Stability and antibacterial activity of chitosan solutions affected by storage temperature and time

Stability of chitosan (Mw of 2025 and 1110 kDa) solutions and their antibacterial activity against gram-positive (Listeria monocytogenes and Staphylococcus aureus) and gram-negative (Salmonella enteritidis and Escherichia coli) bacteria were investigated at 4 and 25 °C after 15-week storage. Viscosity of chitosan solutions (1% (w/v) in 1% (v/v) acetic and/or lactic acid) decreased with increased storage time and temperature. After 15-week storage, the decrease in viscosity ranged from 44 to 48% and 81 to 90% of the initial viscosity value, respectively, at 4 and 25 °C. Antibacterial activity of chitosan solutions (1% (w/v) in 1% (v/v) acetic acid) before and after 15-week storage differed depending on the molecular weight of chitosans, the storage temperature, and the bacteria. In general, chitosan solutions before storage showed higher antibacterial activity than those after 15-week storage. Chitosan solutions stored at 25 °C possessed similar or weaker antibacterial activity compared with those at 4 °C.