Lactic acid (IUPAC scientific name: 2-hydroxypropionic acid) is a compound that functions in a variety of biochemical processes. It is a carboxylic acid with a molecular formula of C3H6O3. It is a carboxylic acid containing a hydroxyl group and is therefore an alpha-hydroxy acid (AHA). In the aqueous solution, its carboxyl group releases a proton and produces the lactate ion CH3CHOHCOO−. Lactate dehydrogenase converts pyruvate to L-lactic acid during fermentation. Lactic acid is continuously produced in general metabolism and exercise, but its concentration generally does not rise.

Lactic acid powder CAS 50-21-5 for cosmetic Typical Properties

Item Specifications
Appearance White mixed granular powder
Lactic Acid content 58-62%
Calcium Lactate content 35-40%
Silicon Dioxide content 1-3%
Moisture < 3%
Reducing sugars Pass Fehling’s test
Chloride < 10ppm
Sulphate < 200ppm
Iron < 10ppm
Heavy metals < 10ppm
Arsenic < 1ppm
Mesophilic bacteria < 1000counts/g
Moulds < 1000counts/g
Yeasts < 1000counts/g

Physical and chemical properties

The pure product is a colorless liquid, and the industrial product is a colorless to pale yellow liquid. Odorless, with
Hygroscopicity. The relative density is 1.2060 (25/4 ° C). The temperature of 18 ° C. The boiling point of 122 ° C (2 kPa). The refractive index nD (20 ° C) 1.4392. It can be miscible with water, ethanol and glycerin, and the aqueous solution is acidic, PKa=3.85. Insoluble in chloroform, carbon disulfide and petroleum ether. It is decomposed by heating under normal pressure, and when it is concentrated to 50%, it partially becomes lactic anhydride, so the product usually contains 10% to 15% of lactic anhydride. Due to the presence of a hydroxyl group and a carboxyl group, an esterification reaction can occur under certain conditions, and there are three kinds of products.

Production method

The main route of the fermentation method is to adjust the pH value to about 50 or 60 dm under the action of lactic acid bacteria; and to obtain crude lactic acid by fermentation for three to five days.
The raw materials of the fermentation method are generally starchy raw materials such as corn, rice, sweet potato (also used as raw materials such as strontium and cellulose, and research has been proposed to recycle lactic acid from kitchen garbage and fish waste). There are many lactic acid bacteria that can produce acid in the lactic acid fermentation stage, but there are not many high-yield acid production, mainly the root mold and lactobacillus. Different strains have different fermentation pathways, which can be divided into homofermentation and heterofermentation. Actually, due to the existence of other physiological activities of microorganisms, it may not be a single fermentation pathway.
The fermentation method is divided into homofermentation and heterofermentation.

Synthetic method
Synthetic method The preparation of lactic acid is a lactonitrile method, an acrylonitrile method, a propionic acid method, a propylene method, etc., and is used only for the industrial production of a lactam-only method (also called an acetaldehyde hydrocyanic acid method) and an acrylonitrile method.

(1) Lactic nitrile method
The lactonitrile method is to continuously feed acetaldehyde and cold hydrocyanic acid into a reactor to form a lactonitrile (or directly use lactonitrile as a raw material), pump a lactonitrile into a hydrolysis kettle, and inject sulfuric acid and water to hydrolyze the lactonitrile. Crude lactic acid is obtained. Then, the crude lactic acid is sent to an esterification kettle, ethanol esterification is added, and the refined lactic acid is obtained by rectification, concentration, and decomposition. Both Sterling Chemical Company of the United States and Musashino Chemical Company of Japan use this method to synthesize lactic acid.

(2) Acrylonitrile method
In the acrylonitrile method, acrylonitrile and sulfuric acid are fed into a reactor for hydrolysis, and the hydrolyzate is sent to an esterification reactor for reaction with methanol; then, ammonium bisulfate is separated, and the crude ester is sent to a distillation column, and the bottom of the column is obtained. The fine ester is further sent to the second distillation column, and is heated and decomposed, and the bottom of the column is diluted with lactic acid, and the product is obtained by vacuum concentration.

(3) Propionic acid method
The propionic acid method uses propionic acid as a raw material, and is chlorinated and hydrolyzed to obtain crude lactic acid; and then esterified, rectified and hydrolyzed to obtain a product. The raw materials of this method are relatively expensive, and are only used by a few manufacturers such as Japan Dasai Road Company. The reaction is as follows:

Enzymatic method

(1) Chloropropionyl enzymatic conversion
The University of Tokyo’s Honsaki

[6] and other studies used purified L-2-haloacid dehalogenase and DL-2-haloacid dehalogenase to act on the substrate L-2-chloropropionic acid and DL-, respectively. 2-chloropropionic acid, dehalogenated to obtain L-lactic acid or D-lactic acid. L-2-haloacid dehalogenase catalyzes L-2-chloropropionic acid, while DL-2-haloacid dehalogenase catalyzes both L-2-chloropropionic acid and L-2-chloropropane The acid forms the corresponding optically active body, catalyzing the simultaneous configuration conversion.

(2) Pyruvate enzymatic conversion
D-lactate dehydrogenase is obtained from the cell viability of Lactobacillus sp. DSM20196, which has the highest activity of lactate dehydrogenase, and D-lactic acid is obtained by using optically active pyruvic acid as a substrate.

The industrial production of lactic acid methods is mainly fermentation and synthesis. Fermentation method is a relatively mature lactic acid production method because of its simple process, sufficient raw materials and early development. It accounts for more than 70 lactic acid production, but the cycle is long, and it can only be produced intermittently or semi-continuously. To international standards. Chemical methods enable large-scale continuous production of lactic acid, and synthetic lactic acid has also been approved by the US Food and Drug Administration (FDA), but raw materials are generally toxic and do not meet green chemical requirements. The enzymatic process is complex and its industrial application remains to be further studied.


Food Industry
1) Lactic acid has strong antiseptic and fresh-keeping effect, and can be used in fruit wine, beverage, meat, food, pastry making, vegetable (olive, cucumber, pearl onion) pickling and canning, food processing, fruit storage, with adjustment pH, bacteriostatic, prolonged shelf life, seasoning, color preservation, and product quality;

2) In terms of seasoning, the unique sour taste of lactic acid can increase the taste of food. Adding a certain amount of lactic acid to salads such as salad, soy sauce and vinegar can maintain the stability and safety of microorganisms in the product while making the taste milder. ;

3) Because of the mild acidity of lactic acid, it can also be used as the preferred sour agent for delicate soft drinks and juices;

4) When brewing beer, adding proper amount of lactic acid can adjust the pH value to promote saccharification, facilitate yeast fermentation, improve beer quality, increase beer flavor and extend shelf life. Used in white wine, sake and fruit wine to adjust pH, prevent the growth of bacteria, enhance the acidity and refreshing taste; buffered lactic acid can be used in hard candy, fruit candy and other confectionery products, with moderate acidity and low sugar conversion rate. Lactic acid powder can be used for powdering various types of candy as a powdery sour agent;

5) Natural lactic acid is a natural intrinsic ingredient in dairy products. It has the taste of dairy products and good anti-microbial effect. It has been widely used in blending yoghurt cheese, ice cream and other foods, and has become a popular dairy sour agent;

6) Lactic acid powder is a direct sour conditioner for the production of steamed bread. Lactic acid is a natural fermented acid, so it can make bread unique. Lactic acid is a natural sour taste regulator. It is used for baking and baking in bread, cakes, biscuits and other baked foods. It can improve the quality of food and maintain color. , extend the shelf life.

Medical aspect

1) Using lactic acid vapor disinfection in wards, operating rooms, laboratories, etc., can effectively kill bacteria in the air, reduce disease and improve health;

2) Widely used as a preservative, carrier, cosolvent, pharmaceutical preparation, pH adjuster, etc. in medicine;

3) Lactic acid polymerizes to obtain polylactic acid. Polylactic acid can be drawn into a silk-spun line. This line is a good surgical suture. After the seam is healed, there is no need to remove the thread. It can be automatically degraded into lactic acid and absorbed by the human body without adverse consequences. In particular, the surgical suture in the body eliminates the trouble of suturing the second operation. The polymer compound can be used as a binder in organ transplantation and bone grafting;

4) Lactic acid can be directly formulated into medicines or daily health care products; such as Jiaoyu private parts shower gel is a formula developed by European experts. It is slow to make mature Lactobacillus lactic acid bacteria, and adds lactic acid to maintain the self-cleaning effect of the vagina.

5) The restriction of muscle vitality and anti-fatigue.

Other industries

1) Lactic acid is used in the fermentation industry to control pH and increase the purity of the ferment;

2) In the cigarette industry, tobacco moisture can be maintained, impurities in tobacco can be removed, taste can be changed, tobacco grade can be improved, lactic acid can neutralize nicotine nicotine, and harmful substances can be reduced to improve tobacco quality;

3) Used in the textile industry to treat fibers, which can make the fibers easy to color, increase the luster, and make the touch soft;

4) Used as a pH regulator and synthetic agent in the paint ink industry; in the plastic fiber industry, it is the preferred raw material for the degradable new material polylactic acid PLA;

5) Lactic acid can also be used as a starting material for polylactic acid to produce a new generation of biodegradable plastics;

6) In the tanning industry, lactic acid can remove the lime and calcium from the leather, making the leather soft and fine, thus making high-grade leather;

7) Lactic acid is often used in the nickel plating process because of its unique complexation constant for nickel. It can also be used as an acid-base buffer and stabilizer in the plating bath. In the microelectronics industry, its unique high purity and low metal content meets the high quality requirements of the semiconductor industry. It is used as a safe organic solvent for the cleaning of photosensitive materials;

8) Lactic acid is used as a pH regulator and a synthetic agent in a variety of water-based coating systems. Such as: coating of electrical deposits. Lactic acid products have a low boiling point and are ideally suited for safe dissolution systems for high solids coatings. The lactic acid product line offers opportunities to produce high solids coatings with good fluid properties;

9) Lactic acid has the functions of cleaning and descaling. It is better for washing and cleaning products than traditional organic detergents, so it can be applied to many descaling products. Such as: toilet, bathroom, coffee machine cleaner. Lactic acid is antimicrobial and can be synergistic when used in combination with other antimicrobial agents such as ethanol.

Cosmetic industry

1) Since L-lactic acid is part of the skin’s inherent natural moisturizing factor, it is widely used as a moisturizer for many skin care products. L-lactic acid is the most effective type of AHA and has little irritation;

2) Since L-lactic acid is naturally present in the hair, the effect is to make the surface of the hair shiny and bright, so lactic acid is often used as a pH regulator for various hair care products;

3) Lactic acid can be used as a moisturizer in various toiletries, such as private body lotion, strip soap and moisturizer. It can be used as a pH regulator in liquid soaps, soaps and shampoos. In addition, the addition of lactic acid in the bar soap reduces the loss of moisture during storage and thus prevents the soap from cracking.

Agricultural livestock industry

1) Lactic acid with an optical purity of more than 99% can be used in the production of slow-release pesticides such as herbicides, which are non-toxic and efficient for crops and soils;

2) Lactic acid polymer is used in the production of agricultural film, which can be used to replace plastic film, which can be decomposed by bacteria and then absorbed by the soil, which is beneficial to environmental protection;

3) Lactic acid is also used in green feed storage and pasture ripening agents;

4) As a growth promoter in pig and poultry feed. Lactic acid can lower the pH in the stomach, activate digestive enzymes, improve the ability of amino acids to digest, and benefit the growth of intestinal epithelium. Piglets are fed a diet containing acidifiers for several weeks after weaning, which can increase body weight by 15% during weaning;

5) Lactic acid inhibits the growth of microorganisms. Lactating piglets are infected with diseases caused by Escherichia coli and Salmonella, and the addition of lactic acid to the feed prevents the growth of pathogenic bacteria in the lower gastrointestinal tract of piglets;

6) Lactic acid can act as a preservative for feed and enhance microbial stabilizers for by-products of feed, grain and meat processing products;

7) Adding lactic acid to the drinking water of poultry and piglets can effectively inhibit the growth of pathogenic bacteria and increase the weight of animals.

Human and lactic acid

For the human body, lactic acid is one of the fatigue substances, and is the waste generated by the body during the process of maintaining body temperature and body heat. Most of the energy we need to survive in our bodies comes from sugar. The blood is sent to various organs to burn as needed to generate heat.

In this process, water, carbon dioxide and pyruvic acid are produced, and pyruvic acid and hydrogen combine to form lactic acid. If the body’s energy metabolism can proceed normally, there will be no accumulation, it will be carried to the liver by the blood, and further decomposed into water and carbon dioxide to generate heat, and fatigue will be eliminated.

If the exercise is too intense or long-lasting, or if the body lacks the vitamins and minerals necessary to break down the lactic acid, then the body’s lactic acid can’t be processed, causing the accumulation of lactic acid. Excessive lactic acid will make the weakly alkaline body fluid acidic, affecting the cells to absorb nutrients and oxygen smoothly, and weaken the normal function of the cells. The muscles that accumulate lactic acid contract, which squeezes the blood vessels, causing poor blood flow, resulting in muscle soreness, chills, headaches, and head sensation. Lactic acid accumulation causes soreness and burnout in the early stage. If it is left untreated for a long time, acidification of the body may cause serious diseases.

Some people use the lazy sleep on holidays to eliminate fatigue, which is ineffective. Chemicals can only be used for temporary relief and have side effects. The correct way is to use appropriate exercise, especially stretching exercise to relax muscles, promote blood circulation, choose balanced and light nutrition, especially foods rich in vitamin B, plus high quality sleep, it will get the best Effect.

New research solution

The body needs a lot of energy during intense exercise. At this time, the production of lactic acid in the human body is higher than the rate at which the lactic acid is removed from the tissue, and the concentration of lactic acid in the tissue is increased. The significance of this process is to reconstitute the nicotinyl adenine dinucleotide (NAD) required for glycolysis to maintain adenosine triphosphate production and to increase the energy supply for exercise.

Pyruvate + NADH +H+→ Lactic Acid + NAD+

Unlike the general description of the rise in lactic acid concentration itself does not cause acidosis, it is not the cause of muscle soreness. In humans, lactic acid does not release protons and therefore is not acidic. Analysis of the glycolytic pathway in humans demonstrates that this process does not cause acidosis.

There is another reason for acidosis caused by intense exercise.
When adenosine triphosphate is split to release energy, it releases a proton. These protons are responsible for acidosis. Aerobic metabolism does not guarantee the production of adenosine triphosphate during intense exercise, so anaerobic metabolism begins. This process produces a large amount of adenosine triphosphate, which releases a large amount of protons upon decomposition, lowering the pH in the tissue and causing acidosis. This is one of the many reasons for muscle soreness during intense exercise. Some people think that lactic acid can cause acidosis by strong ion concentration gradient, but the research on this process is still very imperfect, so it is still unclear whether it exists.