## 4 Discussion
The mechanism of the reaction of the degradation of alginate chains by hydrogen peroxide remains unclear. It was suggested that the attack of a hydrogen atom in position C1, C4 on (1 \(\rightarrow\) 4)-linked polysaccharides caused a division of the glycosidic bond [50], and consequently the formation of carbonyl groups by reducing the end of C-4 (Figure 5a) and delta-lactone groups by reducing the end of C-1 (Figure 5d). In the Figure 5, we present the most probable mechanism of the action of \(\bullet\)OH on a polysaccharide chain. It has been reported that H\({}_{2}\)O\({}_{2}\) treatment under extreme conditions can break the sugar cycle and that recombination reactions between the different radicals can occur [51]; and since the reaction system contained in the presence of excess H\({}_{2}\)O\({}_{2}\), the carbonyl group of the lactones group in the new reducing end generated can be largely oxidized to a carboxyl group [52] as illustrated in Figure 6.  
Nevertheless, very little degradation of the rings was observed by controlling the conditions of degradation (temperature and duration) [49]. It should be mentioned that the depolymerization reaction of ASBB after 6 h gave a fraction with Mw \(<\) 5500 g/mol, 40 times narrower than native alginate ASBB (220,000 g/mol). [PERSON] et al. [53] reported that radical depolymerization of chitosan (383,000 g/mol) using 1.5% of H\({}_{2}\)O\({}_{2}\) generated an oligo-chitosan fraction (10,400 g/mol) after 6 h of hydrolysis. [PERSON] [47] reported that a very rapid scission occurred in the alginate when hydrogen peroxide was in the presence of ascorbate at pH 5.5. Hydrogen peroxide with Cu\({}^{2+}\) and ascorbate were also adopted to produce a LMW of heparin [54]. The same mixture was applied to dermatan sulfate to generate molecular weight fractions of 25,000 to 2000 g/mol [55]. An oligo-fucoidan (32,000 g/mol) [29] was obtained after 6 h of radical hydrolysis of sulfated fucoidan (320,000 g/mol) in the presence of copper acetate II. Under the same reaction, sulfated oligo-galactans were generated with an Mw of 8500 g/mol after 3 h of depolymerization of sulfated galactans [30]. The main drawback of combining  
Figure 5: Proposed action of \(\bullet\)OH on alginate. Reducing end: (**a**) Pyranone groups, (**d**) Lactone groups, and non-reducing end: (**b**), (**c**) glycopranes groups. Figure 6: Oxidation of the reducing end of most oligomers to a carboxyl group. H\({}_{2}\)O\({}_{2}\) and copper acetate II is the need for post-purification of the LMW fractions to remove copper and metallic catalysts. In another study, the thermal degradation of alginate was also documented [32]. [PERSON] and [PERSON] [56] mentioned that the treatment of alginate at temperatures above 250 \({}^{\circ}\)C lead to extensive degradation. In addition, a more recent study by [PERSON] et al. [32] showed the possibility of degradation of alginate to moderate temperatures (20 to 60 \({}^{\circ}\)C). However, the harsh processes (high temperature and pressure) induced simple coloration by sugar degradations or reversion reactions and generated undesirable compounds such as monosaccharides or salts implying post degradation purification [57]. Enzymatic processes have also been reported as the most used method for producing oligo-alignates. Depolymerization of alignates was principally performed by alginate lyases produced by different organisms [7]. Due to the complex structural features of alginate, these organisms usually produce different alginate lyases with various enzymatic properties for alginate utilization [58; 59]. A recent study reported the effectiveness of cellulase to generate oligo-alignates. This degradation resulted in an increase of reducing sugar from 0.105 mg/mL to 0.441 mg/mL [60]. Indeed, hydrochloric acid (HCl) is also the most used chemical reagent for alginate modification; for example, sodium alginate and alginic acid were efficiently depolymerized using aqueous HCl solutions ranging from 0.1 to 1.0 M with pH 2.8 to 4.5 [61].