Green modification of rheological properties of agar and alginate using atmospheric pressure plasma jets (APPJ)

Agar and alginate are both natural polysaccharides widely used in the food industry for their gelling, thickening, and stabilizing properties. This study explored atmospheric pressure plasma jet (APPJ) as a green approach to modify the rheological properties of commercial agar and alginate. The changes in viscosity, flow properties, gelling properties, molecular weight, Raman spectrum, as well as surface morphology were evaluated. After APPJ treatments, the molecular weight of agar decreased (from 63 ± 2 to 45 ± 3 after 20-min treatment and from 61 ± 4 to 35 ± 1 after 30-min treatment) due to the cleavage of the glycosidic bonds, resulting in a lower viscosity and a lower gel strength. Visible separations were observed for sample clustering before and after plasma treatment using principal component analysis (PCA), and surface cracks were visible on SEM imaging. No obvious changes were found in the flow properties. For alginate samples, plasma treatments significantly increased the viscosity due to the creation of more cross-linked “egg-box” structures, along with the changes in flow properties, PCA separation and surface cracks. However, no significant differences were found in the molecular weight and gelling properties. These findings highlight APPJ as a promising green technology for tailoring the rheological properties of agar and alginate.