What affect does the length of cooking time have on the vitamin C content of food?

Prediction

I predict that the longer the length of cooking time is, the lower the vitamin C content will be.

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To keep it a fair test I am only going to have one variable which will be the length of cooking time. I intend to keep everything else constant. So I shall use the same amount of peas, same temperature and volume of water and allow an equal crushing time of each sample.

Equipment needed

* Bunsen burner, tripod, gauze, heat proof mat

* 1 Litre beaker, 600ml beaker, 10cm3 measuring cylinder

* 50ml beaker, 2cm3 syringe, Pasteur pipette

* Stopwatch, 60 frozen peas (5 for each boiling tube), sand, mortar pestal, ice

* 14 boiling tubes, 2 boiling tube holders

* DCPIP (100cm3) 0.01% concentration, 20 ml of Vitamin C standard

* Safety goggles, lab coat

Method

* Gather all equipment

* Set up water bath

* Take a 1L beaker – fill with 500ml of cold water

* Leave to boil – temp 100oC

* Take 10 uncooked peas and place 5 into tube labelled 0 mins

* Place the remains 50 peas into the boiling water

* From the moment they go in start timing.

* At each time interval (2,4,6,8,10mins) take 10 peas and place them into the 2 corresponding boiling tubes (ie. at 2 mins place 5 peas into both tubes marked 2 mins)

* Place complete tubes in ice beaker.

* Once all cooked and cooling take a tube sample, 10cm3 of water and a pinch of sand – place in mortar pestal. Crush for 1 min.

* Next take 2cm3 syringe and fill with DCPIP, put DCPIP in corresponding boiling tube

* Then take the crushed solution, add drop by drop in DCPIP using Pasteur pipette

* Count amount of drops taken to clear the blue coloured DCPIP

* Record results

* Do for all 6 intervals (0,2,4,6,8,10 mins)

* Repeat the experiment

Hypothesis

To reinforce what I have said in my prediction I can say that I know that cooking reduces the amount of vitamin C levels in food.

Safety procedures

Avoid skin or eye contact with DCPIP Wear safety goggles

Wear lab coats When not in use turn Bunsen to an orange flame

Reasons for choice

I am going to use frozen peas as opposed to fresh, raw peas as there is a higher level of vitamin C present. I know this because immediately after harvest 50% of vitamin C may be lost.

I am going to boil the peas as I know that heat disrupts the cell membrane which in turn causes a leakage of Vitamin C. Vitamin C is also water soluble so I know that it can be easily extracted.

I am using six intervals to obtain an accurate set of results which will allow me to see a significant drop in the vitamin C thus proving that the levels of vitamin C do decrease. I shall use a two minute regime as opposed to a one minute regime to ensure I achieve accurate results. I feel that using a one minute time regime would be less accurate as the timings are too close together.

I am going to place the cooked samples in a beaker of ice as I know that enzyme reactions can not occur in very hot or cold surroundings (below 5oC or above 63oC.) I want to ensure that it is a fair test which is why after being cooked I intend to try and stop further reactions taking place.

I am intending to use sand in the preparation of the vitamin C extract as it is an abrasive which will allow me to form the liquid I intend to use. I am using the 10cm3 quantity of water in preparation of the vitamin C extract as I feel that it will be necessary in ensuring I have an adequate amount of solution. 2peas = 1cm3 water.

I am going to use 5 peas for each sample, as peas are all different sizes and by using 5 peas I should have an even sized range for me to test thus making it a fair test.

Secondary source of data

I have used the internet as my secondary source of information. The information I collected explained to me about the levels of vitamin C present in frozen/raw food. It also gave details of how cooking affected these levels.

Testing a standard

I must ensure that I test a standard before I conduct my experiment. This will allow me to determine the Vitamin C content of a known substance. I am going to do this as in a previous experiment we did this and provided a base on which to work on. From here I shall then be able to work out my calculations from the set of results I am going to obtain. I shall use the following equation to do so:

Number of drops of 0.01% VIT C

Vitamin C content = ——————————– * 10 = ….mg/100cm3

Number of drops per sample

Conclusion

I am going to cook an amount of peas using the above method to determine whether the levels of vitamin C decrease when left at different intervals. I shall then test my samples using DCPIP and the calculation above to indicate the vitamin C content of each timed sample.

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