Effect of species, breeds, season and stage of lactation on urea content of milk and its variation during processing of milk and milk products

Urea levels in milk of different species and its breeds; effect of season, stage of lactation and its relationship with fat, SNF and milk yield was investigated. Effect of various processing treatments on changes in urea content of milk and milk products were evaluated. Pooled samples of buffalo (Murrah) and cows (Tharparkar, Sahiwal and Karan Fries) were collected and urea content was estimated over a period of ten days. Average urea content in milk of Murrah, Tharparkar, Sahiwal and Karan Fries was found to be 41.38, 40.85, 38.2and 25.53mg/100 ml, respectively. For both the species studied urea content in milk was influenced by season and it was significantly higher in winter and lower in summer and intermediate in rainy season. Milk urea content was observed to be significantly lower in colostrum of Sahiwal and Murrah; however it was maximum during 2nd and 3rd month of lactation in comparison to normal milk. During stage of lactation, the study revealed negative relationship between urea with fat, SNF content and positive relationship with milk yield. Processing treatments of milk significantly affected the urea level. During Pasteurization (63 degrees C/30 min) and boiling (2 to 5 min) of milk, urea level was increased, whereas during sterilization (121 degrees C/15 min), urea level decreased. The average urea content in dahi, khoa, skim milk powder (roller dried), paneer and paneer whey was found to be 18.78, 184.60, 408, 1.67 and 40.67 mg/100 g, respectively.