Preparation of low-molecular-weight sodium alginate by ozonation

•Degradation of sodium alginate by ozonation.•Molecular weight of sodium alginate declines from 972.3 to 76.7 kDa.•Molecular weight dispersion changes appreciably and M/G is not altered significantly.•No color change of low-molecular-weight sodium alginate obtained by ozonation.•Chemical structure of low-molecular-weight sodium alginate remains intact. Low-molecular-weight sodium alginate (LMWSA) has been reported to possess unique physicochemical properties and bioactivities. There is little information available about degradation of sodium alginate by ozonation. Effect of ozonation on molecular weight, molecular weight distribution, color change, M/G ratio, and chemical structure of sodium alginate was investigated. The molecular weight of sodium alginate decreased from 972.3 to 76.7 kDa in the 80-min period of ozonation at 25 °C. Two different degradation-rate constants were calculated. Molecular weight distribution of the LMWSA changed appreciably. Ozonation cannot lead to color change of LMWSA. The M/G ratio of LMWSA was not altered significantly, compared with that of the original alginate. The FT-IR and 13C NMR spectra indicated the chemical structure of LMWSA obtained by ozonation was not altered appreciably. New insight into the ozonation of alginate will be promisingly opened up. Ozonation of sodium alginate can be a alternative for production of LMWSA.