Bioconservation of hard rent cheese using bacteriophages

Abstract

Several technological approaches are used to increase the safety of perishable food products during their production and realization. In particular, it is the use of temperature, high pressure, ultraviolet radiation and added preservatives. One of the generally recognized and common disadvantages of all these methods is that they have an influence on the microorganisms indiscriminately, that is, they inhibit both pathogenic and potentially beneficial autochthonous lactic acid bacteria of the "normal" microflora of fermented products. The purpose of this investigation was to monitor hard rennet cheeses for the content of Staphylococcus aureus and to develop a technology for its preservation using a lytic staphylococcal bacteriophage. Contamination of milk-raw material and Dutch cheese with Staphylococcus aureus was determined by inoculating the selected samples and carrying out tenfold dilutions on a selective hemoagar medium with 5% sodium chloride, followed by thermostating for +37-48 hours. Isolation of bacteriophages from milk raw materials was carried out by filtering through bacterial filters with pores of 0.45 μm. During the improvement of the technology of Dutch cheese with staphylococcal bacteriophage, two samples of cheese were produced - one experimental with bacteriophage, and the second control - without bacteriophage. It was set up that in milk-raw material, which is processed for the production of hard cheeses, Staphylococcus aureus was not detected in 25 to 40% of the samples, on average 45% of the milk samples were contaminated with this pathogen up to 5×102 CFU/ml and from 18 to 30% samples had a staphylococci content of more than 5×102 CFU/ml. In hard cheeses which are realized in the retail network, Staphylococcus aureus was not isolated in an average of 25% of the samples, while approximately 30% of the samples were contaminated with this microorganism in the amount of more than 5×102 CFU/g, which exceeds the requirements of the standard. Two bacteriophages were selected that showed 75.0-80.0% lytic activity against cultures of Staphylococcus aureus from milk and hard cheeses. These bacteriophages were used in the technology of preserving hard Dutch cheese. The technology of Dutch cheese with staphylococcal bacteriophage has been developed to increase its safety during implementation. The use of lytic bacteriophages for the biocontrol of Staphylococcus aureus in rennet cheese makes it possible to almost completely neutralize them in the technology of production. Therefore, the use of lytic bacteriophages to increase the safety of dairy products is an environmentally clean way of restraining the development of pathogenic bacteria, thereby not influencing on the fermentation microflora of the product.