Changes in the functional properties and molecular weight of sodium alginate following γ irradiation

Abstract

Powdered high viscosity sodium alginate samples were subjected to γ irradiation up to a dose of 8.9 kGy and changes in their functional properties and molecular weight determined. Solution viscosity decreased with increasing irradiation dose at 0.5% and 1.0%. Gels were produced at all doses at 0.5 and 1.0% although gel strength was decreased to ~30% at the highest dose. Molecular weight was calculated from intrinsic viscosity using the Mark-Houwink equation and showed a decrease from ~600 000 to ~200 000 at 8.9 kGy, which paralleled the decrease in solution viscosity and gel strength. A G value for chain breaks per 100 eV was calculated at between 7.4 and 8.5. ESR spectra showed a single symmetric peak, increasing with dose, indicating a similar free radical reaction occurring over the whole range of doses examined. A high shear mixer was also shown to reduce molecular weight of high molecular weight alginate, the effect decreasing with decreasing polymer size following irradiation. Irradiation may be useful as a means of sterilizing sodium alginate provided the reduction in molecular weight is taken into consideration with respect to its end use. An alternative use for gamma irradiation could be the specific production of lower molecular weight species of alginates with known properties.