The aim of this study was to investigate antifungal activity of a range of different molecular weight (MW) chitosan against Penicillium italicum. Our results demonstrate that the antifungal activity was dependent both the MW and concentration of the chitosan. Among a series of chitosan derived from the hydrolysis of high MW chitosan, the fractions containing various sizes of chitosan ranging from 3 to 15 glucosamine units named as chitooligomers-F2 (CO-F2) was found to show the highest antifungal activity against P. italicum. Furthermore, the effect of CO-F2 toward this fungus was significantly reduced in the presence of Ca2+, whereas its effect was recovered by ethylenediaminetetraacetic acid, suggesting that the CO-F2 acts via disruption of Ca2+ gradient required for survival of the fungus. Our results suggest that CO-F2 may serve as potential compounds to develop alternatives to synthetic fungicides for the control of the postharvest diseases.

The effect of chitosan with different molecular weights and other natural substances on dextransucrase (DSase) activity from a representative oral pathogen Streptococcus mutans was elucidated. Among other bioactive substances, amino-monosaccharides such as glucosamine, mannosamine, and galactosamine exerted the enzyme inhibitory activity over 95% of DSase. The specified hydrolysates derived from the hydrolysis of high molecular weight chitosan (HMWC) designated to CTSN, CTSN-P, CTSN-B, and CTSN-S with different molecular weights ranging from 3 to 8 kDa showed the similar inhibitory activity toward DSase. Also, the hyaluronic acid (MW 8.9 kDa), sulfated chitin, and amino-monosaccharides demonstrated the significant activity, CTSN, CTSN-P, CTSN-B, and CTSN-S are of potent bioactive substances that can be prepared in the cheapest way compared with other molecules tested available for antibacterial agent useful for human oral health.