NaCl Spactial Distribution And Staphylococcus Aureus Growth And Models Development In Feta Cheese During The Manufacture And Ripening Process

Feta cheese, a famous white-ripened cheese of Greece, which whole ripening process is finished in brine. In the ripening process, NaCl has an important impact on quality of Feta cheese. According to traditional making procedure, the modified process of Feta cheese was designed with experiment conditions. The ripening process were divided into two stages, stage I was under 16-20℃of 20 days; stage II was under 4℃of 40 days, while both of the brine concentration were 15%. The space distribution of NaCl content was analyzed on day 1, 5,10,15,20,30,40,50 and 60 during the whole ripening process. The geometry cheese can be divided into three layers in vertical direction and twelve measurement locations on each layer. Then NaCl content of each spatial location was measured at regular intervals, and develops a mathematical model of compound function for predicting the NaCl content in cheese, which was composed of power function for stage I and S function for stageⅡ. It has been demonstrated that the model was accurate and feasible through verification. In order to evaluate the impact of NaCl on the growth and survival of pathogen on Feta cheese, Staphylococcus aureus was inoculated into Feta cheese. Under different ripening conditions of four brine concentrations 0%,8%,15% and 20%, two ripening temperatures 4℃and 16℃, the growth curve of Staphylococcus aureus was developed during the ripening process. The Compertz growth models was used to imitate the growth of Staphylococcus aureus during the ripening process under two different temperatures with brine concentration of 15%, which concentration was a traditional and common one used. The both of R2 were larger than 0.99, which showed the models had good fitness for the growth of Staphylococcus aureus.