A Comprehensive Analysis of Diversity, Structure, Biosynthesis and Extraction of Biologically Active Tannins from Various Plant-Based Materials Using Deep Eutectic Solvents

Abstract

This paper explores the emerging subject of extracting tannins from various plant sources using deep eutectic solvents (DESs). Tannins are widely used in the food and feed industries as they have outstanding antioxidant qualities and greatly enhance the flavor and nutritional content of a wide range of food products. Organic solvents are frequently used in traditional extraction techniques, which raises questions about their safety for human health and the environment. DESs present a prospective substitute because of their low toxicity, adaptability, and environmental friendliness. The fundamental ideas supporting the application of DESs in the extraction of tannins from a range of plant-based materials frequently used in daily life are all well covered in this paper. Furthermore, this paper covers the impact of extraction parameters on the yield of extracted tannins, as well as possible obstacles and directions for future research in this emerging subject. This includes challenges such as high viscosity, intricated recovery of compounds, thermal degradation, and the occurrence of esterification. An extensive summary of the diversity, structure, biosynthesis, distribution, and roles of tannins in plants is given in this paper. Additionally, this paper thoroughly examines various bioactivities of tannins and their metabolites.

Keywords: deep eutectic solvents; ellagitannins; extraction; gallotannins; hydrolysable tannins; proanthocyanidins; tannins.

Figure 1

Some examples of structures of the tannin main subgroups.

Figure 2

Example of a trimeric proanthocyanidin. The extension units are gallocatechin and epigallocatechin (PD), and terminal unit catechin (PC). Adapted from Engström 2016 [29].

Figure 3

The biosynthetic pathways leading to phlorotannins, hydrolysable tannins, and proanthocyanidins (adapted from [26,29], created with BioRender.com (accessed on 26 May 2024) [48]). PKSIII: type III polyketide synthase, PAL: phenylalanine ammonia-lyase, C4H: cinnamic acid 4-hydroxylase, 4CL: 4-coumarate-CoA ligase, CHI: chalcone isomerase, CHS: chalcone synthase, FHT: flavanone 3β-hydroxylase, DFR: dihydroflavonol 4-reductase, LAR: leucoanthocyanidin reductase, and ANR: anthocyanidin reductase.