Synergistic depolymerisation of alginate and chitosan by high hydrostatic pressure (HHP) and pulsed electric fields (PEF) treatment in the presence of H2O2

Physically-induced depolymerisation procedures are often preferred for obtaining alginate and chitosan oligo-saccharides as they either do not use or make minimal use of additional chemicals; therefore, separation of the final products is facile. In this work, solutions of three types of alginate with different mannuronic and guluronic acid residues ratio (M/G ratio) and molecular weights (Mw) and one type of chitosan were non-thermally pro-cessed by applying high hydrostatic pressures (HHP) up to 500 MPa (20 min) or pulsed electric fields (PEF) up to 25 kV cm-1 (4000 & mu;m) in the absence or presence of 3 % hydrogen peroxide (H2O2). The impact on the phys-icochemical properties of alginate and chitosan was investigated by rheology, GPC, XRD, FTIR, and 1H NMR. In the rheological investigations, the apparent viscosities of all samples decreased with increasing shear rate, indicating a non-Newtonian shear-thinning behaviour. GPC results reported Mw reductions that ranged between 8 and 96 % for all treatments. NMR results revealed that HHP and PEF treatment predominantly reduced the M/ G ratio of alginate and the degree of deacetylation (DDA) of chitosan, whilst H2O2 promoted an increase in the M/G ratio in alginate and DDA of chitosan. Overall, the present investigation has demonstrated the feasibility of HHP and PEF for rapidly producing alginate and chitosan oligosaccharides.

Automated summary

Physically-induced depolymerisation procedures were used to obtain alginate and chitosan oligo-saccharides. High hydrostatic pressures and pulsed electric fields were found to be effective for rapidly producing these oligosaccharides. The physicochemical properties of alginate and chitosan were investigated using various techniques. The results showed that the treatments led to reductions in molecular weight and changes in the chemical structure of alginate and chitosan.