Antibacterial effect of rice vinegar and microbiological quality of sushi marketed in the city of Brasília, Distrito Federal, Brazil

Abstract

Sushi is a ready-to-eat food composed of rice acidified with vinegar and stuffing of raw fish and vegetables. The acetic acid in the vinegar reduces the pH of the rice and helps in the conservation of the sushi, decreasing the microbial growth. This study aimed to evaluate the antibacterial effect of rice vinegar by determining its minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC); and to determine the microbiological quality of sushi marketed in the city of Brasília, Distrito Federal. We performed microbiological analysis in 10 samples of sushi collected in restaurants specialized in oriental cuisine and 10 samples of sushi collected in places not specialized in oriental cuisine such as supermarkets and bakeries, totaling 20 samples. The analyzes performed were total count of mesophilic and psychrotrophic bacteria, determination of total coliforms and thermotolerant coliforms, count of Staphylococcus aureus, research of Salmonella spp., and the molecular identification of S. aureus by PCR. Rice vinegar had an antibacterial effect for gram positive bacteria (S. aureus and B. cereus) and for gram negative bacteria (S. enterica and E. coli). MBC values ranged from 3.0 to 50.0 mg acetic acid/mL and MIC values ranged from 2.5 to 3.5 mg acetic acid/mL. Most of the sushi samples evaluated in this study (80%) presented acceptable microbiological conditions for consumption according to Brazilian legislation. However, 4 samples (20%) exceeded the acceptable limit for S. aureus and were considered unfit for consumption. The unfit for consumption samples were from restaurants specialized in oriental cuisine. The high presence of S. aureus bacteria in these sushi samples indicates inappropriate hygienic conditions, as this is a bacterium normally associated to inadequate human manipulation.