Development of chitosan biopolymer films by fungal fermentation of waste substrates

Abstract

Zygomycetes are known for their relatively high chitosan content (approximately 10% m/m) in comparison with other fungal genera. In this study, Mucor circinelloides was grown on the following industrial waste substrates: corn steep liquor (CSL); soft drink overflow spillage waste (DBW); and sugarcane molasses (MOL). Biomass production on waste substrates was statistically optimized by Plackett-Burman design in conjunction with Response Surface Methodology, followed by validation of the model. DBW hindered fungal biomass growth and was found to be a statistically insignificant variable and therefore omitted from further optimizations. The validated model produced a biomass of 77.87 g/L, a 2.65-fold increase over the highest-yielding unoptimized medium. Fungal biomass obtained after batch fermentation was subjected to acid-alkaline treatment for chitin extraction from the cell wall and deacetylation of the chitin to chitosan. A yield of 8-9% chitosan was obtained from the fungal biomass. FTIR spectroscopic analysis was conducted on the extracted fungal chitosan to compare extracted chitosan against commercial chitosan and chitosan monomer. The waste-grown, fungal-derived chitosan profiles were similar to those of commercial crustacean chitosan. The extracted chitosan was used in conjunction with additives and solvent systems to create biopolymer variants with differing properties. A library of data from the chitosan biopolymer variants was generated with considerable differences in characteristics based on their composition. Improvements in sample #11 (the most modified formulation) in contrast to the most common chitosan biopolymer film composition used in literature (sample #9), included a 3.37-fold improvement in the static force required to break the film. There was a 3.39-fold increase in tensile strength and an 11-fold reduction in elongation (%) and elongation rates. The creation of these variants will allow the use of these chitosan biopolymers for specific industrial applications.