B17 - decay RP Flashcards
what is the purpose of the decay required practical
foods decay when microorganisms release enzymes onto them
what indicator is used in the decay required practical
cresol red
what is the risk assessment for the decay required practical
chemicals are irritants - irritate skin or eyes - wear eye protection, lab coat and gloves
what is the independent variable in the decay required practical
temperature
what is the dependent variable in the decay required practical
the time taken for pH to change colour of indicator
what are the control variables in the decay required practical
volume/concentration of milk and concentration of lipase
identify possible errors in the decay required practical
measuring colour change is subjective and relies on human judgement
using a digital pH probe and data logger could be used to measure the actual pH and would give a continuous reading
what is the method for the decay required practical
- add lipase to a test tube and place in a water bath at 20 degrees
- in another test tube, add milk and 5 drops of cresol red solution and sodium carbonate (to make it alkaline)
- leave it for 5 minutes to allow solutions to reach same temperature
- add lipase to milk and start stopwatch immediately
- stir the mixture continuously and stop the stopwatch when the colour of the solution changes to yellow
- record the time taken
- repeat this for different temperatures of water bath
explain the results of the decay required practical
as decay relies on enzymes, there will be an optimum temperature for decay
the faster the colour changes to yellow, the more quickly the pH decreased (because fatty acids were produced more quickly by lipase)
in high temperatures the colour may not change because the enzymes have denatured
at low temperatures, the enzymes have less kinetic energy so work more slowly