Rate of Decay

• Method to see the effect of temperature on the rate of decay of fresh milk by measuring the time taken for the pH to change.

  1. Place two test tubes in a hot water bath.
  2. Put 5ml lipase into 1 test tube.
  3. In the other test tube, put in 5ml milk, 5ml sodium carbonate, and 5 drops of cresol red. Also add a thermometer.
  4. Put 2ml of the lipase from TT1 into the other test tube and stir it whilst timing.
  5. Stop timing when the solution turns yellow.
  6. Record results.
• Variables & Limitations


  Independent - Temperature

  Dependent - Time taken for the solution to turn yellow.

  Control(s) - Volume of milk, volume of lipase, volume of sodium carbonate, volume of cresol red, type of milk.

  Limitation(s) - Deciding when the milk turns yellow (so, share results and calculate means)
• Conclusion


  In low temperatures, the time taken to become yellow is longer due to particles having less kinetic energy and therefore moving slower and so, breaking down lipids slower.

  At 40°c, the time taken to become yellow is less due to this being the closest to natural body temperature - so the lipase works fastest to break down the lipids into glycerol and fatty acids.

  At 50°c, the time taken to become yellow increases due to the enzymes denaturing as their active site has changed shape and no longer fits the substrate.