Determining the Amount of Citric Acid within Fruit Juices by Titration
Phoebe Johnston
North Quincy High School
November 20, 2017
Titration is a very useful tool within the world of chemistry, and a popular one due to its many uses during a plethora of experiments. Acid-Base titration according to Chemistry LibreTexts (2016) is the method of using a substance with a known molarity, called a reagent or titrant, that will be slowly dripped through a burette and a stopcock, which is a long flask and a stopping device that only lets a certain amount of liquid through at a time. The substance it is dripped into is one with an unknown molarity, called a analyte or a firearm, which is made into a solution and combined with a small amount of indicator that will change color when enough of the reagent has entered the analyte for it to be at a balanced pH. The indicator ranges from usually methyl orange in titration with a strong acid and a weak base, and phenolphthalein for a weak acids and a strong base. Either can be used if both are strong or weak, but phenolphthalein tends to have a faster reaction closer to the endpoint of the titration. Titration reactions accompany a titration curve, which when graphed creates an s-shaped line that determines when the pH reaches an equivalence point, at a pH of 7. There are also mathematical equations to determine the pH of the unknown substance and equivalence points. According to SoftSchools (2011) this equation is (M)acid x (V)acid = (M)base x (V)base, when M stands for molarity of the acid or base and V stands for volume of the acid or base. This equation can find the concentration of an acidic substance in a titration experiment. Titration is used in medical fields to determine contents of different chemicals in blood or urine, in the food industry to test water contents and fat contents, and in the scientific industry to do many different chemical and biological experiments due to its versatile range of concentrations it can calculate.
Citric Acid is a weak organic tricarboxylic acid that is found naturally within fruits especially citrus fruits and throughout the citric acid cycle, also known as the Krebs cycle. It has a formula of C₆H₈O₇. Citric acid gives citrus fruit a sour taste, due to its acidity. It’s hard to say exactly why there is so much citric acid in citrus fruits, but according to an article by Kimball(1991) it most likely comes from the Krebs cycle, where it migrates through the membranes of organelles and into the juice vacuole of the citrus fruit before all of the citric acid can continue through the cycle. Possibly, this citric acid is there to protect the fruit from bacteria. But there has not been enough research into this to say for sure. But, the bigger role citric acid plays is within the Krebs cycle, a cycle that is most important to cellular respiration. According to Openstax (2015) the Krebs cycle is a closed loop cycle of mostly soluble enzymes except for dehydrogenase within the mitochondria. “The eight steps of the cycle are a series of redox, dehydration, hydration, and decarboxylation reactions that produce two carbon dioxide molecules, one GTP/ATP, and reduced forms of NADH and FADH2.” (Openstax 2015). The citric acid cycle produces very little ATP but does produce the carriers that will carry out the last steps of cellular respiration to produce much more ATP. Citric acid has many uses, however, both biochemical and otherwise. It is a great natural preservative found in citrus fruits but also in some soft drinks. It’s also an environmentally safe cleaning agent and acts like antioxidant. Citric acid is very weak and it doesn’t taste very well on its own or in lemons and limes, but it does play a very important role in preserving citrus fruits and contributing to cellular respiration, which occurs in almost all living things.
Titration is used in many experiments, within both professional and educational realms. Titration is even used in the biomolecular industry, away from chemistry. In this experiment done by Xingding, Manjunatha, and Sivaraman (2011) using snake venom from Echis carinatus to treat an African disease. But, there was a lot of titration in this project. According to these bio molecular scientists, these venoms were first in a powder and then they were made into a solution and centrifuged until are the particles are homogenous. Then they create a compound from the original venom. The compound created and the solution from the original mixture are titrated together to find the properties of the venom’s proteins within Echis carinatus venom and another snake’s venom. This process seemed to work exceedingly well and even beat out the chromatographic ways of how the venom’s properties are usually discovered. “So far this strategy has been successfully used to target the protein(s) for a given compound from the biological mixtures E. carinatus and B.fasciatus venoms in our lab(13)….The most critical step in this protocol is the first round of ITC assay; in other words, titrating the compound against the original biomedical mixture.” (Xingding, et al, 2011). It is important to the topics of this research papers because it shows the importance of titration as a calculation and one of its uses within a field other than chemistry. And it shows that titration must be done with solutions and can be done with acids and bases.
One of the largest presences of citric acid exists in the food industry, where citric acid is used within sodas and other products as a preserving agent and flavoring agent. But a problem arises within some of the forms of packaging acidic foods and beverages, specifically ceramic packaging. Ceramic packaging isn’t as prevalent in everyday consumption, but some more expensive drinks and vinegars are packaged ceramically. However according to chemists Dong, Lu, Liu, Tang, and Wang (2014) many of the glazes used on these ceramic containers are improperly formulated and inappropriately fired which leads to small amounts of toxic chemicals such as lead, cadmium, and others could leak into the acidic contents of the bottle as the acids, even as weak as citric acid, deteriorate the inner glaze of the ceramic product. This could pose a health risk to consumers of these products. In this experiment, the chemists performed Long-term extraction experiments…on glazed tile specimens with 4 and 10% (v/v) acetic acid, 1% (w/v) citric acid, and 1% (v/v) lactic acid solution in three temperature conditions (20, 40, and 60°C)…” (Dong, et al, 2014) to determine the effects of the different acidic pH levels at different storing temperatures to see how they would affect the levels of toxic chemicals entering the liquids. The results showed that at most temperatures the amount of toxic chemicals that were extracted by the acids had a linear dependence on the time the liquids were within the packaging and the rate of extraction increased with temperature and decreased with pH. This relates to the topic of this paper topic because of the obvious use of citric acid, but also because it shows that even as a weak acid citric acid still has a pH of 2.2 and can be somewhat corrosive. Therefore, it is important to know amounts of citric acid within different liquids including fruit juices, and acid base titration can work with a weak acid and a strong base.
Citric acid is an acid that’s extremely close knit to the biological process of cellular respiration. This also means that it’s a useful tool for other biological and biotechnological reasons. According to Ciriminna, Meneguzzo, Delisi, and Pagliaro (2017) The production and global supply of citric acid is actually rather large. “Global supply of citric acid in the course of the last two decades rose from less than 0.5 to more than 2 million tonnes becoming the single largest chemical obtained via biomass fermentation and the most widely employed organic acid.” (Ciriminna, et al, 2017). This weak acid is being used so much because it’s a fairly useful as a preservative, flavourant, emulsifier, and buffing agent that can be used in many different industries including food and pharmaceutical as well as nutraceutical, which would be considered the nutrient supplement industry. Through the critical review of these scientific journalists, it can be concluded that a good amount of the success of citric acid can be contributed to its role in the beverage industry as a sour flavoring or preservant as well as in the fermentation industry, where it was and still is used as a fermentation industry because of its acidic properties. Citric acid is processed in big plants and isolated into two forms, anhydrous and monohydrate. But it often makes a lot of byproducts. This interesting process of fermentation and other processes among citric acid relate to the topics within this paper because it is important to note the relevance of citric acid and in how certain amounts it’s very important to the biological world as well as the chemical world. It has a fair amount of uses and is flourishing currently as a chemical.
Citric acid is a weak acid, and in the food industry, it is considered nothing but a safe to eat additive that gives foods a sharp tangy taste and can act as a preserving agent. But citric acid is important within citrus fruits and and our bodies because of the Krebs cycle, which is important to cellular respiration in both animals and plants. However, taking citric acid is not healthy unless supplied by a doctor as an antacid. According to Multum inc.(2010) “Overdose symptoms may include muscle cramps or twitching, slow heart rate, and seizure (convulsions).” ( Multum 2010) which can be very dangerous. This is why it’s important to measure how much citric acid is within fruit juices, of course consuming fruit juice alone every once and awhile won’t harm anyone, but with certain medications or in certain amounts a day it could damage a person’s health. Acid base titration is the best suited method of determining the concentrates of citric acid because although a weak acid, citric acid is of course an acid and it can be neutralized with base. Both are very integral parts of science because of their varied uses, but in completely different ways.
Bibliography:
Ciriminna, R., Meneguzzo, F., Delisi, R., & Pagliaro, M. (2017). Citric acid: emerging applications of key biotechnology industrial product. Chemistry Central Journal, 11(1). Retrieved from http://libraries.state.ma.us/login?gwurl=http://link.galegroup.com/apps/doc/A484655719/SCIC?u=mlin_s_thomas&xid=8ef00b53
Citric Acid. (n.d.). Retrieved November 15, 2017, from https://www.sciencedaily.com/terms/citric_acid.htm
Dong, Z., Lu, L., Liu, Z., Tang, Y., & Wang, J. (2014). Migration of toxic metals from ceramic food packaging materials into acid food simulants. Mathematical Problems in Engineering. Retrieved from http://libraries.state.ma.us/login?gwurl=http://link.galegroup.com/apps/doc/A425456773/SCIC?u=mlin_s_thomas&xid=b315dd5d
Kimball, D. (1991, January 01). Acids in Citrus Juices. Retrieved November 15, 2017, from https://link.springer.com/chapter/10.1007/978-94-011-3700-3_3
L. (2016, October 22). Acid-Base Titrations. Retrieved November 15, 2017, from https://chem.libretexts.org/Demonstrations_and_Experiments/Lab_Techniques/Titration/Acid-Base_Titrations
Openstax. (n.d.). Oxidation of Pyruvate and the Citric Acid Cycle. Retrieved November 15, 2017, from http://cnx.org/contents/185cbf87-c72e-48f5-b51e-f14f21b5eabd@9.85.
The citric acid cycle. (n.d.). Retrieved November 15, 2017, from https://www.khanacademy.org/test-prep/mcat/biomolecules/krebs-citric-acid-cycle-and-oxidative-phosphorylation/a/the-citric-acid-cycle-2
University of Wisconsin Hospitals and Clinics Authority. (n.d.). Health Information. Retrieved November 15, 2017, from https://www.uwhealth.org/health/topic/multum/poly-citra-k-crystals/d00439a1.html
Xingding, Z. Manjunatha, R. Sivaraman, J.(2011). Application of isothermal titration calorimetry and column chromatography for identification of biomolecular targets. Nature Protocols, vol. 6, no.2, 2011, p. 158+. Science in Context. Retrieved November 15, 2017 from libraries.state.ma.us/login?gwurl=http://link.galegr is oup.com/apps/doc/A249058176/SCIC?u=mlin_s_thomas&xid=82052e5c
Statement of Accountability:
I, Phoebe Johnston, wrote this paper myself and properly cited any quotations or information that was not my own. I further acknowledge that I did not copy this paper in whole or in part from any source on the internet or from published works.I understand that if this statement is found to be false, I will be penalized.