Effect of three modification methods on physicochemical properties of agar

In this study, agar was modified by carboxymethylation, hydrogen peroxide oxidation and hydroxypropylation to compare the solubility, color, gel transparency, gel texture, IR molecular structure and thermal stability before and after the modification, aiming to explore the influence of three modification treatments on the physicochemical properties of agar. The results show that the dissolving temperature, gelling temperature, melting temperature and gel strength decreased significantly after carboxymethylation and hydroxypropyl treatments (P<0.05), whereas the soft elasticity and water holding capacity of agar gel improved; the gel strength of agar was improved by oxidation treatment (P<0.05), from 984 g·cm⁻² to 1 463 g·cm⁻²; after oxidation and hydroxypropylation, the modified agar showed higher whiteness (P<0.05), while carboxymethyl agar was on the contrary (P<0.05). Besides, all modifications had increased the transparency of agar gel significantly (P<0.05). The thermal stability increased with oxidation and hydroxypropylation, but reduced with carboxymethylation. In conclusion, three modification methods can improve physicochemical properties of agar at different extents.