Study of antioxidant capacity and metabolization of quebracho and chestnut tannins through in vitro gastrointestinal digestion-fermentation
Graphical abstract
Introduction
Tannins are secondary metabolites widely distributed in the plant kingdom, extracted from many types of trees and plants and can be present in barks, leaves, wood and also in fruits and roots. These plants generally used for tannin production may contain up to 40% tannin by weight (van Diepeningen et al., 2004). Most raw materials used for industrial production are Chestnut wood (18% of tannin in wood on dry matter), Quebracho hardwood and Mimosa barks (24% in both), Tara pods and Chinese or Turkish gallnut (50% in both). In particular, Schinopsis lorentzii Engl. and Schinopsis balansae Engl., known as red quebracho, are evergreen tree species widespread in the dense subtropical forests of Gran Chaco (Argentina), Bolivia and Paraguay, while Castanea sativa Mill. trees, commonly named chestnut, is found across the Mediterranean region.
The quebracho wood extract (QUE) is among the most industrially produced source of tannins, predominantly composed of oligomers of profisetinidins. It is composed of oligomers in which flavonoid units are condensed together to obtain molecular weight (MW) ranging from 1.000 to 20.000 Da. The composition of QUE was described by Pasch, Pizzi, and Rode (2001) using MALDI-TOF mass spectrometry and Venter, Senekal, et al., 2012, Venter, Sisa, et al., 2012 reported a more detailed description of the linear structures of the polyanthocyanidins oligomers. CHE is characterized by the presence of hydrolysable tannins, composed of a carbohydrate core whose hydroxyl groups are esterified with phenolic acids with a MW ranging from 300 to 5.000 Da (Mueller-Harvey & McAllan, 1992). The chemical composition of CHE has been clarified by using MALDI-TOF mass spectrometry which states that it is an ellagic-type hydrolysable tannin (Pasch & Pizzi, 2002). Castalagin, with the isomer vescalagin, represents around 30% of the product. It has been shown that these substances and their higher oligomers are present in this tannin and are quite stable since they come from the rearrangement of polypentagalloyl glucose, naturally occurring in chestnut wood (Pasch & Pizzi, 2002). The higher oligomers contain repeating units of polygalloyl glucose chain, where galloyl groups can be linked differently to each other (Radebe, Rode, Pizzi, Giovando, & Pasch, 2013).
QUE and CHE are already commercialized in animal feeding, especially for cattle and poultry (Buccioni et al., 2017; Carrasco et al., 2018). Several studies have reported that addition of QUE and CHE to animal feed improved the nutrition and the animal health in both ruminants and monogastric animals (Buccioni et al., 2017, Diaz Carrasco et al., 2016, Henke et al., 2017, López-Andrés et al., 2013, Redondo et al., 2014) Due to their chemical composition, these compounds exert antiviral, antimicrobial, scavenging and antimutagenic effects locally in the intestine as unabsorbable complex structures (Serrano, Puupponen-Pimiä, Dauer, Aura, & Saura-Calixto, 2009). However, since a little amount of tannins or their metabolites might be absorbed from the gastrointestinal tract, systemic effects associated to improvement of endogenous antioxidant activity in different organs are observed (Cires et al., 2017, Serrano et al., 2009). Tannins may interfere with the digestion of nutrients, binding proteins or delaying the absorption of sugar and lipids (Cires et al., 2017). In particular, complexes with proteins are given by the tannins numerous hydroxyl groups and depend on proline content and size of the proteins (Hagerman & Butler, 1981). Given the antinutrient effect, these compounds could be studied as functional substances. There are studies that reported the possible use of tannins in nutrition for celiac disease, by their potential crosslinking activity of wheat gluten (Girard, Bean, Tilley, Adrianos, & Awika, 2018), or in diabetes mellitus thanks to their anthyperglycemic activity (Cires et al., 2017, Williamson, 2013, Yin et al., 2011).
Even though tannins have shown important biological properties, little is known about the bioavailabilty and biological effects of QUE and CHE extracts in humans. In particular, in order to understand how these extracts determine health benefits, it is crucial to study the metabolization of tannins during digestion and fermentation processes. Several authors have tried to understand the metabolisation of tannins contained in fruits (i.e. apples or grapes) or directly of molecules like proanthocyanidins (Appeldoorn et al., 2009, Aura et al., 2013, Bazzocco et al., 2008, Stoupi et al., 2010), evidencing the production of phenolic acids such as 2-(3,4-dihydroxyphenyl) acetic acid, 2-(3-hydroxyphenyl) acetic acid, 2-(4-hydroxyphenyl) acetic acid and 3-(3-hydroxyphenyl) propionic acid.
Taking all this information into account, the overall aim of the present report was to unravel the possible use of QUE and CHE as potential ingredients for the development of functional foods. In order to reach this goal, three different sub-objectives were defined, after in vitro digestion and fermentation of the samples: (i) To study the global antioxidant response of QUE and CHE. (ii) To determine their bioactivity on the gut microbiota, reflected by the production of short chain fatty acids (SCFAs). (iii) To investigate the evolution of the polyphenolic profile of tannins extracts.
Section snippets
Plant material, chemicals and reagents
Tannin extracts (QUE and CHE), obtained by hot water extraction, are commercialized by Silvateam Spa (San Michele di Mondoví, Italia) as powder. QUE, a profisetinidin condensed tannin of 6,25 of degree of polymerization, was previously characterized by Pasch et al. (2001). The composition of CHE, a hydrolysable ellagitannin with 30% of isomers castalagin and vescalagin as representative substances, was described by Pasch & Pizzi (2002). Reagents and inulin were from Sigma-Aldrich (Germany) and
Antioxidant capacity as a result of in vitro gastrointestinal digestion
Global antioxidant capacity (GAR+) has been established as a suitable method to evaluate total antioxidant capacity of fresh and processed foods (Pastoriza, Delgado-Andrade, Haro, & Rufián-Henares, 2011). The GAR+ was determined in the soluble fraction obtained after enzymatic digestion, as well as in the soluble and insoluble fractions of fermented QUE and CHE. As GAR+ is the total antioxidant capacity of the three fractions, it is expressed as a single value. Table 1 and Fig. 2 present the
Conclusion
This is the first study that reports the effect of in vitro gastrointestinal digestion and fermentation of tannin wood extracts on the production of SCFAs, antioxidant capacity and evolution of the polyphenols profile. The global antioxidant response obtained from two assays indicated a higher reducing capacity of the CHE, while QUE showed higher antiradical activity. Tannins have been proven to be important substrates for microbial fermentation and production of SCFAs. In particular, the
Ethics statement
No ethics approval was needed in order to perform the research activities related with this paper since all of them were done in vitro.
Conflict of interest
The authors declare that there are no conflicts of interest.
Acknowledgements
This paper will form part of the doctoral thesis of Silvia Molino, conducted within the context of the “Nutrition and Food Sciences Programme” at the University of Granada.
Formatting of funding sources
This work was supported by project AGL2014-53895-R from the Spanish Ministry of Economy and Competitiveness and by the European Regional Development Fund (FEDER).
References (41)
- et al.
The ferric reducing ability of plasma (FRAP) as a measure of “antioxidant power”: The FRAP assay
Analytical Biochemistry
(1996) - et al.
Gut metabotypes govern health effects of dietary polyphenols
Current Opinion in Biotechnology
(2013) - et al.
Chestnut or quebracho tannins in the diet of grazing ewes supplemented with soybean oil: Effects on animal performances, blood parameters and fatty acid composition of plasma and milk lipids
Small Ruminant Research
(2017) - et al.
Interaction mechanisms of condensed tannins (proanthocyanidins) with wheat gluten proteins
Food Chemistry
(2018) - et al.
Direct measurement of the total antioxidant capacity of foods: The ‘QUENCHER’ approach
Trends in Food Science & Technology
(2009) - et al.
The specificity of proanthocyanidin-protein interactions
Journal of Biological Chemistry
(1981) - et al.
Effect of dietary quebracho tannin extract on milk fatty acid composition in cows
Journal of Dairy Science
(2017) - et al.
MALDI–TOF mass spectrometry of polyflavonoid tannins
Polymer
(2001) - et al.
A physiologic approach to test the global antioxidant response of foods. The GAR method
Food Chemistry
(2011) - et al.
Chronic administration of a microencapsulated probiotic enhances the bioavailability of orange juice flavanones in humans
Free Radical Biology and Medicine
(2015)