Nine hetero-chitooligosaccharides (hetero-COSs) consisting of relatively high molecular weights (90-, 75-, and 50-HMWCOS), medium molecular weights (90-,75-, and 50-MMWCOS), and low molecular weights (90-, 75-, and 50-LMWCOS) were prepared from partially deacetylated hetero-chitosans (90%, 75%, and 50% deacetylated chitosan), and their antioxidant activity based on their scavenging potency on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical was investigated. The results showed that the 90-MMWCOS, prepared from 90% deacetylated chitosan, showed the highest scavenging activity on the DPPH radical. Their scavenging pattern was dose- and time-dependent. Electron spin resonance (ESR) spectrum of DPPH treated with 90-MMWCOS decreased in a time-dependent manner and the reducing power of hetero-COSs increased in a dose-dependent manner. These results indicated that hetero-COSs have an antioxidant activity which is dependent on their degree of deacetylation and molecular weight.
