Relative Microbial Spoilage of Un-gutted and Gutted Cultured Edible Barramundi (Lates calcarifer)

Abstract

Freshness of fish plays an important role in the pricing and market acceptability of fish. Microbial activity is one of the most important factors affecting freshness of fish. Seafood products are vulnerable to microbial spoilage even in chilled storage. Fish flesh contains high levels of free non-protein nitrogen compounds which support post-mortem bacterial growth. Microbial spoilage consequently shortens the shelf-life of the seafood product—making the product unsuitable for consumption because of the growth of undesirable and health threatening micro-organisms. The microbial quality of fish and the shelf-life of fish are both of considerable importance in fish consumption. The consumption of deteriorating seafood poses risks to human health. Although legislation in many countries requires that fish be gutted prior to storage under chilled conditions, the evidence on the effects of gutting on the microbial status of fish is mixed. In this study, the bacterial spoilage of un-gutted and gutted Barramundi is assessed using a microbial assessment method (the standard total plate count (TPC)). Barramundi is a high value cultured fish with high demand in Australian domestic and foreign markets. The materials and methods employed are in accordance with the Australian Food Microbiology Standards AS 5013, AS 5013.1, AS 5013.5 for Total Plate Count (TPC). Sixteen fish, weighing an average of 450g were purchased from a Barramundi farm in Tasmania and processed within 30 minutes of harvest. TPC data from 148 agar plates are analysed using tests of proportions and analysis of variance (ANOVA). The effective sample size is therefore, n=148. The results of microbial tests suggest that gutted fish have a lower bacterial load in the initial days on ice. However, un-gutted fish seem to present relatively lower levels of bacterial counts, particularly after extended periods on ice. These results have implications for fresh fish transportation, storage, filleting and the processing of the different edible cutlets (portions) of Barramundi.