Study of the Effects of Seasonal Changes on the Contents of Protein and Non-protein Nitrogen in the Permeates of 6 Cheese Plants Using Ultra filtration Method.

Over the past decade, cheese making by using ultrafiltration technique significantly increaied in our country. The main reason for this success is the higher yield of this system as compared with the classical methods. In this study during " condacted 1382-1383" samples of the permeates of six cheese making plants mashhad, Isfahan, Shiraz, Tabriz, Khorram Abad and Hamedan were takenand the different types of nitrogen non protein and protein nitrogens. were The results showed a significant difference of the ratio of non protein nitrogen to total nitrogen in Khorram Abad, Tabriz and Isfahan plants. These rates were 80.216, 66.323 and 50.162 percent respectively. Other related results showed no significant differences in the permeates of Mashhad, Shiraz and Hamadan plants. no significant difference was observed among the results from Tabriz plant with Mashhad and Hamadan plants. The ratio of the protein nitrogen to total nitrogen in the permeates of different plants showed that the season factor has been important too and in summer 1382, the difference of above factor was significant with the autumn of the same year. Also, nu significant difference was observed between summer of 1382 with winter 1382 and summer of 1383 at the 5% level. In relation to the difference of above index based on production area, it was found that Isfahan factory (plant) had the highest and Khorramabad factory had the lowest means during under investigation the seasons.We observed a significant difference (P< 0.05) between Isfahan factory with Mashhad, Shiraz, Tabriz and Hamedan factoies