterase inhibitors (ChEI) among natural resources comes from the urgent clinical need for new AChEI compounds with lower toxicity than the most frequently used drugs for Alzheimer’s Disease like donepezil & galantamine, which are selective AChEI and can induce several side effects, particularly hepatoxicity.

Cork oak’s acorn

The results indicated that the leaf extract of cork oak contain molecules capable of inhibiting both AChE and BuChE, and have the potential to be used against several neurodegenerative diseases, specifically AD and Parkinson’s disease (PD).

The scientists showed that the extracts prevent oxidative stress-induced cytotoxicity are a valuable source of antioxidants. [11]

Sorption capacity

The use of cork as a biosorbent was also researched in relation to heavy metals. [6]

Most cork companies consider cork powder as a waste product and use it only as an energy source as a result of its low economic value and high burning capacity. However, as biosorption (the ability of biological materials to accumulate heavy metals) has gained in importance, the good performance and low cost of this natural material is becoming attractive.

Today, removal of heavy metals in waste water is usually achieved using activated carbon, activated alumina or polymer resins, which are non-regenerable and expensive materials.

The fatty acid content and low cost is what makes cork a promising biosorbent for oils and heavy metals such as Cu, Zn, Cr and Ni. [1]

 

 

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References:

[1] Silva, S. P., Sabino, M. A., Fernandes, E. M., Correlo, V. M., Boesel, L. F., & Reis, R. L. (2005). Cork: properties, capabilities and applications. International Materials Reviews, 50(6), 345-365.

[2] Bugalho, M. N., Caldeira, M. C., Pereira, J. S., Aronson, J., & Pausas, J. G. (2011). Mediterranean cork oak savannas require human use to sustain biodiversity and ecosystem services. Frontiers in Ecology and the Environment, 9(5), 278-286.

[3] Pereira, H., Melo, B., & Pinto, R. (1994). Yield and quality in the production of cork stoppers. Holz als Roh-und Werkstoff, 52(4), 211-214.

[4] Abenojar, J., Barbosa, A. Q., Ballesteros, Y., del Real, J. C., Da Silva, L. F. M., & Martínez, M. A. (2014). Effect of surface treatments on natural cork: surface energy, adhesion, and acoustic insulation. Wood science and technology, 48(1), 207-224.

[5] Pereira, H. (1988). Chemical composition and variability of cork from Quercus suber L. Wood Science and Technology, 22(3), 211-218.

[6] Pereira, H. (2015). The rationale behind cork properties: a review of structure and chemistry. BioResources, 10(3), 6207-6229.

[7] Adjami, Y., Ouakid, M. L., Saouli, A., Bensafi, H., Soltani, N., Hayouni, E. A., & Everarts, C. (2009, March). Evaluation of Antioxidant Activity, Antimicrobial and Fungicidal Effect of Organic Extracts of Cork Oak Acorns Infested by Carpophagous Insects. In International Symposium on Medicinal and Aromatic Plants-SIPAM2009 853 (pp. 337-344).

[8] Gil, L. (2011). Environmental, sustainability and ecological aspects of cork products for building. Ciência & Tecnologia de Materiais, 87-90.

[9] Sá-Sousa, P. (2014). The Portuguese montado: conciliating ecological values with human demands within a dynamic agroforestry system. Annals of forest science, 71(1), 1-3.

[10] Custódio, L., Patarra, J., Alberício, F., da Rosa Neng, N., Nogueira, J. M. F., & Romano, A. (2015). Phenolic composition, antioxidant potential and in vitro inhibitory activity of leaves and acorns of Quercus suber on key enzymes relevant for hyperglycemia and Alzheimer’s disease. Industrial Crops and Products, 64, 45-51.

[11] Custódio, L., Patarra, J., Alberício, F., Neng, N. R., Nogueira, J. M. F., & Romano, A. (2013). Extracts from Quercus sp. acorns exhibit in vitro neuroprotective features through inhibition of cholinesterase and protection of the human dopaminergic cell line SH-SY5Y from hydrogen peroxide-induced cytotoxicity. Industrial crops and products, 45, 114-120.

[12] Slatkin, D. J., Doorenbos, N. J., Harris, L. S., Masoud, A. N., Quimby, M. W., & Schiff, P. L. (1971). Chemical constituents of Cannabis sativa L. root. Journal of pharmaceutical sciences, 60(12), 1891-1892.

[13] Cai, Q., Rahn, R. O., & Zhang, R. (1997). Dietary flavonoids, quercetin, luteolin and genistein, reduce oxidative DNA damage and lipid peroxidation and quench free radicals. Cancer letters, 119(1), 99-107.