Investigation Into the effect of pectinase on apple juice extraction.

Andrew McNally/ 28th December 2002/Science Access.

Aim

To investigate how the enzyme pectinase affects the volume of juice produced by apples.

Hypothesis

I suggest the larger the amount of pectinase the higher the volume of juice that is produced. This is because there is more active sites for the break down of the substrate (pectin) meaning the reaction will be take place faster and therefore more juice will be produced in the given time.

Method

Apparatus:

Boiling Tube (x2)
Small Beakers (x2)
Large Beaker
Filter Paper (x2)
Blender
Apples (x2)
Test Tube Rack
Pectinase
Balance
Bunsen Burner
Tripod
Heat Proof Mat
Gauze
Thermometer

Procedure:

Start by setting up two filter funnels using the dampened filter paper and place these into the two boiling tubes. Take the apples and cut them into small cubes then place these together with 80cm3 of distilled water into the blender and blend for approximately 1 minute. Place the contents into the large beaker and whilst stirring heat to a temperature of 80˚C for two minutes. Now place the large beaker into a cold-water bath and cool the contents to about 20˚C, stirring continuously. Then take the cooled apple and separate into two beakers, each beaker should contain exactly 60g of apple. Weigh out two different amounts of pectinase; add these to the separate beakers of apple and stir for two minutes. Transfer the contents of each beaker into the two filter funnels and record the volume of juice collected after 30 minutes using the measuring cylinder.

Conclusion

Although there are a number of anomalies and inaccuracies within the results there is a trend and this trend proves my hypothesis. The results do show that as the amount of enzyme is increased so to is the volume of apple juice.

Interpretation

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Conclusion

Interpretation

We are aware that within the apple cell the juice is mostly contained within the vacuole and the cytoplasm. The cell membrane (cell wall) that holds this in place is a complex matrix structure of cellulose and pectin with the cells themselves being held to one another by more pectin. By blending the apple we have already broken open a great many number of cell walls leading to the apple being more liquid in appearance then when we started. However there is still a high volume of liquid still contained within the cell wall. By adding pectinase to the solution we have introduced an enzyme, which is specifically suited to the breaking down of the cell wall, and thus higher volumes of juice were produced. The way the enzyme works is the same as with all other enzymes.

Pectin is a protein made up of a long chain of amino acids. Once in a chain, hydrogen, disulphide and ionic bonds form at the ‘R Groups’ creating a unique three-dimensional structure and surface. This 3D shape is specific to each protein and therefore (not counting competitive inhibitors) enzymes are only suited to and are specific to their corresponding negative impression or substrate. Pectin offers an active site for the substrate (in this case apple cell wall) to bind to, this forms what is called the enzyme- substrate complex. At this point the enzyme can break the pectin into its constituent parts known as products. Once broken down the pectin products no longer ‘fit’ the active site and are ejected by the enzyme, which is, then again ready to react with more pectin. With the apple it means the apple cell wall has been broken down and therefore the juice can be released.

Evaluation

Although our experiments where conducted with the up most of care I am positive there was some room for improvement. There were a number of sources for error the biggest of which being the number of times the experiment was repeated. On only repeating the experiment once we have left our results open to question. Should one of our two results have been incorrect then without a third result to back up one or the other we are powerless to decide which is correct and which is anomalous.

Due to things beyond our control (a power cut) we did not have the use of water baths in order to keep our samples at the required 80˚c. Again, although we conducted the experiments with care I am sure there was some irregularity with the heating. Should the temperature have risen to above 80˚c I am unsure as to the impact this would have had on cell wall breakdown and therefore final juice extraction.

We were also required to cool the apple sample to a stable 20˚c before adding the pectinase. Should the temperature have been higher in one experiment to another then surely substrate-enzyme reactions would happen more frequently increasing juice yield and disfiguring our results.