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New approaches to the crustaceans prevention of melanosis and quality indices


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.
The production of high-quality Crustaceans requires the definition of quality standards, which allow the producer the placement of the crustaceans. Indole level is used by the U.S. FDA to validate the sensory evaluation of shrimp decomposition and a level of less than 250 µg/kg has been established for Class I shrimps. Sensory evaluation and indole level of fresh shrimps has been demonstrated to show a good correlation. Though, in the present study a very low level of indole was detected during sensory shelf life of pink shrimps at all storage temperatures. Furthermore, all samples presented at shelf life lower indole levels than the limit suggested by the FDA. In contrast, when these limits were attained, TVB-N, TMA-N, TVC and Enterobacteriaceae had increased in the same period to unacceptable levels and pink shrimps considered spoiled by the test panel. The present study confirms that findings of others that indole levels indicated decomposition. However, decomposed shrimp may not necessarily contain indole. In conclusion, indole should be used in conjunction with other quality indices when evaluating the quality of fresh shrimp. Thus, in order to classify a sample of acceptable the following limits could be suggested for Pink shrimp: Total viable counts: 9.10E+5 cfu/g Total Volatile Basic Nitrogen: ≤ 30 mg/100g TMA-N: ≤ 11 mg/100g Indole: ≤ 88 µg/kg Putrescine: ≤ 6 mg/100g Cadaverine: ≤ 7 mg/100g Agmathine: ≤ 7 mg/100g For Penaeus monodon the following limit values could be determined. Change from good to poor quality Total Viable Counts: 5.00E+5 CFU / g Total Volatile Basic Nitrogen: 40-45 mg / 100 g pH value: 7.9 - 8.0 Tyramine: < 7 mg/kg Putrescine: < 6 mg/kg Cadaverine: < 6 mg/kg Change from poor quality to not marketable Total Viable Counts: 1.00E+7 CFU / g Total Volatile Basic Nitrogen: 45-50 mg / 100 g pH value: 7.9 - 8.0 Tyramine: < 7 mg/kg Putrescine: < 6 mg/kg Cadaverine < 6 mg/kg
The application of melanosis inhibitors on crustacean goes back for more than 50 years. Use of inhibitors based on sulphite is the common rule and application is frequently in a less correct way. On account of this products often present exceedingly levels of sulphites which may be dangerous for consumers, namely asthmatic ones. In order to avoid problems arising from deficient crustacean processing it is necessary to render available a process specification for each type of crustaceans, which can involve a detailed description of new applicable inhibitors, conditions of utilization and innovative processing technologies associated, which can be easily followed by fisherman, aquaculture managers, processors and retail market operators. Guidelines of inhibitors application giving standard operating procedures for the preparation of crustaceans of premium quality were prepared together with a draft manual in guide format of the standard operating procedures for the processing of crustaceans. A guidebook was also produced which contains technical advice on the handling and processing of shrimp and Norway lobster during operations onboard and on shore. Advisory information is given on what concerns the application of old and new chemicals for melanosis inhibitory purposes, chilling, freezing, cold storage, processing techniques and safety concerns affecting the quality of the products. It is not expected that this guidebook will answer all the questions about inhibitors and processing technology of crustacean, nevertheless it will provide a contribute for the safe use of food additives and production of better quality products. If the enclosed procedures are followed healthier products with increased shelf life will be available for consumers.
The first part of the study of the impact of new processing technologies using carbon dioxide in the spoilage and melanosis development of deepwater pink shrimp (Parapenaeus longirostris) concerned the comparison of the different mixtures of antimelanosic compounds when used under normal operating procedures, i.e., immersion application. A commercially available product based on sodium metabisulphite, Melaplus (MP-P) was also used also as a control. The second part of the work involved the study of the efficiency of three mixtures of 4 hexylresorcinol with acetic and ascorbic acids plus EDTA and sodium pyrophosphate when used in conjunction with three new processing techniques, (i) carbon dioxide modified refrigerated seawater, (ii) pressurized dissolved carbon dioxide and (iii) soluble gas stabilization. The results from the first phase did not showed the existence of noticeable differences between the different mixtures, both in sensory and biochemical terms. Though the results were similar to the control in what concerned the biochemical parameters, in sensory evaluation the sulphite based mixture performed better. The study of the different processing techniques did not showed the existence of clear differences between the batches submitted to the new processing techniques. The sensory and the biochemical data of the pre-treated batches were, in general, rather similar to the data of the control batch with the respective mixture. It was also possible to verify that these results were in what concerns the sensory properties, worst than the data from the control batch with the sulfite based mixture. In conclusion and in what concerns the sensory evaluation it is evident that the use of the pretreatments with CO2 does not brings any significant advantage. Furthermore the use of CO2 has a detrimental effect on texture of the products and makes them tougher and less pleasant. Moreover, the use of 4-HR either isolated on in conjunction with new processing techniques does not bring about any advantage in what concerns the sensory properties of deepwater pink shrimp. In summary it may observed that the processing with carbon dioxide did not introduce a significant benefit in relation to the processing of the shrimps by dipping. Furthermore, the efficiency of the mixture with 4-HR was also inferior to the one displayed by sodium metabisulphite. It is therefore necessary to continue the effort of research of new melanosis inhibitors, thus testing new formulas. In what concerns the application of liquid ice, was studied the onboard chilling of deepwater pink shrimp with liquid ice versus the traditional chilling with flake ice. The effect on quality of this treatment was determined after catch and during five days of chilled storage, in order to simulate a characteristic fishing trips of the South of Europe. It was considered of interest to establish if the utilization of liquid ice leads to a higher degree of homogeneity of catches with different days of chilled storage and, if for the same period of storage, liquid ice improves the product quality. An experiment was also performed to study the effect of liquid ice on chilled storage of Norway lobster (Nephorps norvegicus) and red shrimp (Aristeus antennatus), having the effect on ATP and formation of derivatives also being followed. From the microbiological and biochemical point of view chilling of shrimp on board with liquid ice showed a slight tendency to improve the quality of crustacean as compared with the traditional flake ice. A slight loss of natural coloration with a tendency to become pale was observed in crustaceans treated with sulphites, although never being rejected. Despite liquid ice is a technological process of great interest, it is possible that the implementation on board in small boats, those one day trip, will not be profitable. In this case the application of liquid ice on land will be adequate. Melanosis is not prevented by liquid ice treatment, although under some circumstances, liquid ice could delay the melanosis onset because the layer of small crystal formed could avoid the permeation of oxygen, and therefore diminish the oxidation. Since 4-hexilresorcinol is insoluble in water care should be taken when using it with liquid ice. To prepare a solution it is necessary to dissolved in a small quantity of ethanol, prior to be added to the liquid ice water. By this manner the 4-HR is effective to act in any aqueous solution, including liquid ice. Liquid ice or binary ice is a new food chilling technique that requires less time to chill products and acts more uniformly than other types of ice. Liquid ice has the potential to be introduced as a successful method for the rapid chilling of crustacean and as a way of reducing the temperature of products below those attained with traditional ice.