MALIC ACID

MALIC ACID

CAS No. : 6915-15-7
EC No. : 230-022-8

Synonyms:
2-Hydroxybutanedioic acid; Hydroxybutanedioic acid; 2-Hydroxysuccinic acid; (L/D)-Malic acid; (±)-Malic acid; (S/R)-Hydroxybutanedioic acid; Malate; malonic acid; maleic acid; Butanol; Butyraldehyde; Crotonaldehyde; Sodium malate; malic acid; DL-malic acid; 6915-15-7; 2-Hydroxybutanedioic acid; 2-Hydroxysuccinic acid; 617-48-1; malate; Butanedioic acid, hydroxy-; hydroxysuccinic acid; Kyselina jablecna; Deoxytetraric acid; hydroxybutanedioic acid; Pomalus acid; Malic acid, DL-; Musashi-no-Ringosan; alpha-Hydroxysuccinic acid; Hydroxybutandisaeure; dl-Hydroxybutanedioic acid; Caswell No. 537; Monohydroxybernsteinsaeure; Succinic acid, hydroxy-; R,S(+-)-Malic acid; 2-Hydroxyethane-1,2-dicarboxylic acid; Kyselina jablecna [Czech]; FDA 2018; (+-)-Malic acid; DL-2-hydroxybutanedioic acid; FEMA No. 2655; FEMA Number 2655; Kyselina hydroxybutandiova [Czech]; Malic acid [NF]; EPA Pesticide Chemical Code 051101; EINECS 210-514-9; EINECS 230-022-8; NSC 25941; (-)-Malic acid; (+-)-Hydroxysuccinic acid; butanedioic acid, 2-hydroxy-; BUTANEDIOIC ACID, HYDROXY-, (S)-; MLS000084707; CHEBI:6650; (+/-)-2-Hydroxysuccinic acid; (+-)-1-Hydroxy-1,2-ethanedicarboxylic acid; Hydroxybutanedioic acid, (+-)-; NSC25941; Malic acid (NF); Malic acid, L-; (+/-)-HYDROXYSUCCINIC ACID; Hydroxysuccinate; L-(-)-MalicAcid; Butanedioic acid, 2-hydroxy-, (2S)-; DL-Malate; Hydroxybutanedioate; DL-Apple Acid; DSSTox_CID_7640; DL-Malic acid, 99+%; (R)-Hydroxybutanedioic acid; (S)-Hydroxybutanedioic acid; Hydroxy Succinic Acid; R-Malic acid; Malicacid; Malicum acidum; Poly(malate); Malate homopolymer; Poly (L-malate); CAS-6915-15-7; Malic acid L-(-)-form; DL-hydroxysuccinic acid; Kyselina hydroxybutandiova; Aepfelsaeure; Deoxytetrarate; NSC 9232; NSC-9232; a-Hydroxysuccinate; R,SMalate; R,SMalic acid; H2mal; Hydroxybutanedioic acid homopolymer; 2-Hydroxysuccinate; R,S-Malic acid; Racemic malic acid; R,S-Malate; alpha-Hydroxysuccinate; .+-.-Malic acid; a-Hydroxysuccinic acid; PubChem20057; (+/-)-Malic acid; Opera_ID_805; 2-hydroxyl-succinic acid; DL-Malic acid, 99%; MALIC ACID,(DL); 2-Hydroxydicarboxylic acid; SCHEMBL856; 2-hydroxy-butanedioic acid; EC 210-514-9; EC 230-022-8; Malic acid-, (L-form)-; ACMC-1B8G6; DL-Malic acid, >=99%; HYOSCYAMINEHYDROBROMIDE; Oprea1_130558; Oprea1_624131; KSC353M3D; DL-HYDROXYSUCOINIC ACID; Butanedioic acid, (.+-.)-; DL(+/-)-MALIC ACID; INS NO.296; 2-HYDROXY-SUCCINIC ACID; DL-HYROXYBUTANEDIOIC ACID; CHEMBL1455497; DTXSID0027640; BDBM92495; CTK2F3631; INS NO. 296; INS-296; DL-Malic acid 6915-15-7; DL-Malic acid, FCC, >=99%; 2-Hydroxyethane-1,2-dicarboxylate; DL-Malic acid, analytical standard; ACN-S004262; HY-Y1311; 2-Hydroxybutanedioic acid; Hydroxybutanedioic acid; 2-Hydroxysuccinic acid; (L/D)-Malic acid; (±)-Malic acid; (S/R)-Hydroxybutanedioic acid; Malate; malonic acid; maleic acid; Butanol; Butyraldehyde; Crotonaldehyde; Sodium malate; malic acid; DL-malic acid; 6915-15-7; 2-Hydroxybutanedioic acid; 2-Hydroxysuccinic acid; 617-48-1; malate; Butanedioic acid, hydroxy-; hydroxysuccinic acid; Kyselina jablecna; Deoxytetraric acid; hydroxybutanedioic acid; Pomalus acid; Malic acid, DL-; Musashi-no-Ringosan; alpha-Hydroxysuccinic acid; Hydroxybutandisaeure; dl-Hydroxybutanedioic acid; Caswell No. 537; Monohydroxybernsteinsaeure; Succinic acid, hydroxy-; STR03457; Tox21_201536; Tox21_300372; ANW-43712; s9001; STL283959; AKOS000120085; AKOS017278471; (+/-)-HYDROXYBUTANEDIOIC ACID; AM81418; CCG-266122; DB12751; LS-2394; MCULE-5852208511; Butanedioic acid, hydroxy-, homopolymer; DL-Malic acid, ReagentPlus(R), 99%; DL-Malic acid, >=98% (capillary GC); DL-Malic acid, ReagentPlus(R), >=99%; DL-Malic acid, USP, 99.0-100.5%; CS-0017784; E-296; DL-Malic acid, SAJ first grade, >=99.0%; DL-Malic acid, Vetec(TM) reagent grade, 98%; Malic acid, meets USP/NF testing specifications; 4-ethoxyphenyltrans-4-propylcyclohexanecarboxylate; Malic acid, United States Pharmacopeia (USP) Reference Standard; Malic acid, Pharmaceutical Secondary Standard; Certified Reference Material

Malic Acid

Malic acid is an organic compound with the molecular formula C4H6O5. It is a dicarboxylic acid that is made by all living organisms, contributes to the sour taste of fruits, and is used as a food additive. Malic acid has two stereoisomeric forms (L- and D-enantiomers), though only the L-isomer exists naturally. The salts and esters of malic acid are known as malates. The malate anion is an intermediate in the citric acid cycle.

Etymology
The word 'malic' is derived from Latin 'mālum', meaning 'apple'. It is also the name of the genus Malus, which includes all apples and crabapples; and the origin of other taxonomic classifications such as Maloideae, Malinae, and Maleae. This derivation is also seen in the traditional German name for malic acid, 'Äpfelsäure' meaning 'apple acid' as well as in modern Greek, 'mēlicon oxy' (Μηλικόν οξύ), after the original European discovery of apples in modern-day Kazakhstan 2350 years ago by Alexander the Great's expeditionary foray into Asia.[citation needed]

Biochemistry
L-Malic acid is the naturally occurring form, whereas a mixture of L- and D-malic acid is produced synthetically.
D-Malic acid
Malate plays an important role in biochemistry. In the C4 carbon fixation process, malate is a source of CO2 in the Calvin cycle. In the citric acid cycle, (S)-malate is an intermediate, formed by the addition of an -OH group on the si face of fumarate. It can also be formed from pyruvate via anaplerotic reactions.

Malate is also synthesized by the carboxylation of phosphoenolpyruvate in the guard cells of plant leaves. Malate, as a double anion, often accompanies potassium cations during the uptake of solutes into the guard cells in order to maintain electrical balance in the cell. The accumulation of these solutes within the guard cell decreases the solute potential, allowing water to enter the cell and promote aperture of the stomata.

In food
Malic acid was first isolated from apple juice by Carl Wilhelm Scheele in 1785.[4] Antoine Lavoisier in 1787 proposed the name acide malique, which is derived from the Latin word for apple, mālum—as is its genus name Malus.[5][6] In German it is named Äpfelsäure (or Apfelsäure) after plural or singular of the fruit apple, but the salt(s) Malat(e). Malic acid is the main acid in many fruits, including apricots, blackberries, blueberries, cherries, grapes, mirabelles, peaches, pears, plums, and quince[7] and is present in lower concentrations in other fruits, such as citrus.[8] It contributes to the sourness of unripe apples. Sour apples contain high proportions of the acid. It is present in grapes and in most wines with concentrations sometimes as high as 5 g/l.[9] It confers a tart taste to wine; the amount decreases with increasing fruit ripeness. The taste of malic acid is very clear and pure in rhubarb, a plant for which it is the primary flavor. It is also a component of some artificial vinegar flavors, such as "salt and vinegar" flavored potato chips.

In citrus, fruits produced in organic farming contain higher levels of malic acid than fruits produced in conventional agriculture.[8]
The process of malolactic fermentation converts malic acid to much milder lactic acid. Malic acid occurs naturally in all fruits and many vegetables, and is generated in fruit metabolism.

Malic acid is a chemical found in certain fruits and wines. It is sometimes used as medicine.
Malic acid is used most commonly for dry mouth. It is also used for fibromyalgia, fatigue, and skin conditions, but there is no good scientific evidence to support these other uses.

In foods, malic acid is used as a flavoring agent to give food a tart taste.
In manufacturing, malic acid is used to adjust the acidity of cosmetics.

How does it work?
Malic acid is involved in the Krebs cycle. This is a process the body uses to make energy. Malic acid is sour and acidic. This helps to clear away dead skin cells when applied to the skin. Its sourness also helps to make more saliva to help with dry mouth.

Uses & Effectiveness?
Possibly Effective for
Dry mouth. Using a mouth spray containing a malic acid seems to improve symptoms of dry mouth better than using a saline mouth spray.
Insufficient Evidence for
Acne. Early research shows that applying an alpha hydroxy acid cream containing malic acid helps reduce signs of acne in some people.
Fibromyalgia. Taking malic acid in combination with magnesium seems to reduce pain and tenderness caused by fibromyalgia.
Fatigue.
Warts.
Scaly, itchy skin (psoriasis).
Aging skin.
Other conditions.
More evidence is needed to rate the effectiveness of malic acid for these uses.

Malic acid is a substance found naturally in apples and pears. It's considered an alpha-hydroxy acid, a class of natural acids commonly used in skin-care products. Also sold in dietary supplement form, malic acid is said to offer a variety of benefits.

Health Benefits
Malic acid is found in fruits and vegetables and is produced naturally in the body when carbohydrates are converted into energy. While some research suggests that malic acid supplements may help people with certain conditions, high-quality clinical trials are needed.
There's some evidence that malic acid supplements may offer these benefits:

Skin-Care Benefits
When applied to the skin, malic acid is said to reduce signs of aging, remove dead skin cells, aid in the treatment of acne, and promote skin hydration.
A number of early studies published in the 1990s and early 2000s indicate that malic acid may be beneficial when applied to the skin. In tests on animals and human cells, the studies' authors found that malic acid may help increase collagen production and reverse sun-induced signs of skin aging.

More recent research on topically applied malic acid includes a small study published in the Journal of Drugs in Dermatology in 2013.1 For the study, researchers assigned people with melasma (a common disorder marked by patches of abnormally dark skin) to a skin-care regimen that included the use of topical vitamin C and malic acid. At an average follow-up of 26 months, the regimen was found to be an effective short-term treatment for melasma.

Physical Performance
Malic acid is also used to boost sports performance when taken in supplement form. It is sometimes combined with creatine supplements in order to improve the body's absorption of creatine. Proponents claim that malic acid can promote energy production, increase exercise endurance, and help fight off muscle fatigue.

For a study published in Acta Physiologica Hungarica in 2015, researchers investigated the effectiveness of a creatine-malate supplement in sprinters and long-distance runners.2 After six weeks of supplementation combined with physical training, there was a significant increase in the physical performance in sprinters, measured by peak power, total work, body composition, and elevated growth hormone levels. In long-distance runners, there was a significant increase in distance covered.

Kidney Stones
Malic acid is a precursor to citrate, a substance believed to prevent calcium from binding with other substances in urine that form kidney stones. Citrate may also prevent crystals from getting bigger by preventing them from sticking together.

According to a preliminary laboratory study published in 2014, malic acid consumption may increase urine pH and citrate levels, making stone formation less likely. The study authors concluded that malic acid supplementation may be useful for the conservative treatment of calcium kidney stones.
In a 2016 review, scientists suggested that given the high malic acid content in pears, future research should explore whether a diet supplemented with pears and low in meat and sodium may reduce stone formation.4

Fibromyalgia
A pilot study published in the Journal of Rheumatology in 1995 found that taking malic acid in combination with magnesium helped alleviate pain and tenderness in people with fibromyalgia.5
For the study, researchers assigned 24 people with fibromyalgia to treatment with either a placebo or a combination of malic acid and magnesium. After six months, those treated with the malic acid/magnesium combination showed a significant improvement in pain and tenderness. However, there's a lack of more recent research on malic acid's effectiveness as a fibromyalgia treatment.

Dry Mouth
The use of a one percent oral malic acid spray has been explored as a treatment for dry mouth. A study published in Depression and Anxiety, for instance, evaluated a one percent malic acid spray compared to a placebo in people with dry mouth resulting from antidepressant use.6 After two weeks of using the sprays when needed, those using the malic acid spray had improved dry mouth symptoms and increased saliva flow rates.

Possible Side Effects
Due to a lack of research, little is known about the safety of long-term or regular use of malic acid supplements. However, there's some concern that intake of malic acid may trigger certain side effects such as headaches, diarrhea, nausea, and allergic reactions.

Although malic acid is generally considered safe when applied to the skin in the recommended amount, some people may experience irritation, itching, redness, and other side effects. It's a good idea to patch test new products.
In addition, alpha-hydroxy acids are known to increase your skin's sensitivity to sunlight.7 Therefore, it's important to use sunscreen in combination with skin-care products containing any type of alpha-hydroxy acid.
Keep in mind that malic acid shouldn't be used as a substitute for standard care. Self-treating a condition and avoiding or delaying standard care may have serious consequences.

Dosage and Preparation
There is no standard dose of malic acid that is recommended. Various doses have been used with adults in studies to investigate the treatment of different conditions.
For example, for fibromyalgia, a product called Super Malic (malic acid 1200 mg and magnesium hydroxide 300 mg) was taken twice daily for six months.

For acne, a cream containing malic acid and arginine glycolate was applied twice daily for 60 days. And lastly, for dry mouth, a mouth spray containing 1 percent malic acid, 10 percent xylitol, and 0.05 percent fluoride was used up to eight times daily for two weeks.
The appropriate dose for you may depend on how you are using the supplement, your age, gender, and medical history. Speak to your healthcare provider for personalized advice.

What to Look For
Malic acid is found naturally in fruits including apricots, blackberries, blueberries, cherries, grapes, peaches, pears, and plums. Malic acid is also found in some citrus fruits.
In food, malic acid may be used to acidify or flavor foods or prevent food discoloration. It may also be used with other ingredients in cosmetics.

Using malic acid as part of your skin care routine may help with concerns such as pigmentation, acne, or skin aging. But keep in mind that it's a good idea to patch test when using new products and to avoid the eye area.
If you choose to take a malic acid supplement, the National Institutes of Health (NIH) offers tips to consumers. The organization recommends that you look for a Supplement Facts label on the product. This label will contain vital information including the amount of active ingredients per serving, and other added ingredients.

Lastly, the organization suggests that you look for a product that contains a seal of approval from a third party organization that provides quality testing. These organizations include U.S. Pharmacopeia, ConsumerLab.com, and NSF International. A seal of approval from one of these organizations does not guarantee the product's safety or effectiveness but it does provide assurance that the product was properly manufactured, contains the ingredients listed on the label, and does not contain harmful levels of contaminants.

Malic acid, when added to food products, is denoted by E number E296. It is sometimes used with or in place of the less sour citric acid in sour sweets. These sweets are sometimes labeled with a warning stating that excessive consumption can cause irritation of the mouth. It is approved for use as a food additive in the EU,[12] US[13] and Australia and New Zealand[14] (where it is listed by its INS number 296).
Malic acid provides 10 kJ (2.39 kilocalories) of energy per gram during digestion.

Production and main reactions
Racemic malic acid is produced industrially by the double hydration of maleic anhydride. In 2000, American production capacity was 5000 tons per year. Both enantiomers may be separated by chiral resolution of the racemic mixture, and the (S)- enantiomer may be specifically obtained by fermentation of fumaric acid.
Self-condensation of malic acid with fuming sulfuric acid gives the pyrone coumalic acid

Coumalic Acid Synthesis
Malic acid was important in the discovery of the Walden inversion and the Walden cycle, in which (−)-malic acid first is converted into (+)-chlorosuccinic acid by action of phosphorus pentachloride. Wet silver oxide then converts the chlorine compound to (+)-malic acid, which then reacts with PCl5 to the (−)-chlorosuccinic acid. The cycle is completed when silver oxide takes this compound back to (−)-malic acid.
Malic acid or cis-butenedioic acid is an organic compound that is a dicarboxylic acid, a molecule with two carboxyl groups. Its chemical formula is HO2CCH=CHCO2H orC4H4O4. Malic acid is the cis-isomer of butenedioic acid, whereas fumaric acid is the trans-isomer. It is mainly used as a precursor to fumaric acid, and relative to its parent maleic anhydride, Malic acid has few applications.

Physical properties
Malic acid has a heat of combustion of -1,355 kJ/mol.,[4] 22.7 kJ/mol higher than that of fumaric acid. Malic acid is more soluble in water than fumaric acid. The melting point of Malic acid (135 °C) is also much lower than that of fumaric acid (287 °C). Both properties of Malic acid can be explained on account of the intramolecular hydrogen bonding[5] that takes place in Malic acid at the expense of intermolecular interactions, and that are not possible in fumaric acid for geometric reasons.

Production and industrial applications
In industry, Malic acid is derived by hydrolysis of maleic anhydride, the latter being produced by oxidation of benzene or butane.
Malic acid is an industrial raw material for the production of glyoxylic acid by ozonolysis.[7]
Malic acid may be used to form acid addition salts with drugs to make them more stable, such as indacaterol maleate.
Malic acid is also used as an adhesion promoter for different substrates, such as nylon and zinc coated metals e.g galvanized steel, in methyl methacrylate based adhesives.

Isomerization to fumaric acid
The major industrial use of Malic acid is its conversion to fumaric acid. This conversion, an isomerization, is catalysed by a variety of reagents, such as mineral acids and thiourea. Again, the large difference in water solubility makes fumaric acid purification easy.

The isomerization is a popular topic in schools. Malic acid and fumaric acid do not spontaneously interconvert because rotation around a carbon carbon double bond is not energetically favourable. However, conversion of the cis isomer into the trans isomer is possible by photolysis in the presence of a small amount of bromine.[8] Light converts elemental bromine into a bromine radical, which attacks the alkene in a radical addition reaction to a bromo-alkane radical; and now single bond rotation is possible. The bromine radicals recombine and fumaric acid is formed. In another method (used as a classroom demonstration), Malic acid is transformed into fumaric acid through the process of heating the Malic acid in hydrochloric acid solution. Reversible addition (of H+) leads to free rotation about the central C-C bond and formation of the more stable and less soluble fumaric acid.
Some bacteria produce the enzyme maleate isomerase, which is used by bacteria in nicotinate metabolism. This enzyme catalyses isomerization between fumarate and maleate.

Other reactions
Although not practised commercially, Malic acid can be converted into maleic anhydride by dehydration, to malic acid by hydration, and to succinic acid by hydrogenation (ethanol / palladium on carbon).[9] It reacts with thionyl chloride or phosphorus pentachloride to give the Malic acid chloride (it is not possible to isolate the mono acid chloride). Malic acid, being electrophilic, participates as a dienophile in many Diels-Alder reactions.

Maleates
The maleate ion is the ionized form of Malic acid. The maleate ion is useful in biochemistry as an inhibitor of transaminase reactions. Malic acid esters are also called maleates, for instance dimethyl maleate.

Use in pharmaceutical drugs
Many drugs that contain amines are provided as the maleate acid salt, e.g. carfenazine, chlorpheniramine, pyrilamine, methylergonovine, and thiethylperazine.

Malic acid (IUPAC systematic name: propanedioic acid) is a dicarboxylic acid with structure CH2(COOH)2. The ionized form of Malic acid, as well as its esters and salts, are known as malonates. For example, diethyl malonate is Malic acid's diethyl ester. The name originates from the Greek word μᾶλον (malon) meaning 'apple'.

History
Malic acid[2] is a naturally occurring substance found in many fruits and vegetables.[3] There is a suggestion that citrus fruits produced in organic farming contain higher levels of Malic acid than fruits produced in conventional agriculture.[4]
Malic acid was first prepared in 1858 by the French chemist Victor Dessaignes via the oxidation of malic acid.[2][5]

Structure and preparation
The structure has been determined by X-ray crystallography[6] and extensive property data including for condensed phase thermochemistry are available from the National Institute of Standards and Technology.[7] A classical preparation of Malic acid starts from chloroacetic acid:[8]

Preparation of Malic acid from chloroacetic acid.
Sodium carbonate generates the sodium salt, which is then reacted with sodium cyanide to provide the sodium salt of cyanoacetic acid via a nucleophilic substitution. The nitrile group can be hydrolyzed with sodium hydroxide to sodium malonate, and acidification affords Malic acid. Industrially, however, Malic acid is produced by hydrolysis of dimethyl malonate or diethyl malonate.[9] It has also been produced through fermentation of glucose.

Organic reactions
Malic acid reacts as a typical carboxylic acid: forming amide, ester, anhydride, and chloride derivatives.[11] Malonic anhydride can be used as an intermediate to mono-ester or amide derivatives, while malonyl chloride is most useful to obtain diesters or diamides. In a well-known reaction, Malic acid condenses with urea to form barbituric acid. Malic acid may also condensed be with acetone to form Meldrum's acid, a versatile intermedate in further transformations. The esters of Malic acid are also used as a −CH2COOH synthon in the malonic ester synthesis.
Additionally, the coenzyme A derivative of malonate, malonyl-CoA, is an important precursor in fatty acid biosynthesis along with acetyl CoA. Malonyl CoA is formed from acetyl CoA by the action of acetyl-CoA carboxylase, and the malonate is transferred to an acyl carrier protein to be added to a fatty acid chain.

Briggs–Rauscher reaction
Malic acid is a key component in the Briggs–Rauscher reaction, the classic example of an oscillating chemical reaction.[12]

Knoevenagel condensation
In Knoevenagel condensation, Malic acid or its diesters are reacted with the carbonyl group of an aldehyde or ketone, followed by a dehydration reaction.
Z=COOH (Malic acid) or Z=COOR' (malonate ester)
When Malic acid itself is used, it is normally because the desired product is one in which a second step has occurred, with loss of carbon dioxide, in the so-called Doebner modification.
The Doebner modification of the Knoevenagel condensation.
Thus, for example, the reaction product of acrolein and Malic acid in pyridine is trans-2,4-Pentadienoic acid with one carboxylic acid group and not two.

Preparation of carbon suboxide
Carbon suboxide is prepared by warming a dry mixture of phosphorus pentoxide (P4O10) and Malic acid.[15] It reacts in a similar way to malonic anhydride, forming malonates.[16]

Applications
Malic acid is a precursor to specialty polyesters. It can be converted into 1,3-propanediol for use in polyesters and polymers and a projected market size of $621.2 million by 2021.[citation needed] It can also be a component in alkyd resins, which are used in a number of coatings applications for protecting against damage caused by UV light, oxidation, and corrosion. One application of Malic acid is in the coatings industry as a crosslinker for low-temperature cure powder coatings, which are becoming increasingly valuable for heat sensitive substrates and a desire to speed up the coatings process.[17] The global coatings market for automobiles was estimated to be $18.59 billion in 2014 with projected combined annual growth rate of 5.1% through 2022.[18]

It is used in a number of manufacturing processes as a high value specialty chemical including the electronics industry, flavors and fragrances industry,[3] specialty solvents, polymer crosslinking, and pharmaceutical industry. In 2004, annual global production of Malic acid and related diesters was over 20,000 metric tons.[19] Potential growth of these markets could result from advances in industrial biotechnology that seeks to displace petroleum-based chemicals in industrial applications.

Malic acid was listed as one of the top 30 chemicals to be produced from biomass by the US Department of Energy.
In food and drug applications, Malic acid can be used to control acidity, either as an excipient in pharmaceutical formulation or natural preservative additive for foods.
Malic acid is used as a building block chemical to produce numerous valuable compounds,[21] including the flavor and fragrance compounds gamma-nonalactone, cinnamic acid, and the pharmaceutical compound valproate.
Malic acid (up to 37.5% w/w) has been used to cross-link corn and potato starches to produce a biodegradable thermoplastic; the process is performed in water using non-toxic catalysts. Starch-based polymers comprised 38% of the global biodegradable polymers market in 2014 with food packaging, foam packaging, and compost bags as the largest end-use segments.

Biochemistry
Malic acid is the classic example of a competitive inhibitor of the enzyme succinate dehydrogenase (complex II), in the respiratory electron transport chain.[26] It binds to the active site of the enzyme without reacting, competing with the usual substrate succinate but lacking the −CH2CH2− group required for dehydrogenation. This observation was used to deduce the structure of the active site in succinate dehydrogenase. Inhibition of this enzyme decreases cellular respiration.[27][28] Since Malic acid is a natural components of many foods, it is present in mammals including humans.

An efficcacy and safety test of a tablet containing 200 mg malic acid (and 50 mg magnesium) was conducted using patients with primary fibromyalgia syndrome. In the first part of the test, 24 patients were given three tablets twice daily (bid) for 4 weeks. In the second part, 16 patients started with three tablets bid and increased the dosage every 3 to 5 days as necessary; at month 6, the average dose was 8.8 tablets per day. (For a 50-kg person, ingestion of six tablets would be equivalent to 24 mg of malate/kg of body weight). In the first part of the study, one test patient reported diarrhea, one reported nausea, and one reported dyspepsia. (In the placebo group, two patients reported diarrhea and one reported dyspepsia.) In the second part of the study, five test patients reported diarrhea, one reported nausea, one reported dyspepsia, one reported panic attacks, and one reported dizziness.

Organic acids in Chinese herbs, the long-neglected components, have been reported to possess antioxidant, anti-inflammatory, and antiplatelet aggregation activities; thus they may have potentially protective effect on ischemic heart disease. Therefore, this study aims to investigate the protective effects of two organic acids, that is, citric acid and L-malic acid, which are the main components of Fructus Choerospondiatis, on myocardial ischemia/reperfusion injury and the underlying mechanisms. In in vivo rat model of myocardial ischemia/reperfusion injury, we found that treatments with citric acid and L-malic acid significantly reduced myocardial infarct size, serum levels of TNF-alpha, and platelet aggregation. In vitro experiments revealed that both citric acid and L-malic acid significantly reduced LDH release, decreased apoptotic rate, downregulated the expression of cleaved caspase-3, and upregulated the expression of phosphorylated Akt in primary neonatal rat cardiomyocytes subjected to hypoxia/reoxygenation injury. These results suggest that both citric acid and L-malic acid have protective effects on myocardial ischemia/reperfusion injury; the underlying mechanism may be related to their anti-inflammatory, antiplatelet aggregation and direct cardiomyocyte protective effects. These results also demonstrate that organic acids, besides flavonoids, may also be the major active ingredient of Fructus Choerospondiatis responsible for its cardioprotective effects and should be attached great importance in the therapy of ischemic heart disease.

Objectives: Assessing the clinical effectiveness of a topical sialogogue on spray (malic acid, 1%) in the treatment of xerostomia induced by antihypertensive drugs. Study Design: This research has been carried out through a randomized double-blind clinical trial. 45 patients suffering from hypertensive drugs-induced xerostomia were divided into 2 groups: the first group (25 patients) received a topical sialogogue on spray (malic acid, 1%) whereas the second group (20 patients) received a placebo. Both of them were administered on demand for 2 weeks. Dry Mouth Questionnaire (DMQ) was used in order to evaluate xerostomia levels before and after product/placebo application. Unstimulated and stimulated salivary flows rates, before and after application, were measured. All the statistical analyses were performed by using SPSS software v17.0. Different DMQ scores at the earliest and final stage of the trial were analysed by using Mann-Whitney U test, whereas Student's T-test was used to analyse salivary flows. Critical p-value was established at p<0.05. Results: DMQ scores increased significantly (clinical recovery) from 1.21 to 3.36 points (p<0.05) after malic acid (1%) application whereas DMQ scores increased from 1.18 to 1.34 points (p>0.05) after placebo application. After two weeks of treatment with malic acid, unstimulated salivary flow increased from 0.17 to 0.242 mL/min whereas the stimulated one increased from 0.66 to 0.92 mL/min (p<0.05). After placebo application unstimulated flow ranged from 0.152 to 0.146 mL/min and stimulated flow increased from 0.67 to 0.70 mL/min (p>0.05). Conclusions: Malic acid 1% spray improved antihypertensive-induced xerostomia and stimulated the production of saliva.

Fourteen patients, 11 males and 3 females, with various forms of ichthyosiformdermatoses were used to evaluate the therapeutic potential of more than 60 chemicals, including malic acid. Malic acid was dissolved in either water or ethanol and incorporated into a hydrophilic ointment of plain petrolatum. The ointment, containing 5% malic acid (pH not specified), was applied twice daily to the appropriate test site for 2 weeks. Daily to weekly observations were made. Malic acid provided 3+ (disappearance of scales from lesions) or 4+ (restoration to normal looking skin) improvement in all patients except one with epidermolytic

Malic acid is an intermediate in the citric acid cycle. It is formed from fumaric acid and is oxidized to oxaloacetic acid. It is also metabolized to pyruvic acid by malic enzyme which is present in many biologic systems, including bacteria and plants. L-Malic and dl-malic acid are both rapidly metabolized in the rat. Orally or ip administered l- or dl-malic acid was extensively eliminated as carbon dioxide (83 to 92%). No differences between the two forms were found in the rates (90 to 95% in 24 hr) or routes of excretion.

Malate occurs in all living organisms as an intermediate in the citric acid cycle. It occurs in relatively high amounts in many fruits and vegetables. Malic acid has two stereoisomeric forms (L- and D-enantiomers), although only the L-isomer exists naturally.
Upon oral and IP administration of radioactive malic acid to rats, most of the radioactivity was excreted as carbon dioxide.
Malic acid is an intermediate in the citric acid cycle. It is formed from fumaric acid and is oxidized to oxaloacetic acid. It is also metabolized to pyruvic acid by malic enzyme which is present in many biologic systems, including bacteria and plants. L-Malic and dl-malic acid are both rapidly metabolized in the rat. Orally or ip administered l- or dl-malic acid was extensively eliminated as carbon dioxide (83 to 92%). No differences between the two forms were found in the rates (90 to 95% in 24 hr) or routes of excretion.

Malic acid is a colorless to white, crystalline solid. It has a sour taste. It is very soluble in water. Malic acid is present naturally in many plants, including flowers, fruits and vegetables, spices, and wine grapes. It is a component in tobacco. It may be formed in the air by reaction of other chemicals with light. Malic acid is formed naturally in animals and humans and used in the process of breaking down sugar into energy in the body. USE: Malic acid is an important commercial chemical used in canning fruits and vegetables to prevent them from spoiling. It is used in various other foods, dry beverage powders, carbonated beverages, and food packaging materials to control acidity. Malic acid is an ingredient in some household cleaners, hair coloring, nail enamels, human and specialty pet shampoos. EXPOSURE: Workers in the food, cleaning and personal care industries may be exposed to malic acid through skin contact and breathing in mists or malic acid salt dusts. The general population is exposed to malic acid from eating foods consumed in a normal diet that contain malic acid. People may breathe in mists or have skin contact while household and personal care products that contain malic acid. If malic acid is released to air, it can be broken down by reaction with other chemicals and some may be in or on particles that eventually fall to the ground. If released to water or soil, it is not expected to bind sediments. It is expected to move easily through soil. Malic acid is not expected to move into air from wet soils or water surfaces. Malic acid is expected to be broken down by microorganisms and is not expected to build up in tissues of aquatic organisms. RISK: Severe skin and eye irritation can occur with direct contact to malic acid or its salts. Allergic skin reactions have been reported in some individuals after eating foods containing malic acid. Erosion of tooth enamel may occur from drinking acidic soft drinks containing malic acid. Weakness, incoordination, convulsions, and breathing difficulties occurred in laboratory animals given very high oral doses of malic acid. Death occurred in some animals. No health problems occurred in laboratory animals, dogs, or cattle fed low-to-moderate doses over time. Malic acid did not cause birth defects or reproductive effects in laboratory animals. The potential for malic acid to cause cancer has not been assessed in laboratory animals. The potential for malic acid to cause cancer in humans has not been assessed by the U.S. EPA IRIS program, the International Agency for Research on Cancer, the U.S. National Toxicology Program 13th Report on Carcinogens, or the California Office of Environmental Health Hazard Assessment. 

Malic acid is prepared commercially in the United States and Canada by hydration of maleic anhydride. ... In this process maleic acid is heated at ca 180 °C (under a pressure of ca 1 MPa), malic acid is yielded as the main product. Byproducts are maleic and fumaric acids. The latter can be separated by filtration and returned to the process stream because of its low water solubility. The filtrate is then concentrated; this causes separation of the malic acid, which is purified by multiple washings, evaporation, and recrystallization until the contents of fumaric and maleic acids are reduced to 7.5 and <500 ppm, respectively. Additional purification is required to prepare pharmacological-grade material.
Malic acid is synthesised by hydration of maleic anhydride under high temperature and pressure to form malic and fumaric acid. The precipitate of the less soluble fumaric acid is separated by centrifugation and the resulting solution is concentrated to form crystals of crude malic acid, which are separated, re-dissolved in water and passed through a decolourization unit containing activated charcoal. After concentration of the solution, pure crystals of malic acid are formed, which are separated and dried.

Malic acid used as a general purpose food additive in animal drugs, feeds, and related products is generally recognized as safe when used in accordance with good manufacturing or feeding practice.
Synthetic flavoring substances and adjuvants /for animal drugs, feeds, and related products/ that are generally recognized as safe for their intended use, within the meaning of section 409 of the Act. 1-Malic acid is included on this list.
The interactions of aqueous solutions of chlorine with some fruit acids (citric acid, DL-malic acid, and L-tartaric acid) different pH values were studied diethyl ether extraction followed by GC/MS analysis indicated that a number of mutagens certain chlorinated propanones and chloral hydrate) are present as major products in some of these samples. A number of fruit juices (orange, grape, apple, pineapple, and grapefruit) were also treated with aqueous solutions of chlorine at their pH values. The products were analyzed by GC/MS. The same mutagens that were formed by the pure acids (citric acid and DL-malic acid) were identified as major products in ether extracts of these samples. All of the major products observed in the chlorination of all five fruit juices are potentially derived from reactions aqueous solutions of chlorine with citric or malic acid and with trace amounts of acetaldehyde and acetone in the juices.

Eight groups of female Sprague-Dawley rats were treated with 281 mg aluminum hydroxide/kg/day by gastric intubation five times a week for fives weeks. Concurrently, animals in seven groups received ascorbic acid (56.3 mg/kg/day), citric acid (62 mg/kg/day), gluconic acid (62.7 mg/kg/day), lactic acid (28.8 mg/kg/day), malic acid (42.9 mg/kg/day), oxalic acid (28.8 mq/kg/day), and tartaric acid (48 mg/kg/day) in the drinking water. The eighth group did not receive any dietary constituent in the water and was designated as the control group. Animals were placed in plastic metabolic cages and urine was collected during the treatment period. The liver, spleen, kidney, brain and bone aluminum levels of each rat were measured, as well as the total amount of aluminun excreted into urine. All the dietary constituents significantly increased the aluminum concentrations in most of the tissues, with ascorbic and citric acids showing the highest rate of aluminum accumulation.

IDENTIFICATION AND USE: Malic acid forms colorless crystals with a characteristic sour taste. It is used as a cosmetic and food ingredient. Malic acid has been tested as experimental therapy for various conditions. HUMAN EXPOSURE AND TOXICITY: Malic acid and its salts are considered as strongly irritant to the skin and mucosa and as a particular risk to the eyes. Exposure via inhalation for those handling the additives is also considered to present a risk. Malic acid was irritating in clinical tests, with less irritation seen as pH of the applied material increased. Patients patch tested with malic acid, placed on a diet that avoided foods containing malic or citric acid, and then challenged with a diet high in malic and citric acid had both immediate urticarial and delayed contact dermatitis reactions. In the absence of data on inhalation toxicity, inhalation of the malate additive should be considered as hazardous. Because of the particle size distribution of the additives and the high dusting potential of the malate salts, it is likely that handling the additives could result in a production of respirable dust that could present a risk to unprotected workers. ANIMAL STUDIES: Malic acid is a component of the Kreb's cycle. Malic acid was relatively nontoxic in acute toxicity studies using animals. In a chronic oral study, feeding malic acid to rats resulted only in weight gain changes and changes in feed consumption. Malic acid did not cause reproductive toxicity in mice, rats, or rabbits. Malic acid was a moderate to strong skin irritatant in animal tests, and was a strong ocular irritant. Malic acid was not mutagenic across a range of genotoxicity tests.

The effect of malic acid on cell renewal was assessed using the dansyl chloride method. Two mg/sq cm of 1 M malic acid in a simple liquid vehicle (15% ethanol [SD 40], 5% ethoxydiglycol, and 5% butylene glycol) was applied to the volar forearm which was stained with dansyl chloride twice daily until all the stain was removed. An 18%, 10%, and 5% increase in cell renewal was observed at pH 3, 5, and 7, respectively.
Thirty-four patients with atopic dermatitis were tested to determine their sensitivity to foods containing malic (and citric) acid. The patients were first patch tested with malic (and citric) acid applied as a 10% aqueous solution under occlusive patches for 48 hours. For 2 weeks, the patients followed a diet that avoided processed foods in which malic (and citric) Acid were used, and then challenged themselves with a diet high in malic (and citric) acid the during the third week. Eighteen patients reacted to both malic and citric acid and 6 patients reacted to only malic acid. Both immediate reactions (seasonal allergic rhinitis and urticaria) and delayed reactions (contact dermatitis) were present. Patch-test results were reliable in predicting results of the challenge with diet.

Acute Exposure/ The oral LD50 values of malic acid for albino CD-1 outbred mice, albino Wistar rats, and Dutch-Belted rabbits were approximately 2.66, 3.5, and 3 g/kg respectively. Each study used 50 animals, consisting of five groups of 5 males and 5 females, and malic acid was administered as a 25% aqueous solution. Mortality was observed for 14 days. Signs of toxicity included ataxia, prostration, convulsions, and death.
Subchronic or Prechronic Exposure/ In two 28-day experiments with beef cattle, reduced feed intakes were observed following the inclusion of DL-malic acid at 22,000 mg/kg complete feed, the lowest dose tested . Dietary supplementation with DL-malic acid or the mixed salts of malic acid at a level of 3,500 mg/kg complete feed did not result in any significant changes in the performance of growing/finishing bull calves (Belgian Blue) over a 148-day period. Performance parameters of average daily weight gain, daily feed intake and feed-to-gain ratio were unaffected by either product when compared with a control group fed unsupplemented feed.

Malic acid's production and use as a chemical intermediate in the synthesis of esters, salts and compounds, as a chelating and buffering agent and as a flavoring agent and acidulant in foods may result in its release to the environment through various waste streams. Malic acid has been identified as chemical component of tobacco smoke which releases the compound directly to the environment. Malic acid occurs in apples and many other fruits and plants. Its occurrence and detection in the ambient atmosphere may result from the photooxidation of atmospheric hydrocarbons. It may also reach the atmosphere through volatilization from plants. If released to air, an extrapolated vapor pressure of 3.28X10-8 mm Hg at 25 °C indicates malic acid will exist in both the vapor and particulate phases in the atmosphere. Vapor-phase malic acid will be degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals; the half-life for this reaction in air is estimated to be 2 days. Particulate-phase malic acid will be removed from the atmosphere by wet and dry deposition. Malic acid has been detected in atmospheric particulate matter and in rain and snow. Malic acid does not absorb at wavelengths >290 nm and, therefore, is not expected to be susceptible to direct photolysis by sunlight. If released to soil, malic acid is expected to have very high mobility based upon an estimated Koc of 1. The pKa values of malic acid are 3.51 and 5.03, indicating that this compound will exist partially in anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts. Volatilization from moist soil surfaces is not expected to be an important fate process based upon an estimated Henry's Law constant of 8.4X10-13 atm-cu m/mole. Malic acid is not expected to volatilize from dry soil surfaces based upon its vapor pressure. Results of screening studies have determined that malic acid biodegrades readily which indicates that biodegradation is expected to be an important fate process in both soil and water. If released into water, malic acid is not expected to adsorb to suspended solids and sediment based upon the estimated Koc. Volatilization from water surfaces is not expected to be an important fate process based upon this compound's estimated Henry's Law constant. An estimated BCF of 3 suggests the potential for bioconcentration in aquatic organisms is low. Hydrolysis is not expected to be an important environmental fate process since this compound lacks functional groups that hydrolyze under environmental conditions. Occupational exposure to malic acid may occur through inhalation and dermal contact with this compound at workplaces where malic acid is produced or used. Monitoring data indicate that the general population may be exposed to malic via inhalation of ambient air and tobacco smoke, ingestion of food and beverages, and dermal contact with consumer products containing malic acid.

Malic acid occurs in apples and many other fruits and plants(1). Malic acid occurs in plants such as apricot, mango, rose, plum, elderberry, buckwheat, strawberry, pineapple, papaya, orange, tangerine, potato, grape, soybean, grapefruit, lettuce, onion, celery, oats, cauliflower, cabbage, brussel sprouts, tobacco, carrot, olive, sunflower, tomato, ginseng, opium poppy, pea, raspberry, sage, and corn(2). Malic acid may occur in atmospheric samples as a result of volatilization from naturally occurring sources or from the atmospheric oxidation of precursor aldehydes(3). Malic acid and other dicarboxylic acids are probably formed in the atmosphere via photooxidation of organic compounds that occur in the atmosphere(4,5).
Malic acid's production and use as a chemical intermediate in the synthesis of esters, salts and compounds, as a chelating and buffering agent and as a flavoring agent and acidulant in foods(1,2) may result in its release to the environment through various waste streams(SRC). Malic acid's identification as a chemical component of tobacco smoke(2) will result in its direct release to the environment(SRC).

Based on a classification scheme(1), an estimated Koc value of 1(SRC), determined from a structure estimation method(2), indicates that malic acid is expected to have very high mobility in soil(SRC). The pKa values of malic acid are 3.51 and 5.03(3), indicating that this compound will exist partially in the anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(4). Volatilization of malic acid from moist soil surfaces is not expected to be an important fate process(SRC) given an estimated Henry's Law constant of 8.4X10-13 atm-cu m/mole(SRC), using a fragment constant estimation method(2). Malic acid is not expected to volatilize from dry soil surfaces(SRC) based upon an extrapolated vapor pressure of 3.28X10-8 mm Hg at 25 °C(5). A 73% of theoretical BOD in 2 weeks using activated sludge in the Japanese MITI test indicates that malic acid is readily biodegradable(6). Results of other screening studies also indicate that malic acid biodegrades readily(7,8). Using C14-radio-labeled malic acid and a 1-hr incubation period, a 6.7% CO2 evolution was observed in a natural soil degradation study(9) demonstrating that biodegradation is expected to be an important fate process in soil(SRC).

Based on a classification scheme(1), an estimated Koc value of 1(SRC), determined from a structure estimation method(2), indicates that malic acid is not expected to adsorb to suspended solids and sediment(SRC). Volatilization from water surfaces is not expected(3) based upon an estimated Henry's Law constant of 8.4X10-13 atm-cu m/mole(SRC), developed using a fragment constant estimation method(2). According to a classification scheme(4), an estimated BCF of 3(SRC), from its log Kow of -1.26(5) and a regression-derived equation(2), suggests the potential for bioconcentration in aquatic organisms is low(SRC). A 73% of theoretical BOD in 2 weeks using activated sludge in the Japanese MITI test indicates that malic acid is readily biodegradable(6). Results of other screening studies also indicate that malic acid biodegrades readily(7,8). Malic acid is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(3).

According to a model of gas/particle partitioning of semivolatile organic compounds in the atmosphere(1), malic acid, which has an extrapolated vapor pressure of 3.28X10-8 mm Hg at 25 °C(2), will exist in both the vapor and particulate phases in the ambient atmosphere. Vapor-phase malic acid is degraded in the atmosphere by reaction with photochemically-produced hydroxyl radicals(SRC); the half-life for this reaction in air is estimated to be 2 days(SRC), calculated from its rate constant of 8.3X10-12 cu cm/molecule-sec at 25 °C(SRC) that was derived using a structure estimation method(3). Particulate-phase malic acid may be removed from the air by wet and dry deposition(SRC). Malic acid has been detected in atmospheric particulate matter and in rain and snow(4,5). Malic acid does not absorb at wavelengths >290 nm(6) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC).

In an aerobic closed bottle screening study using activated sludge and soil inoculum, malic acid had 5-, 15- and 30-day theoretical BODs of 68, 81 and 100% respectively(1). In a Warburg respirometer study using an activated sludge inoculum, theoretical BODs of 6.0-9.6% and 20.8-55.5% were observed over respective incubation periods of 4 and 24 hrs(2). In a Warburg respirometer study using a sewage sludge inoculum, a theoretical BOD of 47.2% was observed over an incubation period of 5 days(3). A theoretical BOD of 56.3% was observed in a standard BOD dilution test using a sewage inoculum(4). In a Warburg respirometer study using a phenol acclimated activated sludge inoculum, a theoretical BOD of 46% was observed over an incubation period of 12 hrs(5). Using C14-radio-labeled malic acid and a 1-hr incubation period, a 6.7% CO2 evolution was observed in a natural soil degradation study(6); when the soil was sterilized via autoclaving, the CO2 evolution was only 0.1%(6). DL-Malic acid, present at 100 mg/L, reached 73% of its theoretical BOD in 2 weeks using an activated sludge inoculum at 30 mg/L in the Japanese MITI test which classified the compound as readily biodegradable(7).

The rate constant for the vapor-phase reaction of malic acid with photochemically-produced hydroxyl radicals has been estimated as 8.3X10-12 cu cm/molecule-sec at 25 °C(SRC) using a structure estimation method(1). This corresponds to an atmospheric half-life of about 2 days at an atmospheric concentration of 5X10+5 hydroxyl radicals per cu cm(1). The rate constant for the reaction of malic acid with hydroxyl radicals in aqueous solutions at pH 1.5-14 is 8.2X10+8 L/mol-sec(2); this corresponds to an aquatic half-life of 2.6 years at an aquatic concentration of 1X10-17 hydroxyl radicals per liter(3). Malic acid does not absorb at wavelengths >290 nm(4) and, therefore, is not expected to be susceptible to direct photolysis by sunlight(SRC). Malic acid is not expected to undergo hydrolysis in the environment due to the lack of functional groups that hydrolyze under environmental conditions(5).

Using a structure estimation method based on molecular connectivity indices(1), the Koc of malic acid can be estimated to be 1(SRC). According to a classification scheme(2), this estimated Koc value suggests that malic acid is expected to have very high mobility in soil. The pKa values of malic acid are 3.51 and 5.03(3), indicating that this compound will exist partially in anion form in the environment and anions generally do not adsorb more strongly to soils containing organic carbon and clay than their neutral counterparts(4).

The Henry's Law constant for malic acid is estimated as 8.4X10-13 atm-cu m/mole(SRC) using a fragment constant estimation method(1). This Henry's Law constant indicates that malic acid is expected to be essentially nonvolatile from water surfaces(2). In addition, the pKa values of malic acid are 3.51 and 5.03(3), indicating that this compound will exist partially in anion form in the environment and the anion form of malic acid will not volatilize from water(SRC). Malic acid's Henry's Law constant indicates that volatilization from moist soil surfaces will not occur(SRC). Malic acid is not expected to volatilize from dry soil surfaces(SRC) based upon an extrapolated vapor pressure of 3.28X10-8 mm Hg(4).
Malic acid was detected in rainwater samples collected from New Brunswick, NJ during 1999-2000 sampling(1). Snow, sleet and rain samples collected in Tokyo Japan in 1992 contained malic acid concentrations of 0.49-6.76 ug/L(2).

In a monitoring study sampling the atmospheric aerosol in the atmosphere of urban Tokyo, Japan during 1988 and 1989, malic acid was detected at concentrations ranging from 3.2 to 100 ng/cu m with an average concentration of 23 ng/cu m(1). Ambient aerosol monitoring conducted throughout 1982 in the Los Angeles, CA area found respective annual ambient average malic acid concentrations of 7.8, 14.3, 16.0, 22.1 and <0.02 ng/cu m at West Los Angeles, downtown Los Angeles, Pasadena, Rubidoux and San Nicolas Island, respectively(2). Aerosol samples (PM2.5) collected in Nanjing China between July 2004 and January 2005 contained mean maleic acid concentrations of 1.89-31.6 ng/cu m during daytime and 1.18-18.1 ng/cu during nightime(3). Aerosol samples collected in Tokyo Japan in 1992 contained malic acid concentrations of 21-33 ng/cu m(4).

Fine aerosol samples collected at the Great Smoky Mountain National Park, Tennessee between July 15 to August 25, 1995 contained malic acid in 9 of 21 daytime samples (2.5-38.5 ng/cu m) and 2 of 10 nighttime samples (4.7-14 ng/cu m)(1). Arctic aerosol samples collected from Alert, Canada during 1987-1988 contained a mean malic acid concentration of 0.026 ng/cu m with a range of <0.003-0.14 ng/cu m(2); elevated diacid levels occurred during extended sunlight times, as opposed to dark periods, suggesting the presence of the diacids (such as malic acid) was due to photooxidation generation from other atmospheric compounds(2). Aerosol samples collected at a forest area in Hungary between June 4 and July 10, 2003 contained a mean malic acid concentration of 40 ng/cu m (range of 16.5-78 ng/cu m)(3).

Malic acid has been found in apples and many other fruits and plants(1). An analysis of Caribbean cassava vegetables found a 0.2% constituent of malic acid(2). Malic acid was detected in six wild edible mushroom species (Amanita caesarea, Boletus edulis, Gyroporus castaneus, Lactarius delicious, Suillus collinitus and Xerocomus chrysenteron)(3). Malic acid occurs in fruits and edible plants such as apricot, mango, rose, plum, elderberry, strawberry, pineapple, papaya, orange, tangerine, potato, grape, soybean, grapefruit, lettuce, onion, celery, oats, cauliflower, cabbage, brussel sprouts, carrot, olive, sunflower, tomato, ginseng, poppy, pea, raspberry, sage, and corn(4).

Malic acid occurs in apples and many other fruits and plants(1). An analysis of Caribbean cassava vegetables found a 0.2% constituent of malic acid(2). Malic acid was detected in six wild edible mushroom species (Amanita caesarea, Boletus edulis, Gyroporus castaneus, Lactarius delicious, Suillus collinitus and Xerocomus chrysenteron)(3). Malic acid has been identified as occurring in tobacco(4). Malic acid was detected in pumpkin(5) and pomegrante fruit(6).

Despite its sinister sounding name, the word malic acid comes from the Latin word malum, which means apple. Malic acid was first isolated from apple juice in 1785, and it’s what gives some foods and drinks a tart taste. If you’re a fan of slightly acidic wine, malic acid probably played a huge role. It’s also a common ingredient in many hair and skin care products that include:
shampoos
body lotions
nail treatments
acne and anti-aging products

Malic acid is part of a family of fruit acids, called alpha hydroxy acids (AHAs). Alpha hydroxy acids stimulate exfoliation by interfering with how your skin cells bond. As a result, dull skin is removed to make way for newer skin. Skin care products that contain malic acid can provide benefits that include:
skin hydration
exfoliation, or the removal of dead skin cells
improved skin smoothness and tone
reduction in wrinkles
Your body also produces malic acid naturally when converting carbohydrates into energy. Movement would be very difficult without malic acid. It’ll probably be no surprise that malic acid also has other health benefits too.

Cleanses and rejuvenates the skin
Malic acid in skin care products is celebrated for its ability to brighten the skin and smooth its texture. That’s why it’s a common ingredient in anti-aging creams.
According to a brain-skin connection studyTrusted Source, higher stress can worsen skin conditions like eczema, acne, and premature aging. And while wine can help reduce stress, external use of malic acid might be a healthier application.

Skin pH balance and hydration
Malic acid is also a humectant. It helps with moisture retention to help your skin stay hydrated.

A 2014 study about the hydration effects of aloe veraTrusted Source used malic acid, glucose, and a chemical compound in aloe vera (acemannan), as markers for fresh gel. Another small study also saw improvements in scales from old wounds after applying an ointment made of malic acid and petroleum jelly, according to the National Institutes of Health (NIH).

Malic acid is often used as an ingredient in cosmetics to balance pH levels. According to Bartek, a manufacturer that makes cosmetic and food grade chemicals, malic acid is more balanced than other fruit acids. It has a better buffer capacity than other AHAs like citric and lactic acid.
Having a better buffer capacity means that you can use more malic acid without upsetting your skin’s acid-base balance, or pH levels. If your skin’s pH level is unbalanced, then your skin’s protective barrier may be destabilized and more prone to dryness or acne.

Anti-aging and scar lightening
AHAs promote a high skin cell turnover rate. This means your skin cells are renewed more quickly, resulting in:
fewer fine lines and wrinkles
more even skin tone
smoother skin texture
decreased blemishes
“Malic acid at higher concentrations can also penetrate into lower levels of the skin to bring about new collagen formation,” says dermatologist Dr. Annie Chiu, director of the Derm Institute in California. Collagen is a protein that helps build and repair cells. It supports the skin and other body tissues’ strength and flexibility and prevents sagging. Collagen production slows down as you age, which is partly why skin loses its elasticity and firmness the older you get.
Using products with malic acid may increase collagen production and reduce signs of aging. Check out beauty blog ‘Hello Glow’ for three DIY (do it yourself) apple-based masks to rejuvenate your face, skin, and hair.

Acne prevention
Whether it’s in a lotion, cleanser, or light peeling agent, malic acid can help remove a buildup of dead cells. This is great for acne-prone skin. When the skin’s pores get clogged with too many dead skin cells and the skin’s natural oil (sebum), blackheads can form. Bacterial infections can also develop and cause breakouts.

“Malic acid breaks down the ‘glue’ that holds the dead skin cells together on the outer layer of the skin,” says Dr. Chiu. When these dead skin cells are swept away, “Your skin looks less dull and when your pores are unclogged, it helps reduce the formation of acne bumps and the discoloration that’s often associated with acne.”
While it sounds like a miracle cure, Dr. Chiu recommends sticking to low doses of malic acid. Unless your doctor recommends it, nonprescription skin care products will contain all the malic acid you need to fight breakouts or sagging skin. Higher doses, such as supplements, should only be taken if recommended by your doctor.

Help with fibromyalgia
Fibromyalgia is a complex disorder that causes pain and fatigue in the muscles. Some research suggests that people with fibromyalgia also have a hard time producing malic acid. While there is little supporting evidence, two studies evaluated whether a combination of high doses of malic acid and magnesium helped reduce muscle pain and tenderness. One study was inconclusive, but suggested that the combination may be beneficial in high doses over a long period of time.

In the other study, people who took the malic acid and magnesium reported significant improvement within 48 hours of starting treatment. This continued for the full eight weeks of the study. After eight weeks of the active treatment dosage, some of the participants were given a placebo instead. People who took the placebo reported reoccurrence of muscle pain within 48 hours.
Unless your doctor recommends malic acid supplements, you should get all the malic acid your body needs from a healthy diet that includes plenty of fruits and vegetables.

Use with caution
Although malic acid is less irritating on the skin than other AHAs, it should still be used with caution. Malic acid can make your skin turn red, itch, or burn, especially around the eyes.

You may want to patch test a product befo