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Use of Green Chemistry for Extraction of Bioactive Compounds from Vegetal Sources
Published in Aidé Sáenz-Galindo, Adali Oliva Castañeda-Facio, Raúl Rodríguez-Herrera, Green Chemistry and Applications, 2020
Adriana C. Flores-Gallegos, Ramsés Misael Reyes-Reyna, Paloma Almanza-Tovanche, Marisol Rodríguez-Duarte, Gerardo M. González, Raúl Rodríguez-Herrera, J.A. Ascacio-Valdés
Condensed tannins are flavonoid polymers bound by C–C bonds, which cannot be hydrolyzed but oxidized by a strong acid to produce anthocyanidins. Hydrolyzable tannins are heterogeneous polymers, that contain phenolic acids and simple sugars; they are smaller in comparison with condensates and hydrolyze more easily (Ávalos and Pérez, 2009). Tannins can also be considered as toxins because of their ability to bind proteins. In plants, terpenes serve as protection against insects, herbivorous animals or high temperatures. As protection against animals, immature fruits contain tannins in the husk, so these compounds repel animal attacks since they generate bitter flavors. However, not all tannins have toxic effects, for example, tannins contained in red wine cause a beneficial effect on human health by blocking the formation of endothelin-1, a signal molecule that causes vasoconstriction (Ávalos and Pérez, 2009).
Properties and Applications of the Phytochemical
Published in Cristobal N. Aguilar, Suresh C. Ameta, A. K. Haghi, Green Chemistry and Biodiversity, 2019
René Díaz-Herrera, Pedro Aguilar-Zarate, Juan Alberto Ascasio-Valdes, Leonardo Sepúlveda-Torre, Juan Buenrostro-Figueroa, Monica L. Chavez-Gonzalez, Janeth Ventura, Cristóbal N. Aguilar
Tannins are polyphenolic compounds, which according to their structure are divided into three groups; hydrolysable tannins which in turn are divided into two groups, since these have a sugar core linked by esterification to gallic acid (gallotannins) or hexahydroxydiphenic acid (HHDP) [ellagitannins (ETs)]; the condensed tannins formed by the monomer flavan-3-ol or flava-3,4-diol; and complex tannins that share the properties of the two previous groups of tannins, hydrolysable and condensed.9 Of the four groups of tannins, ETs are the least studied group due to their diversity and chemical complexity.4 When ETs are exposed to strong acidic or basic conditions, ester bonds are hydrolyzed and the HHDP group is released, which must go through a process of lactonization to become a more stable molecule known as EA (Fig. 9.1).10,12
Tannins for Wood Adhesives,Foams and Composites
Published in Zhongqi He, Bio-based Wood Adhesives, 2017
Tannin or tannins have been used industrially for almost 50 years. They can be used as adhesives for interior and exterior wood bonding so that they are excellent alternatives to the petroleum—derived phenolic resins for the production of particleboard, plywood, glulam and finger jointing. The word “tannin” defines two classes of phenolic chemical compounds:hydrolysable tannins which are mixtures of simple sugars and ester of glucose with gallic and digallic acids;condensed tannins consisting of flavonoid units with varying degrees of condensation.
Vegetable tannin composition and its association with the leather tanning effect
Published in Chemical Engineering Communications, 2020
Priscila Auad, Franciela Spier, Mariliz Gutterres
The minimum size and reactivity required to have a tanning capacity can be achieved in a number of ways, and the most common way in nature seems to be the binding of esters or gallic acids to the central part of a carbohydrate. These molecules are easily hydrolyzed with acids, bases, or enzymes and are therefore called hydrolyzable tannins (Grasel et al., 2016a). Despite their non-polymer origin, this family of tannins can form complex structures (Belgacem and Gandini, 2008). The hydrolyzable tannins are chemically divided into gallotannins and ellagic tannins. Galotannins are glucose and polyesters of gallic acid commonly found in nature, and they release gallic acid when hydrolyzed. Meanwhile, ellagic tannins are characterized by a glucose center esterified with at least one unit of hexahydroxydiphenyl acid, which is formed by the oxidative coupling of two units of gallic acid (Belgacem and Gandini, 2008). On the other hand, other polyphenolic mixtures present in plants do not undergo hydrolysis, with these being called condensed tannins or proanthocyanidins. They are oligomers or polymers of the basic structure of flavan-3-ol (Koleckar et al., 2008).