Process optimization and characterization of ultrasonically extracted chitosan

Abstract

• Ultrasound-assisted alkali deacetylation was a novel approach to maximize chitosan yield and its degree of deacetylation • Lowering sodium hydroxide concentrations • Minimizing processing times and energy consumption The study aims to optimize and characterize the chitosan extracted from tilapia fish scales using ultrasound-assisted alkali deacetylation. This research work presents a novel technique of chitosan extraction to maximize its yields and degree of deacetylation. Fish scales consist of 6.82% moisture content on a dry basis, 8.24% ash content, 28% proteins, 4.5% lipids, 14.6% minerals, and 37.84% chitin. The chitosan is extracted from scales while effectively removing protein, lipid, and mineral components. In the demineralization and deproteination stages, 99% of non-chitin components are removed. Maximum yield, 94%, and maximum deacetylation degree, 88%, are optimized at the best operating conditions: 20% sodium hydroxide concentration, 54°C temperature, and 20 minutes of sonication time through an ultrasound-assisted alkali hydrolysis process. The extracted chitosan is characterized with Fourier transform infrared, thermogravimetric and x-ray diffraction to confirm its functional groups, thermal stability and crystallinity index, respectively. Moreover, scanning electron microscopy reveals its structural morphology. The density, molecular weight, viscosity, and solubility in acetic acid of an extracted chitosan are 1.42 g/cm 3 , 52.6 kDa, 17.8 mPa · s, and 78%, respectively. Chitosan also shows a fat-binding capacity of 325% and a water-binding capacity of 469%. In this research, chitosan had minimum inhibition zones of 19 and 22 mm against E. coli ATCC 25922 and S. aureus ATCC 25904, with optical densities of 0.032 and 0.015, respectively. The R 2 values indicate how well the model’s adequacy predicted the yield and deacetylation degree of chitosan. For the yield, the R 2 , adjusted-R 2 and predicted-R 2 are 0.9952, 0.9890 and 0.9409, respectively. However, the R 2 , adjusted-R 2, and predicted-R 2 of the degree of deacetylation are 0.9964, 0.9918 and 0.9627 respectively. Graphical Abstract