Chemical Treatments for Reducing the Yellow Discoloration of Channel Catfish (Ictalurus punctatus) Fillets

Abstract

Three sets of experiments were conducted to investigate effects of various chemical pretreatments on the color and carotenoid changes of yellow discolored channel catfish fillets. First, the relationship between fresh fillet color and carotenoid content was studied. The next set of experiments was to determine the color change and carotenoid contents in catfish fillets during storage. The final set of experiments was to evaluate the efficacy of chemical pretreatments for preventing or reversing yellow discoloration in channel catfish fillets during storage. A strong linear relationship between the b-value of fresh whole fillets and total content of the three major carotenoids (lutein, zeaxanthin and alloxanthin) was found with a correlation coefficient of 0.76. The intensity of the yellow color of the fresh catfish fillets appears to be mainly related to the sum of the major carotenoid contents. Yellow discolored catfish became darker and more yellow after 12 d refrigerated storage. With increased time, the sum of carotenoid contents (lutein, zeaxanthin and alloxanthin) of dark yellow discolored fillets decreased (P<0.01). Ascorbic acid, BHA, citric acid and sodium metabisulfite were not successful at reducing the yellow discoloration. Sodium bicarbonate reduced the fillet yellowness, but the fillets turned darker after 12 days of storage. Sodium bisulfite gave the best results, with fillets being brighter and less yellow after storage. No evident improvement was found by combining these two chemicals together. The sum of the carotenoid contents (lutein, zeaxanthin and alloxanthin) in untreated fillets significantly decreased compared to fresh fillets (P<0.1). However, the sum of the carotenoid contents in fillets treated by various chemical pretreatments did not differ significantly from the untreated fish. The catfish industry may improve the color of their discolored fillets by using chemical pretreatments that include sodium bisulfite. The exact mechanism of bisulfite’s action requires further study.