1) Measure 24.27ml(25g) of lactose free and whole milk into separate test tubes(50ml). Mix 3.225g of
milk powder with 21.775ml of distilled water, based on the 88.1% water composition in milk.
2) Heat 50°C for 5 min. in water bath.
3) Centrifuge at 3500rpm for 10 min. All fat will float on top.
4) Remove the fat layer using a spatula
5) At 40°C, add 1ml of 10% acetic acid in increments of 0.5ml while stirring using the vortex machine. Casein precipitates.
6) Centrifuge for 8 min. at 3500 rpm.
7) Decant the supernatant(whey) to another test tube, and then to each, add 0.22 g of CaCO3 .
8) Heat in water bath at 60°C, then let it cool. Lactalbumins and lactoglobulins precipitates.
9) Add 15ml of ethanol 95% to each test tube with stirring, then heat to 60°C for 4 min. Layers of different densities and solutes separate.
10) Centrifuge for 5 min. at 3500 rpm
11) Transfer to a pre-weighed test tube.
12) Place in heater at 60°C for 2 hours.
13) Continue heating at 80°C for 20 hours.
14) Freeze dry with vacuum for 24 hours.
Lactose/fat free milk has the greatest percentage carbohydrate with an average of 5.379%. On the other hand, the experimental results showed that whole milk and powdered milk statistically have the same percentage lactose with averages of 4.556% and 4.884% respectively.
The lactose content of the milk has been fully preserved when the milk is dried and turned into powder. However, unlike powdered milk which can stay fresh for a long period of time at room temperature, the bacteria present in whole milk that has not been pasteurized will convert the lactose present in milk into lactic acid gradually, making the milk sour.
This project compares the percentage lactose between whole milk and powdered milk while using lactose/fat free milk as control.
Science Fair Project done By Zhuo (Matthew) Sun