The degradation of chitosan with the aid of lipase from Rhizopus japonicus for the production of soluble chitosan

Lipase from Rhizopus japonicus degraded chitosan resulting in soluble chitosan hydrolysates with molecular weight of about 30-50 kDa as shown by size exclusion chromatography. Optimal temperature for the hydrolysis of chitosan was 40C. The chitosan degradation products were fractionated stepwise according to their molecular weights by, ultrafiltration with the filtration range of over 0.1 mum, 0.1 mum to 30 kDa, 30 kDa to 10 kDa, 10 to 3 kDa, and 3 to 0.2 kDa. These fractions exhibited molecular weights of 50, 41, 41, 35, and 30 kDa, respectively. The molecular weights did not coincide with the pore size of filter membranes. Chitosan hydrolysate exhibited almost the same structural composition in IR spectra as chitosan flakes, except the peak of 1550 nm(-1) that appeared to be the COO, residue shifted from sodium acetate buffer to amine residue of chitosan. All fractions showed high solubility at neutral pH. The chitosan hydrolysates exhibiting molecular weights between 30 and 41 kDa were considered to be most suitable as a food additive or functional agent as demonstrated by sensory evaluation.