Honey and Its Biomimetic Deep Eutectic Solvent Modulate the Antioxidant Activity of Polyphenols

Abstract

Honey is a highly valued natural product with antioxidant, antimicrobial and anti-inflammatory properties. However, its antioxidant activity (AOA) is not as high as that of other honeybee products, such as propolis. Several polyphenol-honey formulations have been proposed up to now, most of them using maceration of biomass in honey or mixtures with liquid extracts, which either limit polyphenols bioavailability or destroy the characteristics of honey. To improve the health benefits of honey by increasing AOA and keeping its structural and sensory properties, we propose its enrichment in a polyphenol extract of raspberry after solvent evaporation. A honey-biomimetic natural deep eutectic solvent (NaDES) was prepared and compared with honey. The main polyphenols found in the raspberry extract were tested in combination with honey and NaDES, respectively. The AOA was determined by DPPH, ABTS, CUPRAC, and FRAP methods. The AOA behaviour of honey-polyphenol mixtures varied from synergism to antagonism, being influenced by the AOA method, polyphenol type, and/or mixture concentration. The honey-biomimetic NaDES resulted in similar AOA behaviour as with honey mixed with polyphenols. Honey seems to have additional properties that increase synergism or reduce antagonism in some cases. Honey and its biomimetic NaDES modulate AOA of polyphenols extract.

Keywords: antagonism; antioxidant activity; biomimetic NaDES; honey; natural deep eutectic solvent (NaDES); polyphenol-enriched honey; polyphenols; raspberry extract; synergism.

Figure 4

Comparison between the ATR-FTIR spectra of honey and the main components of GFSw—glucose, fructose, and sucrose (A) and between the ATR-FTIR spectra of honey and GFSw NaDES (B). The absorption bands from 1419 cm⁻¹ and 1345 cm⁻¹ are characteristic of the bending vibrations of O-CH and C- CH in the structure of carbohydrates or of the bending vibrations coming from OH from the C-OH group. The bands from about 1255–1140 cm⁻¹ are characteristic of the stretching vibration of C-H or C-O from carbohydrates. The vibration with a maximum of about 1100 cm⁻¹ is a band that can come from the C-O vibration in the C-O-C group. The bands of approximately 1055, 1025, 990, and 777 cm⁻¹ can be assigned to C-O stretching from the C-OH group or C-C from the carbohydrate structure. The band at 987–988 cm⁻¹ is characteristic of the glycosidic bond C-O-C. The spectral area from 898 to 818 cm⁻¹ is characteristic of the anomeric vibrational region of carbohydrates or the C-H deformation group [37,38].

Figure 1

Isobolograms of honey (H) and raspberry extract (RE) based on IC₅₀ (half-maximal inhibitory concentration) and IC₂₀ (inhibitory concentration at 20% substrate inhibition) for DPPH (A), and ABTS (B) methods, and based on EC_{1mM Trolox} (effective concentration at 1 mM Trolox equivalent of the samples) for CUPRAC (C) and FRAP (D) methods. The error bars from three measurements are shown for each value. Confidence intervals at 95% confidence are shown by dashed lines.

Figure 2

Isobolograms of honey (H) and caffeic acid (CA) based on IC₅₀ (half-maximal inhibitory concentration) and IC₂₀ (inhibitory concentration at 20% substrate inhibition) for DPPH (A) and ABTS (B) methods, and based on EC_{1mM Trolox} (effective concentration at 1 mM Trolox equivalent of the samples) for CUPRAC (C) and FRAP (D) methods. The error bars from three measurements are shown for each value. Confidence intervals at 95% confidence are shown by dashed lines.

Figure 3

Isobolograms of honey (H) and epicatechin (EP) based on IC₅₀ (half-maximal inhibitory concentration) and IC₂₀ (inhibitory concentration at 20% substrate inhibition) for DPPH (A) and ABTS (B) methods, and based on EC_{1mM Trolox} (effective concentration at 1 mM Trolox equivalent of the samples) for CUPRAC (C) and FRAP (D) methods. The error bars from three measurements are shown for each value. Confidence intervals at 95% confidence are shown by dashed lines.

Figure 5

TGA/DTG curves of honey and DES mimetic with honey (GFSw,) and of the main components of GFSw (glucose, saccharose, fructose).

Figure 6

Differential scanning calorimetry (DSC) heating thermograms of honey and GFSw. First cooling cycle in the range of temperatures from 0 °C to −75 °C (A), first heating cycle in the range of temperatures from −75°C to 100 °C (B), second cooling cycle in the range of temperatures from 0 °C to −75 °C (C), second heating cycle in the range of temperatures from −80 °C to 100 °C (D).

Figure 7

SEM micrographs of spray-dried honey and GFSw at 200× and 600× magnification.

Figure 8

X-ray diffractograms of honey (red) and GFSw (black).

Figure 9

Isobolograms of NaDES (GFSw) and raspberry extract (RE) based on IC₅₀ (half-maximal inhibitory concentration) and IC₂₀ (inhibitory concentration at 20% substrate inhibition) for DPPH (A), and ABTS (B) methods, and based on EC_{1mM Trolox} (effective concentration at 1 mM Trolox equivalent of the samples) for CUPRAC (C) and FRAP (D) methods. The error bars from three measurements are shown for each value. Confidence intervals at 95% confidence are shown by dashed lines.

Figure 10

Isobolograms of NaDES (GFSw) and caffeic acid (CA) based on IC₅₀ (half-maximal inhibitory concentration) and IC₂₀ (inhibitory concentration at 20% substrate inhibition) for DPPH (A), and ABTS (B) methods, and based on EC_{1mM Trolox} (effective concentration at 1 mM Trolox equivalent of the samples) for CUPRAC (C) and FRAP (D) methods. The error bars from three measurements are shown for each value. Confidence intervals at 95% confidence are shown by dashed lines.

Figure 11

Isobolograms of NaDES (GFSw) and epicatechin (EP) based on IC₅₀ (half-maximal inhibitory concentration) and IC₂₀ (inhibitory concentration at 20% substrate inhibition) for DPPH (A), and ABTS (B) methods, and based on EC_{1mM Trolox} (effective concentration at 1 mM Trolox equivalent of the samples) for CUPRAC (C) and FRAP (D) methods. The error bars from three measurements are shown for each value. Confidence intervals at 95% confidence are shown by dashed lines.