Creating a grading scheme for fresh ice-stored White snapper (Lutjanidae spp.) and Rabbit fish (Siganus sutor) using quality indices
Currently, the Kenya fisheries industry does not have an official grading scheme for fresh fish. Due to lack of an appropriate and locally developed grading scheme, this study used the Quality Index Method to develop a grading scheme for iced Rabbitfish and White snapper through a shelf life study. The two fish were bought from fishermen at the landing beach after delayed icing of 4-6 hr. The two fish were placed into gutted and ungutted lots. Both lots were layered with ice and stored in insulated boxes. Three iced fish from each batch were sampled on days 4, 8, 12, 16, 20, 24 and 30 for ungutted lots but up to 34 days for the gutted fish. Sensory attributes of the fish including appearance of skin, color of slime, color and odor of gills were selected for development of a quality index scheme by a trained sensory panel. Total viable counts (TVC) were determined at 22 and 37oC as well as hydrogen sulphide-producing bacterial counts at 22oC. Free fatty acid level, pH and total volatile basic nitrogen were also determined on experimental fish over the storage period. The shelf life of gutted Rabbitfish and White snapper was 32 and 28 days, respectively; ungutted Rabbitfish and White snapper, had shelf lives of 28 and 24 days, respectively. The TVC and hydrogen sulphide-producing bacterial log was 6.1±0.21 and 5.8±0.55 CFU/g at the point of rejection of ungutted Rabbitfish and log 6.3±0.24 and 5.8±0.28 CFU/g for ungutted White snapper. For gutted Rabbitfish and White snapper, TVC and hydrogen sulphide-producing bacterial log were 5.9±0.19 and 5.3±0.11 CFU/g and log 5.9±0.22 and 5.4±0.21 CFU/g, respectively at point of rejection by the taste panel. Gutting the two fish species increased shelf life by about 4 days. The quality index scheme developed in this work was appropriate for creating commercial grades of the two marine fish. The select sensory parameters and QI are suitable, while TVBN, FFA, pH, TVC and hydrogen sulphide-producing bacterial count are not appropriate for rapid commercial grading of fresh, ice-stored White snapper and Rabbitfish.
Key words: Grading, White snapper, Rabbitfish, ice, quality index
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