Hydrogen Peroxide Effects on Natural-Sourced Polysacchrides: Free Radical Formation/Production, Degradation Process, and Reaction Mechanism-A Critical Synopsis

Abstract

Numerous reactive oxygen species (ROS) entities exist, and hydrogen peroxide (H₂O₂) is very key among them as it is well known to possess a stable but poor reactivity capable of generating free radicals. Considered among reactive atoms, molecules, and compounds with electron-rich sites, free radicals emerging from metabolic reactions during cellular respirations can induce oxidative stress and cause cellular structure damage, resulting in diverse life-threatening diseases when produced in excess. Therefore, an antioxidant is needed to curb the overproduction of free radicals especially in biological systems (in vivo and in vitro). Despite the inherent properties limiting its bioactivities, polysaccharides from natural sources increasingly gain research attention given their position as a functional ingredient. Improving the functionality and bioactivity of polysaccharides have been established through degradation of their molecular integrity. In this critical synopsis; we articulate the effects of H₂O₂ on the degradation of polysaccharides from natural sources. Specifically, the synopsis focused on free radical formation/production, polysaccharide degradation processes with H₂O_2, the effects of polysaccharide degradation on the structural characteristics; physicochemical properties; and bioactivities; in addition to the antioxidant capability. The degradation mechanisms involving polysaccharide's antioxidative property; with some examples and their respective sources are briefly summarised.

Keywords: antioxidant capacity; biological/food systems; catalysed degradation; free radical; hydrogen peroxide; molecular modification; polysaccharide.

Figure 1

The electron transport chain is a series of electron transporters embedded in the inner mitochondrial membrane that shuttles electrons from NADH and FADH₂ to molecular oxygen. In the process, protons are pumped from the mitochondrial matrix to the intermembrane space, and oxygen is reduced to form water (Source: Electron Transport Chain [50]).

Figure 2

The role of hydrogen peroxide (H₂O₂) in cell dysfunction and transformation.

Figure 3

Proposed mechanism of oxidation of gallocatechin (Source: Nakayama et al. [61]).

Figure 4

Production of hydrogen peroxide (H₂O₂) by polyphenols via autoxidation (Source: Akagawa et al. [62]).

Figure 5

Schematic diagram for the oxidation of β-D-glucose, as catalysed by glucose oxidase (Source: Adányi et al. [85]).

Figure 6

Schematic diagram of cholesterol oxidation and isomerization catalysed by cholesterol oxidase (Source: Adányi et al. [85]).

Figure 7

Proposed reaction mechanism of OH• on a polysaccharide chain. The diagram shows some of the proposed reaction mechanism of polysaccharide (homogalacturonan) exerting its antioxidant capacity on OH•, where the short lines (- - -) depicts the polysaccharide chain continuation. This figure presents the predicted reactions occurring after •OH abstracts a hydrogen atom from C-1 (reactions c1–c4), C-3 (reactions b1–b3), C-4 (reactions d1–d4) or C-5 (reactions a1–a4). Abstraction of hydrogen from C-2 (not shown) is expected to give products directly comparable with those shown for C-3. (Source: Vreeburg et al. [140]).