Effect of storage time and type of fruits on mass percentage of citric acid available

How does the mass percentage of citric acid available from citrus fruits (lemon, lime, oranges) depends on the storage time and the types of citrus fruits and fresh lime taken?

Citrus fruits are a regular part of my diet and during this Covid-19 a lot of health experts had advised to consume more of the citrus fruits as they used to build our immunity. Therefore, I had made it a habit to prepare these juices and store it in the refrigerator so I could drink it whenever I want. However, I observed that the flavor of the juice is changing over time which made me curious, “Why does the flavour of the juice change over time ?” and “What are the sources for citric acid ?” . I wanted to understand why this change in flavour took place; is this also affecting the nutritional value. I also investigate whether this change in nutritional value is the same for all citrus fruits or varies among fruits. This would help me understand what is the best citrus fruit which is  safest to store for longer periods of time and which has least change in flavour, proving the best fruit juice to be consumed. As I had so many questions about this topic I decided to do some research to help me understand this, I came across an article which discusses the key ingredient in citrus fruits, which is citric acid itself and the article explained how there are different amounts of citric acid in the different fruits. I made the connections to the concept learned during Chemistry class like the concept of titration as an analytical procedure for quantitative estimations of acids and bases. I realized I wanted to connect something I learned from class and to understand how to apply it to real life applications and planned to use it in an experiment.

Citric acid: is a weak organic acid that has the molecular formula C6H8O7. It occurs naturally in citrus fruits. It belongs to the functional group carboxylic acid group. It is naturally found in citrus fruits like lemon, lime, orange, grapefruits, pomelos and is used widely in industry as an acidifier, as a flavoring and chelating agent. Citric is soluble in Water and dissolves in absolute (anhydrous) ethanol. Citric acid is a weak organic acid present naturally in living cells. Citric acid is an alpha-hydroxy acid with a three carbon skeleton, which has three carboxylic acid groups (COOH), and one hydroxyl group (OH). It is used as a cleaning agent which is used on a daily basis in the kitchen. It is used to add a sour taste to soft drinks and other food items, in shampoos, food coloring. It is a natural preservative. It is used to remove the chalky deposit from evaporators, kettles, boilers.

• Word Equation: Citric Acid Sodium Hydroxide → Sodium Citrate Water
• Chemical Equation: C₆H₈O₇ (aq) + 3NaOH (aq) →  C₆H₅O₇Na₃ (aq)+ 3H₂O₄ (aq)

When you look at the structure of citric acid, you can see that there are three carboxylic acid groups, which mean that there need to three NaOH for each of the atoms to react with each one of them

Titration is a qualitative analysis technique that can be used to calculate the concentration of an unknown solution with the use of a solution with a known concentration. The process is usually carried out by gradually adding a standard solution ( solution of known concentration) of titration titrant with a  burette essentially a long, graduated measuring tube with a stopcock and a delivery tube at its lower end until the color change at the end point. The change in color occurs due to use of indicator, usual phenolphthalein³

The citric acid percentage content of each fruit (lemon lime, orange will does not depend on storage time.

The citric acid percentage content of each fruit (lemon lime, orange will does not depend on storage time.

• Chemicals were used in a manner that avoids wastage.
• All chemicals were disposed off into a chemical waste bin to avoid interaction with the environment.
• Unused chemicals were returned to the laboratory, safely.

Minimal amount of chemicals were used to conduct trials, keeping in mind the economic concerns and environmental effects.

Preparing 100 cm³ of 0.1 mol.dm^-3 NaOH solution

Molar The solution made has to be a volume of 100 cm³ and concentration 0.1 mol dm-³  -3.

Thus, the number of moles can be calculated from the formula:

Number of moles (n) = molar concentration ( C)  X     volume in dm³ (V ) = \((0.010 X\frac{100}{1000})\) = 0.001

Mass of NaOH to be used

= number of moles X Molar Mass= 0.001 X 39.997

= 0.039997 g

= 0.04 g (rounded of two decimal places)

• For lemon, squeeze it to remove the juice into a beaker. For lime and lemon use a machine to remove the juice and pour into a beaker.
• Filtrate the juice using a funnel with filter pare, empty the filtrate in another beaker.
• First rinse the pipette with some distilled  water.
• Take 20.00 ±0.05 cm³ of the juice from the filtrate using a pipette into a 100cm³ flask
• Juice should be diluted by adding distilled water until the mark reaches 100 cm³, start it using a glass rod.
• Pouring the solution in a fresh beaker and use a pipette to take 20.00 ±0.05 cm³ again
• Pour this into a conical flask, then add a few drops of phenolphthalein indicator

• Take initial reading of NaOH  from the burette (two decimal places)
• Drop NaOH into the juice slowly, drop by drop until the color changes pink
• Check and the record the reading on the burette
• Calculate amount of NaOH (initial reading -  final reading)
• Calculate the moles of citric acid reading to the NaOH, use this information to calculate the mass of citric acid.
• Using this information calculate the percentage of mass
• The data was collected in 3 trials and the same procedure was repeated for lemon juice, orange juice.
• All steps were repeated for 5 days, three trials and the same procedure for all three fruits.

For Day 1, Trial-1

Initial burette reading = 0.00 ± 0.05 cm³

Final burette reading = 7.20 ± 0.05 cm³

Difference in burette reading = Final – Initial = (7.20 ± 0.05 cm³) – (0.00 ± 0.05 cm³) = 7.20 ± 0.10 cm³

As the data collected is of acid base titration, the reading that is repeated (concordant or precise reading) has been chosen as an average instead of calculating arithmetic average to procure more accurate data.

For example, for Day-1, the three trial values for difference in burette readings are 7.20 ± 0.05 cm³, 7.00 ± 0.05 cm³ and 7.00 ± 0.05 cm³ respectively. So, the reading 7.00 ± 0.05 cm³ repeats itself twice and is thus the precise or concordant reading. Thus, the average reading is taken as 7.00 ± 0.05 cm³

For Day-1, Standard deviation (SD) = \(\frac{(7.20-7.00 )^2+(7.00-7.00)^2 +(7.00-7.00)^2}{3} = 0.12\)