Tannins are a group of compounds belonging to a larger class of substances known as polyphenols, which are a type of antioxidant.
Tannins are found in various plant tissues, including leaves, seeds, bark, wood, and fruit.
They play several key roles in plant physiology, such as protection against predation and contributing to plant growth.
There are two main types of tannins: hydrolyzable tannins and condensed tannins.
Hydrolyzable tannins can be broken down into simpler substances by the action of water and certain enzymes.
They are usually complex structures made up of sugar molecules linked to other components such as gallic acid or ellagic acid.
Condensed tannins, also known as proanthocyanidins, are polymers of flavonoid units, and they do not readily hydrolyze.
From a nutritional and health perspective, tannins are often discussed in terms of their antioxidant properties, which can help
to neutralize harmful free radicals in the body. However, because they can inhibit the absorption of certain nutrients in the
digestive system, they are also considered anti-nutritional factors in some contexts.
In the context of food and beverage, tannins contribute to flavor complexity, color, and the aging process of wine. They also
play a role in traditional processes such as the tanning of leather, where they bind to proteins in animal hides and make
them resistant to water and microbial damage.
Some points regarding tannins in herbal leaf extracts are provided below:
- Herbs like witch hazel, sage, rosemary, and yarrow are known for their high tannin contents.
Astringency - Tannins in herbal leaf extracts are responsible for the
astringent properties of many of these herbs. Astringency is the drying, tightening, and sometimes puckering sensation
that you experience when you consume certain foods or drinks. For example, it's the tannins that give black tea, red wine, and certain fruits like
unripe apples or persimmons their characteristic mouthfeel.
Hydrolyzable Tannins - These are found in some herbs like witch hazel
(Hamamelis virginiana). Two types of phenolic acids commonly found in hydrolyzable tannins are gallic acid and ellagic acid.
Some points regarding tannins in bark are provided below:
- Tannins play essential roles in the tree's defenses against pests and diseases, and they contribute to the tree's growth and repair.
Hydrolysable Tannins - These tannins can be hydrolyzed into simpler phenolic
compounds, such as gallic acid or ellagic acid, and a sugar molecule. They are found in the bark of many tree species, including oak,
chestnut, and myrobalan.
Condensed Tannins - Also known as proanthocyanidins,
these tannins are polymers of flavonoid units and are not readily hydrolysed. They are found in high quantities in the bark of some trees,
like pine and spruce.
Industry Applications - Bark tannins are widely used in industry. For instance, the
bark of oak trees is a major source of tannins used in the tanning of leather. During the tanning process, the tannins bind to the
collagen proteins in the animal hides, making them resistant to decomposition and conferring durability.
Health Applications - Bark tannins have antioxidant properties and potential
antimicrobial, antiviral, and anticancer effects.
Phlorotannins are the main tannins in brown seaweed, being unique to this biomass type. The content of these compounds can vary
significantly depending on the seaweed species, the stage of growth, and environmental factors such as sunlight, temperature,
and nutrient availability. Some of the the different types of phlorotannins
seen in brown seaweed are described below:
- These are phlorotannins where the phloroglucinol units are connected by ether linkages. An example of a phlorethol found in brown
seaweeds like Fucus vesiculosus (bladderwrack) is tetraphlorethol A.
Fuhalols and Fucols - Fuhalols are similar to phlorethols but have additional
hydroxyl groups. Fucols, on the other hand, consist of phloroglucinol units linked through aryl-aryl bonds. An example of a fucol
is trihydroxyfucol, which has been found in species like Ascophyllum nodosum (knotted wrack).
Eckols - These phlorotannins contain a dibenzodioxin linkage.
An example is eckol, which has been identified in Ecklonia cava, a type of brown seaweed common in Korea and Japan.
Carpotannins - These are a group of phlorotannins with a unique structure,
where the phloroglucinol units are linked through both aryl-aryl and ether bonds.
An example of this type is carpogel, found in Carpomitra costata.
Fucophlorethols - These are complex phlorotannins where fucol and phlorethol
units are connected through ether linkages.
The extraction process, including the solvents and methods used, can influence the concentration and types of tannins present in the final extract.
It is often the case that a balance needs to be found between fully-extracting all tannins while also ensuring that the compounds that are
obtained are of a high quality and not degraded.
At Celignis we have extensive experience in the design and optimisation of extraction protocols for a wide variety of chemical constituents from
many different biomass types. If needed we can also work on processes to separate and purify the target compounds.
Click here to read more about Celignis's Bioprocess Development Services for the extraction of
chemicals from biomass.
This conference is being organised under the auspices of the Interreg Northwest Europe-funded THREE C Project, entitled 'Creating and sustaining Charcoal value chains to promote a Circular Carbon economy in NWE Europe'.
The conference will highlight both Irish stakeholders who are currently working in the biochar and carbon products sector, but also partners from the THREE C project (covering Netherlands, Luxembourg, Germany, Belgium, France and Wales, as well as Ireland) who have interesting stories and products to share.
Read about the wide variety of analysis packages we have for biochar
Click here to read about the different analysis packages that Celignis offers for the evaluation on biochars. These analyses cover properties relevant to a wide variety of applications, including soil amendment, carbon sequestration, bioenergy, and biomaterials.
For a short period we are offering two TGA analyses for the price of one!
To celebrate the arrival of our thermogravimetric (TGA) equipment, we are offering, for a limited time period, two TGA analyses for the price of one. Click here to read more about TGA analyses at Celignis and to see the various packages on offer.
To avail of this special offer please mention the code (TGA-AUGUST) in an email or when placing an order via the Celignis Database.
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