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 oligosaccharides 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 (M_w) and one type of chitosan were non-thermally processed by applying high hydrostatic pressures (HHP) up to 500 MPa (20 min) or pulsed electric fields (PEF) up to 25 kV cm^-1 (4000 μm) in the absence or presence of 3 % hydrogen peroxide (H₂O₂). The impact on the physicochemical 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 M_w 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.