DL-Malic acid
[CAS# 6915-15-7]

Identification

• Classification: Chemical reagent >> Organic reagent >> Fatty acid
• Name: DL-Malic acid
• Synonyms: DL-Hydroxysuccinic acid; DL-2-Hydroxybutanedioic acid; DL-Apple acid
• Molecular Formula: C₄H₆O₅
• Molecular Weight: 134.09
• CAS Registry Number: 6915-15-7 (617-48-1)
• EC Number: 230-022-8
• SMILES: C(C(C(=O)O)O)C(=O)O

Properties

• Solubility: 0.5 M (water, 20 °C)
• Density: 1.609 g/mL
• Melting point: 130 °C
• Boiling point: 150 °C (decomp.)
• Flash point: 203 °C

Safety Data

• Hazard Symbols: GHS07 Warning
• Risk Statements: H315-H319
• Safety Statements: P264-P264+P265-P280-P302+P352-P305+P351+P338-P321-P332+P317-P337+P317-P362+P364

Hazard Classification

Hazard	Class	Category Code	Hazard Statement
Eye irritation	Eye Irrit.	2	H319
Skin irritation	Skin Irrit.	2	H315
Serious eye damage	Eye Dam.	1	H318
Acute toxicity	Acute Tox.	4	H302
Specific target organ toxicity - single exposure	STOT SE	3	H335
Acute toxicity	Acute Tox.	4	H303
Skin sensitization	Skin Sens.	1	H317

Discovery and Applications

Malic acid, a naturally occurring organic compound, was first isolated in 1785 by Swedish chemist Carl Wilhelm Scheele from unripe apples. The name malic is derived from the Latin word malum, meaning apple, reflecting its natural source. Scheele‘s discovery marked a significant advancement in organic chemistry, as malic acid became one of the earliest identified plant acids. Its chemical structure was later elucidated in the 19th century, revealing that malic acid is a dicarboxylic acid with two functional carboxyl groups. This compound plays a crucial role in the citric acid cycle (Krebs cycle), which is vital for cellular respiration in all aerobic organisms. Today, malic acid is recognized for its versatile applications in food, medicine, and cosmetics due to its tart flavor and beneficial properties.

Malic acid is extensively used in the food industry as an acidulant to enhance flavor and preserve the freshness of various products. Its naturally tart taste is ideal for balancing sweetness and adding a tangy flavor to beverages, candies, and dairy products. In soft drinks and fruit juices, malic acid provides a longer-lasting sour taste compared to citric acid. It also acts as a pH regulator and preservative, helping to extend the shelf life of processed foods. Additionally, malic acid is used in confectionery to create sour candies and in baked goods to improve dough strength and texture.

Malic acid is incorporated into nutritional supplements due to its role in the citric acid cycle, where it helps produce energy by aiding in the conversion of carbohydrates, fats, and proteins into carbon dioxide and water. This property makes malic acid a valuable component in energy-boosting supplements. It is also included in formulations for managing conditions like fibromyalgia and chronic fatigue syndrome (CFS), as it may help alleviate muscle fatigue and improve stamina.

In cosmetics, malic acid serves as an alpha-hydroxy acid (AHA), known for its exfoliating properties. It is commonly used in skincare products to promote the shedding of dead skin cells, enhance skin texture, and improve overall complexion. Malic acid helps in reducing the appearance of fine lines, wrinkles, and hyperpigmentation, making it a key ingredient in anti-aging treatments. Its ability to maintain skin hydration and stimulate collagen production further supports its use in moisturizers and peels.

Malic acid has therapeutic applications in oral health care. It is included in toothpaste and mouthwashes for its ability to stimulate saliva production, which helps maintain oral hygiene and prevent dry mouth. Additionally, malic acid's mild antimicrobial properties contribute to its use in treating bad breath and oral infections. Its role in the citric acid cycle also supports its use in managing metabolic acidosis, a condition where the body produces excessive acid or when the kidneys are not removing enough acid from the body.

In agriculture, malic acid is used to adjust soil pH, making it more conducive to plant growth. It can act as a chelating agent, helping to make essential minerals more available to plants. In environmental applications, malic acid helps in metal cleaning and as a natural descaling agent due to its ability to dissolve mineral deposits.

Malic acid is employed in various industrial processes. It is used in the production of biodegradable polymers and plasticizers. It also serves as a buffering agent in pharmaceutical formulations, helping to stabilize the pH and enhance the solubility of active ingredients.

References

2024. The role of citric acid and enzyme activities on sourness in pineapple fruit after low temperature storage. Horticulture, Environment, and Biotechnology, 65(6).
DOI: 10.1007/s13580-024-00660-0

1998. Mechanism of the Protective Effect of Sodium Malate on Cisplatin-Induced Toxicity in Mice. Biological and Pharmaceutical Bulletin, 21(2).
DOI: 10.1248/bpb.21.121

1984. Kinetic mechanism in the direction of oxidative decarboxylation for NAD-malic enzyme from Ascaris suum. Biochemistry, 23(22).
DOI: 10.1021/bi00318a011