Development of turbidity index as field method to detect mixing of heated milk with raw milk
The 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 as a field method in detecting the extent of addition of heated milk. The tests were conducted on five different treatments namely, Milk sample A (100% Heated milk), Milk sample B (75% Heated milk + 25% Raw milk), Milk sample C (50% Heated milk + 50% Raw milk), Milk sample D (25% Heated milk + 75% Raw milk) and Milk sample E (100% Raw milk). Samples were examined by chemical analysis including fat content, protein content, dry matter content, ash content, pH, acidity, turbidity test, and precipitation content of plasma. There was a highly significant difference (p<0.001) in case of fat, protein and precipitate contents of plasma as affected by extent of addition of heated milk. A statistically significant difference (p<0.05) was also found for ash content. On the other hand, no significant difference was found in case of dry matter content, pH and acidity of milk. A strong correlation (R2=0.819) was observed between the amount of precipitate and proportion of heated milk mixed with raw milk. A field method was devised on the basis of extent of turbidity, which was in fact amount of precipitate formed in the milk plasma as a function of extent of the addition of heated milk to raw milk.
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