Turbidity Index for the Detection of Heated Milk

This research was undertaken to determine the amounts of precipitate formed in the milk plasma due to mixing of different levels of heated milk with raw milk, and to establish a turbidity index, which will be helpful in detecting the extent of addition of heated milk. Because, presence of whey protein into plasma after filtration add its subsequent coagulation during boiling of the plasma for the turbidity test to give a positive result is an indication of the milk being raw. But, the amount of whey protein drained into plasma upon turbidity test should vary as a function of proportion of heated milk added. The analysis revealed that there was a highly significant difference (p¿0.001) in case of fat, protein and precipitate content of plasma as affected by extent of addition of heated milk. However, no significant difference was found in case of dry matter, pH and acidity of milk. A strong correlation (R2=0.819) was found between the amount of precipitate and proportion of heated milk mixed with raw milk. An index was developed using the turbidity test on the basis of amount of precipitate formed in the milk plasma as a function of extent of the addition of heated milk to raw milk.