Impiego di ozono per il controllo di Listeria monocytogenes in diverse tipologie di formaggio

The purpose of this study was to investigate the bactericide effect of ozone on Listeria monocytogenes and to evaluate the effectiveness of its application on pathogen contaminated surfaces of Ricotta Salata, Taleggio DOP and Gorgonzola DOP cheeses. Eight minutes exposure to UV generated gaseous ozone, with a concentration 4 ppm, reduced the cell number of bacteria cultured by more than 99% on ALOA agar. The ozonization was tested at three different ripening times and the cheeses were inoculated with two different levels of inoculum. The L. monocytogenes content was evaluated before and after the treatment and after 7 days of conservation at 4°C. With regard to Ricotta Salata cheese, the treatment reduced the contamination to below 10 CFU/g, and no growth was observed even after 7 days. For both Taleggio DOP and Gorgonzola DOP, the ozone treatment was effective on cheeses with short ripening periods (6 and 3 days respectively) otherwise only a slight reduction was observed. In addition, an evaluation of the effect of the treatment on the sensorial characteristics of the cheeses was carried out: the layer just below the rind was modified in its flavour by a lower presence of compounds derived from lipolysis (free fatty acids and their derivatives), and few oxidation products were found in the same layer.