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New 4-hexylresorcinol based mixtures for melanosis prevention in crustacean

The result deals with the effect of 4-hexylresorcinol as antimelanotic and its effect on microorganisms. Residual analyses in dipping solutions and shrimp meat were also performed. The inhibitory effect of 4-hexylresorcinol (HR) was proved in a real and model system in several crustacean species (Norway lobster, deepwater pink shrimp, imperial tiger prawn and black tiger shrimp). In model system, HR exerted a reversible inhibitory effect of polyphenoloxidase, resulting in a formation of colourless compounds. In real system, HR was proved to be efficient as antimelanotic by dipping, spraying and dusting, always on board in order to stop melanosis process as soon as possible. Live crustaceans from aquaculture were immersed in solutions with HR for 1-2 hours before death, and they did not develop melanosis during storage. On death crustaceans, the best application method was spraying, using seawater (1 l) to dilute the antimelanosic. Immersion with seawater (relation crustaceans : water of 1:2), after dilution of antimelanotic, and at low temperatures, was more homogeneous, but crustaceans were damaged by handling, especially deepwater pink shrimp. The additive was spread more heterogeneously when it was added by dust, and favoured the penetration into the muscle in the first days of iced storage, but manipulation can be dangerous by fishermen and it is not recommended. The appearance of the crustaceans during storage was much better and very fresh-looking when organic acids (citric, ascorbic and acetic acid) and chelants [EDTA and sodium pyrophosphate (PPi)] accompanied HR. The best formulation (w/w) consisted of a moderate concentration of HR 0.1%, citric acid 0.5%, ascorbic acid 0.5%, acetic acid 0.3%, EDTA 500 ppm, PPi 1.5%. Minor concentrations of HR (0.05%) could be used to treat Norway lobsters, unlike pink shrimp. The results underscored the differing efficacy of HR depending on the season in which the shrimp were caught, due to inhibition was less effective in autumn and winter, coinciding with moulting. About the effect of formulations with HR on spoilage, in certain studies it increased the microbial quality of prawns, but these results were not definitive. Regarding the amount of additives retained in muscle after treatment, smaller shrimp contained higher levels of hexylresorcinol. The residual levels of HR in the shrimp meat (P. monodon) treated with low quantities of 4-hexylresorcinol [0.3-1.8 ppm (w/w), 0.05 g/l (w/v)] were according to the FAO/WHO Expert Committee on Additives (JECFA), who established 2 mg/kg as the maximum limit for the HR residue in the consumable portion of crustaceans. However, this concentration was not enough to stop melanosis process efficiently during the microbial shelf life of shrimp. The residual levels in deepwater pink shrimp treated previously with at least 0.2 % (w/w), 0.1 % (w/v) HR exceeded considerably the limit referred above. Cooking, freezing and thawing showed also a very low efficiency in the reduction of residues from the initial loads to acceptable values. During treatment the residues of samples treated with HR increased almost linearly in function of application time. The HR residues in the shrimp edible tissue treated with 0.1% of HR presented concentrations around 2.5 mg/kg with 3 and 15 min treatments and increased to 8.2 mg/kg with the expansion of the immersion time (60 min). The highest levels of HR residues were always analyzed in the samples treated with 0.25% solutions and the maximum HR level (15.6 mg/kg) was attained with a 60 min immersion treatment. When the shrimp was submitted to cooking after thawing slightly lower HR residues were analyzed. The washing of samples also reduced the amount of residues. Freezing and thawing processes may enhance the interaction of the 4 HR residues with the muscle matrix. On the other hand, the determination of citric acid and ascorbic acid did not show any residual in the shrimp meat. The content represents < 10 mg/100g. Also, no limit values exist for the two acids. This means there is no danger from consumption of these treated crustaceans to the consumer. Furthermore, microbiological growth in the dipping solutions after immersions was determined. The solution of HR did not evidence any tendency for an increase of the bacterial counts even after 29 hours of utilization and though the initial load of the shrimp was higher than it is normally expected onboard. Thus, the microbiological growth is not a problem if the HR dip solutions are used for a large period. For the 4-hexylresocinol residue determination in dipping solutions, a slight increase in the HR concentration was accounted for the decrease in the solution volume since part of the solution was removed by the shrimp. Nevertheless and though this slight increase the major conclusion to evidence was that no decrease in the 4-HR concentration is visible even after 8 dips and 29 hours of solution use.

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