New Development of beta-Chitosan from Jumbo Squid Pens ( Dosidicus gigas) and its Structural, Physicochemical, and Biological Properties

β-chitin/chitosan extracted from newly utilized jumbo squid ( Dosidicus gigas) pens were investigated in respect to their physicochemical properties, polymeric structures, deacetylation and depolymerization characteristics, and antioxidant and antibacterial activities. These functional properties were further compared with α-chitin/chitosan prepared from shrimp shells. Due to the low mineral content (< 1%) and negligible pigment in squid pens, demineralization and depigmentation steps could be omitted when extracting β-chitin. Molecular weight (Mw) and moisture content of deproteinized β-chitin were significantly higher than those of α-chitin. Crystallographic structure of β- chitin was distinguished from that of α-chitin, in which β-chitin had less inter-molecular hydrogen bond than α-chitin along with lower crystallinity (CI). β-chitin could convert into α-form as the result of alkali treatment, and the resulted α-chitin exerted significantly higher moisture absorption ability than the native α-chitin, thus retaining higher susceptibility of native β-chitin by means of the polymorphic destruction. The Kurita method using NaOH was an effective deacetylation treatment to obtain β-chitosan with high Mw and a wide range of DDA, and cellulase was more susceptible than lysozyme to degrade β-chitosan for obtaining low Mw of product. To obtain similar DDA of α- and β- chitosan, lower concentrations of NaOH and shorter reaction times were required for β- chitin than that for α-chitin. In addition, β-chitosan was more susceptible to cellulase hydrolysis than α-chitosan. High Mw (280-300 kDa) of β-chitosan exerted extremely lower half maximal effective concentrations (EC50) than α-chitosan, i.e., higher antioxidant activity based on DPPH radical scavenging activity and reducing ability. The 75% DDA/31 kDa β-chitosan exerted higher inhibition against E. coli (lower MIC) than that of 75% DDA/31 kDa α-chitosan, whereas opposite result was observed in 90% DDA/74-76 kDa α- and β-chitosan. This difference could be due to the impact of the different structural properties between α- and β-chitosan on chitosan conformations in the solution, altering the surface phenomenon of protonated chitosan with negatively charged bacterial cells in the suspension. Therefore, jumbo squid pens can be commercially employed to extract functional β-chitin/chitosan with desirable structural, physicochemical, and biological activities.