Characterisation of chitosan from blowfly larvae and some crustacean species from Kenyan marine waters prepared under different conditions

Abstract

Isolation of chitosan from cuticles of blue bottlefly larvae Calliphora erythrocephala, and shells of crab Sylla cerrata, lobster Panulirus ornatus, prawn Paeneaus indicus was carried out. The yield of chitin was 12.0%, 23.0%, 15.7% and 28.0% respectively. In the same order the yield of chitosan was 66.0%, 74.6% 74.3% and 75.0% from chitin. Ash in the crab and lobster chitosan demineralised with 0.5M HCl was 30.2 and 22.4% respectively. This was reduced to 0.2 % for lobster and 0.4% for crab using 2M HCl for demineralisation and 0.5M HCL was adequate for demineralisation of prawns to bring the ash content to < 1%. The ash content in the blowfly larvae was negligible. The conditions used for chitosan isolation in blowfly larvae were milder requiring no demineralisation step. The time to obtain soluble chitosan in 1% v/v acetic acid was 8 hr for crab and lobster at 100°C deacetylation and 4 hr at 120°C while for prawns it was 6 hr at 100°C and 3 hr at 120°C deacetylation temperature. The average molecular weight ( ̄M V ) for crabs was 556,000 after 8 hr deacetylation and 148,000 at 140°C deacetylation temperature. With 2M HCl used for demineralisation first, it was 439,000 for a 4 hr period. Crabs, first demineralised then deprotenised the ̄M V was 155,000 for a 3 hr deacetylation at 120°C and 417,000 for 1 hr deacetylation. An 8 hr deacetylation at 100°C for lobsters gave ̄M V of 791,000. It was reduced to 560,000 after 4 hr of deacetylation at 120°C and to 236,000 at 140°C for 3 hr. Prawns had a ̄M V of 507,000 after 6 hr deacetylation at 100°C and reduced to 455,000 after a 3 hr deacetylation. For insect larvae, at 100°C deacetylation for 4 hr the ̄ M V was 413,500 while for 1 hr, 2 hr and 2.5 hr deacetylation time at 120°C it was 369,000, 308,500 and 263,000 respectively. The degree of deacetylation (DD) increased with temperature and time of deacetylation. For crab, demineralised then deproteinised, it increased from 72.9% in 1 hr then 81.5% in 3 hr. In prawn chitosan it was 60.0% for the 6 hr deacetylation at 100°C and 69.2% for 3 hr deacetylation at 120°C. The DD of insect larvae was 62.56% after 4 hr of deacetylation at 100°C. When deacetylated at 120°C it was 64.0% after 1 hr, 79.9% after 2 hr and 80.7% after 2.5 hr. The moisture content showed a slight increase with DD. Temperature increase and time of deacetylation caused a decrease in ̄M V and a more conservative increase in DD.