Concord and Niagara Grape Juice and Their Phenolics Modify Intestinal Glucose Transport in a Coupled in Vitro Digestion/Caco-2 Human Intestinal Model.

Sydney Moser,Jolynne Wightman,Bruce Hamaker,Jongbin Lim,Mohammad Chegeni,Mario Ferruzzi

doi:10.3390/nu8070414

Abstract

While the potential of dietary phenolics to mitigate glycemic response has been proposed, the translation of these effects to phenolic rich foods such as 100% grape juice (GJ) remains unclear. Initial in vitro screening of GJ phenolic extracts from American grape varieties (V. labrusca; Niagara and Concord) suggested limited inhibitory capacity for amylase and α-glucosidase (6.2%–11.5% inhibition; p < 0.05). Separately, all GJ extracts (10–100 µM total phenolics) did reduce intestinal trans-epithelial transport of deuterated glucose (d7-glu) and fructose (d7-fru) by Caco-2 monolayers in a dose-dependent fashion, with 60 min d7-glu/d7-fru transport reduced 10%–38% by GJ extracts compared to control. To expand on these findings by assessing the ability of 100% GJ to modify starch digestion and glucose transport from a model starch-rich meal, 100% Niagara and Concord GJ samples were combined with a starch rich model meal (1:1 and 1:2 wt:wt) and glucose release and transport were assessed in a coupled in vitro digestion/Caco-2 cell model. Digestive release of glucose from the starch model meal was decreased when digested in the presence of GJs (5.9%–15% relative to sugar matched control). Furthermore, transport of d7-glu was reduced 10%–38% by digesta containing bioaccessible phenolics from Concord and Niagara GJ compared to control. These data suggest that phenolics present in 100% GJ may alter absorption of monosaccharides naturally present in 100% GJ and may potentially alter glycemic response if consumed with a starch rich meal.

Highlights

On average, Americans consume 0.43 gallons per capita of grape juice (GJ) annually, makingGJ the third most commonly consumed juice in the US [1]
Since extracts were standardized for total phenolics, these results suggest that the qualitative phenolic profile of Niagara GJ, which is primarily composed of non-anthocyanin flavonoids and phenolic acids and minimal amounts of anthocyanins (Table 2), may be most critical to consider in selection of juices and merits additional investigation as targeted modifiers of intestinal glucose transport
SO2 treatment did not impact relative bioaccessibility of phenolics from Niagara GJ. These results logically suggest that starting concentration of phenolics in 100% GJ have a direct impact on concentration of phenolics available for interactions in the gut and ultimate stability and accessibility of phenolics in the small intestine

Summary

Introduction

Americans consume 0.43 gallons per capita of grape juice (GJ) annually, makingGJ the third most commonly consumed juice in the US [1]. Native American Concord and Niagara grape cultivars are sources for production of purple and white juice, respectively. Both grapes and their corresponding juices are well established sources of nutrients and bioactive phenolic compounds, including flavan-3-ols, flavonols, stilbenes, phenolic acids and, for Concord grapes, anthocyanins [2,3,4,5]. With total phenolic and anthocyanin levels reported as high as 2900 mg/L and 880 mg/L, respectively, for 100% Concord GJ and high levels of phenolics in 100% Niagara GJ, these products can be significant contributors to health promoting phytochemicals [4]. Primary outcomes mediated by Concord GJ include increased flow mediated dilation, decreased platelet aggregation, modulation of low density lipoprotein (LDL) oxidation lag time, and improved memory function and brain signaling

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