Malic Acid

Product Overview

Malic acid, chemically named 2‑hydroxybutanedioic acid, is a typical hydroxy‑dicarboxylic acid. It gets its name for its wide occurrence in natural fruits and vegetables such as apples and grapes. Containing a chiral carbon atom in its molecule, it is mainly divided into two industrial grades: L‑malic acid and DL‑malic acid. L‑malic acid is the natural biological configuration with excellent biocompatibility; DL‑malic acid is an artificially synthesized racemic mixture. The pure product appears as white crystals or crystalline powder, odorless, with soft and long‑lasting sour taste and refreshing after‑taste, and slight hygroscopicity.

Malic acid is readily soluble in water and ethanol, slightly soluble in acetone, and insoluble in non‑polar organic solvents such as ether and benzene. With both carboxyl and hydroxyl functional groups in its molecular structure, it delivers excellent performance in acidity adjustment, flavour modification, metal chelation, antioxidant synergism, buffering and moisturizing. It can decompose upon heating at high temperatures. Compared with citric acid, malic acid provides milder sourness with longer retention. It serves as a core organic acid raw material in food flavouring, daily‑use chemicals & personal care, pharmaceutical preparations and fine chemical industries.

Basic Parameters

Production Processes

1. Chemical Synthesis Process (Mainstream Industrial Process for DL‑Malic Acid)

Chemical Reaction Equations

Hydration of maleic acid (cis‑butenedioic acid) under high pressure:

Hydration of fumaric acid (trans‑butenedioic acid) under high pressure:

Process Conditions

Reaction temperature: 180‑220 ℃

Reaction pressure: 1.0‑1.8 MPa

Reaction time: 3‑8 h

Raw materials: maleic acid, fumaric acid (maleic acid can also be obtained via hydrolysis of maleic anhydride)

Key Equipment

Corrosion‑resistant lined high‑pressure reactor, concentration kettle, crystallizer, centrifuge and drying equipment.

Complete Refining Process

Upon reaction completion, materials are cooled, and low‑solubility by‑product fumaric acid is removed by filtration. The mother liquor is decolorized with activated carbon, concentrated under reduced pressure and cooled for crystallization. Subsequent centrifugal separation, washing and drying yield finished DL‑malic acid.

2. Biological Fermentation / Bioconversion Process (Main Preparation Route for L‑Malic Acid)

The biological method stereospecifically produces L‑malic acid, including one‑step fermentation, two‑step fermentation and immobilized cell‑enzyme transformation.

2.1 One‑Step Fermentation (Direct Fermentation, mainly laboratory‑scale, not for large‑scale industrialization)

Strains: Aspergillus flavus, Aspergillus oryzae, Aspergillus parasiticus and other moulds

Carbon‑source substrates: glucose, maltose, sucrose, starch and other saccharide raw materials

Principle: Microbial sugar metabolic pathways directly accumulate L‑malic acid.

Simplified overall reaction:

2.2 Two‑Step Fermentation (Mainstream Industrial Route for L‑Malic Acid)

It consists of two sequential fermentation phases employing two types of functional microorganisms:

Step 1: Rhizopus fermentation for fumaric acid production
Strains such as Rhizopus chinensis or Rhizopus arrhizus use glucose as carbon source to produce fumaric acid.

Step 2: Microbial bioconversion of fumaric acid into L‑malic acid
Microorganisms including Pichia membranifaciens, Proteus vulgaris, Bacillus spp. or Sporobolomyces are introduced. Intracellular fumarase catalyses stereospecific hydration of fumaric acid to exclusively form L‑malic acid.

3. Natural Extraction Process (Traditional Process, Largely Phased‑out)

Principle: Extract L‑malic acid from fruit juices naturally rich in malic acid such as apple and grape juice.

Process flow: Fruit juice is boiled, followed by addition of milk of lime to form calcium malate precipitate. Calcium salt precipitate is collected by filtration and acidified with sulfuric acid for double‑decomposition reaction to release free L‑malic acid. Subsequent concentration and crystallization complete refining.

Reaction equations:

4. Cutting‑edge R&D Progress (Not Large‑scale Industrialized, Literature‑reported)

4.1 Metabolically‑engineered Acid‑tolerant Saccharomyces cerevisiae (Research Group led by Liu Long, Jiangnan University)

Through adaptive laboratory evolution, metabolic pathway reconstruction and transporter engineering, acid‑tolerant Saccharomyces cerevisiae is constructed. In a 3‑L fermenter, L‑malic acid titer reaches 232.9 g/L. No extra neutralizer is required during fermentation, which greatly simplifies downstream processing.

4.2 One‑step Fermentation from Biomass (Research Group led by Tian Chaoguang, Tianjin Institute of Industrial Biotechnology, Chinese Academy of Sciences)

Myceliophthora thermophila serves as the chassis strain. Competitive metabolic pathways are knocked out and reducing‑power supply is enhanced. Raw corn cobs act as the sole carbon source. In a 5‑L bioreactor, one‑step fermentation achieves L‑malic acid titer of 157.6 g/L with yield of 0.55 g/g corn cob and product purity of 99%. Titer exceeds 100 g/L in ton‑scale fermenters. This technology can directly utilize agricultural and forestry wastes to cut raw‑material costs.

4.3 D‑Malic Acid Bioconversion Technology

Low‑cost maleic acid (~20 RMB/kg) is used as substrate. Engineered strains realize one‑step bioconversion for D‑malic acid production. In shake‑flask tests, 100% conversion is achieved with 25 g/L substrate; 90% conversion with 50 g/L substrate. It features mild reaction conditions and short cycle, showing good economic potential.

Product Grades

1. Food‑grade Malic Acid

Food‑grade malic acid includes L‑malic acid and DL‑malic acid complying with two separate national standards. The two differ in configuration and shall not be used interchangeably.

Applicable Standards: L‑malic acid complies with GB 1886.40‑2025 National Food Safety Standard - Food Additive L‑Malic Acid; DL‑malic acid complies with GB 25544‑2010 National Food Safety Standard - Food Additive DL‑Malic Acid.

Main Applications: Food processing such as beverages, confectionery, jams, jellies, ice cream, canned foods and compound seasonings, functioning as acidity regulator and flavour improver with certain colour‑protection effect. L‑malic acid is prepared via microbial fermentation / enzymatic transformation; DL‑malic acid is chemically synthesized. Their permitted usage scopes in food differ per national standards.

Core Quality Indicators

Malic acid content (calculated as ): ≥99.0% for L‑malic acid; 99.0%‑100.5% for DL‑malic acid.

Configurational characteristics: Specific optical rotation of L‑malic acid: −1.6°~−2.6°; Specific optical rotation of DL‑malic acid: −0.10°~+0.10°.

Heavy metals and contaminants: Lead (Pb) ≤2.0 mg/kg, total arsenic (As) ≤1.0‑2.0 mg/kg. Strict control over toxic related substances including fumaric acid and maleic acid (cis‑butenedioic acid); test items also include residue on ignition, chlorides, sulfates and clarity of solution.

2. Pharmaceutical‑grade (Pharmacopoeia‑grade) Malic Acid

Applicable Standards: Domestic standards follow Pharmacopoeia of the People's Republic of China for pharmaceutical excipients. Overseas standards include USP (United States Pharmacopeia), BP (British Pharmacopoeia) and EP (European Pharmacopoeia). Both L‑malic acid and DL‑malic acid specifications for pharmaceutical excipients are available.

Main Applications: Pharmaceutical excipient serving as acidifier, pH buffer, antioxidant synergist and solubilizer in oral preparations, topical formulations, mouth‑wash solutions, etc. It is only used as excipient instead of active pharmaceutical ingredient.

Core Quality Indicators

Assay: Content of malic acid (on anhydrous basis) ≥99.0%.

Related substances: Rigorous limits for fumaric acid, maleic acid, individual unknown impurities and total impurities. Maleic acid is a strictly controlled key item.

Other controlled items: Water content, clarity and colour of solution, residue on ignition, heavy metals, arsenic salts, readily oxidizable substances and water‑insoluble matter. Microbial limit test is added in some pharmacopoeia editions.

3. Industrial‑grade Malic Acid

Applicable Standards: No mandatory unified national standard in China; industrial standards or enterprise technical specifications are adopted. Both L‑malic acid and DL‑malic acid configurations are available.

Main Applications: Industrial cleaning agents, metal surface treatment, resin curing agents, plasticizers for synthetic materials, organic‑synthesis intermediates, textile auxiliaries and other chemical‑industry fields. Forbidden for food, pharmaceutical and feed applications.

Core Quality Indicators

Malic acid content: Mainstream specification ≥99.0%; customized specifications available per customer requirements.

Impurity‑control features: Main test items cover appearance, purity, moisture and water‑insoluble matter. Tolerance limits for toxic impurities such as heavy metals, arsenic, maleic acid and fumaric acid are significantly relaxed compared with food‑grade and pharmaceutical‑grade products; no food‑safety‑oriented control is implemented.

4. Feed‑grade Malic Acid

Applicable Standards: No unified national standard in China; industry standards for feed additives or enterprise filed specifications apply. Commercially available products are predominantly L‑malic acid.

Main Applications: Feed additive for ruminants. It modulates ruminal fermentation pathways to reduce methane emission from ruminants, raise propionic‑acid proportion and improve feed conversion ratio. It also adjusts feed acidity and optimizes animal intestinal microenvironment.

Core Quality Indicators

Malic acid content: Typically ≥99.0%.

Impurity control: Limits for heavy metals and arsenic are moderately relaxed versus food‑grade; harmful impurities including fumaric acid and maleic acid must be controlled.

Industrial Chain

Malic acid is a core raw material for fine biochemical industry with well‑developed, closed‑loop supporting industrial chains. Upstream key raw materials include maleic anhydride, fumaric acid, glucose, specialized microbial strains, industrial purified water and auxiliary reagents for decolorization, desalination and precipitation. Downstream sectors cover food processing, biomedicine, daily‑use chemicals & cosmetics, fine chemicals, environmental‑protection auxiliaries and feed processing.

Safety, Storage and Transportation

Malic acid is a low‑hazard, mildly irritating organic weak acid. It is non‑flammable, non‑explosive and non‑corrosive and is not classified as hazardous chemical. It shall be stored and transported as ordinary general‑purpose chemical goods. It features strong hygroscopicity. Powder dust exerts mild irritation on conjunctiva and respiratory mucosa without major safety risks.

Storage Requirements: Store in dedicated dry, cool, ventilated and clean chemical warehouses. Keep packages fully sealed to isolate air and moisture and prevent moisture‑induced caking. Stack separately; avoid co‑storage with strong alkalis and strong oxidants to prevent neutralization and oxidative deterioration. Food‑grade and pharmaceutical‑grade products shall be stored in separate zones to avoid cross‑contamination.

Transportation Requirements: Comply with general‑purpose chemical cargo transportation regulations. Take protective measures against rain, moisture, sunlight exposure and package breakage & leakage; maintain intact sealed packages. Do not transport together with toxic, odorous, corrosive or strongly alkaline goods. For food‑grade products, maintain clean transportation environment to eliminate contamination risks.

Safety Characteristics: Physicochemically stable under sealed ambient‑temperature storage conditions, with high non‑toxicity and biosafety. Only powder dust may mildly irritate mucous membranes; no corrosion or fire‑explosion hazards. Operators shall wear dust‑proof respirators and protective gloves and ensure adequate ventilation at work sites. In case of eye contact, rinse eyes thoroughly with plenty of running water. No major safety hazards exist under proper storage, transportation and operation.

Frequently Asked Questions (FAQ)

Q: What are the core differences between L‑malic acid and DL‑malic acid, and what are the selection criteria?

A: They share nearly identical molecular formula and basic physicochemical properties. The key differences lie in chiral configuration and biological compatibility. L‑malic acid is the natural biological configuration that can be normally metabolized by human bodies without adverse effects. Its superior biocompatibility suits scenarios requiring high safety such as food processing, pharmaceutical preparations and high‑end personal‑care products. DL‑malic acid is artificially synthesized racemic mixture without biological metabolic activity. It is cost‑effective and only applicable to industrial auxiliaries and general synthetic conditions; its applications in certain food scenarios are restricted. They cannot substitute for each other arbitrarily.

Q: How to prevent moisture absorption and caking during malic acid storage?

A: Malic acid is strongly hygroscopic. It rapidly absorbs water vapour from air under high‑humidity conditions, leading to caking and slight purity decline. This is a physical change instead of chemical deterioration. Preventive measures include keeping packages fully sealed without leakage; maintaining low‑humidity, constant‑temperature and well‑ventilated warehouses; minimizing frequent warehouse door opening to reduce humid air convection; no open‑air stacking or rain exposure. Slightly caked material may be reused after drying, sieving and re‑inspection. Severely dampened material can only be used after passing full‑index testing.

Q: What are the differences among industrial‑grade, food‑grade and pharmaceutical‑grade malic acid in China?

A: They have identical core chemical components. Differences reside in impurity‑control stringency, optical‑rotation purity and compliance qualifications. Industrial‑grade products adopt relaxed impurity specifications and are only fit for industrial manufacture; contact with food and human skin is prohibited. Food‑grade products undergo deep decolorization and impurity removal with strict heavy‑metal limits and food‑compliance qualifications for legal food‑processing applications. Pharmaceutical‑grade products adopt high‑optical‑purity L‑configuration with the most stringent impurity limits and highest biosafety for high‑end pharmaceuticals and precision preparations.

China boasts leading malic‑acid industrial technology and production capacity worldwide. Mature processes for both DL‑type chemical synthesis and L‑type bioconversion are mastered with complete upstream‑raw‑material support and large‑scale mass production. Products cover multi‑configuration and multi‑grade requirements and meet high‑end international standards. China acts as a major supply base for domestic food, chemical and pharmaceutical industries as well as one of the world's key producers and exporters of malic acid.