Elsevier

Journal of Functional Foods

Volume 49, October 2018, Pages 188-195
Journal of Functional Foods

Study of antioxidant capacity and metabolization of quebracho and chestnut tannins through in vitro gastrointestinal digestion-fermentation

https://doi.org/10.1016/j.jff.2018.07.056Get rights and content

Highlights

Abstract

Quebracho (QUE) and chestnut (CHE) are natural sources of tannins, but there are no connection between QUE, CHE and human health. The study investigated the antioxidant response and metabolization of tannin extracts trough in vitro digestion-fermentation. The FRAP assay pointed a higher reducing capacity of CHE than QUE (6.90 vs. 5.07 mmol Trolox/g), in contrast to a stronger scavenging activity of QUE (8.16 mmol Trolox/g vs 6.70 mmol Trolox/g). The results obtained showed a decrease of the antioxidant capacity of tannins after microbial fermentation, but a high prebiotic activity through release of short-chain fatty acids of both CHE (11.14 mmol/g) and QUE (4.79 mmol/g) was observed. The UPLC-MS investigations on digested and fermented tannins gave an identification and semi-quantification of 18 compounds, including hydrolysable and condensed tannins and their metabolites. The results represent a valid basis for further studies on the potential use of these wood extracts in human diet.

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).

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