Characterization and application of chitosan extracted from local fungal sources

Abstract

Chitosan is an adaptable and multifunctional biopolymer which can be applied in various fields such as food preservation, medical, agricultural, water treatment etc. The main sources of industrially produced chitosan nowadays are the crustaceans including shrimps, crabs and squids. Production of chitosan from fungal sources, however, can be advantageous because of high degree of deacetylation, homogeneity in polymer length and better antimicrobial activity over crustacean sources. In this study, two locally obtained fungal species Aspergillus niger and Saccharomyces cerevisiae were investigated as alternative sources of chitosan. A. niger was isolated from moldy onions and cultured in potato dextrose broth. S. cerevisiae was bought from local market and kept in sporulating medium. Chitosan was extracted from the mycelia of A. niger and the sporulated yeast cells through treatment with sodium hydroxide and acetic acid. The maximum yields of chitosan were 16.15 ± 0.95 mg/g dry biomass from A. niger at 12th day and 20.85 ± 0.35 mg/g dry biomass from S. cerevisiae at 4th day. The extracted fungal chitosan was characterized using FTIR (Fourier Transform Infrared Spectroscopy) and acid base titration method to determine degree of deacetylation (DD%). Using FTIR method, DD% of chitosan from A. niger and S. cerevisiae were found to be 61.39% and 63.41% respectively. Using acid base titration method, DD% of chitosan from A. niger and S. cerevisiae were found to be 59.61% and 53.28% respectively. Chitosan obtained from S. cerevisiae was further studied to test antimicrobial efficacy of fungal chitosan. Agar well diffusion method was utilized to find zone of inhibition. At a concentration of 2 g/L, fungal chitosan had shown the maximum inhibition zone diameter of 15.48 ± 0.07 mm. The degree of deacetylation and antimicrobial activity of the fungal chitosan was comparable with data obtained from literature and the results indicate that these fungal species have potential to be alternative chitosan sources.