Effects Of Testing Temperature And Water Activity Of Cheddar Cheese On Dielectric Properties

The physicochemical and dielectric property changes of Cheddar cheeses which were stored at 4℃ and 8℃were studied for the ripening period 0d-90d.The dielectric property variation with water activity was studied within the water activity range 0.295-0.959.The results showed that:1)The moisture content of the cheese samples stored at 4 ℃ was higher than that of 8℃,whereas,the water activity of all cheese samples was lower than that of 8℃during the ripening time(0d-90d).2)The pH value of the cheese samples showed a tendency that decrease first and then rise for the samples both at 4 ℃and 8 ℃.3)There was no evident difference in ripening degree index for both 4℃ storage cheese and 8℃ samples before the ripening time 40d.But after 40d,the ripening degree index of cheese sample stored at 8 ℃ was obviously higher that of 4 ℃.4)For the same storage temperature of cheese samples,the dielectric constant ε’and dielectric loss factor ε" all varied with ripening degree index,the variance analysis showed that the ripening period influence was more significant than testing temperature influence(P<0.05).5)The dielectric constant ε’ and the dielectric loss factor ε" both increased with the increase of water activity and isothermal temperature.When the isothermal temperature was 20℃ and the water activity was less than 0.87,the increase extent of the dielectric constant ε’ and the dielectric loss factor ε" were comparatively small,and when water activity was larger than 0.87,their increase amplitudes were obvious.When the isothermal temperature was 40 ℃ and the water activity was less than 0.87,the increase amplitude of the dielectric constant ε’ and the dielectric loss factor ε"were comparatively large,and when water activity was larger than 0.87,their increase amplitudes were not obvious.