lactic acid

[r ǔ su ā n]

Organic compound

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This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Lactic acid is a kind of carboxylic acid with the chemical formula C three H six O three , containing hydroxyl, belonging to α- Hydroxy acid (AHA). In aqueous solution, its carboxyl group releases a proton to produce lactate ion CH three CH(OH)COO − 。

Chinese name: lactic acid
Foreign name: 2-Hydroxypropanoic acid
lactic acid
Alias: α- Hydroxypropionic acid 、 2-hydroxypropionic acid
chemical formula: C three H six O three
molecular weight: ninety point zero eight
CAS login number: 50-21-5，79-33-4（L），10326-41-7（D）
Melting point: L: 53 °C，D: 53 °C，D/L: 16.8 °C
Boiling point: 122 ℃

Water solubility: Arbitrary mixing with hydropower
Density: 1.209 g/cm ³
Appearance: It is colorless, clear or yellowish viscous liquid; Almost odorless, slightly sour; Hygroscopic
Flash point: More than 110 ℃
Security description: S26； S39； S45； S36/37/39
Hazard symbol: Xi； C
Hazard description: R34； R38； R41
UN dangerous goods number: one thousand seven hundred and sixty

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A brief history of research

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In 1780, Swedish chemist Carl Wilhelm Scheele isolated lactic acid from yoghurt.^{[6 ]}

In 1808, Swedish chemist Jons Jakob Berzelius found lactic acid accumulation in the muscles of living animals in motion for the first time, and he believed that the acid found in muscles was the same as that found in yoghurt by Carl Wilhelm Scheele.^{[6 ]}

In the 19th century, scientists began to study the metabolic source of lactic acid. In 1847, German chemist Von Liebigdiscovered lactic acid in the muscle tissue of dead organisms. In 1858, Carl Folwarczny found lactic acid in the blood of a leukemia patient. In 1877 and 1879, Nasse concluded that lactic acid was derived from sugar through experiments. In the 1940s, the concept of glycolysis pathway was proposed, so lactic acid was considered as the end product of glycolysis under hypoxia.^{[6 ]}

In subsequent studies, it was found that hypoxia was not the main reason for lactic acid production. Lactic acid can actually be used as fuel in many tissues. Since 1985, Brook has tracked the flow of carbon intermediates during rest, exercise and recovery through a large number of isotope tracers, and combined intravenous measurement of lactate exchange with muscle biopsy to explore the lactate exchange between cells, thus introducing the concept of lactate shuttle mechanism.^{[6 ]}

In 1923, Warburg and Minami found that tumors can cause acidification of Ringer's solution of glucose. In 1927, Warburg found that the artery supplying the tumor always had a lower level of lactic acid and a higher level of glucose than the vein draining the tumor, even under the normal oxygen environment, the result was still the same. In 1972, Efraim Racker called the phenomenon that tumor cells consume a large amount of glucose and produce a large amount of lactic acid when they have enough oxygen supply as the "Warburg" effect.^{[6 ]}

Since the 1990s, scientists have believed that lactic acid is an active molecule that can regulate immune response. It can be used as a source of energy or play a variety of regulatory functions under physiological and pathological conditions.^{[6 ]}

definition

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During fermentation lactate dehydrogenase take pyruvic acid Convert to L-lactic acid 。 In general the new supersedes the old And lactic acid is constantly produced during exercise, but its concentration Generally, it will not rise. The concentration of lactic acid will increase only when the production process of lactic acid is accelerated and the lactic acid cannot be transported away in time. The transportation speed of lactic acid is affected by a series of factors, including Monocarboxyl transporter 、 lactate dehydrogenase Concentration and Isomer form Oxidizing capacity of tissue. Generally speaking, the concentration of lactic acid in blood is 1-2mmol/L when not exercising, and can rise to 20mmol/L when exercising intensely.

Generally speaking, when the energy of the organization cannot pass through Aerobic respiration The concentration of lactic acid will rise when the tissue cannot obtain enough oxygen or cannot process oxygen quickly enough. under these circumstances Pyruvate Dehydrogenase Unable to convert pyruvate into Acetyl CoA Pyruvate begins to accumulate. In this case, if lactate dehydrogenase does not reduce pyruvate to lactate, the glycolysis process and Adenosine triphosphate The synthesis of is suppressed.

The process of lactic acid production is: pyruvate+NADH+H + → Lactic acid+NAD + +2H

The significance of this process lies in the reconstruction of glycolysis Nicotinamide adenine dinucleotide （NAD + ）To keep Adenosine triphosphate Synthesis of. In oxygen rich Muscle cell Middle lactic acid can be oxidized to pyruvate, and then directly used as fuel for tricarboxylic acid cycle. It can also be used in liver The circulation of endogenous gluconeogenesis is transformed into glucose 。 Lactobacillus Bacteria of genus can also carry out Lactic acid fermentation 。 These bacteria can live in the mouth, and the lactic acid they produce causes dental caries Reason for. In medicine, lactic acid is often used in lactate Ringer's solution. It is equal to human blood sodium chloride 、 potassium chloride And lactic acid in distilled water. Often used after injury, surgery or burn Lactic acid Ringer's solution To replace the blood loss.

essential information

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Structural

Name: lactic acid

English name: Lactic acid; 2-Hydroxy propionic acid

Other names: 2-hydroxypropionic acid; α- Hydroxypropionic acid; Propanolic acid

Configuration: L-type; Type D; DL type

CAS registration number: 50-21-5 (DL); 79-33-4（L）^[3] ； 10326-41-7（D）^[4]

Molecular formula: C three H six O three^[2-4]

Simple structure: CH three CH(OH)COOH

Abbreviation: HL (where L represents lactate)

Molecular weight: 90.078^[2]^[4]

Relative density: 1.200

Melting point: 18 ℃

Density: 1.209

Boiling point: 122 ℃ (15 mmHg)

Dissociation constant: pKa=4.14 (22.5 ℃)

Flash point: more than 110 ℃

Combustion heat: 15.13kJ/kg

Isotonic volume: 2.3% (W/V) solution and plasma isotonic

Solubility: miscible with ethanol (95%), ether and water, insoluble in chloroform

Physical and chemical properties

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Pure products are colorless liquids, and industrial products are colorless to light yellow liquids. Odorless, hygroscopic. The relative density is 1.2060 (25/4 ℃). Melting point 18 ℃. Boiling point 122 ℃ (2kPa). Refractive index n D (20℃)1.4392。 It is miscible with water, ethanol and glycerin, and the aqueous solution is acidic, p K a =3.85。 Insoluble in chloroform, carbon disulfide and petroleum ether. It is decomposed by heating under normal pressure. When it is concentrated to 50%, part of it becomes lactic anhydride, so the product often contains 10%~15% lactic anhydride. With hydroxyl and carboxyl groups, esterification reaction can take place under certain conditions, and there are three kinds of products.

Toxicity: oral LD of rats fifty 3.73g/kg body weight; ADI has no restrictions.

Lactic acid has two isomers: D-type and L-type^[1] 。

The rats were divided into three groups. The dosage of DL type, D-type and L-type lactic acid in each group was 1.7 g/kg body weight. Three hours after oral administration, the anatomical examination showed that DL type lactic acid could increase the liver sugar in the liver, and 40%~95% of it was absorbed and transformed within three hours; D-type and L-type lactic acid increase lactate in blood and excrete it from urine.

Toxicological properties

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Under various pathological conditions, lactic acid accumulates in the blood circulation, which can cause lactic acidosis. There are many reasons for hyperlactaemia and the resulting lactic acidosis, mainly due to the increased production of lactic acid and the decreased excretion or utilization of lactic acid.^{[6 ]}

Symptoms of lactic acidosis include cold, muscle pain, dyspnea, stomach discomfort, arrhythmia, etc.^{[7 ]}

Physiological function

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Lactic acid has many biological activities. It is the key energy carrier. Lactic acid is the main energy source in the tricarboxylic acid cycle, and even glucose must be converted into lactic acid before entering the tricarboxylic acid cycle. Moreover, lactic acid is involved in the repair of body damage and the maintenance of tissue homeostasis, which can solve inflammation and maintain the restoration of tissue homeostasis. Lactic acid is also an important signal molecule, which participates in regulating a variety of pathophysiology. It is closely related to the function of intestinal stem cells and plays an important role in the maintenance of intestinal barrier and immune homeostasis. It can also inhibit the activation of intestinal epithelial cells by proinflammatory factors and maintain the stability of intestinal epithelial cells. In addition, it can also regulate dendritic cell activation and antigen expression.^{[8 ]}

Production method

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Fermentation

The main way of fermentation is to adjust the pH value of about 5 by sugar under the action of lactic acid bacteria, and maintain about 50~60dm; The crude lactic acid was obtained by fermentation for 3-5 days.

The raw materials for fermentation are generally starchy materials such as corn, rice, sweet potato, etc. (also alfalfa, cellulose, etc. are used as raw materials. Some studies have proposed that kitchen garbage and fish body waste should be recycled to produce lactic acid). There are many lactic acid bacteria that can produce acid in the lactic acid fermentation stage, but few of them can produce acid with high quality, mainly including Rhizopus and Lactobacillus. Different strains have different fermentation paths, which can be divided into homotypic fermentation and heterotypic fermentation. In fact, due to other physiological activities of microorganisms, it may not be a single fermentation path.

The fermentation method can be divided into homotypic fermentation and heterotypic fermentation.

Synthetic method

The synthetic methods for preparing lactic acid include acrylonitrile method, acrylonitrile method, propionic acid method, propylene method, etc. The only acrylonitrile method (also called acetaldehyde hydrocyanic acid method) and acrylonitrile method used in industrial production.

(1) Lactonitrile process

The lactonitrile method is to continuously send acetaldehyde and cold hydrocyanic acid into the reactor to generate lactonitrile (or directly use lactonitrile as raw material), pump lactonitrile into the hydrolysis kettle, inject sulfuric acid and water, and hydrolyze lactonitrile to obtain crude lactic acid. Then, the crude lactic acid is sent into the esterification kettle, and ethanol is added for esterification. After rectification, concentration and decomposition, refined lactic acid is obtained. Both Sterling Chemical Company in the United States and Musashino Chemical Company in Japan used this method to synthesize lactic acid.

(2) Acrylonitrile process

Acrylonitrile method is to send acrylonitrile and sulfuric acid into the reactor for hydrolysis, and then send the hydrolysate into the esterification reactor for reaction with methanol; Then put Ammonium bisulfate After separation, the crude ester is sent to the distillation tower, and the refined ester is obtained at the bottom of the tower; Then the refined ester is sent to the second distillation tower for heating and decomposition, and dilute lactic acid is obtained at the bottom of the tower, and the product is obtained through vacuum concentration.

(3) Propionic acid method

The propionic acid method uses propionic acid as raw material, chlorinates and hydrolyzes to obtain crude lactic acid; The product is obtained by esterification, rectification and hydrolysis. The raw material price of this method is relatively expensive, which is only used by a few manufacturers such as Japan Dajilu Company.

CH three CH two COOH →CH three CHClCOOH→CH three CH(OH)COOH

Enzymatic method

(1) Chloropropionate enzymatic conversion

In the research of Tokyo University, Honazaki et al., purified L-2-halogenated acid dehalogenase and DL-2-halogenated acid dehalogenase were used to act on the substrates L-2-chloropropionic acid and DL-2-chloropropionic acid, respectively, to dehalogenate L-lactic acid or D-lactic acid. L-2-halogenated acid dehalogenase catalyzes L-2-chloropropionic acid, while DL-2-halogenated acid dehalogenase can not only catalyze L-2-chloropropionic acid, but also catalyze L-2-chloropropionic acid to generate corresponding optical rotator, which catalyzes simultaneous configuration transformation.

(2) Pyruvate enzymatic conversion

D-lactate dehydrogenase was obtained from Lactobacillus tumefaciens DSM20196 with the highest activity of lactate dehydrogenase, and D-lactate was obtained by using inactive pyruvate as the substrate.

The main methods of industrial production of lactic acid are fermentation and synthesis. The fermentation method has become a relatively mature lactic acid production method due to its simple process, sufficient raw materials and early development, accounting for more than 70% of lactic acid production, but the cycle is long, and it can only be produced intermittently or semi continuously, and the quality of domestic fermented lactic acid can not reach the international standard. The chemical method can realize the large-scale continuous production of lactic acid, and the synthetic lactic acid has also been approved by the U.S. Food and Drug Administration (FDA), but the raw materials are generally toxic and do not meet the requirements of green chemistry. Enzymatic process is complex, and its industrial application needs further research.

purpose

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Food industry

1. Lactic acid has a strong antiseptic and fresh-keeping effect. It can be used in fruit wine, beverage, meat, food, cake making, vegetable (olives, cucumbers, pearl onions) pickling, canned processing, grain processing, and fruit storage. It can adjust pH, inhibit bacteria, extend shelf life, flavor, maintain food color, and improve 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 in salad, soy sauce, vinegar and other condiments can maintain the stability and safety of microorganisms in the product, while making the taste more mild;

3. Due to its mild and moderate sour taste, lactic acid can also be used as the first choice for carefully prepared soft drinks and fruit juices;

4. When brewing beer, adding an appropriate amount of lactic acid can not only adjust the pH value to promote saccharification, which is conducive to yeast fermentation, improve beer quality, but also increase beer flavor and extend the shelf life. It is used in liquor, sake and fruit wine to regulate pH, prevent the growth of miscellaneous bacteria, and enhance the sour taste and refreshing taste; Buffer lactic acid can be used in hard sugar, fruit sugar and other candy products, with moderate acidity and low sugar conversion rate. Lactic acid powder can be used to powder all kinds of candy, as a powdery sour agent;

5. Natural lactic acid is a natural and inherent component in dairy products. It has the taste of dairy products and good anti microbial effect. It has been widely used in blended yogurt, cheese, ice cream and other foods, and has become a popular yogurt for dairy products;

6. Lactic acid powder is a direct acid taste regulator used in the production of buckwheat head. Lactic acid is a natural fermented acid, so it can make bread have a unique taste; As a natural acid taste regulator, lactic acid is used for flavoring and bacteriostasis in baked foods such as bread, cake and biscuit, and can improve the quality of food, maintain color and extend the shelf life.

Medicine

1. The use of lactic acid steam disinfection in wards, operating rooms, laboratories and other places can effectively kill bacteria in the air, reduce disease and improve health;

2. In medicine, it is widely used as antiseptic, carrier agent, cosolvent, pharmaceutical preparation, pH regulator, etc;

3. Poly (lactic acid) is obtained by polymerization of lactic acid. Poly (lactic acid) can be drawn into silk and spun into thread. This thread is a good surgical suture. After the suture is healed, it does not need to be removed, and can be automatically degraded into lactic acid and absorbed by the human body, without adverse consequences. In particular, the internal surgical suture avoids the trouble of secondary surgical suture removal. The polymer compound can be used as an adhesive in organ transplantation and bone bonding;

4. Lactic acid can be directly prepared into medicine or daily health care products for use;

5. Section muscle vitality and anti fatigue constraints.

Other industries

1. Lactic acid is used in fermentation industry to control pH value and improve the purity of fermentation products;

2. In the cigarette industry, it can maintain tobacco humidity, remove impurities in tobacco, change taste, and improve tobacco grade. Lactic acid can also neutralize nicotine and nicotine, reduce harmful ingredients to human body, and improve tobacco quality;

3. It is used to treat fibers in the textile industry, which can make fibers easy to dye, increase luster, and make them soft to touch;

4. Used as pH regulator and synthetic agent in coating ink industry; It is biodegradable in the plastic fiber industry new materials The preferred raw material of PLA;

5. Lactic acid can also be used as the starting material of polylactic acid to produce a new generation of all Biodegradable plastics ；

6. In the leather industry, lactic acid can remove the lime and calcium in the leather, making the leather soft and compact, thus making high-grade leather;

7. Due to its unique complexation constant to nickel, lactic acid is often used in nickel plating process. It can also be used as an acid-base buffer and stabilizer in electroplating bath. In the microelectronics industry, its unique high purity and low metal content meet the requirements of the semiconductor industry for high quality. As a safe organic solvent, it can be used Photosensitive material Cleaning;

8. Lactic acid, as a pH regulator and synthetic agent, can be used in the bonding system of various water-based coatings. Such as: electrodeposit coating. Lactic acid products have low boiling points and are very suitable for safe dissolution systems developed for high solid coatings. The lactic acid product series provides an opportunity to produce coatings containing high solids with good fluid performance;

9. Lactic acid has the function of cleaning and descaling, and its performance for washing and cleaning products is better than that of traditional organic detergent, so it can be used in many descaling products. Such as: toilet, bathroom, coffee machine cleaner. Lactic acid has antimicrobial properties. When it is used together with other antimicrobial agents such as ethanol, it can produce synergistic effects.

Cosmetics

1. Because L-lactic acid is a part of the skin's inherent natural moisturizing factor, it is widely used as a moisturizer in many skin care products. L-lactic acid is the most effective AHA with little irritation;

2. Because L-lactic acid naturally exists in the hair and its role is to make the hair surface shiny, lactic acid is often used as a pH regulator for various hair care products;

3. Lactic acid can be used as a humectant in various bath and washing products, such as private bath liquid, bar soap and skin cream. It can be used as a pH regulator in liquid soap, soap and shampoo. In addition, lactic acid added to bar soap can reduce water loss during storage, thus preventing soap from drying.

Agriculture and animal husbandry

1. Lactic acid with optical purity of more than 99% can be used in the production of slow-release pesticides, such as herbicides, which is non-toxic, harmless and efficient to crops and soil;

2. Lactic acid polymer can be used to produce agricultural film instead of plastic film, which can be decomposed by bacteria and absorbed by soil, which is conducive to environmental protection;

3. Lactic acid can also be used as green feed storage agent and forage ripening agent;

4. It is used as a growth promoter in pig and poultry feed. Lactic acid can reduce the pH value in the stomach, activate digestive enzymes, improve amino acid digestion, and is beneficial to the growth of intestinal epithelium. Piglets fed with acidifier for several weeks after weaning can gain 15% of their weight during weaning;

5. Lactic acid can inhibit the growth of microorganisms. Piglets during lactation will be infected with diseases caused by Escherichia coli and Salmonella. Adding lactic acid in the feed can prevent the growth of pathogenic bacteria in the lower gastrointestinal tract of piglets;

6. Lactic acid can be used as feed preservative and microbial stabilizer to enhance the 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 speed of animal weight gain.

Pharmacopoeia information

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source

This product is a mixture of 2-hydroxypropionic acid and its condensate, containing lactic acid and C three H six O three Calculated as 85.0% - 92.0% (g/g).

character

This product is colorless or almost colorless clear viscous liquid, almost odorless, hygroscopic, and the aqueous solution shows acidic reaction.

This product can be mixed with water and ethanol at will.

relative density

The relative density of this product (general rule 0601) is 1.20~1.21.

identify

The identification reaction of the water solution of this product, namely, the sensible lactate (general rule 0301).

inspect

colour

Take this product and compare it with the yellow No. 1 standard colorimetric solution (general rule 0901 method 1). It should not be deeper.

chloride

Take 3.0g of this product and check it according to the law (general rule 0801). Compared with the control solution made of 6.0mL of standard sodium chloride solution, it should not be more concentrated (0.002%).

sulfate

Take 2. Og of this product and check it according to the law (general rule 0802). Compared with the control solution made of 2.0mL of standard potassium sulfate solution, it should not be more concentrated (0.010%).

Citric acid, oxalic acid, phosphoric acid or tartaric acid

Take 0.50g of this product, add proper amount of water to make it 5mL, mix it evenly, use ammonia test solution to make it slightly alkaline, add 1mL of calcium chloride test solution, heat it in a water bath for 5 minutes, without turbidity.

Carbonizable substance

Take 5mL of 95% (g/g) sulfuric acid and place it in a clean test tube. Pay attention to adding 5mL of this product along the tube wall to form two liquid layers. After standing at 15 ℃ for 15 minutes, the color of the interface shall not be darker than the pale yellow.

reducing sugar

Take 0.50g of this product, add 10mL of water, mix well, use 20% sodium hydroxide solution to neutralize, add 6mL of alkaline copper tartrate test solution, heat and boil for 2min, no red precipitate is allowed.

Ignition residue

Not more than 0.1% (general rule 0841).

Calcium salt

Take 1.0g of this product, add 10mL of water to dissolve it, add ammonia test solution to neutralize it, and add several drops of ammonium oxalate test solution to avoid turbidity.

ferric salt

Take 1.0g of this product and check it according to the law (general rule 0807). Compared with the control solution made of 1.0mL of standard iron solution, it should not be deeper (0.001%).

heavy metal

Take 2.0g of this product, add 10mL of water and 1 drop of phenolphthalein indicator solution, add an appropriate amount of ammonia test solution until the solution turns pink, add 3mL of dilute hydrochloric acid and an appropriate amount of water to make it 25mL, and check according to the law (General Rule 0821, Method 1), the content of heavy metals should not exceed 10 parts per million.

Arsenite

Take 2.0g of this product, add 23mL of water to dilute it, add 5mL of hydrochloric acid, and check according to the law (the first method of general rule 0822), which should meet the requirements (0.0001%).

Assay

Take about 1g of this product, precisely weigh it, add 50mL of water, precisely add 25mL of sodium hydroxide titrant (1mol/L), boil it for 5 minutes, add 2 drops of phenolphthalein indicator solution, titrate it with sulfuric acid titrant (0.5mol/L) when it is hot, and correct the titration result with blank test. Every 1mL of sodium hydroxide titrant (1mol/L) is equivalent to 90.08mg of C three H six O three 。

Storage

Sealed storage.^[5]

security information

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Safety terminology

S26：In case of contact with eyes, rinse immediately with plenty of water and seek medical advice.

In case of contact with eyes, please immediately flush with plenty of water and seek medical advice.

S36/37/39：Wear suitable protective clothing, gloves and eye/face protection.

Wear appropriate protective clothing, gloves and goggles or masks.

S45：In case of accident or if you feel unwell, seek medical advice immediately (show the label whenever possible.)

In case of accident or discomfort, seek medical advice immediately (show the label if possible).

Risk terminology

R34： Causes burns.

Causes burns.

R38： Irritating to skin.

Irritating to skin.

R41：Risk of serious damage to the eyes.

Serious damage to eyes.

matters needing attention

High concentration lactic acid has strong irritation and corrosiveness to skin and mucous membrane, so it is necessary to wear appropriate protective clothing, gloves, goggles or masks when using lactic acid. Moreover, lactic acid has serious damage to the eyes. If it comes into contact with the eyes accidentally, it needs to be immediately washed with a large amount of water and asked the doctor for advice.^{[9 ]}

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