Resumo

INTRODUCTION: A common practice to prevent melanosis in shrimp is to immerse them in aqueous solutions with ice and sodium metabisulfite (Na₂S₂O₅). The antimelanosic potential of this chemical additive is widely recognized, however its antimicrobial activity is not yet well established. This work was aimed at determining the antimicrobial effects of this additive. MATERIALS AND METHODS: The sodium metabisulfite dilution was done by adding 12.5 g of this substance in 1000 mL of water, as recommended by Brazilian’s law, so that residual sulfur dioxide (SO₂) does not exceed 100 mg kg^-1. Two groups were created: without Na₂S₂O₅ (C) and with Na₂S₂O₅ (M), each one had five samples of white shrimp (Litopenaeus vannamei), weighing 160 g each. The samples from group M were immersed in a Na₂S₂O₅ solution for 10 minutes, and the ones on group C were not exposed to any treatment. Two samples from each group were vacuum packed and three were packed in atmospheric air. On days 3, 6 and 9 of refrigerated storage (10°C) the search for coagulase positive staphylococci and for Salmonella sp. were performed as required by ANVISA for whole raw shrimp, besides these, the standard plate count for psychrotrophic and mesophilic bacteria was also executed. RESULTS: The analysis of coagulase positive staphylococci showed the absence of these bacteria in all samples. The Salmonella sp. search found positive samples only in group C (3^rd and 6^th day). The psychrotrophic bacteria were not found in any of the 3^rd day samples; on the 6^th day the count for the M group was 5.9x10⁴ log cfu g^-1 for the samples packed in air; for the ones vacuum packed and for all the group C samples counts were greater than 2.0x10⁵ log cfu g^-1; the 9^th day samples from both groups, M and C had counts greater than 2.0x10⁵ log cfu g^-1. The mesophilic bacteria count, however, revealed a peculiar finding. Group M means were 3.7x10⁵, 4.13x10⁴, and greater than 2.0x10⁵ log cfu g^-1 on days 3, 6 and 9, respectively. Meanwhile group C had averages of 5.0x10⁵, 1.6x10⁵, and 4.7x10 log cfu g^-1 also on days 3, 6 and 9, respectively. CONCLUSIONS: The antimicrobial potential of sodium metabisulfite was evidenced by group M results, which showed lower counts in all analysis performed, except in the mesophilic count on the 9^th day of storage.