Applications of Tannins in Industry

*Akhlash P. Singh and Sunil Kumar*

## **Abstract**

Tannins are water-soluble natural polyphenols mainly present in plant-based materials, including food. Tannins play a very significant role as a raw material for sustainable green industries. Therefore, they are mainly used in diverse types of industries such as leather, feed, fisheries, beverages, etc. They also find application as potential medicinal agents, antioxidants, metal chelators; and cater as inhibitors of harmful pro-oxidative enzymes and of lipid peroxidation process. Recently, several important properties like antiseptics, anticarcinogenic, and anti-inflammatory of tannins have been documented in the human that make them suitable candidates for pharmaceuticals and nutraceutical industries. Because of current concerns related to synthetic compounds used in the human health and food industries, which leave highly adverse effects on the human body and environment, tannins can offer an alternative to these harmful chemicals in recently emerging industries.

**Keywords:** tannins, nutraceutical, wood, leather, pharmaceuticals industries and antibacterial activity

### **1. Introduction**

Biochemically, tannins are sort of secondary metabolites predominantly available in the plant-based foods and beverages. The name "tannin" is originated from the industrial process of "leather tanning," in which animal hides are converted into leather through downstream processing. It is worthwhile to mention that tannins were used in this process from historic times. On the basis of their presence, various parts of plants such as bark, wood, leaves, seeds, roots, and even the plant galls are the major sources of tannin extractions used for various purposes (**Table 1**). Algae is also rich source of tannin-based compounds such as phlorotannins which comprise of antioxidant, antidiabetic, anti-inflammatory, and antitumor properties evaluated in the case of human [1, 2]. In addition to health benefits, phlorotannins isolated from brown seaweeds have been used in the cosmetics also [3]. Some researchers have defined tannins as "Any phenolic compound of sufficiently high molecular weight containing sufficient hydroxyls and other suitable groups (i.e., carboxyls) to form effectively strong complexes with protein and other macromolecules under the particular environmental conditions being studied" [4].

Plant tannins are a large group of natural phenolic compounds which contain a range of molecular weight between 500 and 3000 Da. Currently, they have been divided into three main subgroups: (1) hydrolysable tannins, (2) condensed tannins, and (3) phlorotannins. Hydrolysable tannins are highly soluble in water; biochemically, they consist of a central core of a carbohydrate (D-glucose) with



*Note: Table indicates that tannin and its components are present in most of the parts of the plants which offered great level of medicinal sources or pharmaceutical agents [59].*

### **Table 1.**

*Plant species containing tannins and their medicinal use.*

its hydroxyl groups or polyol esterified with phenolic compounds such as gallic acid (3,4,5-trihydroxybenzoic acid) or hexahydroxydiphenic acid, which also known as ellagic acid (ellagitannin). Hydrolysable tannins mainly originated from Pentagalloylglucose (2-O-digalloyl-1, 3, 4, 6-tetra-O-galoyl-α-D-glucopyranose),

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*Applications of Tannins in Industry*

*DOI: http://dx.doi.org/10.5772/intechopen.85984*

Dilleniidae, and Rosidae species [6].

complex tannins, and (4) condensed tannins.

cosmetology, and pharmaceutical industries.

kilotons by 2025 in comparison of 242.9 kilotons in 2015 [9].

with other green materials in new emerging industries.

which is a basic structural unit of hydrolysable tannins. The main source of structural diversity among the hydrolysable tannins is the presence of diverse types of oxidative linkages that give rise to oligomeric compounds with molecular weight between 2000 and 5000 Da [5]. Characteristic examples of hydrolysable tannins are (1) gallic acid; (2) hexahydroxydiphenic acid; (3) ellagic acid; and (4) pentagalloylglucose, which contain a central glucose molecule as the core attached with multiple gallic acid units, while ellagitannins are associated to hexahydroxydiphenic acid. Hydrolysable tannins are mainly present in angiosperm and dicotyledons. Both gallotannins and ellagitannins may synthesize individually or in the form of a mixture in plants. Gallic acid has been extracted from plant families, for example, Ericaceae,

Geraniaceae, or Fagaceae; whereas, ellagic acid is available in Hamamelidae,

Naturally occurring condensed tannins are polyphenolic bioflavonoids, are polymers of polyhydroxy flavan-3-ol units, for example, (+)-catechin and (−)-epicatechin-2, (+)-gallocatechin, and flavan-3, 4-diols. They are also known as proanthocyanidins (PA) that ascribed to their hydrolysis to anthocyanidins in heated ethanol treatment. Due to presence of stereoisomerisms in hydroxylation patterns at three chiral centers, bond positions, and type of interflavan bond; proanthocyanidins are present in variety of active forms, for example, (1) (+)-catechin; (2) (−)-epicatechin; (3) (+)-gallocatechin; (4) (−)-epigallocatechin; and (5) (−)-epigallocatechin gallate. Among them, (+) catechin and (−) epicatechin are predominantly present in nature [7]. There are several plant species which offer rich source of proanthocyanidins (see **Table 1**). Proanthocyanidins can be obtained from red wine, green tea, cocoa, and chocolate. However, condensed tannins can further be classified on the basis of reaction rate like, slow reacting tannins like quebracho and mimosa and fast reacting tannins like pine and pecan (*Carya illinoensis*) [5, 7, 8]. Furthermore, some researcher also classified tannins into four different classes based on their structural properties, namely, (1) gallotannins, (2) ellagitannins, (3)

After the industrial revolution, most of the synthetic chemicals were used in the diverse types of industries including food, pharma, beverage, leather, and other industries. But prolonged applications of synthetic chemicals in the area of health and other industries left a myriad of adverse effects on environment and human health. Therefore, current focus has been shifted on alternative natural compounds like tannins that can be exploited in the form of functional food, nutraceutical,

The global tannin market is expanding very rapidly; according to estimation, 1076.3 kilotons tannin was required in 2015 which expected to rise with CAGR of 5.8% from 2016 to 2025. The demand was mainly in the wine, leather, pharmaceuticals, and wood industries. In case of USA, approximately 282.4 kilotons tannins were produced; its 62.3% is used in leather industries alone. Europe is another emerging market for tannins and tannin-based products. It is due to large scale wine production, which is accounted for 38% revenue generations in Europe. Hence, global market size for tannin related industries may increase up to \$3.3 billion by 2025. The applications of condensed tannins are expected to increase up to 424.8

But, there are several unresolved issues linked with applications of tannins such

as antinutrient effect, resistance to enzymatic hydrolysis, and lack of complete information about their interactions with other biomolecules and mode of actions in human and animals. The aim of this chapter is to present a brief discussion on the application of tannins in modern industries and to review their positive and negative aspects. It also shows that tannins are being used as sustainable raw material

#### *Applications of Tannins in Industry DOI: http://dx.doi.org/10.5772/intechopen.85984*

*Tannins - Structural Properties, Biological Properties and Current Knowledge*

**parts**

parts

5. *Syzygium cumini* Bark Corilagin and related

11. *Diospyros kaki* Thunb. Fruit Proanthocyanidin

6. *Quercus robur* L. Bark Grandinin, castalagin, and

Leaves, stem, and bark

1. *Krameria triandra* L. Root Tannic acid, rhataniatannic

**Major components Medicinal use**

Chronic diarrhea, menorrhagia, urinary diseases, bleeding from the bowels, bad throat, and antibacterial agents for the eyes, nose, and

Inflammations, wound healings, diarrhea, inflammation of bowel bacterial, fungal, and viral infections

lymphadenitis, and

Bad throat, asthma, dysentery, and ulcers

Diarrhea, itching, and

gums

bites

hepatitis

burning

Wound healing

Gastritis and ulcers

Fever, diabetes, and gum diseases

Antiseptic and cardiovascular diseases

viral infection

acid, peculiar acid principle, krameric acid, phlobaphene, phloroglucin, and proanthocyanidins

epigallocatechin, catechins, and proanthocyanidins

Root Sanguiin H-6 Dysentery and insect

Leaves Geraniin Intestinal disorders

Agrimoniin and potentillin Diarrhea, cough,

Roots Pentadigalloylglucose, pedunculagin,

ellagitannins

glucogallin

Leaves Catechins and other

Pod Gallocatechin-gallate,

12. *Quercus infectoria* Oliv. Gall Tannic acid Bacterial, fungal, and

*Note: Table indicates that tannin and its components are present in most of the parts of the plants which offered great* 

condensed tannins

oligomers based on catechin, gallocatechin, catechin-3-O-gallate, and gallocatechin-3-O-gallate

methyl gallate, catechin, catechin gallate, galloylglucose, and epicatechin

Geraniin, phenazine derivative of geraniin, Corilagin, and furosin.

**S. no. Name of plant species Plant** 

2. *Potentilla erecta* (L.) Rauschal

3. *Sanguisorba officinalis* L.

7. *Phyllanthus* 

Exell

Paxt.

8. *Geranium thunbergii* Siebold exLindl. &

9. *Mouriri pusa* Gardn. (Melastomataceae)

10. *Acacia nilotica* (L.) Willd. exDelile.

4. *Potentilla kleiniana* Aerial

*muellerianus* (Kuntze)

*level of medicinal sources or pharmaceutical agents [59].*

*Plant species containing tannins and their medicinal use.*

its hydroxyl groups or polyol esterified with phenolic compounds such as gallic acid (3,4,5-trihydroxybenzoic acid) or hexahydroxydiphenic acid, which also known as ellagic acid (ellagitannin). Hydrolysable tannins mainly originated from Pentagalloylglucose (2-O-digalloyl-1, 3, 4, 6-tetra-O-galoyl-α-D-glucopyranose),

**118**

**Table 1.**

which is a basic structural unit of hydrolysable tannins. The main source of structural diversity among the hydrolysable tannins is the presence of diverse types of oxidative linkages that give rise to oligomeric compounds with molecular weight between 2000 and 5000 Da [5]. Characteristic examples of hydrolysable tannins are (1) gallic acid; (2) hexahydroxydiphenic acid; (3) ellagic acid; and (4) pentagalloylglucose, which contain a central glucose molecule as the core attached with multiple gallic acid units, while ellagitannins are associated to hexahydroxydiphenic acid. Hydrolysable tannins are mainly present in angiosperm and dicotyledons. Both gallotannins and ellagitannins may synthesize individually or in the form of a mixture in plants. Gallic acid has been extracted from plant families, for example, Ericaceae, Geraniaceae, or Fagaceae; whereas, ellagic acid is available in Hamamelidae, Dilleniidae, and Rosidae species [6].

Naturally occurring condensed tannins are polyphenolic bioflavonoids, are polymers of polyhydroxy flavan-3-ol units, for example, (+)-catechin and (−)-epicatechin-2, (+)-gallocatechin, and flavan-3, 4-diols. They are also known as proanthocyanidins (PA) that ascribed to their hydrolysis to anthocyanidins in heated ethanol treatment. Due to presence of stereoisomerisms in hydroxylation patterns at three chiral centers, bond positions, and type of interflavan bond; proanthocyanidins are present in variety of active forms, for example, (1) (+)-catechin; (2) (−)-epicatechin; (3) (+)-gallocatechin; (4) (−)-epigallocatechin; and (5) (−)-epigallocatechin gallate. Among them, (+) catechin and (−) epicatechin are predominantly present in nature [7]. There are several plant species which offer rich source of proanthocyanidins (see **Table 1**). Proanthocyanidins can be obtained from red wine, green tea, cocoa, and chocolate. However, condensed tannins can further be classified on the basis of reaction rate like, slow reacting tannins like quebracho and mimosa and fast reacting tannins like pine and pecan (*Carya illinoensis*) [5, 7, 8]. Furthermore, some researcher also classified tannins into four different classes based on their structural properties, namely, (1) gallotannins, (2) ellagitannins, (3) complex tannins, and (4) condensed tannins.

After the industrial revolution, most of the synthetic chemicals were used in the diverse types of industries including food, pharma, beverage, leather, and other industries. But prolonged applications of synthetic chemicals in the area of health and other industries left a myriad of adverse effects on environment and human health. Therefore, current focus has been shifted on alternative natural compounds like tannins that can be exploited in the form of functional food, nutraceutical, cosmetology, and pharmaceutical industries.

The global tannin market is expanding very rapidly; according to estimation, 1076.3 kilotons tannin was required in 2015 which expected to rise with CAGR of 5.8% from 2016 to 2025. The demand was mainly in the wine, leather, pharmaceuticals, and wood industries. In case of USA, approximately 282.4 kilotons tannins were produced; its 62.3% is used in leather industries alone. Europe is another emerging market for tannins and tannin-based products. It is due to large scale wine production, which is accounted for 38% revenue generations in Europe. Hence, global market size for tannin related industries may increase up to \$3.3 billion by 2025. The applications of condensed tannins are expected to increase up to 424.8 kilotons by 2025 in comparison of 242.9 kilotons in 2015 [9].

But, there are several unresolved issues linked with applications of tannins such as antinutrient effect, resistance to enzymatic hydrolysis, and lack of complete information about their interactions with other biomolecules and mode of actions in human and animals. The aim of this chapter is to present a brief discussion on the application of tannins in modern industries and to review their positive and negative aspects. It also shows that tannins are being used as sustainable raw material with other green materials in new emerging industries.
