Use of ozone gas to limit the growth of molds and yeasts in the room of maturation of fresh cheeses. Preliminary results.

In the manufacture of fresh cheeses one of the main drawbacks is the mold proliferation on the surface of the product. Therefore, the use of chemical agents with antimicrobial activity is almost mandatory. However, the industry’s interest is oriented toward alternatives preferably in line with consumers expectations for food products with a short list of ingredients. In this study, the antimicrobial efficacy of ozone against molds and yeasts that contaminate the rooms of fresh cheese maturation has been tested. The experiment was conducted using 2 adjacent rooms with a volume of 360 m3 each. Five successive batches of cheese obtained in as many days were considered for experimental purposes. At the end of the salting phase (in brine for 48 h) the cheeses of each batch were equally split between the 2 rooms. The cheeses were settled on plastic shelves located in the opposite side of the door. In one room were placed 4 ozone generators (2 near the door and 2 in the opposite side) operating according to corona discharge with a production capacity of 5 g ozone/h each one. The emission of ozone was continued for 28 consecutive days from 6:00 pm to 4:00 am. The microbial samples were taken by scrubbing 100 cm2 surface area both for shelves (accurately sanitized before the beginning of the trial) and for cheese. The scrubs were collected the day after the cheese manufacture, at the end of first, second, third and fourth week of maturing. In all cases the collections were taken at 8:00 am. At the fourth week, microbial analysis was also conducted on 25 g of crust cheese removed for a thickness of about 2 mm. The molds and yeasts cells collected were submitted to grown on DRBCA AGAR BASE and OGYE AGAR BASE at 25° C for 5 days. The scrubs coming from the room used as control showed molds charges that were in the order of magnitude of 1 log in the first sampling time rising up to 3-4 logs after 28 days both for shelves and cheeses. The yeasts showed more variable values in the first sampling time (from 1 to 3 logs) and higher values at the end of the experiment (up to 5 logs). In the room submitted to ozone treatment the microbial behavior was completely different. The molds were almost absent from all the surfaces tested already at the end of the first week of maturing time and this situation persisted until the end. The yeasts showed a linear decrease until disappearing at the end of the third week. In conclusion, the employment of ozone in gaseous form seems to be able to eliminate molds and yeasts both from shelves surface and from the crust of fresh cheeses. That of ozone is a technology relatively easy to use that leaving no residual is also environmental friendly. It was defined as GRAS by the US-FDA and employed as direct food additive. In Italy the Ministry of Health in 1996 recognized the ozone for the treatment of water and air as a tool for the sterilization of confined environments contaminated by viruses, bacteria, spores, molds and mites.