The Reciprocal Interactions between Red Raspberry Polyphenols and Gut Microbiome Composition: Preliminary Findings
Authors: Zhang Xuhuiqun , Sandhu Aman , Schill Kristin M. , Edirisinghe Indika , Burton‐Freeman Britt 
Published: November 2023

Background

Red raspberries (Rubus idaeus L.) contain a variety of polyphenols, principally anthocyanins and ellagitannins. Anthocyanins, undergoing metabolism and biotransformation, are absorbed as methylated, sulphated or glucuronidated parent structures or phenolic acids by gut microbiota. Ellagitannins are hydrolyzed to ellagic acid in the stomach and/or the small intestine and further catabolized to urolithins by gut microbiota. Consistent exposure of certain polyphenols to the gut microbiota may act as prebiotic‐like substances feeding the beneficial gut bacteria and changing the gut microbiome composition and function. The dichotomy between the biotransformation of polyphenols into their metabolites by gut microbiota and the modulation of gut microbiome composition by polyphenols is hypothesized to contribute to positive health outcomes.

Objectives

The present study examined the regular consumption of red raspberry purée or fructo‐oligosaccharide (FOS) on gut microbiome composition and subsequent bioavailability of red raspberry polyphenols in healthy volunteers.

Methods

An 8‐week pilot study, including two 4‐week chronic treatments and 3 postprandial days, served as a feasibility study and mechanism to collect multiple biological specimens for method development. An ultra high‐performance liquid chromatography (HPLC) coupled with electrospray ionization quadrupole time of flight (QTOF) and triple quadrupole (QQQ) mass spectrometer in positive and negative ion modes were used to identify and quantify the phenolic compounds in red raspberry purée, plasma and urine samples. Fecal samples were used for metagenomic study. The sequencing of the 16S ribosomal RNA gene was utilized to study the gut microbiome composition.

Results

The red raspberry purée ingested contained 49.30 ± 1.45 mg/100 g fresh weight (FW) anthocyanins and 39.35 ± 1.61 mg/100 g FW ellagitannins. After 4‐week red raspberry purée (125g/d) treatment, the abundance of Firmicutes dropped from 83.66% to 48.98%, whereas that of Bacteroidetes increased markedly from 5.99% to 34.79%. At the genus level, the abundance of Akkermansia increased from 0.65% to 6.20%. After 4‐week FOS (positive control, 8 g/d) treatment, the abundance of Firmicutes dropped from 69.91% to 53.93%, whereas that of Bacteroidetes increased from 19.04% to 36.80%. The effects of gut microbiome composition on red raspberry polyphenols biotransformation and their metabolites will be disclosed upon the analysis of plasma and urine metabolites. The results of the pilot study indicate an expanded study is feasible and warranted with preliminary results suggesting marked changes in the gut microbiota composition we hypothesize to influence polyphenol metabolite profiles and systemic health. All the methods and preliminary results will be applied for an expanded study.

Support or Funding Information

Project supported by National Processed Raspberry Council and Investigator (Burton‐Freeman/Edirisinghe) various donor funds.