Separation of chito-oligomers with several degrees of polymerization and study of their antioxidant activity

Chitooligomers (COS) with degree of polymerization (DP) ranging from 2 to 12 was prepared by acid hydrolysis of chitosan and five fractions were separated from the prepared COS by CM Sephadex C-25 column. The fractions were desalted by activated charcoal extraction. The components of each fraction were analyzed by TLC, HPLC and MALDI-TOFMS. Five fractions mainly contained trimer (95.7%), tetramer and pentamer (90.9%), pentamer (85.6%), hexamer (89.5%) and heptamer to decamer (94.7%), respectively. The antioxidant activities of each fraction and COS mixture were investigated, including hydroxyl and superoxide radical scavenging activity and reducing power. The activities of the six COSs were in a dose-dependence manner and related to their DP. The COS with low DP showed better effect of scavenging hydroxyl radical and reducing power than that with high DP. In contrast, the superoxide radical scavenging activity of all the tested COSs increased with DP increasing.