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Malic acid is a succinic acid composed of 2-hydroxy dicarboxylic acid in which one of the hydrogens attached to carbon is replaced by a hydroxyl group. The molecular formula for malic acid is C4H6O5. It functions as a food acidity regulator as well as a fundamental metabolite. The salts in the malic acid are called malates and it is this salt that contributes to the sour taste in fruits.
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Key Terms: Maleic acid, succinic acid, fumaric acid, decarboxylation, malates, malic acid, acid
Malic Acid Chemical Properties
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C4H6O5 Malic Acid Structural Formula
Properties of Malic Acid
Key properties of Malic Acid are:
| Particulars | Details |
| Density | 1.609 g⋅cm |
| Appearance | Colourless |
| Molecular Formula | C4H6O5 |
| Melting Point | 130 °C |
| Solubility in water | 558 g/L (at 20 °C) |
| Molar Mass | 134.087 g·mol−1 |
| Acidity | pKa1 = 3.40; pKa2 = 5.20 |
Also Read: Sulfuric Acid (H2SO4)
Malic Acid Uses
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Malic acid, with global consumption of 55,000 tonnes in 2006, is primarily used in the beverage (51%) and food (42%), industries, and it accounts for 10% of the food and beverage industry as an acidulant. Learn more about the uses of malic acid in the pointers chalked down below:
- Malic acid is used to rejuvenate and improve skin conditions in the production of skincare products.
- Malic acid is produced during metabolic cycles in the cells of plants, animals, and humans. The compound provides energy to cells as well as carbon skeletons for the formation of amino acids. Every day, the human body produces and degrades a large amount of Malic acid.
- Malic acid is used to make medical products such as throat lozenges, cough syrups, effervescent powdered preparations, toothpaste, and mouthwash.
- Malic acid is present in food preparation as a flavour enhancer for confectionaries, beverages, fruit preparations and preserves, desserts, and bakery products.
- Green apples' sourness is enhanced by malic acid. It is found in grapes and imparts a tart flavour to the wine. Malic acid is a source of extreme tartness when added to food products. In sour sweets, it is combined with or substituted for less sour citric acid.
Also Read: Aspartic Acid
Production of Malic Acid
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The dicarboxylic acid malic acid synthesised as part of the tricarboxylic acid cycle can be produced in excess by certain microorganisms. Although malic acid is produced in smaller quantities than citric acid, it has industrial applications as an acidulant in foods and pharmaceuticals, among other things.
The production of this organic acid from byproducts of industrial bioprocessing has only recently been investigated. Microbes have been shown to be capable of producing malic acid from coproducts generated during biofuel production. Malic acid has been shown to be synthesised by Aspergillus species on thin stillage, a byproduct of corn-based ethanol production, and crude glycerol, a byproduct of biodiesel production.
Read More: Acids, Bases and Salts
Furthermore, the fungus Ustilago trichophora has been shown to produce malic acid from glycerol. In terms of bacteria, it has been demonstrated that a strain of the thermophilic actinobacteria thermobifida fusca can produce malic acid from cellulose and treated lignocellulosic biomass. Using agricultural biomass converted to syngas or bio-oil as a substrate for fungal bioconversion is an alternative method of producing malic acid.
Also Read: Importance of Ph
Things To Remember
- Maleic acid is a dicarboxylic acid, or molecule with two carboxyl groups, which is an organic compound. It is butenedioic acid’s cis isomer.
- Malic acid is a chemical that can be found in a variety of fruits and wines. It is occasionally used to treat dry mouth, fibromyalgia, fatigue, and skin conditions.
- Malates are the salts of it. All living organisms produce it, and it contributes to the sour taste of fruits. Because of this property, it is frequently used as an artificial additive.
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Malate is an important component of biochemistry. Malate is a source of CO2 in the Calvin cycle during the C4 carbon fixation process.
Also Read: Nucleic Acids
Sample Questions
Ques: Malic acid is found in _____. (2 marks)
Milk
Apples
Lemons
Vinegar
Ans: Apples.
Malic acid is primarily found in apples. The word ‘malic’ is derived from the Latin word ‘malum’ meaning apple.
| Food Item | Acids Found |
| Milk | Lactic Acid |
| Apple | Malic Acid |
| Lemon | Citric Acid |
| Vinegar | Acetic Acid |
Ques: Is malic acid the same as maleic acid? (2 marks)
Ans: Malic acid and maleic acid are two distinguished dicarboxylic acids. Malic acid is an organic compound with the chemical formula C4H6O5 while maleic acid is an organic compound having the chemical formula HO2CCH=CHCO2H. The only difference between malic acid and maleic acid is that the former is a saturated dicarboxylic acid, while the latter is an unsaturated dicarboxylic acid.
Ques: Discuss the role of malic acid in biochemistry. (5 marks)
Ans: It is extremely important in biochemistry. It is a source of CO2 in the Calvin cycle as part of the C4 carbon fixation process. (S)-malate is an intermediate in the acid cycle.
It is also produced by the carboxylation of phosphoenolpyruvate within plant leaf guard cells. It's also a double anion. It frequently accompanies potassium cations during solute uptake into guard cells. In order to maintain the cell's electrical balance. The accumulation of those solutes within the guard cell lowers the solute potential. Furthermore, it allows water to enter the cell and promotes stomatal aperture.
Ques: What is referred to as decarboxylation of malic acid in biochemistry? (4 marks)
Ans: The conversion of malic acid to lactic acid has been proven to be a direct decarboxylation action carried out by a single enzyme. These bacteria have the ability to metabolise citric acid in addition to decarboxylation of malic acid. Citric acid is only found in trace amounts in grapes and wine unless it is added. Although citric acid metabolism is not always visible in commercial winemaking, it can have a significant impact on the formation of diacetyl and thus on the flavour of the wine.
Ques: Discuss some of the applications of malic acid. (3 marks)
Ans: Malic acid is commonly used in the food sector to sweeten or tartan fruit and vegetable juices, carbonated soft beverages, jams, wines, and candies. It's also used to modify pH in cosmetics including self-tanning cream, cleaning form, and facial cream. Metal cleaning, textile finishing, water treatment, fabric dying, and as a monomer for the manufacture of poly(-l-malic acid) are all possibilities.
Ques: What is malolactic fermentation? (2 marks)
Ans: A large number of lactic acid bacteria convert malic acid to lactic acid, which is commercially significant in the wine industry. This type of fermentation is commonly referred to as malolactic fermentation.
Ques: Explain the conversion of fumaric acid to malic acid. (3 marks)
Ans: For the bioconversion of fumaric acid to L-malic acid, bacterial strains from the genus Nocardia were used. Under various conditions, the ability of the bacterial strain Nocardia sp. CCM 4837/A to produce L-malic acid from fumaric acid was investigated. The ideal temperature for bioconversion was around 37 °C, and the ideal pH was around 8.0. To boost enzyme activity, an inductor (fumarate salt) was added to the fermentation medium. The presence of the detergent Triton X-100 (0.02-0.1 percent) in the reaction mixture significantly increased fumarase enzyme activity.
Ques: What is the respiration rate of malic acid? (3 marks)
Ans: When malic acid is used as the respiratory substrate, the amount of CO2 released exceeds the amount of oxygen consumed. Malic acid has a respiratory quotient of 1.33. Respiratory quotients are the ratios of carbon dioxide released to oxygen consumed during the complete oxidation of a substrate. The reaction for complete oxidation of a compound in respiration is: CxHyOz + (x + y/4 – z/2) O2 → x CO2 + (y/2) H2O
Ques: How is malic acid manufactured? (3 marks)
Ans: Maleic anhydride is double hydrated to produce racemic malic acid in the laboratory. In the year 2000, the United States' production capacity was 5000 tonnes per year. The chiral resolution of the racemic mixture can be used to separate the enantiomers. S-Malic acid is produced through the fermentation of fumaric acid. The pyrone coumalic acid is produced by self-condensation of malic acid in the presence of fuming sulfuric acid.
Ques. What kind of test is used to determine whether a solution is a base or an acid? (3 marks)
Ans. A simple chemical test known as a litmus test is used to determine whether a solution is a base or an acid. We can identify with the use of litmus paper whether a solution is basic, neutral, or acidic.
In the solution, if the red litmus turns blue color then it is basic in nature, if the blue litmus paper turns into red color then the solution is said to be acidic in nature, and if the color does not change then it is said to be neutral in nature. By the use of a pH scale, we can also determine the solution. The solution is neutral if the pH is 7, if the pH is less than 7, it is said to be acidic, and the solution is basic if the pH is more than 7.
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