Microbial and physicochemical modifications of hake (Merluccius merluccius) steaks stored under carbon dioxide enriched atmospheres

Abstract

Microbial counts (total viable, Brochothrix thermosphacta, lactic acid bacteria and Enterobacteriaceae), biochemical parameters [pH, total volatile nitrogen, nucleotide breakdown products, non-volatile amines, D(À) and L() lactic acid and short-chain fatty acids] and sensory attributes (colour and odour) of refrigerated (2°C) hake (Merluccius merluccius) steaks under carbon dioxide enriched air (CO 2 /air, 20/80 v/v and CO 2 /air, 40/60 v/v) and air atmospheres were determined. When compared with air, sensory results showed shelf-life extension of 4 and 11 days for 20% and 40% CO 2 -enriched atmospheres, respectively. Microbial and biochemical results also revealed that the 40% CO 2 -enriched atmosphere was the most effective packaging type for refrigerated hake. # 2000 Society of Chemical Industry Keywords: modi®ed atmospheres; shelf-like; hake steaks INTRODUCTIONHake is undoubtedly the most popular ®sh in the Spanish market due to the volume of its sales and its price. According to the most recent data, in Spain over 6 kg are consumed per person per year, both in the fresh and frozen form.1 Fresh hake accounts for more than 50% of the total fresh ®sh consumption and frozen hake for approximately 80% of the total frozen ®sh consumption. Of the twelve hake species known to date, eight are currently marketed in Spain, the most important of which is the European hake (Merluccius merluccius). This is a demersal species which generally inhabits depths of 70±370 m and is very common on the edge of the continental slope. It can be found in Atlantic waters from Norway to Mauritania, the North sea, the Mediterranean and the Black sea. Hake is mainly sold in the fresh form (around 80%), and is usually sold whole or in ®llet or steak form. When prepared as skinned ®llets, the usable proportion exceeds 40%.

Effect of Antimicrobial Edible Coatings and Modified Atmosphere Packaging on the Microbiological Quality of Cold Stored Hake (Merluccius merluccius) Fillets

“…Enterobacteriaceae, LAB, and H 2 S-producing bacteria were undetectable (<1 log cfu/g). Other authors have reported also low counts at the beginning of the experiment, showing better and acceptable microbiological quality [27,28].…”

Effect of Modified Atmosphere Composition on the Metabolism of Glucose byBrochothrix thermosphacta

“…The relationship between CO 2 percentage and the total concentration of acetic acid was not clear. The observations for hake (24) followed a trend similar to that found in this study, with production of acetic acid being lowest in the absence of CO 2 and greater at 20 than at 40% CO 2 . In similar experiments with salmon (8), no differences were observed in acetic acid production at 0, 20, and 40% CO 2 .…”

“…Greater acetoin-diacetyl production under high oxygen concentration and no effect of oxygen on production of L-lactic acid were reported. B. thermosphacta was also the dominant microorganism in MAP hake (24) and salmon steaks (8), and a greater accumulation of lactic acid was detected at high CO 2 concentrations. Acetic acid and ethanol did not accumulate during the stationary phase; these metabolites may have been used as substrates for other reactions.…”

“…Therefore, this bacterium plays an important role in the spoilage of MAP meat (1, 6, 16, 28) and fish (8,17,18,24). The main factor limiting the shelf life of refrigerated MAP food is offensive odor development resulting from microbial metabolism (28).…”

“…The results of Ordóñez et al (22,24) suggest that the inclusion of oxygen in CO 2 -enriched atmospheres could enhance the aerobic metabolism of B. thermosphacta. It is therefore of interest to determine which combinations of CO 2 and O 2 delay the oxidation of myoglobin but also ensure that the metabolism of B. thermosphacta remains dominantly anaerobic.…”