3 min, and a one-time microwave radiate action, with tea/water ratio of 1:20 (Li
and Jiang 2010).
5. Ultrasound/sonication-assisted extraction method demonstrates excellent
solvent penetration into cellular materials. In this process, optimal extraction
conditions for several hydrolysable tannins came about by way of treatment
with 19.7% ethanol, for 26.4 min, at 24 °C (Lee et al. 2013). Of note, for
deriving catechins from commercial Chinese tea samples, the novel dynamic
ultrasound-assisted extraction method was found to be more effective than static
ultrasound-assisted extraction (Gu et al. 2007).
6. Extraction by lyophilisation can be done by lyophilizing sample and maceration by acetone and water in 4:1 ratio overnight. After that, extracted sample is
shaken on planar shaker for several hours (3 h.) and it is then centrifuged to get
the supernatant, which is concentrated and frozen. Then the frozen material is
taken and extracted again with methanol (Suvanto et al. 2017).
21.6 Physical and Chemical Properties of Tannins
• These are high molecular weight phenolic compounds. These are complex
organic, non-nitrogenous and non-crystalline substances.
• Physically, tannins have a colour of reddish brown and dark brown, it possess a
state of non-crystalline matter and a taste with bitterness and puckering (Jaiswal
et al. 2018). A tannin can also possess light yellow or white amorphous or shiny
powder like appearance (Li et al. 2013). Tannins are soluble in water, acetone,
glycerol, dilute alkalies and alcohols; sparingly soluble in ethyl acetate, chloroform and insoluble in benzene. Gallotannins are rapidly soluble but ellagitannins are slowly soluble in water in comparison to gallotannin (Mingshu et al.
2006). They are practically insoluble in ether, carbon-disulphide and benzene
(Maximilian Nierenstein and Skene 1934).
• Tannins show its individual characteristics when they are treated with mineral
acids. Hydrolysable tannin is hydrolyzed into gallic acid or ellagic acid when it
gets a treatment with different mineral acids like HCl or H 2 SO 4 . Upon dry
distillation, hydrolysable tannin results in the production of pyrogallol and
phenolic compounds. Condensed tannins, upon acid treatment in elevated
temperature, it polymerizes and is converted into a red insoluble complexes,
called phlobaphenes (Pizzi 2019).
• Precipitation and astringency: Tannins form insoluble cross-linked complexes
by interacting with protein molecules. They combine with skin and hide to form
leather through a process of crosslinking the skin collagen (Khanbabaee and
Van Ree 2001) and with gelatin and isinglass to form an insoluble compound.
They combine with alkaloids to form tannates, most of which are insoluble in
732
S. Mal and D. Pal
and Jiang 2010).
5. Ultrasound/sonication-assisted extraction method demonstrates excellent
solvent penetration into cellular materials. In this process, optimal extraction
conditions for several hydrolysable tannins came about by way of treatment
with 19.7% ethanol, for 26.4 min, at 24 °C (Lee et al. 2013). Of note, for
deriving catechins from commercial Chinese tea samples, the novel dynamic
ultrasound-assisted extraction method was found to be more effective than static
ultrasound-assisted extraction (Gu et al. 2007).
6. Extraction by lyophilisation can be done by lyophilizing sample and maceration by acetone and water in 4:1 ratio overnight. After that, extracted sample is
shaken on planar shaker for several hours (3 h.) and it is then centrifuged to get
the supernatant, which is concentrated and frozen. Then the frozen material is
taken and extracted again with methanol (Suvanto et al. 2017).
21.6 Physical and Chemical Properties of Tannins
• These are high molecular weight phenolic compounds. These are complex
organic, non-nitrogenous and non-crystalline substances.
• Physically, tannins have a colour of reddish brown and dark brown, it possess a
state of non-crystalline matter and a taste with bitterness and puckering (Jaiswal
et al. 2018). A tannin can also possess light yellow or white amorphous or shiny
powder like appearance (Li et al. 2013). Tannins are soluble in water, acetone,
glycerol, dilute alkalies and alcohols; sparingly soluble in ethyl acetate, chloroform and insoluble in benzene. Gallotannins are rapidly soluble but ellagitannins are slowly soluble in water in comparison to gallotannin (Mingshu et al.
2006). They are practically insoluble in ether, carbon-disulphide and benzene
(Maximilian Nierenstein and Skene 1934).
• Tannins show its individual characteristics when they are treated with mineral
acids. Hydrolysable tannin is hydrolyzed into gallic acid or ellagic acid when it
gets a treatment with different mineral acids like HCl or H 2 SO 4 . Upon dry
distillation, hydrolysable tannin results in the production of pyrogallol and
phenolic compounds. Condensed tannins, upon acid treatment in elevated
temperature, it polymerizes and is converted into a red insoluble complexes,
called phlobaphenes (Pizzi 2019).
• Precipitation and astringency: Tannins form insoluble cross-linked complexes
by interacting with protein molecules. They combine with skin and hide to form
leather through a process of crosslinking the skin collagen (Khanbabaee and
Van Ree 2001) and with gelatin and isinglass to form an insoluble compound.
They combine with alkaloids to form tannates, most of which are insoluble in
732
S. Mal and D. Pal