Eficácia do bacteriófago P100 e sais de ácidos orgânicos no controle da contaminação porListeria monocytogenes inoculada artificialmente em queijos

Abstract

Despite recent advances in technologies to control pathogens in foods, consumers have been looking for "natural" foods, i.e., submitted to less aggressive treatments and free of chemical preservatives. The use of substances considered GRAS or "Generally Recognized as Safe" is a good alternative. Among these substances, we can cite the bacteriophages, which are viruses that infect bacteria and are widely distributed environment, and salts of organic acids short chain. The cheeses are foods often pointed as potential vehicles of contamination by Listeria monocytogenes, an important pathogen causing disease transmitted by food and its importance has been growing since the 1980s. Although the number of disease cases per year is relatively low, the infection can be serious, with mortality rate at 30%. The cheeses have a number of conditions for the development of microorganism: intense manipulation in processing, storage and distribution; high water activity, especially in soft cheeses with medium and high humidity; mixture of different ingredients; in addition, to food being kept under cooling, which particularly favors the growth of Listeria monocytogenes. In view of this, the objective of this study was to evaluate the efficacy of bacteriophage P100 and salts of organic acids to control contamination by Listeria monocytogenes in soft cheeses, “Minas Frescal” and “Coalho”. The viable cell count of Listeria monocytogenes, mix of serotypes 1/2a and 4b, was determined in control samples and samples treated by bacteriophage P100 and organic acids at 0 (zero) and seven days storage at 10 °C. The results show that the treatments were effective for controlling bacteria at time 0 (zero) and after seven days under refrigeration, leading to a reduction of about two logarithm cycles at time 0 (zero) for both types of cheese, which was statistically significant (p<0.05). However, in seven days of storage there was an increase in the population of the microorganism (psychotropic character), resulting in a lower decimal reduction (DR), 1 log cycle approximately, but this reduction was statistically significant (p<0.05) too. There was no difference between the types of organic acids used (p>0.05). This study provides a valuable contribution, and a pioneer in Brazil, by using the bacteriophage P100 and salts of organic acids in typical Brazilian foods ready to eat, since there are no reports in the national scientific literature on the effectiveness of these additives in cheese.