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The effect of gutting on sensory, microbiological, and chemical properties of European hake (Merluccius merluccius var. mediterraneus) stored in ice was studied. Gutting of hake noticeably affected the development of gram-negative bacteria: counts of Enterobacteriaceae, Shewanella putrefaciens, and Pseudomonas throughout ice storage were higher in gutted than in ungutted samples. These differences in microbial loads were also reflected in the lower sensory scores of both raw and cooked hake, in the quicker trimethylamine accumulation, and in the higher contents of putrescine, cadaverine, tyramine, and histamine found in gutted hake. All of the fish quality indicators studied showed that gutting made hake more susceptible to spoilage during ice storage and decreased its shelf life by 4 days.

Biogenic amine accumulation was studied during the ice storage of Mediterranean hake. Sensory analysis and counts of Shewanella, Pseudomonas, enterobacteria, psychrotrophic, and mesophilic bacteria provided complementary information on hake spoilage. Putrescine and cadaverine were the main amines accumulated, whereas histamine and tyramine were minor amines but had qualitative interest from the hygienic point of view. Although all biogenic amines were less abundant than in pelagic fish, they may also be used as indicators of freshness and/or spoilage in hake. Cadaverine was the amine best correlated with Shewanella, which was the specific spoilage organism. Therefore, cadaverine may be regarded as the specific spoilage biogenic amine for hake stored at chilling temperatures. However, the biogenic amine index, which considers cadaverine, putrescine, histamine, and tyramine, has several advantages as an indicator of hake quality. Taking into account sensory data, an acceptability limit of the biogenic amine index could be established in 15 to 20 microg/g.

Fresh Mediterranean hake (Merluccius merluccius var. mediterraneus), a species mainly caught off the shores of Spain, was stored at usual temperatures: in ice (commercial chain) and under refrigeration (home). Sensory and chemical analyses were performed throughout the storage time to determine the changes that took place and evaluate the effect of the storage temperature. Storage in ice resulted in a slight accumulation of volatile and biogenic amines in hake. When it was stored at 6-8 degrees C, a significant production of both trimethylamine and total volatile basic nitrogen (TVB-N) was observed, and biogenic amines were formed. Sensory analysis revealed that hake stored in ice was inedible after 29 days, the figure for refrigerated hake being 20 days. There was a nonsignificant correlation (p > 0.05) between TVB-N values and sensory score in hake stored at 0 degrees C. In all other cases, a significant correlation (p < 0.001) between volatile parameters and sensory analysis was found.

The reliability of flow injection/gas diffusion (FIGD) methods to determine trimethylamine (TMA-N) and total volatile basic nitrogen (TVB-N) in hake was studied in order to find an alternative and accurate, simple, cheap, and rapid method for non-protein nitrogen determination. FIGD methods involved extracting volatile amines with 7.5% trichloroacetic acid, followed by the injection of the extracts into the FIGD manifold, previously adjusted for TMA-N or TVB-N determinations. Each determination took approximately 2 min. Reliability was satisfactory in linearity, precision, recovery, and sensitivity. There was good correlation (p < 0.001) between FIGD and the classic official methods, for both TMA-N and TVB-N determinations, and also between FIGD and the gas chromatographic procedure described for TMA-N. These results proved that FIGD methods are simpler, cheaper, and faster than current official procedures. To check the suitability of FIGD procedures over a wide range of analyte concentrations, changes of both TMA-N and TVB-N and the P ratio values throughout the ice storage of hake were monitored. The usefulness of each of these potential freshness indicators for hake is discussed.