Food Ellagitannins: Structure, Metabolomic Fate, and Biological Properties

*Karen Johana Ortega Villalba, Fabrice Vaillant Barka, Carlos Vélez Pasos and Pablo Emilio Rodríguez*

## **Abstract**

Food sources of ellagitannins (ETs) are numerous, and dietary intake of these compounds is estimated up to 12 mg/day in some countries, even though ETs have been considered in the past as not bioavailable like other tannins and were mostly neglected by nutritionists. Nonetheless, new insights show that ETs are bioconverted by microbiota in the gut into metabolites called urolithins, which are bioavailable and can reach relatively high physiological concentration in the body up to 7 days after ingestion. According to the initial structure of ETs in the food source, the extent of bioconversion into urolithins may differ but all urolithins are susceptible to exert potential health benefits. Nonetheless, due to the intervention of microbiota, the production and excretion of urolithins are highly variable according to individuals, which have led to the classification of consumers into metabotype. According to metabotype, the potential health benefits of ellagitannins may differ among consumers. In in vitro, cellular and animal studies, numerous health benefits of ellagitannins and urolithins are reported mainly for the chemoprevention of hormone-dependent cancer and cardiovascular disease. Nonetheless, ellagitannins deserve closer attention from the scientific community to unravel more biological properties of this particular compound.

**Keywords:** ellagitannins, urolithins, microbiota, metabotype, chemoprevention

#### **1. Introduction**

Ellagitannins are food compounds that were quite neglected by nutrionists until last decade. As part of tannins, they had no good reputation and they were considered as antinutritional compounds. But new scientific insights have changed these perspectives, and ellagitannins now attract the attention of food scientists, nutritionists and consumers since the number of published papers on these compounds has considerably increased during the last decade. Ellagitannin is a hydrolyzable polymer contrary to the rest of the family of tannins and can be hydrolyzed to more simple monomers that can be eventually metabolized and that can become bioavailable with subsequent exposition of the body to these metabolites. For sure, if ellagitannins are widely present in nature, only few food sources are reported with relatively high content of this compound, and consequently exposition of consumers to food ellagitannins is relatively low, especially in the Western diet. But given

the health potential of ETs, ET-rich food now belongs to the select group of functional foods, and their consumption should be considerably enhanced in the future. Actually, given the main food source of ellagitannins such as berries and nuts, we can easily assume that the exposure to this compound and their metabolites was considerably higher in the hunter-gatherer diet than in modern time. Without presuming that an increase in ET intake would reduce significantly the impact of certain chronic diseases due to modern lifestyle, it is reasonable to argue that ETs have been part of our evolutionary history and they could potentially perform health care functions. New scientific insights presented in this chapter on the in vivo metabolisms of ellagitannins and the potential biological activities of generated metabolites tend to support this hypothesis. This review presents the main food source of ellagitannins, their general chemical structure, and how technologies and storage could eventually affect ellagitannin composition in processed foods. Then, we will review the metabolomic fate and the bioavailability of ellagitannins in humans, which is strongly related to the performance of intestinal microbiota, and finally, we will present a summary of the main biological activities, attributed to ETs and their derived metabolites.
