OPTIMIZATION OF HYDROLYSIS TO PRODUCE WATER-SOLUBLE CHITOSAN AND ITS ANTIFUNGAL EFFECT ON POSTHARVEST ANTHRACNOSE IN MANGO

Water-soluble chitosan, the product of chitosan hydrolysis with particular biological characteristics, has been used in the fields of food storage and plant protection. Hydrogen peroxide was used to optimally degrade the crude chitosan into water-soluble chitosan (WSC). The mathematical model between independent factors (H₂O₂ level, time and temperature) and the recovery of WSC was constructed to optimize the degradation conditions using response surface methodology. The optimal conditions for highest recovery of WSC were 5.4% of H₂O₂, 47.1°C and 3.4 h, with the predicted recovery of 87.2%. The fungal strain Colletotrichum gloeosporioides, isolated from mango naturally infected by typical anthracnose, was used to study the antifungal activity of WSC in vitro. Results indicated that C. gloeosporioides was much sensitive to WSC, the inhibitory effect increased as the WSC increased. The concentration of 0.8% WSC completely inhibited the mycelial growth of C. gloeosporioides on PDA media and the 50% PIRG (percentage inhibition of radial growth) value was achieved with the concentration of 0.1% WSC. The micrograph study showed that WSC can cause distortion, rupture, and thinning of the conidial cell wall of C. gloeosporioides. These results indicate the high potential of WSC as an antifungal agent for future commercial application.