Ultrasound-Assisted Extraction of Chitosan from Squid Pen: Molecular Characterization and Fat Binding Capacity

Abstract

Chitosan from squid (Loligo formosana) pens were prepared and characterized. First, ultrasonication condition was optimized for deproteinization of squid pens using central composite design (CCD) of response surface methodology (RSM). Squid pens were ultrasonicated at amplitude 69% for 41.46 min at the solid/solvent ratio of 1:18 yielded 34% (w/w) chitin with the lowest remaining protein. Therefore, ultrasonication effectively reduced the extraction time for chitin production from squid pens as compared to traditional method (5 hr). When the resultant chitin was subjected to deacetylation at different temperatures and times, yield and degree of deacetylation (DDA) of chitosan were in the range of 50% to 65% (w/w) and 78% to 90%. Intrinsic viscosity and molecular weight (MW) of chitosan were in the range of 3.2 to 6.52 dL/g and 1.2 × 10⁵ to 3.2 × 10⁵ Da, respectively. All the chitosans with different DDA were able to bind oil droplets under the mimicked pH condition of gastrointestinal tract. Chitosan produced by deacetylation at 130 °C for 2 hr (CH130-2) showed the optimum yield (54%) and had medium MW (1.5 × 10⁵ Da). DDA of CH130-2 determined using ¹ H-NMR was 89%, which was similar to that (87%) obtained from FTIR. XRD results showed destruction of chitin structure and decreased crystallinity index from 55% to 27% after deacetylation. CH130-2 stabilized the emulsion under the simulated gastrointestinal conditions. Therefore, it could be used as dietary fiber to control the adsorption of fat/oil in the human digestive tract. PRACTICAL APPLICATION: Chitin and chitosan are marketable products manufactured from crustacean shells. However, extraction of chitin is time consuming. Ultrasonication has been used for extraction of various biomolecules from different sources. It effectively lowers the processing time and enhances extraction yield. Therefore, application of ultrasonication with optimized condition using RSM could reduce extraction time and enhance yield of chitin from squid pen. Chitin from squid pen could be further converted to chitosan with high DDA. Chitosan was able to act as a dietary fiber and reduce fat absorption in gastrointestinal tract. Thus, this information is of benefit for squid processing industry to exploit squid pen, a processing byproduct.

Keywords: Loligo formosana; chitin and chitosan; deacetylation; squid pen; ultrasonication.