Research Project

Determination of Vitamin C Content in Fruit Juices

 and commercial fruit juices via (acid base) redox titration.

Literature Review

Vitamin C is an essential supplement that is required for humans to keep their overall health at desired state. Humans (and other isolated species) do not have the ability to synthesise Vitamin C vis-à-vis other species, making it an obligation for them to intake it.  For many centuries, the condition scurvy was infamously known to baffle humankind. Specifically for seafaring men and explorers, this mysterious ailment inflicted aching pain and suffering, making each journey a gamble with death. It was not until 1930, that scientists were able to determine the substance for curing scurvy, and thus referring it to “Vitamin C” (American Chemical Society, 2019).

Benefits of Vitamin C include protection against immune system inadequacy, prenatal health problems, eye disease, skin wrinkling and also cardiovascular disease. Looking at the studies, one can derive that Vitamin C does indeed provide numerous benefits to the body. For example, a contemporary study published in Seminars in Preventive and Alternative Medicine looked and analysed over 100 studies over 10 years and concluded that Vitamin C did indeed include many benefits, such as the ones mentioned above.

Vitamin C is also required for the biosynthesis of collagen, certain neurotransmitters and L-carnitine. In 2018, the University of Maryland conducted a study and concluded that Vitamin C intake can reduce the pressure that’s built up on the bones in a condition known as osteoarthritis. This could potentially prevent a person from being diagnosed with arthritis. (University of Maryland Medical Center, 2018).

It can also assist in protein metabolism. (Y, 2019) Vitamin C also provides the essential nutrients that help maintain the connective tissue and bones in our bodies. It ensures the optimal functionality of several enzymes, by activating certain liver-detoxifying systems. Vitamin C also acts as an antioxidant, as it reacts directly with free radicals in the aqueous state. This is important as it protects cellular function and as a result, this function can aid in fighting bacterial infections and increase the rate of regeneration of burns or wounds. (Mason, 2007)

The chemical name for Vitamin C is ascorbic acid, and primarily exists in 2 forms- L-ascorbic acid and D-ascorbic acid. The L variety can be found naturally, i.e in fruits or vegetables but can also be found in its synthetic form (such as supplements), both versions being interchangeable with their benefits. The D variety carries indistinguishable antioxidant properties but not the vitamin C content of L-ascorbic acid. In addition, the D form is not used in forms of supplement. Although they are both chemically Vitamin C, the nutrient packed properties differ amongst them, affecting their bioavailability. (SmartyPants Vitamins, 2019) 

A deficiency in Vitamin C can ultimately be the leading factor to scurvy. Subclinical deficiencies can lead to signs of inadequate wound healing and ulceration.  Early signs of deficiencies are not too fatal, and may range from general weakness, shortness of breath, lethargy, and possibly aching of the limbs. As time progresses, other prominent conditions may become evident, such as petechiae after the application of a sphygmomanometer (blood pressure monitor), perifollicular haemorrhages, bleeding and swollen gums, pallor/anaemia (unhealthy pale appearance after a result of prolonged bleeding). Unfortunately, groups that are at high risk with these conditions include smokers, patients with diabetes and the elderly. (Mason, 2007)

Some people automatically assume that if a drink is advertised as ‘natural’ it will contain as many nutrients and vitamins as the source it has been derived from. However,  one must keep in mind companies will favour satisfaction of their target more, and thus meaning that commercial fruit juices (and sometimes the natural fruit juices) will contain flavourings  and chemicals that will enhance the flavour and preserve the liquids for longer. Also, commercial fruit juices react with oxygen, which proves that most of the nutrients are lost due to oxidation. The method that will be used is a titration method, where Vitamin C in fruit juices were titrated against aqueous sodium dichlorophenolindophenol with starch as an indicator.

Aim:

• The aim of the experiment is to analyse the different concentrations of Vitamin C in fresh and commercial fruit juices. Comparison of the results will give one the idea of the differences in the amounts of Vitamin C.

– Fruits used: Orange, lime and grapefruit.

Hypothesis:

• I acknowledge that fresh fruit juices will have a higher concentration of Vitamin C compared to the commercial fruit juices. Also, I predict that amongst all the fresh fruits, orange will have an abundance of Vitamin C compared to the other fruits, as it is notable to have a high amount of Vitamin C.

Apparatus:

• Fresh fruit juices (orange, lime and grapefruit)
• Commercial fruit juice (orange, lime and grapefruit)
• 10ml of ascorbic acid
• DCPIP solution (2,6-dichlorophenolindophenol)
• Deionised/ Distilled Water
• 25ml of 0.5% Oxalic acid
• 250ml Beaker
• 250ml Conical Flask
• Knife
• 25ml measuring cylinder
• Titration kit (Boss, clamp + stand, funnel and tile)
• Filter paper and Buchner Funnel
• Pipetman 1000 with the pippete tips

Method:

• Initially, a solution of ascorbic acid was produced. This was done by weighing 0.2g of the ascorbic acid solution into 1 Litre of deionised/distilled water. The concentration of Ascorbic acid could also be calculated by using the following two formulas.

 Concentration = Mole ÷ Volume ∴  Conc = (Mass/Mr) ÷  Volume

• Shortly after, a solution of DCPIP was made by weighing 0.24g of it into 1 Litre of deionised water. The exact same formulas were utilised to work out the concentration of DCPIP.

• 25ml of 0.5% oxalic acid was thoroughly measured and transferred into a 250ml conical flask. Using a pipetman, the 10ml of ascorbic acid was added into the conical flask.

• Using the titration apparatus, several trial titres were observed. This was carried out by the accurate titration of ascorbic solution against the DCPIP solution. At one specific point (endpoint), the colour change of DCPIP to pink was seen as it reacted fully with the ascorbic acid. Therefore, the volume was recorded of the DCPIP used was recorded.

• The liquids of the natural fruits were extracted using the knife to cut them in half. Squeezing them and using a Buchner funnel and filter ensured that the seeds and skin of the fruits remained separate from the juices. The juice was obtained with no impurities.

• A portion of one of the fruit juices (10ml to be exact) was pipetted into the conical flask that had contained oxalic acid, which was made prior to this step. An additional 10ml of deionised water was also added.

• Repeats were conducted thrice with each fruit. At the end, the average result was calculated after obtaining each result for each fruit.

Calculations needed towards the latter stages:

       Mole of vitamin C =