Simulated Gastric and Intestinal Fluid Electrolyte Solutions as an Environment for the Adsorption of Apple Polyphenols onto β-Glucan

Abstract

Interactions with dietary fibers in the gastrointestinal tract might affect the potential bioactivities of phenolic compounds. In this study, the interactions between apple phenolic compounds and β-glucan (a dietary fiber) were studied by studying the adsorption process in simulated gastric and intestinal fluid electrolyte solutions. Phenolic compounds were extracted from apples, adsorbed onto β-glucan (2 h, 37 °C, in gastric or intestinal fluid electrolyte solutions), and determined using high performance liquid chromatography. Phenolic compounds (flavan-3-ols, flavonols, phenolic acids, and dihydrochalcone) were stable in the gastric fluid (pH 3). In the intestinal fluid (pH 7), flavan-3-ols were not found and chlorogenic acid isomerized. Polyphenols from the apple peel (up to 182 and 897 mg g^-1) and flesh (up to 28 and 7 mg g^-1) were adsorbed onto β-glucan in the gastric and intestinal fluids, respectively. The adsorption was affected by the initial concentration of the polyphenols and β-glucan and by the environment (either gastric or intestinal fluid electrolyte solution). By increasing the initial polyphenol amount, the quantity of adsorbed polyphenols increased. Increasing the amount of β-glucan decreased the amount adsorbed. The results can be helpful in explaining the fate of phenolic compounds in the gastrointestinal tract.

Keywords: adsorption capacity; dietary fiber; gastrointestinal tract; phenolic compounds.

Figure 1

Chromatogram of apple peel and flesh extract before adsorption, scanned at 280 nm, with all detected phenolic compounds. Detected phenolic compounds. 1—procyanidin B1, 2—(+)-catechin, 3—procyanidin B2, 4—chlorogenic acid, 5—chlorogenic acid isomer 2*, 6—(−)-epicatechin, 7—phloretin-2-xyloglucoside*, 8—quercetin-3-galactoside, 9 + 10—quercetin-3-glucoside + quercetin-3-rutinoside*, 11—quercetin derivative 1*, 12—quercetin derivative 2*, 13—quercetin derivative 3*, 14—quercetin-3-xyloside, 15—quercetin-3-rhamnoside. *—tentative identification.

Figure 2

The amounts of individual phenolic compounds from apple peel adsorbed onto β-glucan (mg g⁻¹ of β-glucan) in gastric fluid electrolyte solution with added (A) 15 mg L⁻¹ β-glucan, (B) 30 mg L⁻¹ β-glucan and in the intestinal fluid electrolyte solution with added (C) 15 mg L⁻¹ β-glucan and (D) 30 mg L⁻¹ β-glucan. Volumes of phenolic compound extracts were 100, 200 and 300 μL. The significant differences between the amount adsorbed with different initial volumes of phenolic compound extract according to post-hoc Tukey test (p < 0.05) are marked by different letters above bars.

Figure 3

The amounts of individual phenolic compounds from apple flesh adsorbed onto β-glucan (mg g⁻¹ of β-glucan) in gastric fluid electrolyte solution with added (A) 15 mg L⁻¹ β-glucan, (B) 30 mg L⁻¹ β-glucan, and in the intestinal fluid electrolyte solution with added (C) 15 mg L⁻¹ β-glucan and (D) 30 mg L⁻¹ β-glucan. Volumes of phenolic compound extracts were 100, 200 and 300 μL. The significant differences between the amount adsorbed with different initial volumes of phenolic compound extract according to post-hoc Tukey test (p < 0.05) are marked by different letters above bars.

Figure 4

Total amount of adsorbed phenolic compounds from apple peel onto β-glucan in simulated (A) gastric and (B) intestinal fluid electrolyte solutions. The amount of β-glucan was 15 and 30 mg L⁻¹. Phenolic compound extract volumes were 100, 200 and 300 μL. The significant differences between the total amount of adsorbed phenolic compounds with different initial amount of β-glucan were analyzed with post-hoc Tukey test (p < 0.05), the same letter above bars shows no significant difference.

Figure 5

Total amount of adsorbed phenolic compounds from apple flesh onto β-glucan in simulated (A) gastric and (B) intestinal fluid electrolyte solutions. The amount of β-glucan was 15 and 30 mg L⁻¹. Phenolic compound extract volumes were 100, 200 and 300 μL. The significant differences between the total amount of adsorbed phenolic compounds with different initial amount of β-glucan according to post-hoc Tukey test (p < 0.05) are marked by different letters above bars.

Figure 6

Principal component analysis of adsorption capacities of all individual phenolic compounds from apple peel (A) in the gastric solution, (B) in the intestinal fluid electrolyte solution. Principal component analysis of (C) total adsorption capacities of phenolic compounds from apple peel in both gastric and intestinal fluid electrolyte solutions. Principal component analysis of adsorption capacities of all phenolic compounds from apple flesh (D) in the gastric solution, (E) in the intestinal fluid electrolyte solution. Principal component analysis of (F) total adsorption capacities of phenolic compounds from apple flesh in both gastric and intestinal fluid electrolyte solutions.