Strawberry Processing Does Not Affect the Production and Urinary Excretion of Urolithins, Ellagic Acid Metabolites, in Humans

Abstract

The study of fruit and vegetable processing and its effects on the levels of health-promoting constituents and their bioavailability and metabolism is very relevant to understanding the role of these constituents in human health. Strawberry polyphenols, and particularly ellagitannins and ellagic acid, have been associated with the health benefits of this berry for humans. These compounds are transformed into urolithins by the gut microbiota, and these metabolites exert several biological activities that could be responsible for the health effects of strawberries. Processing potentially increases the extraction of ellagitannins from the strawberry achenes and the release of ellagic acid from ellagitannins. It is of interest to evaluate the effect of processing on strawberry ellagitannin microbial metabolism compared with fresh strawberries. This study shows that no significant differences in the production and excretion of urolithins were found between the intake of fresh strawberries and that of a thermally processed strawberry puree containing the same amount of strawberries. Processing increases the amount of free ellagic acid 2.5-fold, but this had no effect on the transformation in urolithins by the gut microbiota or in the excretion of urolithin metabolites (urolithin glucuronides) in urine, showing that the release of ellagic acid from ellagitannins is not a relevant factor affecting the microbial metabolism. All of the volunteers produced urolithin A, but only 3 of 20 volunteers produced and excreted urolithin B. It is confirmed that some volunteers were efficient producers of urolithins, whereas other produced much lower amounts. These results show that processing does not modify the potential health effects of strawberry polyphenols.

Physiological Properties of Dietary Ellagitannin-Rich Preparations Obtained from Strawberry Pomace Using Different Extraction Methods

“…It is known that urolithins, the main metabolites of ellagitannins, after participation in the metabolic process are excreted with urine and faeces [Truchado et al, 2012;Espin et al, 2007]. Seeram et al [2007] demonstrated that metabolites of pomegranate ellagitannins administered to mice are concentrating in higher quantities in intestinal tissues and in prostate.…”

Role of the small intestine, colon and microbiota in determining the metabolic fate of polyphenols

“…There are no intravenous dosing data for the C 6 -C 3 , C 6 -C 2 or C 6 -C 5 catabolites. A study in which volunteers consumed a bolus dose of strawberry purée containing ellagitannins has demonstrated that the unique urolithin catabolites were still detected in urine 90 h later suggesting that the ellagitannin substrate may have bound to the mucosa and not moved with the unbound digesta [98]. It is likely that a similar phenomenon will occur with proanthocyanidins which also bind strongly to proteins, and possibly thearubigins, but because their catabolites are not unique it would be more difficult to demonstrate than with the ellagitannins (see Figs 2 and 5).…”

Gastrointestinal stability of urolithins: an in vitro approach

“…The presence of a food matrix and the interactions of urolithins with different co-ingested dietary components may modify their stability during their transit through the GIT [43]. Another limitation of this work is the lack of data on Uro A-gluc, one of the main circulating metabolites derived from ellagitannin consumption [20][21][22][23][24]. However, this compound is not commercially available and could not be easily synthesized during the course of this work.…”

“…To which extent structurally intact urolithins are bioavailable is something that deserves further studies with epithelial and hepatic cell models, aiming at investigating the transport and metabolism of these ellagitannin-derived metabolites. Nevertheless, the ability of the human colon to absorb urolithins, which then become available at systemic circulation level, has been repeatedly confirmed [20][21][22][23][24]. Future research on animal models is also required to fully establish whether orally supplemented urolithins may be well tolerated and efficiently absorbed.…”

“…ellagitannin-containing foods [20][21][22][23][24]. However, considerable inter-individual variability in urolithin excretion levels has been observed.…”