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

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.