Stability of Polyphenols under Alkaline Conditions and the Formation of a Xanthine Oxidase Inhibitor from Gallic Acid in a Solution at pH 7.4

Abstract

The stability of 20 different types of polyphenols that are constituents of edible plants was evaluated under different pH conditions (in buffer solutions at pH 6.8, 7.4, and 8.3). Carnosol was the most unstable, followed by myricetin, quercetin, carnosic acid, nordihydroguaiaretic acid, baicalein, gallic acid, and hydroxytyrosol. They were more unstable at a higher pH, which may be attributed to their enhanced redox properties in alkaline solutions, determined by their antioxidant and prooxidant activity. The xanthine oxidase (XO) inhibitory activity of the reaction products under alkaline conditions was evaluated. XO activity was significantly inhibited by the product produced from gallic acid in pH 7.4 solution. The structural analysis of this reaction product revealed that a gallic acid dimer, purpurogallin-8-carboxylic acid, was formed and played a role in the resulting XO inhibitory activity.

Gallic acid oxidation products alter the formation pathway of insulin amyloid fibrils

“…One report demonstrated that when this process is carried out at pH 7.4, a o -quinone is produced and changes in the solution’s absorbance spectra can be observed 26 . In another instance, incubation of GA at neutral pH lead to the formation of a gallic acid dimer 30 . Oxidation at highly basic conditions was shown to yield ellagic acid 31 .…”

In vitro digestibility and release of a mango peel extract encapsulated within water-in-oil-in-water (W1/O/W2) emulsions containing sodium carboxymethyl cellulose

“…However, the incorporation of mango peel PC into food products represents a challenge due to their susceptibility to oxidative reactions during processing conditions (pH, time, temperature, oxygen availability) and unpleasant taste (such as bitterness and astringency). In addition, a number of studies have shown that PC extracts are susceptible to oxidation at physiological intestinal pH (∼ 6.0-7.5), limiting their bioavailability and potential health benefits [8][9][10][11] . Therefore, the encapsulation of PC may reduce these problems and enhance food products properties.…”

L‐Carnitine‐Based Bio‐Ionic Liquids as Antioxidants

“…The low ability to inhibit XO with ILs results mainly from the properties of the acids used in their synthesis. Despite the high antioxidant activity, the activity of gallic acid towards the XO enzyme is described as low [72,73] . Studies by Honda et al.…”