Effects of treatment with chitosan and antimelanogenesis agents on discoloration of chilled and frozen stored shrimp

The effect of chitosan in combination with polyphenol oxidase (PPO) inhibitors and other additives (citric acid, rosemary extract) to inhibit or slow down melanosis during chilled and frozen storage was investigated. Fresh deepwater pink shrimps (Parapenaeus longirostris) were dipped in different solutions containing combinations of sodium metabisulphite (2500 mg/L), 4-hexylresorcinol (50 mg/L), chitosan (5 g/L), citric acid (200 mg/L) and rosemary extract (50 mg/L) and stored at 4 degrees C for six days and at -18 degrees C for twelve months. During storage, changes in colour were defined sensorially and instrumentally. Chitosan alone showed no effect on discoloration, but in combination with PPO inhibitors showed an additional inhibitory effect on melanosis formation. No noticeable darkening was observed during frozen storage in all treated shrimps, whereas signs of blackening were noticeable from the third month; 50 mg/L of 4-hexylresorcinol were more effective than 2500 mg/L of sodium metabisulphite in the prevention of melanosis development after shrimping.