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外観
無色～わずかにうすい黄色, 澄明の液体
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種類
乳酸の分子式はCH3CH(OH)COOHであり、1つの炭素が4種の異なる原子、原子団 (乳酸の場合は、-H、-OH、-COOH、-CHM3) と結合しています。このような炭素を不斉炭素原子と呼び、不斉炭素原子をもつ化合物は分子式が同じでも構造的に異なっています。
鏡像異性体や光学異性体と呼ばれ、別の物質として扱われます (右手と左手の関係と同様) 。このため、乳酸には、L-乳酸、D-乳酸の2種類が存在し、これらの等量混合物をDL-乳酸と呼びます。L-乳酸、D-乳酸の融点はそれぞれ53℃ですが、DL-乳酸は16.8℃です。また天然にはL体が多く存在します。
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性質
乳酸は分子量90.08で、無臭ですが、酸性でやわらかみのある酸味がある液体です。比重は1.207で、融点が16.8° (DL体) 、沸点が122℃、水、アルコール、エーテル等には非常によく溶けます。一方、クロロホルム、二硫化炭素、ベンゼンなどには不溶です。
乳酸は、生体内では解糖系代謝経路の最終産物であり、多くの動植物の組織に存在しています。また、乳の発酵物や食品にも多く含まれています。
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定義
本品は、次の化学式で表される有機酸である。
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溶解性
水、エタノール及びジエチルエーテルに極めて溶けやすく、クロロホルム、石油ベンジン及び二硫化炭素にほとんど溶けない。
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解説
乳酸，ニュウサン，2-ヒドロキシプロパン酸ともいう．代表的なα-ヒドロキシ酸．不斉炭素をもち，L-，D-，DL-乳酸の3種類の異性体が存在する．L-乳酸は動物の組織や器官に存在し，疲労した筋肉中に蓄積されるので肉乳酸ともいわれる．発酵法やDL-乳酸から分割して得られる．
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用途
酸味剤。
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化粧品の成分用途
pH調整剤、保湿.湿潤剤、保水剤、剥離剤、皮膚コンディショニング剤、香料
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効能
矯味剤
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商品名
乳酸 (健栄製薬); 乳酸 (小堺製薬)
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化学的特性
Lactic acid, CH3CHOHCOOH, also known as 2-hydroxypropanoic acid, is a hygroscopic liquid that exists in three isometric forms. I-lactic acid is found in blood and animal tissue as a product of glucose and glycogen metabolism. d-Iactic acid is obtained by fermentation of sucrose (corn refining), The racemic mixture is present in foods prepared by bacterial fermentation or prepared synthetically. Lactic acid is soluble in water,alcohol,and ether. It is used as a solvent, in manufacturing confectionery, and in medicine.
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天然物の起源
Reported found in Papaver somniferum L.; it is a constituent of wine and sour milk; the two optically active
isomers are found in muscular tissues and are formed by the action of lactic acid–producing bacteria in several fermentation processes. Also reported found in guava, grapes, melon, wheat bread, cheeses, yogurt, milk, cream, buttermilk, egg, cooked beef,
cognac, cider, sherry, grape wine, beer, grape brandy, whiskey, cocoa, coffee, tea, mango, sake, wort, dried, bonito, cassava, Bourbon
vanilla, chicory root, Cape gooseberry and cherimoya.
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使用
lactic acid (sodium lactate) is a multi-purpose ingredient used as a preservative, exfoliant, moisturizer, and to provide acidity to a formulation. In the body, lactic acid is found in the blood and muscle tissue as a product of the metabolism of glucose and glycogen. It is also a component of the skin’s natural moisturizing factor. Lactic acid has better water intake than glycerin. Studies indicate an ability to increase the water-retention capacity of the stratum corneum. They also show that the pliability of the stratum corneum layer is closely related to the absorption of lactic acid; that is, the greater the amount of absorbed lactic acid, the more pliable the stratum corneum layer. Researchers report that continuous use of preparations formulated with lactic acid in concentrations ranging between 5 and 12 percent provided a mild to moderate improvement in fine wrinkling and promote softer, smoother skin. Its exfoliating properties can help in the process of removing excess pigment from the surface of the skin, as well as improving skin texture and feel. Lactic acid is an alpha hydroxy acid occurring in sour milk and other lesser-known sources, such as beer, pickles, and foods made through a process of bacterial fermentation. It is caustic when applied to the skin in highly concentrated solutions.
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定義
ChEBI: A 2-hydroxy monocarboxylic acid that is propanoic acid in which one of the alpha-hydrogens is replaced by a hydroxy group.
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調製方法
Lactic acid is prepared by the fermentation of carbohydrates, such
as glucose, sucrose, and lactose, with Bacillus acidi lacti or related
microorganisms. On a commercial scale, whey, corn starch,
potatoes, or molasses are used as a source of carbohydrate. Lactic
acid may also be prepared synthetically by the reaction between
acetaldehyde and carbon monoxide at 130–200°C under high
pressure, or by the hydrolysis of hexoses with sodium hydroxide.
Lactic acid prepared by the fermentation of sugars is levorotatory;
lactic acid prepared synthetically is racemic. However, lactic
acid prepared by fermentation becomes dextrorotatory on dilution
with water owing to the hydrolysis of (R)-lactic acid lactate to (S)-
lactic acid.
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製法
製法には発酵法と合成法とがある。発酵法では、糖質を原料として乳酸菌による乳酸発酵により生成され、これは発酵乳酸とよばれる。乳酸菌の種類によってD-またはL-乳酸、あるいはラセミ体が生成される。合成法では、アルデヒドとシアン酸より乳酸ニトリル、乳酸メチルエステルを経て得られる。用途としては、食品添加物に指定されており、合成酒の配合剤、清涼飲料水、ドロップ、ゼリー、アイスクリームなどの酸味剤、清酒醸造用として発酵初期に雑菌の生育防止などに用いられる。乳酸飲料には広く用いられ、食品にもっとも古くから広く使用されている。このほか、医薬品などにも用いられる。
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一般的な説明
A colorless to yellow odorless syrupy liquid. Corrosive to metals and tissue. Used to make cultured dairy products, as a food preservative, and to make chemicals.
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空気と水の反応
Soluble in water.
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健康ハザード
Inhalation of mist causes coughing and irritation of mucous membranes. Ingestion, even of diluted preparations, has a corrosive effect on the esophagus and stomach. Contact with more concentrated solutions can cause severe burns of skin or eye.
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火災危険
Combustible material: may burn but does not ignite readily. When heated, vapors may form explosive mixtures with air: indoors, outdoors and sewers explosion hazards. Contact with metals may evolve flammable hydrogen gas. Containers may explode when heated. Runoff may pollute waterways. Substance may be transported in a molten form.
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化学性质
光学異性体が存在する
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使用用途
乳酸は、生分解性プラスチックの1つであるポリ乳酸やポリエステルポリオール等の原料として使用されています。また、医薬の原料として使用されている他、安定化剤、可溶化剤、緩衝材、pH調整剤などの医薬品添加物としても使用されています。
その他、食品工業でも広く利用されており、酸味料やpH調整剤等として、飲料や味噌、醤油、漬物、チーズ、香料、シロップなど、さまざまな食品に利用されています。化粧品や農薬、染色工業の還元剤、皮革加工用 (脱灰) なども用途の1つで、市販されているものとしては、40%、50%、90%品が主流です。
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応用例（製薬）
Lactic acid is used in beverages, foods, cosmetics, and pharmaceuticals
as an acidifying agent and acidulant.
In topical formulations, particularly cosmetics, it is used for its
softening and conditioning effect on the skin. Lactic acid may also
be used in the production of biodegradable polymers and microspheres,
such as poly(D-lactic acid), used in drug delivery
systems.
Lactic acid is also used as a food preservative. Therapeutically,
lactic acid is used in injections, in the form of lactate, as a source of
bicarbonate for the treatment of metabolic acidosis; as a spermicidal
agent; in pessaries for the treatment of leukorrhea; in infant feeds;
and in topical formulations for the treatment of warts.
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工業用途
lactic acid showed good depressing effect on hornblende, pyroxene and biotite during
flotation of hematite and ilmenite minerals.
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安全性
Lactic acid occurs in appreciable quantities in the body as an end
product of the anaerobic metabolism of carbohydrates and, while
harmful in the concentrated form , can be
considered nontoxic at the levels at which it is used as an excipient.
A 1% v/v solution, for example, is harmless when applied to the
skin.
There is evidence that neonates have difficulty in metabolizing
(R)-lactic acid, and this isomer and the racemate should therefore
not be used in foods intended for infants aged less than 3 months
old.
There is no evidence that lactic acid is carcinogenic, teratogenic,
or mutagenic.
LD50 (guinea pig, oral): 1.81 g/kg
LD50 (mouse, oral): 4.88 g/kg
LD50 (mouse, SC): 4.5 g/kg
LD50 (rat, oral): 3.73 g/kg
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製造方法
乳酸の製造方法には、乳酸菌等の微生物を用いる発酵法と、アルデヒドと青酸を出発原料として化学合成する方法があります。
発酵法
麦芽でデンプンを糖化し、これに炭酸カルシウムを加えて麦芽汁を作ります。麦芽汁に乳酸菌を加えて6~8時間発酵し、49℃で攪拌し続けると8~10日で発酵が完了します。その後、石灰乳を加えて弱アルカリ性にした後、再結晶により精製を行います。硫酸により再溶解させた後、ろ過、蒸発濃縮により工業用乳酸水溶液が得られます。
合成法
アセトアルデヒドに青酸を作用させ、シアンヒドリンを合成し、これを加水分解することで乳酸を合成します。
CH3CHO + HCN → CH3CH(OH)CN
CH3CH(OH)CN + 2H2O → CH3CH(OH)COOH +NH3
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貯蔵
Lactic acid is hygroscopic and will form condensation products
such as polylactic acids on contact with water. The equilibrium
between the polylactic acids and lactic acid is dependent on
concentration and temperature. At elevated temperatures lactic acid
will form lactide, which is readily hydrolyzed back to lactic acid.
Lactic acid should be stored in a well-closed container in a cool,
dry place.
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合成方法
乳酸菌による発酵生産
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不和合性
Incompatible with oxidizing agents, iodides, and albumin. Reacts
violently with hydrofluoric acid and nitric acid.
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規制状況(Regulatory Status)
GRAS listed. Accepted for use as a food additive in Europe.
Included in the FDA Inactive Ingredients Database (IM, IV, and SC
injections; oral syrups and tablets; topical and vaginal preparations).
Included in medicines licensed in the UK. Included in the
Canadian List of Acceptable Non-medicinal Ingredients.
