Upcycling shrimp shells using supercritical CO2 assisted by enzymatic pretreatment: astaxanthin, protein, and amino acids.

Shrimp shell, a by-product of the food industry, can be effectively upcycled to obtain astaxanthin and proteins/amino acids that can be used as ingredients in functional food and cosmetics. This study aimed to evaluate the effectiveness of SC-CO₂ in extracting astaxanthin from shrimp shell by investigating the effects of different parameters such as enzymatic pretreatment (papain and neutral protease at 0.2-3.0%, w/v), pressure (100-300 bar), temperature (40-60 °C), and co-solvent (ethanol). In addition, the hydrolysate and residue from the enzymatic pretreatment and the residues from the extractions were characterized for protein and amino acid contents. Using enzymatic pretreatment (2.0%, w/v) followed by SC-CO₂ (300 bar/60 °C) increased the total extraction yield from 2.7 to 3.2%, with papain and neutral protease, respectively. Furthermore, extraction with SC-CO₂ + ethanol (batch and continuous) as co-solvent resulted in a higher astaxanthin content (25.7 (batch) and 26.0 (continuous) μg/g shrimp shell) compared to SC-CO₂ (4.1 μg/g shrimp shell). The results showed that SC-CO₂ + ethanol assisted by enzymatic pretreatment produced a similar astaxanthin content compared to untreated samples as part of the astaxanthin was removed in the hydrolysates during the enzymatic pretreatment. Furthermore, soluble protein was removed in the hydrolysate along with free amino acids after the enzymatic pretreatment, while the residue after SC-CO₂ extraction showed a higher concentration of protein/amino acids.