Effect of Recycling Ohmic Heating on the Preparation of Chitosan from the Portunus trituberculatus Crab Shells

The effect of recycling ohmic heating on the deacetylation, structure, and properties of chitosan prepared from Portunus trituberculatus crab shells was investigated. The effect of six proteases on deproteinization was examined. Deacetylation was carried out using four cycles of heating, in which heating methods included cyclic water bath heating, cyclic ohmic heating, and a combination of recycling ohmic and water bath heating. The structure and properties of chitosan were determined by Fourier transform infrared spectroscopy (FTIR), differential scanning calorimeter (DSC), scanning electron microscope (SEM), dielectric properties, and rheological properties. A combination of many factors, including acid protease and pepsin, was chosen for complex proteolytic deproteinization. Ohmic heating took 2/5 of the time and used 1/2000 of the energy required for water bath heating. FTIR, DSC, dielectric properties, and SEM results showed that the chitosan characteristic after ohmic heating treatment met commercial requirements. Chitosan’s FTIR spectra and dielectric loss values at low frequencies after three cycles of combined ohmic and water bath heating were most similar to those of commercial chitosan without destroying its thermal stability. After the three cycles, the degree of chitosan deacetylation using combined ohmic and water bath heating reached 94.38 ± 0.21%, improving deacetylation compared with the traditional method.