E270 (Lactic Acid) is an organic acid found in nature and in many foods and milk sugars. It is produced by the metabolism of the human body and is formed when there is a situation of oxygen deficiency and sugar consumption. For example during muscular exertion and anaerobic respiration, the process by which cells produce energy without oxygen around.

It is generated by pyruvic acid under anaerobic conditions in skeletal muscles, the brain, red blood cells and the kidney. It is eliminated in a relatively short time, from a few minutes to a few hours. Lactate (produced from lactic acid) disappears very quickly at a rate of 320mmol/l/h, mostly through liver metabolism and in reconversion lactate reverts to pyruvate (1).

Industrially, it is obtained by fermentation from pyruvate using lactate dehydrogenase. It is produced by fermentation with Lactobacillus plantarum, a micro-organism widely used in the food industry, which can produce quantities of lactic acid in a lower pH environment. Another bacterium, Pediococcus pentosaceus, helps with fermentation.

Lactic acid comes in the form of a colourless to yellow odourless syrupy liquid or as a fine white powder.

What it is used for industrially and where it is used

Food

In foodstuffs it is labelled in the European list of food additives with the number E270 and has an acidifying and antibacterial function. It is used as an acidity corrector, antioxidant in meat, wine, beverages, confectionery, vegetables (onion, olive, cucumber), marinated and canned foods, grain processing, fruit preservation.

As a pH regulator it maintains the colour of food, improves the quality of the product in which it is incorporated and enhances taste.

Pharmaceutics and medicine

Lactic acid is a pharmaceutical intermediate used in the production process of pharmaceuticals and medicines such as erythromycin and infusion therapy. The antifungal property of lactic acid, and in particular its inhibition of mycotoxigenic fungi, depends on the ability of the strain to produce specific organic acids, and these acids may differ from strain to strain (2).

This study summarises the natural antimicrobial compounds produced by lactic acid bacteria that are responsible for maintaining safe and stable food products and highlights a wide range of potential applications (3).

In dermatology, it is used in the same way as other alpha-hydroxy acids (citric acid, glycolic acid, tartaric acid, malic acid) to combat the appearance of keratoses and acne (4).

Cosmetics

To maintain the pH value between 4 and 5 and as a wetting agent.  Lactic acid is an organic acid which is part of the alpha hydroxy acids recently used as surface peeling agents.

A polymer of lactic acid of synthetic origin, poly-l-lactic acid has been shown to improve facial wrinkles and is used as a filler for those who do not want to undergo cosmetic surgery (5).

Tanning industry

Lactic acid is used in the degreasing of hides and in their decalcination, i.e. the process of removing the lime attached to the leather fibres. Lactic acid improves the quality of degreasing as it is able to lower the pH. 

Textile industry

Lactic acid reduces the chromate content of wool and prevents oxidation of the fibre. In silk and rayon finishing, it is used as a pH regulator to lighten and increase the colour of the yarn.

Other uses :

• Beekeeping. As an antidote to Varroa, a parasitic mite that attacks bee larvae.
• Agriculture.  As a herbicide
• Animal husbandry. To inhibit bacteria and effectively increase the weight of livestock.
• Beer. To inhibit bacteria, promote yeast development, enhance flavour and improve beer yield.

For more information:

Lactic acid studies

Typical optimal characteristics of the commercial product Lactic acid

Appearance	Colourless to yellow liquid
Assay	88.3%
Boiling Point	227.6±0.0 °C at 760 mmHg
Melting Point	18ºC
Density	1.3±0.1 g/cm3
Stereochemical	≥98%
Residue on ignition	< 0.1%
Heavy Metal	<10mg/kg
Lead	< 0.5mg/kg
Cyanide	< 5mg/kg
Chloride	< 0.1%
Arsenic	< 3mg/kg
Sulfate	< 0.25%
Iron	< 10mg/kg
Safety

• Molecular Formula: C₃H₆O₃ 
• Linear Formula CH₃CH(OH)COOH
• Molecular Weight: 90.078 g/mol
• Exact Mass   90.031693
• UNII: 3B8D35Y7S4
• CAS: 50-21-5  152-36-3  598-82-3  31587-11-8  92129-90-3  1104201-86-6  1148011-07-7  1384255-85-9  947236-64-8
• EC Number: 200-018-0  295-890-2  209-954-4  608-645-5
• DSSTox Substance ID DTXSID7023192
• IUPAC  2-hydroxypropanoic acid
• InChI=1S/C3H6O3/c1-2(4)3(5)6/h2,4H,1H3,(H,5,6)  
• InChl Key      JVTAAEKCZFNVCJ-UHFFFAOYSA-N
• SMILES   CC(C(=O)O)O
• MDL number  MFCD00004520
• PubChem Substance ID    24901202
• ChEBI  78320
• ICSC    0501
• FEMA   2611  
• RTECS   OD2800000
• UN   3265
• NCI   C80130
• NSC   367919
• FEMA Number: 2611
• Beilstein Registry Number 1209341
• Council of Europe no. 4c
• Flavis number 8.004

Synonyms: 

• DL-Lactic acid
• 2-hydroxypropanoic acid
• 2-hydroxypropionic acid
• Milk acid
• Polylactic acid
• lactate
• 1-Hydroxyethanecarboxylic acid
• Aethylidenmilchsaeure
• alpha-Hydroxypropionic acid
• (+-)-2-Hydroxypropanoic acid
• Tonsillosan
• Acidum lacticum
• Racemic lactic acid
• Propanoic acid, 2-hydroxy
• (+/-)-Lactic acid
• Ethylidenelactic acid
• Lactovagan

References_______________________________________________________________

(1) Pundir CS, Narwal V, Batra B. Determination of lactic acid with special emphasis on biosensing methods: A review. Biosens Bioelectron. 2016 Dec 15;86:777-790. doi: 10.1016/j.bios.2016.07.076. 

(2) Guimarães A, Venancio A, Abrunhosa L. Antifungal effect of organic acids from lactic acid bacteria on Penicillium nordicum. Food Addit Contam Part A Chem Anal Control Expo Risk Assess. 2018 Sep;35(9):1803-1818. doi: 10.1080/19440049.2018.1500718. 

(3) Ibrahim SA, Ayivi RD, Zimmerman T, Siddiqui SA, Altemimi AB, Fidan H, Esatbeyoglu T, Bakhshayesh RV. Lactic Acid Bacteria as Antimicrobial Agents: Food Safety and Microbial Food Spoilage Prevention. Foods. 2021 Dec 17;10(12):3131. doi: 10.3390/foods10123131.

(4) Tang SC, Yang JH. Dual Effects of Alpha-Hydroxy Acids on the Skin. Molecules. 2018 Apr 10;23(4):863. doi: 10.3390/molecules23040863.

(5) Breithaupt A, Fitzgerald R. Collagen Stimulators: Poly-L-Lactic Acid and Calcium Hydroxyl Apatite. Facial Plast Surg Clin North Am. 2015 Nov;23(4):459-69. doi: 10.1016/j.fsc.2015.07.007.