Thermo-mechanical decolourization process for shrimp chitin (Pandalus borealis)

Abstract

Pandalus borealis is a thin-shelled shrimp species with medium pigmentation. The polysaccharide chitin, which makes up approximately 20 % of the shell, can be extracted and used in many different industries. The main extraction steps are deproteination and demineralization, followed by an assessment of the colour. White, off-white, or beige chitin is desired for most industrial applications. If required, residual pigmentation is typically removed in a decolourization step (DC) using oxidizing reagents or solvents. Disadvantages include safety and environmental concerns, unspecific oxidation reactions and high volatility of reagents. To date, a green process alternative is not documented. P. borealis chitin, deproteinated in alkali solution, does not require further DC. Enzymatic deproteination is nowadays preferred in the interest of sustainable processing, but it produces chitin with inferior colour quality. Based on the known thermal instability of the shrimp pigments and the porosity of chitin particles, the present study hypothesizes that the colour quality of enzymatically purified chitin can be enhanced by a washing process using high-shear and hot water. We develop a novel, chemical-free alternative for decolourization and assess its effectiveness compared to solvent and oxidizing reagents. Chitin properties are assessed by colorimetry, XRD, NMR, TGA, bulk density, and fat/water-binding capacities (FBC/WBC). Our findings suggest that the innovative thermo-mechanical DC process can produce a colour quality comparable to solvent DC without resulting in deacetylation, changes in crystallinity, or thermal stability. Thermo-mechanical DC enhanced WBC/FBC of chitin, which is an important property in hydrogel and drug delivery applications.