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Studies On Vitamin C Degradation in Fruit.

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Studies On Vitamin C Degradation in Fruit. Introduction and background. Vitamin C is of vital significance in the metabolism of most organisms, however interestingly the primates including monkeys and man, guinea pigs and the Indian fruit bat are the only known higher species to be susceptible to the lack of the vitamin However micro-organisms do not form this chemical. In other words ascorbic acid is not synthesised within the cells of these species. Normally the liver is the site of ascorbic acid formation, but in birds, reptiles and amphibians the site of synthesis is the kidneys. The chemical is widely distributed in brain tissue at around 150mg/Kg, in the lens of the eye 250mg/Kg and in the adrenals 400mg/Kg. Tissue levels are highest at birth and greatly reduce in old age. A large percentage in any foodstuff is lost on storage or cooking. It is also known that addition of sodium bicarbonate to maintain the green colour of vegetable during cooking can destroy 70-90% of Vitamin C content The deficiency disease associated with this vitamin is known as scurvy. This is characterised by problems associated with connective tissues, including failure of normal bone formation in children, poor wound healing and increased capillary fragility leading to haemorrhage (especially in the skin, together with effects on teeth and gums. ...read more.


if possible repeat these readings to reduce random errors. 7. The titration should now be repeated using the standard ascorbic acid solution referred to as the standard. Record the titre as st. As DCPIP turns water a pink colour by itself an increase in accuracy can be obtained by counting the drops to make the same colour change as is observed in the original titration. This is known as a blank test. 5 cm3 of distilled water were placed in a boiling tube and DCPIP gradually added from the burette until a pink colouration was obtained The volume of DCPIP used call BL. 8 For those groups using a coloured fruit such as strawberry or blackcurrant a modification is advised. Add 1ml of trichlormethane to the boiling tube before titration commences. The end point now is when a pink permanent colour is seen in the organic phase. 9 Samples of fruit juice will be stored in the refrigerator labelled for subsequent use. A new titration has to be carried out in the subsequent analysis. A 30 cm3 diluted sample will be placed in a boiling tube, tightly bunged, labeled with the fruit and experimenter and left refrigerated for one week, around 5 degrees Celsius. ...read more.


Special care has to be taken to avoid cross contamination with the apparatus. Any conical flask that is used for the titration must be thoroughly washed with water, distilled water and dried. In between replicates some groups would not have achieved this ideal. In the burette when adding the DCPIP solution care must be taken that the level drains down to where it can be read. Whilst working on the experiment time is allowing oxidation of the L Ascorbic acid by molecular oxygen. Thus inevitable underestimation will arise on that score. It is unlikely that the vitamin C content of fruits degrades when ripe at similar rates across the plant kingdom. Some fruits such as apples for example degrade at a much slower rate than strawberries say. A hard cuticle prevents immediate aerial oxidation. When the fruit is crushed and filtered as in this experiment, the vitamin C should degrade at a more or less constant rate in all the specimens and to that extent this experiment is a well designed one. Another problem with some groups is that after one week they may not have re-standardised their vitamin C solution with fresh DCPIP. It is important to do this if in fact the tablets are manufactured with some degree of variation in them 1 1 ...read more.

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