Chapter 2 The nutrients in food
Read our general notes on Risk Assessment
I am having real trouble finding a method on investigating the effect of cooking on the vitamin C content in cabbage. Could you give me quick run-down on the procedure? I want to do it using DCPIP and already know how to standardize the solution.
Igloo says
Following your standardisation of the DCPIP dye solution:
1 Weigh out a certain mass of cabbage leaves(a).
2 Use a liquidiser together with some dilute phosphoric acid(b) and blend the mixture.
3 Transfer the mixture through a muslin filter(c) to a large measuring cylinder. Rinse out the liquidiser with more phosphoric acid and transfer the washings to the measuring cylinder(d).
4 Make up to a chosen mark with more phosphoric acid, and ensure thorough mixing by stirring with a long glass rod or by other means.
5 Titrate portions of this solution with your DCPIP solution until consistent readings are obtained.
6 Repeat the procedure, but on this occasion boil the cabbage leaves in water for a given length of time before returning to step 2 above. It might also be useful to deal with the cooking water in the same way as you did with the cooked leaves.
7 Eventually you should be able to find out how much vitamin C remained in the cooked leaves, how much was leached out into the cooking water and how much was destroyed in the process.
Points to note (referred to in the text above)
(a) You will need to decide on a suitable mass of leaves.
(b) Vitamin C is reasonably stable in acid conditions, hence the use of phosphoric acid. Why isn’t phosphoric acid used for the boiling process in step 6?
(c) Why is it necessary to filter the mixture, and why not use filter paper?
(d) Why do you think that a measuring cylinder will suffice in these experiments, rather than using a volumetric flask?
Other suggestions
Take your leaves from one particular part of the cabbage for all the experiments above, but maybe repeat the entire procedure using a different part of the cabbage or even using a different variety.
A titration using the phosphoric acid alone is worth carrying out too. This serves as a “blank”. Why do you think that it is a good idea to do this?
Always carry out a risk assessment before starting any practical work, and check with your teacher.
Risk assessment
Before attempting any practical work based on the advice and suggestions on this website, you must do the following. Identify any hazards, assess the risks from these hazards, and then decide appropriate control measures to reduce the risks. You must have these approved by those in authority in your school or college laboratory. Do not rely on what is said on this website.
For further guidance see our tutorial on Risk Assessment.
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updated: 04 March 2005
