Resíduos de antimicrobianos em leite pasteurizado e o efeito inibidor sobre bactérias lácticas para elaboração de produtos lácteos fermentados

Abstract

The presence of antimicrobial residues in milk represents a serious public health problem. For this reason, some legal measures have been taken by the governments, as a sale of antimicrobial drugs under medical or veterinary medical prescription, observation of Good Agricultural Practices, and the definition of maximum residue limits (MRLs) in foods of animal origin. However, the established MRL do not take into account effects on technology and manufacturing of dairy products, but only the protection of public health. Under the technological aspect, lactic bacteria are indispensable in the production of fermented dairy products, because promote controlled acidification and improve the texture and flavor of the product. Thus, the guiding hypothesis of this study is that antimicrobial residues in milk, even below the MRL, are capable of negatively altering the fermentative response of lactic bacteria. Five antimicrobials (amoxicillin, ceftiofur, gentamicin, sulfamethazine and tetracycline, representing the five main antimicrobial groups included in the National Plan for the Control of Residues and Contaminants of the Ministry of Agriculture, Livestock and Supply (MAPA), in five different concentrations (0, 0.50, 0.75, 1.0 and 1.25 of the respective MRL), which were tested against three commercial lactic cultures, DELVO® FRESH FC-211 (Lactococcus lactis subsp. lactis e Lactococcus lactis subsp. cremoris), DELVO® CHEESE CP-101 (Streptococcus thermophilus) and DELVO® FRESH YS-131 (Lactobacillus bulgaricus e Streptococcus thermophilus). Widely used in the manufacture of cheeses and yogurts. The milk came from three different animals, proven untreated with antimicrobials. Experimental controls and treatments were analyzed with respect to fermentative kinetics. The inhibitory effect of the antimicrobial substances was determined by the variation in the acidification curve as well as the time to reach the final reference pH of each fermentation. Ceftiofur and tetracycline inhibited the culture activity containing Streptococcus thermophilus, even when employed at concentrations below their respective MRL. The culture composed of Lactococcus lactis ssp. lactis and Lactococcus lactis ssp. cremoris was inhibited by ceftiofur and gentamicin antimicrobials, even when used at concentrations below their MRL. Ceftiofur also inhibited the mixed culture of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus, at concentrations below its MRL. Thus, the results of the present study indicate that concentrations below the antimicrobial MRL in milk may negatively interfere with the fermentative activity of lactic acid bacteria.