The effect of molecular weights of chitosan on the synthesis and antifungal effect of copper chitosan

Pathogenic fungi such as Alternaria alternata (A. alternata) can decimate crop yields and severely limit food supplies when left untreated. Unfortunately, the chemical fungicides currently used to solve this issue create problems of their own in the form of high prices and environmental damage. Copper chitosan (CuCts) is a promising alternative fungicide for developing agricultural areas due to being inexpensive and nontoxic. Chitosan polymers' properties depend on their molecular weight, classified as high molecular weight chitosan (HMWc) and low molecular weight chitosan (LMWc). LMWc shows lower viscosity, greater solubility, and greater antimicrobial activity. However, LMWc is produced from HMWc through an expensive process. Therefore, we wanted to investigate the effect of HMWc and LMWc on producing CuCts as an antifungal agent. We hypothesized that LMWc CuCts would exhibit greater fungal inhibition due to the beneficial properties of LMWc. Using a unique bulk synthesis method, we produced HMWc CuCts and LMWc CuCts and then tested them on A. alternata with the poisoned food technique by comparing fungal growth and fungal inhibition. Indeed, LMWc CuCts showed significantly greater fungal inhibition. Our work serves as an important stage of the development of CuCts as a viable and available alternative to chemical fungicides in the future.