Physicochemical characteristics of chitosan from swimming crab (Portunus trituberculatus) shells prepared by subcritical water pretreatment

Gengxin Hao,Kazufumi Osako,Yanyu Hu,Linfan Shi,Aixiu Cui,Wuyin Weng,Jun Chen

doi:10.1038/s41598-021-81318-0

Abstract

The physicochemical properties of chitosan obtained from the shells of swimming crab (Portunus trituberculatus) and prepared via subcritical water pretreatment were examined. At the deacetylation temperature of 90 °C, the yield, ash content, and molecular weight of chitosan in the shells prepared via subcritical water pretreatment were 12.2%, 0.6%, and 1187.2 kDa, respectively. These values were lower than those of shells prepared via sodium hydroxide pretreatment. At the deacetylation temperature of 120 °C, a similar trend was observed in chitosan molecular weight, but differences in chitosan yield and ash content were not remarkable. At the same deacetylation temperature, the structures of chitosan prepared via sodium hydroxide and subcritical water pretreatments were not substantially different. However, the compactness and thermal stability of chitosan prepared via sodium hydroxide pretreatment was lower than those of chitosan prepared via subcritical water pretreatment. Compared with the chitosan prepared by sodium hydroxide pretreatment, the chitosan prepared by subcritical water pretreatment was easier to use in preparing oligosaccharides, including (GlcN)2, via enzymatic hydrolysis with chitosanase. Results suggested that subcritical water pretreatment can be potentially used for the pretreatment of crustacean shells. The residues obtained via this method can be utilized to prepare chitosan.

Highlights

Swimming crab (Portunus trituberculatus) is an economically important aquatic species widely distributed in the coastal waters of China, Japan, and Korea[1]
When the deacetylation temperature was increased to 120 °C, chitosan yields and ash contents decreased
When the deacetylation temperature was increased to 120 °C, the characteristic peaks of chitin disappeared, and obvious changes were detected among the prepared chitosans in the spectral bands between 1400 and 1300 cm−1, which corresponded to OH– bending v ibrations[28]

Summary

Introduction

Swimming crab (Portunus trituberculatus) is an economically important aquatic species widely distributed in the coastal waters of China, Japan, and Korea[1]. The meat protein should be recovered and chitin/ chitosan should be extracted from crab by-products. The effects of subcritical water temperature (140–230 °C) on the properties of swimming crab shell extracts containing meat protein were investigated. The traditional deacetylation for preparing chitosan from chitin requires a solution with high alkali content (40–60%), leading to severe environmental pollution[14]. Owing to chitin shortage associated with the traditional preparation of crab shells, this study aimed to prepare chitosan from swimming crab shells via subcritical water pretreatment instead of alkali treatment. Another strategy applied was increasing the deacetylation temperature to decrease the alkali concentration for deacetylation. The results of the present study may aid in the development of new approaches for extracting chitosan/oligosaccharides from crustacean shells

Objectives

Results

Conclusion