Decomposition of trimethylamine oxide related to the use of sulfites in shrimp¹

 

Israel H.A. CINTRA², Norma B.P. OGAWA³, Maria R. SOUZA³, Fábio M. DINIZ², Masayoshi OGAWA^3,*

 

 

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SUMMARY

Currently, sulfites are employed on board to inhibit melanosis (blackspot) on crustaceans. However, when used in excess this chemical compound not only can cause adverse reactions in SO₂-sensitive individuals, but also favors the decomposition of trimethylamine oxide (TMAO) into dimethylamine (DMA) and formaldehyde (FA), thus compromising the quality of the product, which can be observed mainly through the texture change of the meat after cooking. This study was conducted to verify the increase of the contents of DMA and FA by the excessive use of sodium metabisulfite in white shrimp (Penaeus schmitti). For laboratory trials, shrimp were beheaded, washed and immersed in a 2% sodium metabisulfite solution for 10 minutes. Specimens were stored either on ice and maintained for 48 hours in refrigeration, or stored in a freezer for 48 hours. Samples were collected at intervals of 0, 24 and 48 hours, and analyzed for residual SO₂, TMAO, TMA, DMA and FA. The immersion of shrimp in a 2% sodium metabisulfite for 10 minutes favored the decomposition of TMAO which greatly increased the contents of DMA and FA. The FA and DMA measured in fresh shrimp was low. Moreover, the storage of shrimp tails on ice resulted in a significant reduction of the TMA, DMA, FA and residual SO₂ contents compared to the specimens under frozen storage.

Keywords: sulfites in shrimp, trimethylamine oxide, dimethylamine, formaldehyde.

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RESUMO

Decomposição do óxido de trimetilamina relacionada ao uso de sulfitos em camarão. O uso de sulfitos é uma prática utilizada a bordo para prevenir a melanose (manchas pretas) em crustáceos. No entanto, este composto, além de causar reações alérgicas em pessoas sensíveis ao SO₂ quando usado em excesso, proporciona a decomposição do óxido de trimetilamina (OTMA) em dimetilamina (DMA) e formaldeído (FA), comprometendo assim a qualidade do pescado, principalmente no que se refere ao endurecimento da carne após cozimento. O presente trabalho foi desenvolvido com a finalidade de se verificar o aumento dos níveis de DMA e FA pelo uso em excesso de metabissulfito de sódio em camarão branco, Penaeus schmitti . Em laboratório, os exemplares foram descabeçados, lavados e imersos em solução de metabissulfito de sódio a 2% por 10 minutos. Uma parte foi acondicionada em gelo e mantida por 48 horas em refrigerador; outra foi congelada em salmoura e estocada em freezer por 48 horas. Foram determinados SO₂ residual, OTMA, TMA, DMA e FA em amostras coletadas com 0, 24 e 48 horas. A prática de imersão dos camarões em solução de metabissulfito de sódio a 2% por 10 minutos favoreceu a decomposição do OTMA ocasionando acentuado aumento nos níveis de DMA e FA; verificou-se em camarões recém mortos um pequeno conteúdo de FA e DMA; o acondicionamento das caudas de camarão em gelo proporcionou uma redução sensivelmente maior nos níveis de TMA, DMA, FA e SO₂, do que quando estocadas congeladas.

Palavras-chave: sulfitos em camarão, óxido de trimetilamina, dimetilamina, formaldeído.

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1 - INTRODUCTION

Shrimp is one of the most important export commodity of Northern Brazil, mainly as a frozen product to USA and Japan. Upon landing, the shrimp is thawed, processed and submitted once more to freezing, which procedures may induce the formation of black spots or melanosis.

An usual procedure of inhibiting melanin formation is the immersion of the crustacean in a sulfite solution. In Brazil, the Federal Inspection Service of the Ministry of Agriculture allows the use of sodium bisulfite (NaHSO₃) and metabisulfite (Na₂S₂O₅• H₂O) on shrimp up to a residual level of SO₂ of 100 ppm (mg/1000g), which is the maximum amount allowed by importers. The literature suggests the immersion of shrimp into a solution of sodium metabisulfite at 1.25% for 1 min [10].

Melanosis is strongly influenced by traumatism and molting cycle; therefore, if the crustaceans are not properly handled on board when alive, the concentration of sulfite solution and time of immersion suggested by literature would not prevent melanosis [7].

Currently, fishermen use a greater concentration of sulfite and/or a longer period of immersion, because upon landing in the industry, the washing and storage steps in the industrial processing would reduce the residual SO₂.

Even though the level of SO₂ can be reduced by the period of storage, its initial high values will favor the degradation of trimethylamine oxide (TMAO), which is an amine that naturally occurs in marine fish and shellfish, in dimethylamine (DMA) and formaldehyde (FA). Yamanaka et al. [17] and Yoshida & Imaida [18] suggested that the production of FA could be induced in shrimp treated with sodium bisulfite used to prevent melanosis.

TMAO is an osmorregulator and is found in all the marine species at varied amounts usually from 1 to 7% of muscle tissue (dry weight basis) [3].

Under the viewpoint of process technology, the consequences of FA and DMA production in fish and shellfish includes the loss of water holding capacity and toughening of muscle after cooking, which generates a decrease in product acceptability [4].

FA is a prejudicial substance to human health and, therefore, its use as a preservative is prohibited in food. A threshold value of 5 ppm is accepted in packed food, when the packaging material is a FA-based resin [9]. The natural occurrence of FA in fruits and vegetables, seafood and fermented food is in some cases inevitable. In the case of seafood, FA in frozen fish of gadoid species has been known to occur by the enzymatic action of TMAOase.

Under chilling conditions the content of TMAO in fish and shellfish is degraded by non-enzymatic reaction, producing mainly the tertiary amine TMA, and not DMA and FA, as usually happens under frozen conditions. However, Ogawa et al. [8] verified the accumulation of these compounds (FA and DMA) in lobster kept on ice, submitted to the excessive use of sulfites.

The main objective of this paper was to verify the occurrence of FA and DMA in shrimp for interference of sodium metabisulfite, during a period of ice preservation and frozen storage, aiming for the enhancement of the product quality.

 

2 - MATERIAL AND METHODS

2.1 – Material

Fresh white shrimp (Penaeus schmitti) were purchased from a local fishery market a few hours after they had been caught on the coast of Fortaleza - Ceará. Samples for analysis consisted of shrimp tail muscles weighing from 7.7 to 16.5 g. Shrimp were transported to the laboratory on ice in polystyrene boxes.

2.1.1 - Immersion procedure

Shrimps were weighed, beheaded, washed to remove hemolymph and submitted to immersion in a 2% sodium metabisulfite solution at 5^oC for 10 minutes. Control samples were immersed into water at 5^oC for 10 minutes.

At the end of treatment, a portion was maintained in the refrigerator at 10^oC, covered with ice, for 48 hours and the remaining portion of the samples was frozen in brine, a saturated solution of commercial salt (30%) + sugar (40%) and stored in freezer at -18^oC.

Ice-stored shrimp tails were analyzed with 0, 24 e 48 hours of preservation and samples submitted to freezing were analyzed at 0, 24, 48 hours and 10, 20, 30, 40 and 50 days of frozen storage.

2.2 – Chemical analyses

The muscle tissue from each sample was chopped thoroughly and analyzed for residual sulfur dioxide (SO₂), TMA, DMA, FA and TMAO. SO₂ was measured using the distillation method as described by Nishikawa and Aranha [6]. Trimethylamine (TMA) was determined by the method of Dyer with minor changes [16]. The dithiocarbamate method was employed for the determination of DMA. The FA content was determined according to the method of Woyewoda et al. [16] using the Nash reagent. The TMAO was reduced to TMA using TiCl₃. The content of TMAO was estimated by the difference of TMA before and after reduction.

2.3 – Statistical Analysis

Analytical determinations were run in triplicate with five determinations for each analysis. The data collected were subjected to one-way analysis of variance (ANOVA). Significant differences between mean values were determined by the Duncan’s New Multiple Range Test at 95 % confidence level according to Steel and Torrie [12]. These procedures were performed using the statistical package SPSS [11].

 

3 – RESULTS AND DISCUSSION

3.1 – Preservation on Ice

Compared to the control samples, at zero time of storage, sodium metabissulfite-treated samples had their FA values increased from 1.11 ± 0.05 to 8.93 ± 0.26 mg/100g and DMA content from 0.05 ± 0.01 to 0.91 ± 0.02 mg/100g, or respectively 8 and 18.2 times greater (Figure 1). This fact evidenced the interference of the use of sulfite on the formation of these compounds. Wada [15] suggests that the treatment with sulfites can provoke the formation of FA in the muscle, where the precursor would be TMAO. YAMANAKA et al. [17] verified quantitative changes of TMAO, TMA, DMA and FA in shrimp treated with sodium bisulfite for 5 minutes, packed in plastic bags and maintained in refrigerator (3° C). The same author related the increase of the content of FA with the storage period, the chemical reaction of TMAO with NH₃, amino acids, amino radicals, etc. provoked by the treatment with sulfites.

On the contrary, a reduction of approximately 86.9 % on the content of FA from zero time to 48 hours of storage on ice is shown in Figure 1. It was observed that sulfite-treated samples had a statistically significant reduction of the values of FA and DMA, every 24 hours on ice (P < 0.05). After a period of 48 hours of preservation on ice, these values reached levels close to those of the control samples. This may be due to washing with the defrost water during the period of ice preservation.

 

 

The content of TMAO in the control samples was significantly decreased from 68.22 ± 7.34 mg/100g (0 h) to 47.75 ± 3.66 mg/100g after 48 hours of storage (Figure 1). However, an equal profile was not observed for the treated samples where the TMAO content was statistically similar at the monitored times (P > 0.05).

A decrease of the TMA values was observed for both control and treated samples, respectively from 0.24 ± 0.06 to 0.16 ± 0.07 mg/100g and 0.71 ± 0.07 to 0.25 ± 0.03 mg/100g (Figure 1).

It was noticed in this study that, even fresh shrimp, samples showed low contents of DMA and FA, a fact that was not observed in lobster tails by OGAWA et al. [8]. However, the intestinal tract was not removed from our samples, contrarily to OGAWA et al. [8] that had extirpated them from lobsters. CASTELL et al. [1] and FLORES & CRAWFORD [2] verified difference in the contents of DMA and FA in fresh shrimp muscle with and without the intestinal tract.

According to TOKUNAGA [13], all substances related to the formation of FA and DMA could be extracted witch chilled water. The autor evidenced that the bleaching of the muscle of Alaska pollack in water before frozen storages cuases a decrease in the content of FA and DMA. According to OGAWA et al. [8], the immersion of lobster tails in cold water and brine, or defrost water reduces the content of these substances.

It was also noted that the residual SO₂ in the shrimp muscle was around 138 ppm few hours after they had been caught, which is beyond the allowed limit by the Brazilian Legislation, or 100 ppm (Figure 3). A significant reduction from 137.85 ± 2.05 to 104.77 ± 6.69 ppm during the first 24 hours and after 48 hours to 79.3 ± 21.92 mg/1000g was observed for treated-samples stored on ice (P < 0.05). As SO₂ is also soluble in water, there is a trend that this compound would be leached out by the defrost water, in case shrimp is preserved on ice. MENESES & OGAWA [5] reports a reduction on the levels of SO₂ during a period of conservation on ice. TSUKUDA & AMANO [14] also verified a reasonable reduction according to the period of storage.

 

 

 

 

3.2 - Frozen storage

Both FA and DMA contents for the sulfite-treated samples showed higher values than control (Figure 2). However, this difference occurred in a smaller proportion when compared to shrimps preserved on ice. These values for treated and control samples at zero time switched from 0.99 ± 0.09 to 4.74 ± 0.97 mg/100g (4.8 times greater) and from 0.10 ± 0.02 to 0.32 ± 0.10 mg/100g (3.2 times greater), respectively to FA and DMA. This corroborates with the findings of Ogawa et al. [8] that observed reduced values for these compounds due to the immersion of lobster tails in brine.

Up to 48 hours, the FA content of treated samples did not suffered any considerable variation and were not statistically different (P > 0.05), being around 4.6 mg/100g (Figure 2). After 10 days of frozen storage an increase was noticed up to 6.92 mg/100g and up to 10.11 mg/100g on the 50^th day (Figure 4). The experimental control did not show large variations during the same period of frozen storage, and was maintained closed to 1.00 mg/100g (Figure 4).

 

 

Likewise, the DMA content of treated samples did not present significant changes (P > 0.05), showing relatively constant values up to 24 hours. However, DMA content increased to a value significantly different after 48 hours (Figure 2). The frozen storage was able to double the DMA content after 50 days (Figure 4).

The TMAO content of either treated sample or experimental control indicated no large increase or tendency over 48 hour of storage (Figure 2). Furthermore, no trend was shown in the sulfite-treated and untreated samples during the 50-day frozen storage period for the TMAO content. Values were close to the mark of 55 and 51 mg/100g for treated and untreated shrimps, respectively (Figure 4).

An approximately stable profile was also verified in the TMA values of the treated sample. This may be due to the fact that at freezing temperatures, TMAO is degraded enzymically, mainly in DMA and FA, not occurring significant increases to the levels of TMA. Values were close to 0.52 mg/100g for the treated samples.

 

4 - CONCLUSIONS

It was demonstrated in this study that the immersion of shrimp in a 2% sodium metabisulfite solution for 10 minutes favors the increasing of the contents of DMA and FA in the muscle. The FA and DMA measured in fresh shrimp were low for samples not submitted to the sulfite-immersion. Moreover, the storage of shrimp tails on ice, for a period of 48 hours, washed out a significant quantity of these substances, including the residual SO₂. Frozen storage was responsible to, at least, double the contents of DMA and FA of sulfite-treated samples.

 

5 - REFERENCES

[1] CASTELL, C. H.; NEAL, W. & SMITH, B. Formation of dimethylamine in stored sea fish. J. Fish. Res. Board Canada, v. 27, p. 1685-1690, 1970.        [ Links ]

[2] FLORES, S. C. & CRAWFORD, D. L. Postmortem quality changes in iced pacific shrimp (Pandalus jordani). J. Food Sci., v. 39, p. 575-579, 1973.        [ Links ]

[3] HUSS, H. H. El pescado fresco: su calidad y cambios de calidad. Roma, FAO/DANIDA, 1988, 131p. (FAO Colección FAO: Pesca, 29).        [ Links ]

[4] KELLEHER, S. D.; BUCK, E. M.; HULTIN, H. O.; PARKIN, K. L.; LICCIARDELLO, J. J. & DAMON, R. A. Chemical and Physical changes in red hake blocks during frozen storage. J. Food Sci., v. 47, p. 65-70, 1982.        [ Links ]

[5] MENESES, A. C. S. & OGAWA, M. Uso do bissulfito de sódio na preservação da "Mancha preta", em camarões, durante estocagem em gelo, e estimação do dióxido de enxofre residual. Arq. Ciên. Mar, v. 17, p. 89-93, 1977.        [ Links ]

[6] NISHIKAWA, A. M. & ARANHA, S. Métodos físicos e químicos para controle do pescado. In: Seminário sobre controle de qualidade na indÚstria de pescado, 1988, Santos. Anais... p. 165-195.        [ Links ]

[7] OGAWA, M., PERDIGÃO, N. B., SANTIAGO, M. E. & KOZIMA, T. T. On physiological aspects of black spot appearance in shrimp. Bull. Japan. Soc. Sci. Fish., v. 50, p. 1763-1769, 1984.        [ Links ]

[8] OGAWA, M.; PERDIGÃO, N. B.; CINTRA, I. H. A.; PARENTE, P. & NISHIDE, E. Decomposition of trimethylamine oxide by excessive use of sulfite in spiny lobster. Crustaceana, v. 68, p. 138-145, 1995.        [ Links ]

[9] PEARSON, D. The Chemical Analysis of Foods. 7^th ed. New York, Churchill Livingstone, p. 40-41, 1976.        [ Links ]

[10] SILVA, M. M. C. & CAVALCANTE, P. P. L. Perfil do setor lagosteiro nacional. Brasília, IBAMA, 1994. 80p. (Coleção Meio Ambiente. Série: Estudos-Pesca, 12).        [ Links ]

[11] SPSS. Statistical Package for the Social Sciences, Advanced Statistics, Release 6.0, Chicago, SPSS Inc., 1993, p. 31-144.        [ Links ]

[12] STEEL, R. G. D. & TORRIE, J. H. Analysis of variance I: The one-way classification. In: Principles and Procedures of Statistics, New York, McGraw-Hill, 1960. p. 99-132.         [ Links ]

[13] TOKUNAGA, T. Studies on the development of dimethylamine and formaldehyde in Alaska pollack muscle during frozen storage. Bull. Hokkaido Reg. Fish. Res. Lab., v. 29, p. 108-122, 1964.        [ Links ]

[14] TSUKUDA, N. & AMANO, K. Effect of sodium bisulfite on prevention of blackening prawn and the remaining amount in prawn. Bull. Tokai Reg. Fish Res. Lab., v. 72, p. 9-19, 1972.        [ Links ]

[15] WADA, S. 7. Ebi no Riyou Kako. In: Nippon no Ebi Sekai no Ebi. Edited by Tokyo University of Fisheries, Seisando-shoten Kaka, Tokyo, 1984. p. 190-202.         [ Links ]

[16] WOYEWODA, A. D.; SHAW, S. J.; KE, P. J. & BURNS, B.G. Recommended laboratory methods for assessment of fish quality. Canadian Tech. Rep. Fish. Aquatic Sci., v. 1448, p. 143-149, 1986.        [ Links ]

[17] YAMANAKA, H.; KIKUCHI, T. & AMANO, K. Studies on the residue of sulfur dioxide and the production of formaldehyde in the prawn treated with sodium bisulfite. Bull. Japan. Soc. Sci. Fish., v. 43, p. 115-120, 1977.        [ Links ]

[18] YOSHIDA, A. & IMAIDA, M. Studies on the formation of formaldehyde in the bleached shrimps with sulfite. J. Food Hyg. Soc., v. 21, p. 288-293, 1980.        [ Links ]

 

6 - ACKNOWLEDGMENTS

This research was supported in part by a grant-in-aid from the CNPq (Conselho Nacional de Desenvolvimento Científico e Tecnológico) of The Ministry of Science and Technology, and FUNCAP (Fundação Cearense de Amparo à Pesquisa), Brazil. The assistance of Mr. Dennis Hartnett for revising the manuscript, is also acknowledged.

 

 

¹ Recebido para publicação em 12/12/97. Aceito para publicação em 28/09/99.

² Centro de Pesquisa e Extensão Pesqueira do Norte do Brasil, Campus da Faculdade de Ciências Agrárias, Belém, PA, Brasil, CEP: 66.077-530

³ Universidade Federal do Ceará, Departamento de Engenharia de Pesca, Laboratório de Recursos Aquáticos, Fortaleza, CE, Brasil, CEP: 60.356-000

* A quem a correspondência deve ser enviada.