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. 2022 Oct 13;27(20):6851.
doi: 10.3390/molecules27206851.

Maillard and Hydrolytic Reactions in Subcritical Water Extraction of Bioactive Compounds from Licorice

Rui Fan  1   2 , Yanxiang Gao  2
Affiliations

Maillard and Hydrolytic Reactions in Subcritical Water Extraction of Bioactive Compounds from Licorice

Rui Fan et al. Molecules. .

Abstract

Nowadays, subcritical water extraction (SWE) techniques are extensively investigated worldwide, while the thermal reactions that inevitably occur under subcritical water conditions are rarely studied. In order to investigate the behaviors of the different reactions during SWE of bioactive compounds from licorice, the Maillard reaction process was accessed via their products and the hydrolytic reaction was analyzed according to the kinetic parameters. In addition, the contents of total phenolics and flavonoids in the extracts obtained at the different temperatures were determined and total antioxidant capacities were evaluated by HPLC-ABTS+. The results showed that flavonoids and phenolics from licorice as well as new compounds generated via the Maillard reaction contributed to the antioxidant activity of the extracts. The fluorescence, color and absorbance of the extracts showed that the degree of the Maillard reaction increased with the rise of the extraction temperature. The kinetics of extraction for glycyrrhizic acid showed that it was firstly extracted by diffusion, and then was hydrolyzed into glycyrrhetinic acid 3-O-mono-β-D-glucuronide and glycyrrhetinic acid following a first-order mechanism. These findings could provide deep insights into the SWE process and a new method for producing glycyrrhetinic acid 3-O-mono-β-D-glucuronide and glycyrrhetinic acid.

Keywords: Maillard reaction; antioxidant; glycyrrhetinic acid; glycyrrhetinic acid 3-O-mono-β-D-glucuronide; glycyrrhizic acid.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The study design of the thermal reactions in subcritical water extraction of bioactive compounds from licorice.
Figure 2
Figure 2
The effect of extraction temperature on the content of total flavonoids, total phenolics (a) and glycyrrhizic acid (b) and the effect of extraction temperature on total antioxidant activity (c). The results are expressed as the mean ± standard deviation (n = 3); different letters indicate significant differences (p < 0.05) and the same letters indicate insignificant differences.
Figure 2
Figure 2
The effect of extraction temperature on the content of total flavonoids, total phenolics (a) and glycyrrhizic acid (b) and the effect of extraction temperature on total antioxidant activity (c). The results are expressed as the mean ± standard deviation (n = 3); different letters indicate significant differences (p < 0.05) and the same letters indicate insignificant differences.
Figure 3
Figure 3
HPLC-ABTS·+ chromatographic profiles and HPLC-MS/MS information regarding the extracts at different temperatures. (a–d) was the chromatographic profiles at 100, 140, 200 and 280 °C; (e) the HPLC-MS/MS information [24,25,26,27,28,29].
Figure 3
Figure 3
HPLC-ABTS·+ chromatographic profiles and HPLC-MS/MS information regarding the extracts at different temperatures. (a–d) was the chromatographic profiles at 100, 140, 200 and 280 °C; (e) the HPLC-MS/MS information [24,25,26,27,28,29].
Figure 3
Figure 3
HPLC-ABTS·+ chromatographic profiles and HPLC-MS/MS information regarding the extracts at different temperatures. (a–d) was the chromatographic profiles at 100, 140, 200 and 280 °C; (e) the HPLC-MS/MS information [24,25,26,27,28,29].
Figure 4
Figure 4
The analysis of indicators of Maillard reaction in the extracts at different temperatures, (a) total reducing sugars and total amino acids contents; (b) 5-HMF and furfural contents. The results are expressed as the mean ± standard deviation (n = 3); different letters indicate significant differences (p < 0.05), and the same letters indicate insignificant differences.
Figure 5
Figure 5
Thermal hydrolysis of glycyrrhizic acid under different temperatures and times, (a) the content of glycyrrhizic acid; (b) the content of GAMG; (c) the content of glycyrrhetinic acid. GAMG: glycyrrhetinic acid 3-O-mono-β-D-glucuronide.The results are expressed as the mean ± standard deviation (n = 3); different letters indicate significant differences (p < 0.05) and the same letters indicate insignificant differences.
Figure 5
Figure 5
Thermal hydrolysis of glycyrrhizic acid under different temperatures and times, (a) the content of glycyrrhizic acid; (b) the content of GAMG; (c) the content of glycyrrhetinic acid. GAMG: glycyrrhetinic acid 3-O-mono-β-D-glucuronide.The results are expressed as the mean ± standard deviation (n = 3); different letters indicate significant differences (p < 0.05) and the same letters indicate insignificant differences.
Figure 6
Figure 6
The kinetic parameters at different temperatures, (a–c) the fitting curve of the extraction and hydrolytic rate constant at 140 °C, 160 °C, and 180 °C, respectively; (d) the Arrhenius plot.
Figure 7
Figure 7
The schematic diagram of subcritical reaction system.
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