Hydrochloric acid (HCl) is a strong, highly corrosive, and colorless solution of hydrogen chloride gas dissolved in water. It is an essential component of the gastric acid produced by the stomach. In the human body, hydrochloric acid plays a critical role in the digestion of food, particularly proteins.
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The primary function of hydrochloric acid[1] in the stomach is to create an acidic environment, which aids in the breakdown of food and the activation of digestive enzymes. It also serves as a barrier against harmful microorganisms that may enter the digestive system through ingested food.
The role of acid in our stomach is primarily related to digestion. The stomach produces hydrochloric acid[1] (HCl), which plays several crucial roles in breaking down food and facilitating nutrient absorption. Here are the main functions of stomach acid:
The acidity of stomach acid is crucial for the functioning of the digestive system. However, excessive acid production or other factors can lead to conditions like acid reflux, gastroesophageal reflux disease (GERD), or peptic ulcers. In such cases, medical intervention may be necessary to manage the acid levels and alleviate associated symptoms.
In our stomach, primarily two types of acid play significant roles in the digestive process. The balance of these acids and protective mechanisms is essential for proper digestion and overall gastrointestinal health. Any disruptions in this balance, such as excessive acid production[1] or damage to the protective lining, can lead to digestive disorders and conditions like acid reflux, peptic ulcers, or gastritis. In such cases, medical attention and proper management are necessary to restore equilibrium and alleviate symptoms. The two acids are:
Hydrochloric acid[1] is the primary acid in the stomach and gets secreted by specialized cells known as parietal cells. It is a strong and highly corrosive acid that creates an acidic environment in the stomach, with a pH ranging from approximately 1.5 to 3.5. As mentioned earlier, the main functions of hydrochloric acid are to denature proteins, activate pepsinogen into pepsin (an enzyme that starts protein digestion), and create an acidic environment for activating other enzymes.
Gastric acid[2] refers to the collective acidic components of the stomach's secretions, including hydrochloric acid and other substances, such as pepsinogen (the precursor to pepsin). When mixed, these components form gastric acid, which is essential for the digestive process in the stomach.
Acid, specifically hydrochloric acid (HCl), plays a crucial role in the digestion of food within the stomach. When we eat, the stomach's parietal cells secrete hydrochloric acid to create an acidic environment with a pH ranging from approximately 1.5 to 3.5. This acidic milieu serves several essential functions in the digestion process.
Firstly, the highly acidic environment denatures proteins present in the ingested food. Proteins in foods like meat and dairy have complex structures that need unraveling for proper digestion. Hydrochloric acid breaks down the protein's three-dimensional structure, exposing the peptide bonds between amino acids. This process[1] is vital because it enables subsequent digestive enzymes to access and cleave the protein into smaller peptide fragments.
Secondly, hydrochloric acid facilitates the activation of pepsin, a digestive enzyme responsible for protein digestion. Pepsinogen, the inactive precursor of pepsin, is released by the stomach's chief cells. However, it requires an acidic environment to undergo an enzymatic cleavage that converts it into its active form, pepsin. The hydrochloric acid in the stomach provides this acidic environment, allowing pepsinogen to transform into active pepsin. Once activated, pepsin effectively breaks down proteins into smaller peptide chains, further broken down by other digestive enzymes in the small intestine, eventually yielding individual amino acids that can get absorbed into the bloodstream for various bodily functions.
Stomach acid, primarily hydrochloric acid (HCl), is a potent defense mechanism against ingested bacteria and pathogens. When harmful microorganisms get ingested with food or water, they encounter a highly acidic environment. The low pH of stomach acid, which ranges from approximately 1.5 to 3.5, can kill many bacteria and pathogens that enter the digestive system. The acidic conditions disrupt the integrity of bacterial cell membranes, leading to their lysis or destruction. Additionally, the low pH denatures and inactivates certain bacterial enzymes and proteins, rendering them non-functional and incapable of causing infection or harm to the body.
Furthermore, stomach acid helps prevent[1] the overgrowth of harmful bacteria in the intestines by reducing their numbers. The stomach's acidic environment reduces the microbial load of ingested food, creating a protective barrier against the entry of harmful microorganisms into the rest of the digestive system. This action is crucial in maintaining a healthy gut flora balance, thus preventing the proliferation of pathogenic bacteria that may cause gastrointestinal infections and illnesses. Stomach acid, therefore, plays a vital role in protecting the body from potential bacterial threats and maintaining the overall health of the gastrointestinal system.
While stomach acid is highly corrosive and capable of breaking down ingested food, it also has an essential protective function for the stomach lining. The stomach is lined with a thick layer of mucus that acts as a physical barrier between the stomach acid and the underlying tissues. This mucus layer is rich in bicarbonate ions, alkaline compounds that help neutralize the acidic environment surrounding the stomach lining.
Bicarbonate ions released by the stomach's epithelial cells combine with hydrogen ions (H+) from the hydrochloric acid, forming water (H2O) and carbon dioxide (CO2). This neutralization reaction raises the pH level near the stomach lining, creating a less acidic environment that helps protect the stomach's delicate tissues from the corrosive effects of stomach acid. The combination of the mucus layer, bicarbonate neutralization, and ongoing cell regeneration work in concert to protect the stomach lining from damage and maintain the overall health of the gastrointestinal tract.
When there is excessive production of acid in the stomach or an imbalance in the protective mechanisms, it can lead to a condition known as hyperacidity or acid hypersecretion. This condition can cause several symptoms and may lead to various gastrointestinal disorders.
One common condition associated with excessive stomach acid is gastroesophageal reflux disease (GERD). In GERD, the excess acid can flow back into the esophagus, leading to heartburn, chest pain, and regurgitation of stomach contents into the throat. Excess stomach acid can also contribute to the development of peptic ulcers. The stomach lining has protective mechanisms to shield it from acid, but if these defenses are compromised, acid can erode the lining and form open sores or ulcers.
Acid reflux and gastroesophageal reflux disease[4] (GERD) are related conditions involving the backflow of stomach acid into the esophagus. Acid reflux occurs when the lower esophageal sphincter (LES), a muscular ring that acts as a valve between the esophagus and the stomach, weakens or relaxes inappropriately. GERD is a more chronic and severe condition characterized by frequent and troublesome acid reflux episodes that may cause damage to the esophagus and lead to complications if left untreated.
Low stomach acid – hypochlorhydria[3] - is a condition where the stomach produces inadequate hydrochloric acid (HCl). In individuals with low stomach acid, the digestive process may get impaired, leading to difficulties in digesting proteins properly and absorbing essential nutrients like vitamins and minerals.
Maintaining a healthy stomach acid level is essential for optimal digestion and overall gastrointestinal health. Here are some tips to help promote healthy stomach acid levels:
Remember that individual factors can affect stomach acid levels, and only a healthcare professional can determine the best approach for maintaining a healthy stomach acid balance. If you experience persistent digestive issues or symptoms of acid reflux, seek medical evaluation for an accurate diagnosis and appropriate management.
Stomach acid aids in digestion and helps keep your digestive health in check. Therefore, balancing acid levels in your stomach remains imperative. Here are answers to some of the frequently asked questions concerning gut health and the role of stomach acid.
Q1. Why is stomach acid necessary for digestion?
Your immune system and digestion both benefit from hydrochloric acid. It aids in the digestion of protein, the absorption of vital nutrients, and the management of viruses and bacteria that may otherwise infect your digestive system.
Q2. Can low stomach acid cause digestive problems?
You cannot adequately digest or absorb food's nutrients if your stomach acid level is insufficient. Indigestion, malnutrition, and even bacterial overgrowth result from this. Fortunately, testing and treating hypochlorhydria is not too difficult.
Q3. Are there any dietary factors that can affect stomach acid levels?
Maintaining stomach acid levels requires nutrients like iron, zinc, and B vitamins. Low stomach acid can be caused by a poor diet, nutritional loss from illnesses, stress, smoking, alcohol use, or both.
Q4. Can stress influence stomach acid production?
The body's reaction to stress causes gastric regeneration to slow down, which causes the gastric mucosa to atrophy. The stomach's blood flow reduces, which increases the stomach's susceptibility to acid-pepsin ulceration and hyperacid secretion.
Q5. How does stomach acid kill bacteria and prevent infections?
Histamine, released by enterochromaffin-like cells in response to gastrin, is the main factor stimulating gastric acid secretion. When the pH is less than 3.0, the HCl and pepsin in gastric juice can kill bacteria in 15 minutes. Bacterial overgrowth may happen if the pH increases over 4.0.
In conclusion, the acid in our stomach, primarily hydrochloric acid (HCl), plays a pivotal role in digestion and the overall health of the gastrointestinal system. Its acidic properties enable the breakdown of complex proteins, initiating digestion and facilitating the activation of digestive enzymes. Additionally, stomach acid acts as a critical defense mechanism, creating an inhospitable environment for harmful bacteria and pathogens that come with food. While stomach acid is essential for proper digestion and protection against infections, an imbalance in acid levels can lead to conditions like acid reflux and GERD, necessitating medical attention and appropriate management. Maintaining a healthy stomach acid balance through lifestyle modifications, dietary choices, and stress management is fundamental to promoting efficient digestion and ensuring overall gastrointestinal well-being.
References:
[1] https://pubchem.ncbi.nlm.nih.gov/compound/Hydrochloric-Acid
[2] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC/
[3] https://my.clevelandclinic.org/health/diseases/-hypochlorhydria#
Lactic acid is a naturally occurring organic acid that can be used in a wide variety of industries, such as the cosmetic, pharmaceutical, chemical, food, and, most recently, the medical industries. It can be made by the fermentation of sugars obtained from renewable resources, which means that it is an eco-friendly product that has attracted a lot of attention in recent years. In , the U.S. Department of Energy issued a report that listed lactic acid as a potential building block for the future. Bearing the importance of lactic acid in mind, this review summarizes information about lactic acid properties and applications, as well as its production and purification processes.
Download PDFLactic Acid Production to Purification: A Review
Andrea Komesu,a,* Johnatt Allan Rocha de Oliveira,b Luiza Helena da Silva Martins,a Maria Regina Wolf Maciel,a and Rubens Maciel Filho a
Lactic acid is a naturally occurring organic acid that can be used in a wide variety of industries, such as the cosmetic, pharmaceutical, chemical, food, and, most recently, the medical industries. It can be made by the fermentation of sugars obtained from renewable resources, which means that it is an eco-friendly product that has attracted a lot of attention in recent years. In , the U.S. Department of Energy issued a report that listed lactic acid as a potential building block for the future. Bearing the importance of lactic acid in mind, this review summarizes information about lactic acid properties and applications, as well as its production and purification processes.
Keywords: Lactic acid; Fermentation; Renewable resources; Separation processes
Contact information: a: School of Chemical Engineering, University of Campinas, Box , -970, Campinas-SP, Brazil; b: Nutrition College, Federal University of Pará (UFPA), -110, Belém-PA, Brazil; *Corresponding author:
INTRODUCTION
Lactic acid, or 2-hydroxypropionic acid (CAS 50-21-5), is the most widely occurring hydroxycarboxylic acid (Datta and Henry ). It is a natural organic acid with a long history of applications in the food, pharmaceutical, textile, and chemical industries (Ouyang et al. ). In recent years, the demand for lactic acid has increased considerably because of its use as a monomer in the preparation of polylactic acid (PLA) (Abdel-Rahman et al. ; Ouyang et al.; Shi et al. ), which is a biodegradable and biocompatible polymer that is used in a wide variety of applications. Its uses range from packaging and fibers to foams (Abdel-Rahman et al.) and applications in biomedical devices (Lasprilla et al. ). Lactic acid can be produced by fermentation or chemical synthesis. Production by the fermentation process has attracted interest because of its advantages, which are the production of pure isomers (L(+)- or D(-)-lactic acid), use of renewable and low cost raw materials, low energy consumption, and mild conditions required for operation.
Lactic acid was first discovered in sour milk in by the Swedish chemist Scheele (Lima et al.). In , Fremy carried out lactic acid fermentation with various carbohydrates, such as sugar, milk, starch, and dextrin (Holten et al. ). In , Pasteur discovered that lactic acid was not a component of milk, but a metabolite that certain microorganisms produced by fermentation (Benninga ).
In the last few decades, the production of lactic acid has substantially increased primarily because of the development of new uses and products. Global lactic acid demand was estimated to be 714.2 kilo tons in , and it is expected to grow annually by 15.5% to reach 1,960.1 kilo tons by (Abdel-Rahman and Sonomoto ). The three largest consumer markets in the world are the United States (31% of total lactic acid consumption in ), followed by China and Western Europe. China surpassed Western Europe due to export demand, as well as consumption in the food and beverage industry. The world’s top three lactic acid manufacturers, which are Purac, Cargill and Henan Jindan Lactic Acid Technology Co., Ltd., boasted a combined capacity of 505,000 tons in . Cargill mainly supplies lactic acid products to its subsidiary – NatureWorks for production of polylactic acid (PR Newswire )
In , the U.S. Department of Energy issued a report on the chemicals that are considered potential building blocks for the future (Jong et al. ), and lactic acid was included.
Bearing the importance of lactic acid in mind, this review summarizes information about lactic acid properties and its applications. Production and purification processes are also discussed.
LACTIC ACID PROPERTIES
Lactic acid is a yellow to colorless liquid (at 15 °C and 1 atm), and is odorless. It is the simplest hydroxycarboxylic acid. Thermodynamic properties are shown in detail in Table 1.
Table 1. Thermodynamic Properties of Lactic Acid (Holten et al. ; Perry and Chilton )
Lactic acid is both an alcohol and acid, and it has an asymmetric carbon that confers optical activity. It can be found in two optically active forms, L(+)-lactic acid and D(-)-lactic acid, or in racemic form, which is a mixture of L(+)-lactic acid and D(-)-lactic acid. The two isomers have the same physical properties (melting point, solubility, dissociation constant, density, etc.) and the same chemical properties, except when in reactions where other compounds with optical activity are present. One consequence of those reactions is the difficulty in separating the compounds through traditional techniques (chromatography, distillation, and fractional crystallization). Thus, it is necessary to select appropriate separation techniques when using substances with optical activity. The pure isomers have greater value than the racemic mixture because they are used for specific industrial applications, e.g., L(+)-lactic acid is used in the synthesis of L(+)-polylactic acid, a biodegradable semi-crystalline and thermosetting polymer. Another application is D(-)-polylactic acid production, where the D(-)-isomer of lactic acid is used.
Additionally, isomers behave differently in living tissues. L(+)-Lactic acid is found in living organisms more often than D(-)-lactic acid. In the human body, only L(+)-lactic acid is produced during muscle contraction (Trindade ). For applications in food and in medicine, L(+)-lactic acid is preferred because the metabolic conversion of L(+)-lactic acid in the body is faster than for D(-)-lactic acid. Different methods of production result in different amounts of isomers. In lactic acid production by chemical synthesis, only a racemic mixture is obtained, where the concentrations of the isomers are equal, whereas fermentation allows for producing one isomer in a greater amount.
APPLICATIONS
Lactic acid has a wide range of applications in chemicals, pharmaceuticals, and food, and it is a precursor to several products. The uses and demand of lactic acid are shown in Fig. 1. Although commercially available long ago, it is only in recent decades that new uses have resulted in a great increase in the demand.
Fig. 1. Uses and demand of lactic acid (The Essential Chemical Industry Online )
In the food industry, which accounts for a large portion of the demand (35%), lactic acid has a number of uses. It is used as an acidulant because of its mild acidic taste when compared with other acids used in food, and as a preservative in olives and pickled vegetables. It is also used as a flavoring agent, pH regulator, and inhibitor of residual bacteria in food processing, such as for sweets, breads, soft drinks, beer, and other products. It is an essential ingredient in fermented foods as well, like yogurt, butter, and canned vegetables.
Lactic acid has applications in the leather tanning industry, in descaling processes, in the textile industry as a mordant (fixative) for dyeing, and can replace ethylene glycol in antifreeze, which results in a higher efficiency and lower cost. In the chemical industry, lactic acid can be converted to ethanol, propylene glycol, and acrylic polymers. Lactic acid derivatives, salts, and esters are used as solvents, emulsifiers, and plasticizers (Trindade ). Lactic acid is also used in the production of propylene oxide, acetaldehyde, acrylic acid, propanoic acid, 2,3-pentanedione, ethyl lactate, lactide, and polylactic acid.
In the pharmaceutical industry, lactic acid is used in implants, pills, dialysis, surgical sutures, and controlled drug release systems. In the cosmetic industry, lactic acid is used in the manufacture of hygiene and aesthetic products because of its moisturizing, antimicrobial, and rejuvenating effects on the skin. It is also used in oral hygiene products (Castillo Martinez et al. ).
New applications for lactic acid have been developed, such as the production of biodegradable and biocompatible PLA polymers (Abdel-Rahman et al. ), solvents, and oxygenated chemicals. Polymer production accounts for the largest portion of lactic acid demand (39%). In polymer applications, water is removed from lactic acid (CH3CHOHCOOH) in the presence of acid catalysts to form lactides (C6H8O4), as shown in Eq. 1:
(1)
Lactides are polymerized to obtain the biodegradable thermoplastic polymer, PLA. There is a growing demand for PLA derivatives to substitute conventional plastic materials, as well as for use in materials for medical devices (Gao et al. ). L(+)-Lactic acid provides a high yield of lactide, which in turn yields polymers with a high molecular weight, high degree of crystallinity, and high tensile strength. These polymers are transparent, which is important for packaging applications; have long shelf lives because they slowly degrade by hydrolysis (which can be controlled by composition and molecular weight adjustment); and their characteristics are similar to polymers generated from fossil fuels. Lactic acid polymers have the advantage of being produced by renewable carbohydrates. Other desired properties can be obtained by copolymerization with other oxygen monomers.
A large number of patents and articles about lactic acid polymers have been published in recent years (Jompang et al. ; Padee et al. ; Pivsa-Art et al. ; Li et al. ; Shi et al.). Although demand for PLA has expanded, its current production capacity of 450 million kg per year is dwarfed by the 200 billion kg of total plastics produced per year. This low production volume is, for the most part, due to the high manufacturing costs. On an industrial scale, the targeted manufacturing cost of the lactic acid monomer is less than 0.8 US$/kg because the selling price of PLA must decrease by roughly half of its present price of 2.2 US$/kg to be able to compete with fossil fuel-based plastics (Wee et al. ; Okano et al. ). The majority of the cost of manufacturing PLA is associated with lactic acid monomer production costs (Okano et al.).
The use of lactic acid in the manufacture of green solvents, which are environmentally friendly solvents, is another area for potential growth. In particular, using lactate esters from alcohols with low molecular weights in the formulation of pesticides (Sasson et al. ; Baur et al. ) and other bioactive components because of its low toxicity has a high potential for growth.
Oxygen chemical derivatives from lactic acid are widely produced, and include propylene glycol, propylene oxide, acrylic acid, and acrylate esters (Datta and Henry ).
Although there is a wide range of applications, the use of lactic acid is still limited by the final production costs associated with the downstream processes, which are responsible for 30% to 40% of total production costs of lactic acid (López-Garzón and Straathof ).
MANUFACTURING TECHNOLOGIES
The lactic acid molecule is found naturally in plants, microorganisms, and animals, and may also be produced by the fermentation of carbohydrates or by chemical synthesis from coal, petroleum products, and natural gas. Industrially, lactic acid can be produced by chemical synthesis or by fermentation. Figure 2 shows the two main processes of lactic acid production.
Although racemic lactic acid is always produced by chemical synthesis from petrochemical resources, an optically pure L(+)- or D(-)-lactic acid can be obtained by microbial fermentation of renewable resources when the appropriate microorganism is selected (Wee et al. ). Depending on the application, one form of the optically pure lactic acid is preferable over the other. Additionally, microbial fermentation offers advantages, including cheap renewable substrates, low production temperatures, and low energy consumption (Abdel-Rahman et al.). Because of these advantages, it is the production process that is used most often.
Fig. 2. Overview of the two manufacturing methods of lactic acid, chemical synthesis and microbial fermentation (Wee et al. )
Chemical Synthesis
Lactic acid production by chemical synthesis using the lactonitrile route, which was a by-product of acrylonitrile technology, was discovered in by Wislicenus (Benninga ). The reactions involved are described in Eqs. 2 to 5,
(2)
(3)
(4)
(5)
In Eq. 2, hydrogen cyanide (HCN) is added to liquid acetaldehyde (CH3CHO) in the presence of a base catalyst under high pressure when lactonitrile is produced (Pal et al. ). Then in Eq. 3, lactonitrile is recovered, purified by distillation, and hydrolyzed using sulfuric acid (H2SO4) to obtain lactic acid (CH3CHOHCOOH) and ammonium salt ((NH4)2SO4). In Eq. 4, lactic acid is esterified with methanol (CH3OH), and the methyl lactate (CH3CHOHCOOCH3) formed is recovered, purified by distillation, and hydrolyzed with acidified water to produce lactic acid and methanol. Methanol is separated by distillation and recycled in Eq. 5.
The first company to produce lactic acid by chemical synthesis in significant amounts was Monsanto (Texas, USA) in . They produced 40% (4,500 tons) of the lactic acid consumed in the USA (Trindade ). Industrial production by chemical synthesis was also used by Sterling Chemicals, which ended production in early . In the east, Musashino Chemical also used this technology, but recently they changed their production process to fermentation (John et al. ).
Chemical process routes include base-catalyzed degradation of sugars, oxidation of propylene glycol, hydrolysis of chloropropionic acid, nitric acid oxidation of propylene, and the reaction of acetaldehyde, carbon monoxide, and water at high temperatures and pressures (Gao et al. ). Although there are many possible routes for the production of lactic acid by chemical synthesis, none of these routes are technically and economically feasible (Datta et al. ; Gao et al. ), except for the routes that use lactonitrile as the raw material.
Lactic acid production by a chemical route is expensive and dependent on by-products from other industries, which are derived from fossil fuels (Datta and Henry ). Furthermore, chemical synthesis produces a racemic mixture of lactic acid (Abdel-Rahman et al. ; Pal et al. ) and for many specific applications, only one of the lactic acid isomers is desired. The problems of expensive raw materials, impurity of the product, and dependence on other industries for raw materials can be bypassed by using biotechnological processes based on fermentation (Pal et al.).
Carbohydrate Fermentation
Worldwide lactic acid production from microbial fermentation accounts for around 90% of the total lactic acid production (Hofvendahl and Hahn-Hägerdal ) and has attracted interest because of its numerous advantages compared with chemical synthesis, such as production of pure isomers and the use of renewable resources as fermentation substrates.
The fermentation process is characterized by the biological degradation of the substrate (glucose) by a population of microorganisms (biomass) into metabolites, such as ethanol, citric acid, and lactic acid (Silveira ). Several microorganisms and raw materials can be used in the production of lactic acid (Table 2). A fermentation product with high purity is obtained when a pure substrate is used, such as sucrose from sugarcane and sugar beet, which results in a reduction in the cost of purification.
Table 2. Lactic Acid Production using Different Substrates and Microorganism
Unfortunately, the high cost of sugar makes it unfeasible for use. However, waste products from food industries, agricultural industries, sugarcane mills, and biomasses can be used, which is advantageous from an environmental and economic standpoint.
Raw material cost is one of the major factors in the economic production of lactic acid. Since substrate cost cannot be reduced by process scale-up, extensive studies currently are underway to search for novel substrates for lactic acid production (Abdel-Rahman et al. ).
Starchy materials, such as wheat, corn, maize, cassava, potato, rice, rye, barley (Wang et al. ; Nakano et al. ; Li et al. ; Prückler et al. ) are potential raw material for lactic acid production. The advantages is that starchy materials can avoid glucose repression, which occurs when high concentration of glucose in the medium would inhibit growth of lactic acid bacteria (Nakano et al. ). Approximately 90% of the commercially available lactic acid is produced by submerged fermentation of corn (Wang et al. ).
Lignocellulose biomass is also a promising source for lactic acid production because its represents the most abundant global source of biomass (Hama et al. ; Hu et al. ; Eom et al. ). It can be used to obtain sugar solutions that may be usefully exploited for the production of lactic acid through the following steps: (a) pretreatment to break down the lignocellulosic structure, (b) enzymatic hydrolysis to depolymerize lignocellulose to fermentative sugars, and (c) sugar fermentation to lactic acid (Idler et al., ). Although the cost of lignocellulose is low, the pretreatment step makes the whole process cost-inefficient. This occurs because of the following reasons: (a) additional cost of enzymes and chemicals, (b) inhibitory compounds generated during chemical hydrolysis (e.g. furfural, 5-hydroxymethylfurfural, and some organic acids) that are inhibitory to the microorganisms used in fermentation, (c) production of mixed sugars such as pentoses, which cannot be fermented by the majority of producer strains. To overcome these challenges, direct conversion of polymeric sugars is of great interest (Abdel-Rahman and Sonomoto ). In addition, hydrothermal pretreatment is one of the simplest and most promising methods. In this process, only hot water is used as the reaction medium (Eom et al. ), reducing operating and maintenance costs (Eom et al. ).
Recently, the manufacturing of cheese has been reported to produce large volumes of whey as a byproduct (Li et al. ). Several studies have recently reported lactic acid production using whey (Tejayadi et al. , Kim et al. ; Li et al. ). Whey is a potent and suitable raw material for lactic acid production because it consists of lactose, protein, fats, water-soluble vitamins, mineral salts, and other essential nutrients for microbial growth (Panesar et al. ).
Food waste is other potential raw material for lactic acid production because it is usually rich in carbohydrates. In addition, it is advantageous as an effective method of environmental waste management (Tashiro et al. ; Abdel-Rahman and Sonomoto ; Tang et al. ).
Another approach for production of lactic acid is from glycerol, which is a by-product of biodiesel production. The conversion of glycerol to lactic acid can be categorized into hydrothermal (Kishida et al. ; Yin et al. ) and heterogeneous catalysis methods (Auneau et al. ).
Microalgae are another potential raw material for lactic acid fermentation. Microalgae do not contain lignin, which simplifies conversion into fermentation substrate. In addition, microalgae grow almost anywhere, have an extremely short harvesting cycle of approximately 1 to 10 days (Nguyen et al. ), and have high fermentable sugar contents.
Several reviews have been published about novel substrates and developments of biotechnology processes for lactic acid production by fermentation (Vaidya et al. ; Datta and Henry ; Abdel-Rahman et al. ; Abdel-Rahman et al. ).
Microorganisms used in fermentation can be divided into two groups: bacteria and fungi (Wee et al. ). The choice of which type of microorganism to use depends primarily on the carbohydrate that is to be fermented, as a microorganism’s metabolism differs with different sources of carbon (Lunelli ).
Most lactic acid bacteria (LAB) are cocci, with the exception of Lactobacilli and Carnobacterium, which are rods. LAB are unable to synthesize ATP by respiration, and their major end product from the energy-conserving fermentation of sugars is lactic acid. Most LAB are facultative anaerobic, catalase negative, nonmotile, and non-spore forming. They normally have a high acid tolerance and can survive at pH 5 and lower. Their high acid tolerance gives them a competitive advantage over other bacteria. The optimal temperature for growth varies between the genera from 20 to 45 °C (Hofvendahl and Hahn-Hägerdal ). LAB can be classified into two groups according to fermentation end-product, homofermentative and heterofermentative. There are two kinds of heterofermentative LAB, obligatory and facultative. Figure 3 shows the catabolic pathways for LAB.
Homofermentative LAB convert glucose almost exclusively to lactic acid, while heterofermentative LAB catabolize glucose into ethanol, CO2, and lactic acid. Homofermentative LAB normally metabolizes glucose by the Embden-Meyerhof-Parnas pathway (glycolysis). Glycolysis only results in lactic acid as the end product of glucose metabolism. Two molecules of lactic acid are produced per glucose molecule, which results in a yield of more than 0.90 g/g. Lactobacillus acidophilus, Lactobacillus amylophilus, L. bulgaricus, Lactobacillus helveticus, and L. salivarius are all homofermentative LAB (Castillo Martinez et al. ).
Obligatory heterofermentative LAB ferment sugar by the 6-phosphogluconate/ phosphoketolase pathway, while facultative heterofermentative LAB use both pathways for fermentation. Lactobacillus brevis, L. fermentum, L. parabuchneri, and L. reuteri are obligatory heterofermentative LAB. Facultative heterofermentative LAB are L. alimentarius, Lactobacillus plantarum, Lactobacillus casei, Lactobacillus rhamnosus, Lactococcus lactis, Lactobacillus pentosus, and Lactobacillus xylosus (Castillo Martinez et al. ).
LAB have complex nutrient requirements because of their limited ability to synthesize B vitamins and amino acids (Hofvendahl and Hahn-Hägerdal ) and so require a nutritionally rich medium for growth.
Many LAB produce only one isomer of lactic acid, but sometimes, depending on operating conditions, small amounts of both isomers can be produced. Organisms that produce the D(-)- or L(+)-isomer have two lactate dehydrogenase enzymes (LDH), which differ in their stereospecificity. Some Lactobacillus species produce the L(+)-isomer, and when those isomers accumulate, lactic acid is converted into the D(-)-isomer until equilibrium is reached and a racemic mixture is formed (Narayanan et al. ). Lactobacillus helveticus and Lactobacillus plantarum produce a racemic mixture (Hofvendahl and Hahn-Hägerdal ).
Although the majority of lactic acid processes are carried out with LAB, there are filamentous fungi, such as Rhizopus, that can utilize glucose aerobically to produce lactic acid. Rhizopusspecies, such as R. oryzae and R. arrhizus, have amylolytic enzymatic activity, which enables them to convert starch directly to L(+)-lactic acid. Several studies have reported on the use of Rhizopus for lactic acid production (Yin et al. ; Liu et al. ; Yu et al. ; Guo et al.; Wu et al. ; Saito et al. ).
Fig. 3. The catabolic pathways for lactic acid bacteria are (A) homofermentation, (B) heterofermentation, and (C) mixed acid fermentation. P= phosphate, BP= biphosphate, LDH= lactate dehydrogenase, PFL= pyruvate formate lynase, and PHD= pyruvate dehydrogenase (Hofvendahl and Hahn-Hägerdal )
Fungal fermentation has some advantages. For example, R. oryzae requires only a simple medium and produces L(+)-lactic acid, but it also requires vigorous aeration because R. oryzae is an obligate aerobe. The low production rate in fungal fermentation, below 3 g/L/h, is most likely due to the low reaction rate caused by mass transfer limitations. Lower product yields in fungal fermentation are also partially attributed to the formation of by-products, such as fumaric acid and ethanol (Wee et al. ).
Other than the substrate source and microorganism, some parameters that may affect the fermentation efficiency are the pH and temperature of the medium, nitrogen and vitamins sources, fermentation operation, and by-products formation.
The pH of the fermentation decreases according to the amount of lactic acid that is produced. To control the pH, a base is added to the medium, such as calcium carbonate, calcium hydroxide, or sodium hydroxide, because in an acidic medium, lactic acid production is either zero or minimal. The pH control can also be done by extraction, adsorption, or electrodialysis of lactic acid (Hofvendahl and Hahn-Hägerdal ). Several studies show that a pH value of approximately 6.5 is the optimal pH for growth and lactic acid production (Silveira ). A pH below 5.7 is only optimal for Lactobacillus strains, which are known to tolerate lower pHs than Lactococci(Hofvendahl and Hahn-Hägerdal ). The batch fermentation process at a controlled pH significantly improves lactic acid production, yield, and productivity by different LAB strains, e.g., Lb. Delbrueckii, E. mundtii QU 25 and E. faecium (Abdel-Rahman et al. ).
Temperature is an important parameter for bacteria growth (Silveira ) and relates to the growth kinetics parameters of LAB, lactic acid production, and substrate consumption. Among LAB, most lactic acid productivity studies have been conducted at temperatures ranging from 30 to 43 °C (Abdel-Rahman et al. ).
Nitrogen sources and vitamins are important primarily because of the limited ability of bacteria to synthesize B vitamins. The main sources of nitrogen are yeast extract and ammonium sulfate (Yin et al. ; Zhou et al. ; Jin et al. ). In terms of industrial processes, the use of yeast extract has a high cost, although it is best for the cultivation of lactic acid bacteria. Ammonium sulfate is a practical alternative, mostly because of its lower cost. Inexpensive nitrogen sources supplements (e.g. flour of pigeon pea, red lentil gram, black gram, bengal gram, green gram, soya bean, baker’s yeast) have been studied to replace commercial peptone and yeast extract (Altaf et al. , ). The addition of other nutrients into the medium generally has a positive effect on the lactic acid production; sources include peptone and meat extract (Hofvendahl and Hahn-Hägerdal ).
Lactic acid is usually produced in batch mode, but continuous and fed-batch modes can also be used. Fermentation in batch mode has superior conversion and yield compared to continuous fermentation, but the volumetric productivity is lower. In a batch process, all of the substrate gets used, whereas in a continuous process, there is a residual substrate concentration that is always present. The highest productivity possible for continuous fermentation is due to the high dilution ratio and the possibility of maintaining the process for a long period of time. The choice of operation mode depends on the costs of the substrate and the capital investment. If the substrate is expensive, the yield is maximized, by either batch or semicontinuous operation. If investment costs are high, the volumetric productivity is maximized by continuous operation (John et al.). A high volumetric productivity is achieved by a cell recycle system, which results in a high cell density with complete glucose conversion (Ohleyer et al. ).
Production of other organic acids during lactic acid fermentation depends on the purity and quality of the inoculum, metabolic route used, and process conditions, which should prevent external contamination. By-products, such as acetic acid, formic acid, carbon dioxide, and ethanol, can be produced, but for efficient lactic acid production, formation of by-products should be avoided or kept to a minimum (Hofvendahl and Hahn-Hägerdal ).
The manufacturer Archer Daniels Midland began using the fermentation process for lactic acid production in the early s. At the end of , Cargill joined Dow Chemical, creating Cargill-Dow, and started producing a polymer by PLA-based fermentation technology. In early , Cargill broke away from Dow and established NatureWorks LLC. The biggest producers of lactic acid by fermentation now include NatureWorks LLC, Purac (Netherlands), Galactic (Belgium), Cargill (USA), and several Chinese companies, such as CCA (Changzhou) Biochemical Co. Ltd., Henan Jindan Lactic Acid Co. Ltd., and Mushashino Chemical Co. Ltd. Currently, NatureWorks LLC is leading the lactic acid polymers market in terms of production and technology (John et al.; Abdel-Rahman et al. ). NatureWorks LLC built a lactic acid plant in Blair, USA, with a production capacity of 180,000 tons per year, which started operation in (Wee et al. ; John et al. ).
SEPARATION AND PURIFICATION PROCESSES
Separation processes are essential to the chemical industry and other related industries. Approximately 40% to 70% of operating and capital costs are associated with the separations steps (Wankat ). In lactic acid production processes, development of an effective method of lactic acid separation and purification from fermentation broth is extremely important for economic viability. Although the difference between the boiling point of lactic acid and water is relatively large, it is almost impossible to obtain pure crystalline lactic acid. This is because lactic acid has a high affinity for water and a dimer of lactate is formed when lactic acid concentrations are sufficiently high (Lunelli ).
Lactic acid process in a classical way involves a series of downstream treatments such as precipitation, conventional filtration, acidification, carbon adsorption, evaporation, crystallization, and others (Pal et al. ). The number of downstream processing steps strongly influences the quality and the price of the product (Idler et al. ).
Open sources provide only limited data about industrial product recovery processes (Idler et al. ). Otherwise, the separation steps are widely discussed in literature, such as precipitation (Rauch et al. ; Min et al. ; Kwak et al. ; Nakano et al. ), solvent extraction (Malmary et al. ; Wasewar et al. ; Matsumoto et al. ; Yankov et al. ; Alkaya et al. ; Krzyzaniak et al. ), membrane separation processes, and others. Membrane separation processes that have been studied include reverse osmosis, electrodialysis, and ultrafiltration (Kim and Moon ; Choi et al. ; Madzingaidzo et al. ; Li and Shahbazi ; González et al. ; Ecker et al. ; Lu et al. ; Ramchandran et al. ; Sikder et al. ; Dey and Pal ; Pal and Dey ; Wang et al. ).
Efficient lactic acid yields and purities can be obtained from these purification technologies, and several advances have been developed, but many drawbacks are still reported. In the precipitation process, the drawbacks include high cost of reagents and the necessity of filtration and other separation processes, especially when a product of higher purity is required. From an environmental standpoint, the generation of large amounts of wastewater is a major drawback. Furthermore, to produce one ton of lactic acid, approximately one ton of low-cost calcium sulfate is needed (Pal et al. ), which poses serious problems in terms of waste treatment. In solvent extraction, a high exchange area for efficient separation is necessary, which requires expensive equipment. Its application in in situ extractive fermentation is limited by solvent recovery done in stripping steps and the high toxicity of the extractant to the microorganisms (Gao et al. ). Membrane separation processes are promising technologies, but the high cost of membranes and the polarization and fouling problems limit the use of electrodialysis processes on a large scale.
In recent years, many studies have been completed that attempt to solve the problems of traditional separation process by instead using non-traditional distillation separations (Komesu at al. ), such as reactive distillation (Asthana et al. ; Kumar et al. ; Lunelli et al.) and molecular distillation (Wei et al. ; Xu et al. ; Chen et al. ; Komesu et al.). Another worthwhile approach is the direct fermentation of organic lactates, such as aminium lactates (piperazinium dilactate, imidazole lactate and hexamethylenediamine dilactate), for the manufacture of high purity lactic acid (Idler et al. ).
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Furthermore, new studies on lactic acid recovery processes are required to develop a more efficient and economically attractive process for industrial applications.
CONCLUSIONS
According to this review, it is possible to observe the importance of lactic acid because of its widespread use and applications. The literature reports many lactic acid applications, such as cosmetics, pharmaceutical products, chemistry, food, and more recently in the medical area. The largest demand is in food and polymers application. Lactic acid produced by fermentation offers several advantages: low substrate costs, production temperature and energy consumption. However, lactic acid production is still limited by the final production cost, which is associated with the downstream process that requires many steps and makes the process expensive. Therefore, it is necessary to develop more efficient and viable technologies.
ACKNOWLEDGEMENTS
The authors are grateful for the financial support from the São Paulo Research Foundation (FAPESP), Project /-5.
REFERENCES CITED
Abdel-Rahman, M. A., and Sonomoto, K. (). “Opportunities to overcome the current limitations and challenges for efficient microbial production of optically pure lactic acid,” J. Biotechnol. 236, 176-192. DOI: 10./j.jbiotec..08.008
Abdel-Rahman, M. A., Tashiro, Y., and Sonomoto, K. (). “Lactic acid production from lignocellulose-derived sugars using lactic acid bacteria: Overview and limits,” J. Biotechnol.156(4), 286-301. DOI: 10./j.jbiotech..06.017
Abdel-Rahman, M. A., Tashiro, Y., and Sonomoto, K. (). “Recent advances in lactic acid production by microbial fermentation processes,” Biotechnol. Adv. 31(61), 877-902. DOI: 10./j.biotechadv..04.002
Adsul, M. G., Khire J. M., Bastawade, K. B., and Gokhale, D. V. (). “Lactic acid production from cellobiose and cellotriose by Lactobacillus delbrueckii mutant Uc-3,” Appl. Environ. Microb. 73(15), -. DOI: 10./AEM.-07
Alkaya, E., Kaptan, S., Ozkan, L., Uludag-Demirer, S., and Demirer, G. N. (). “Recovery of acids from anaerobic acidification broth by liquid–liquid extraction,” Chemosphere 77(8), -. DOI: 10./j.chemosphere..08.027
Altaf, M., Naveena, B. J., and Reddy, G. (). “Screening of inexpensive nitrogen sources for production of L(+) lactic acid from starch by amylolytic Lactobacillus amylophilus GV6 in single step fermentation,” Food Technol. Biotechnol. 43, 235-239.
Altaf, M., Naveena, B.J., and Reddy, G. (). “Use of inexpensive nitrogen sources and starch for L(+) lactic acid production in anaerobic submerged fermentation,” Bioresource Technology. 98, 498-503. DOI: 10./j.biortech..02.013
Asthana, N., Kolah, A., Vu, D. T., Lira, C. T., and Miller, D. (). “A continuous reactive separation process for ethyl lactate formation,” Org. Process Res. Dev. 9(5), 599-607. DOI: 10./op
Auneau, F., Arani, L.S., Besson, M., Djakovitch, L., Michel, C., Delbecq, F., Sautet, P., and Pinel, C. (). “Heterogeneous transformation of glycerol to lactic acid,” Top. Catal. 55, 474-479.
Bai, D., Wei, Q., Yan, Z., Zhao, X., Li, X., and Xu, S. (). “Fed-batch fermentation of Lactobacillus lactis for hyper-production of l-lactic acid,” Biotechnol. Lett. 25(21), –. DOI: 10./A:
Baur, P., Davies, L. E., Pontzen, R., and Rochling, A. (). “Use of lactate esters for improving the action of agricultural pesticides,” U. S. Patent No. A1.
Benninga, H. A. (). A History of Lactic Acid Making, Kluwer Academic Publishers, Dordrecht, Netherlands.
Büyükkileci, A. O., and Harsa, S. (). “Batch production of L(+) lactic acid from whey by Lactobacillus casei (NRRL B-441),” J. Chem. Technol. Biot. 79(9), -. DOI: 10./jctb.
Castillo Martinez, F. A., Balciunas, E. M., Salgado, J. M., González, J. M. D., Converti A., and Oliveira, R. P. S. (). “Lactic acid properties, applications and production: A review,” Trends Food Sci. Tech. 30(1), 70-83. DOI: 10./j.tifs..11.007
Chen, L., Zeng, A., Dong, H., Li, Q., and Niu, C. (). “A novel process for recovery and refining of L-lactic acid from fermentation broth,” Bioresour. Technol. 112, 280-284. DOI: 10./j.biortech..02.100
Choi, J., Kim, S., and Moon, S. (). “Recovery of lactic acid from sodium lactate by ion substitution using ion-exchange membrane,” Separ. Purif. Technol. 28(1), 69-79. DOI: 10./S-(02)-X
Datta, R., and Henry, M. (). “Lactic acid: Recent advances in products, processes and technologies – A review,” J. Chem. Technol. Biot. 81(7), -. DOI: 10./jctb.
Datta, R., Tsai, S., Bonsignore, P., Moon, S., and Frank, J. R. (). “Technological and economic potential of poly (lactic acid) and lactic acid derivatives,” FEMS Microbiol. Rev. 16(2-3), 221-231. DOI: 10./-(94)-4
Dey, P., and Pal, P. (). “Modelling and simulation of continuous L (+) lactic acid production from sugarcane juice in membrane integrated hybrid-reactor system,” Biochem. Eng. J. 79, 15-24. DOI: 10./j.bej..06.014
Ecker, J., Raab, T., and Harasek, M. (). “Nanofiltration as key technology for the separation of LA and AA,” J. Membrane Sci. 389, 389-398. DOI: 10./j.memsci..11.004
Eom, I.-Y., Oh, Y.-H., Park, S. J., Lee, S.-H., and Yu, J.-H. (). “Fermentative L-lactic acid production from pretreated whole slurry of oil palm trunk treated by hydrothermolysis and subsequent enzymatic hydrolysis,” Bioresource Technol.185, 143-149.
Gao, C., Ma, C., and Xu, P. (). “Biotechnological routes based on lactic acid production from biomass,” Biotechnol. Adv. 29(6), 930-939. DOI: 10./j.biotechadv..07.022
Gao, M., Shimamura, T., Ishida, N., Nagamori, E., Takahashi, H., Uemoto, S., Omasa, T., and Ohtake, H. (). “Extractive lactic acid fermentation with tri-n-decylamine as the extractant,” Enzyme Microb. Tech. 44(5), 350-354. DOI: 10./j.enzmictec..12.001
González, M. I., Alvarez, S., Riera, F. A., and Álvarez, R. (). “Lactic acid recovery from whey ultrafiltrate fermentation broths and artificial solutions by nanofiltration,” Desalination228(1-3), 84-96. DOI: 10./j.desal..08.009
Gullón, B., Yáñez, R., Alonso, J. L., and Parajó, J. C. (). “L-lactic acid production from apple pomace by sequential hydrolysis and fermentation,” Bioresour. Technol. 99(2), 308-319. DOI: 10./j.biortech..12.018
Guo, Y., Yan, Q., Jiang, Z., Teng, C., and Wang, X. (). “Efficient production of lactic acid from sucrose and corncob hydrolysate by a newly isolated Rhizopus oryzae GY18,” J. Ind. Microbiol. Biot. 37(11), -. DOI: 10./s-010--2
Hama, S., Mizuno, S., Kihara, M., Tanaka, T., Ogino, C., Noda, H., and Kondo, A. “Production of D-lactic acid from hardwood pulp by mechanical milling followed by simultaneous saccharification and fermentation using metabolically engineered Lactobacillus plantarum,” Bioresource Technology. 187, 167-172. DOI: http://dxdoiorg//jbiortech
Hofvendahl, K., and Hahn-Hägerdal, B. (). “Factors affecting the fermentative lactic acid production from renewable resources,” Enzyme Microb. Tech. 26(2-4), 87-107. DOI: 10./S-(99)-6
Holten, C. H., Müller, A., Rehbinder, D., and Ilra, S. (). Lactic Acid: Properties and Chemistry of Lactic Acid and Derivatives, Chemie, Weinheim, Germany.
Hong, A. C., Tanino, K., Peng, F., Zhou, S., Sun, Y., Liu, C., and Liu, D. H. (). “Strain isolation and optimization of process parameters for bioconversion of glycerol to lactic acid,” J. Chem. Technol. Biot. 84(10), -. DOI: 10./jctb.
Hu, J., Zhang, Z., Lin, Y., Zhao, S., Mei, Y., Liang, Y., and Peng, N. (). “High-titer lactic acid production from NaOH-pretreated corn stover by Bacillus coagulans LA204 using fed-batch simultaneous saccharification and fermentation under non-sterile condition,” Bioresour. Technol.182, 251-257. DOI: 10./j.biortech..02.008
Idler, C., Venus, J., and Kamm, B. (). “Microorganisms for the production of lactic acid and organic lactates,” Microbiology Monographs 26. DOI 10./978-3-662--7_9
Jin, B., Huang, L. P., and Lant, P. (). “Rhizopus arrhizus – A producer for simultaneous saccharification and fermentation of starch waste materials to L(+)-lactic acid,” Biotech. Lett.25(23), -. DOI: 10./B:BILE...d0
John, R. P., Anisha, G. S., Nampoothiri, K. M., and Pandey, A. (). “Direct lactic acid fermentation: Focus on simultaneous saccharification and lactic acid production,” Biotechnol. Adv. 27(2), 145-152. DOI: 10./j.biotechadv..10.004
John, R. P., Nampoothiri, M., and Pandey, A. (). “Fermentative production of lactic acid from biomass: An overview on process developments and future perspectives,” Appl. Microbiol. Biot. 74(3), 524-534. DOI: 10./s-063--6
Jompang, L., Thumsorn, S., On, J. W., Surin, P., Apawet, C., Chaichalermwong, T., Kaabbuathong, N., O-Charoen, N., and Srisawat, N. (). “Poly(lactic acid) and poly(butylene succinate) blend fibers prepared by melt spinning technique,” Energy Procedia 34, 493-499. DOI: 10./j.egypro..06.777
Jong, E., Higson, A., Walsh, P., and Wellisch, M. (). Bio-based Chemicals Value Added Products from Biorefineries, IEA Bioenergy Task 42 Biorefinery, Amsterdam, Netherlands.
Kim, Y. H., and Moon, S. (). “Lactic acid recovery from fermentation broth using one-stage electrodialysis,” J. Chem. Technol. Biot. 76(2), 169-178. DOI: 10./jctb.368
Kim, H.O., Wee, Y.J., Kim, J.N., Yun, J.S., and Ryu, H.W. (). “Production of lactic acid from cheese whey by batch and repeated batch cultures of Lactobacillus sp. RKY2,” Appl. Biochem. Biotechnol. 131, 694-704.
Kishida, H., Jin, F., Zhou, Z., Moriya, T., and Enomoto, H. () “Conversion of glycerin into lactic acid by alkaline hydrothermal reaction,” Chem. Lett. 34, - .
Komesu, A., Martins, P. F., Lunelli, B. H., Oliveira, J., Maciel Filho, R., and Wolf Maciel, M. R. (). “Evaluation of lactic acid purification from fermentation broth by hybrid short path evaporation using factorial experimental design,” Separ. Purif. Technol. 136, 233-240. DOI: 10./j.seppur..09.010
Komesu, A., Wolf Maciel, M. R., Oliveira, J., Martins, L. H. S., and Maciel Filho, R. (). “Purification of lactic acid produced by fermentation: Focus on non-traditional distillation processes,” Separation &Purification Reviews. DOI: 10./..
Krzyżaniak, A., Leeman, M., Vossebeld, F., Visser, T. J., Schuur, B., and Haan, A. B. (). “Novel extractants for the recovery of fermentation derived lactic acid,” Separ. Purif. Technol. 111, 82-89. DOI: 10./j.seppur..03.031
Kumar, R., Mahajani, S. M., Nanavati, H., and Noronha, S. B. (). “Recovery of lactic acid by batch reactive distillation,” J. Chem. Technol. Biot. 81(7), -. DOI: 10./jctb.
Kwak, H., Hwang, D. W., Hwang, Y. K., and Chang, J. (). “Recovery of alkyl lactate from ammonium lactate by an advanced precipitation process,” Separ. Purif. Technol. 93, 25-32. DOI: 10./j.seppur..03.025
Laopaiboon, P., Thani, A., Leelavatcharamas, V., and Laopaiboon, L. (). “Acid hydrolysis of sugarcane bagasse for lactic acid production,” Bioresour. Technol. 101(3), -. DOI: 10./j.biortech..08.091
Lasprilla, A. J. R., Martinez, G. A. R., Lunelli, B. H., Jardini, A. L., and Maciel Filho, R. (). “Poly-lactic acid synthesis for application in biomedical devices – A review,” Biotechnol. Adv.30(1), 321-328. DOI: 10./j.biotechadv..06.019
Li, W., Xu, Z., Chen, L., Shan, M., Tian, X., Yang, C., Lv, H., and Qian, X. (). “A facile method to produce graphene oxide-g-poly(L-lactic acid) as an promising reinforcement for PLLA nanocomposites,” Chem. Eng. J. 237, 291-299. DOI: 10./j.cej..10.034
Li, Y., and Shahbazi, A. (). “Lactic acid recovery from cheese whey fermentation broth using combined ultrafiltration and nanofiltration membranes,” Appl. Biochem. Biotech. 129-132, 985-996. DOI: 10./ABAB:132:
Li, Z., Lu, J., Yang, Z., Han, L., and Tan, T. (). “Utilization of white rice bran for production of L-lactic acid,” Biomass Bioenerg. 39, 53-58. DOI: 10./j.biombioe..12.039
Lima, U. A., Aquarone, E., Borzani, W., and Schmidell, W. (). Biotecnologia Industrial Processos Fermentativos e Enzimáticos, Blucher, São Paulo, Brazil.
Liu, T., Miura, S., Yaguchi, M., Arimura, T., Park, E. Y., and Okabe, M. (). “Scale-up of L-lactic acid production by mutant strain Rhizopus sp. Mk-96- from 0.003 m3 to 5 m3 in airlift bioreactors,” J. Biosci. Bioeng. 101(1), 9-12. DOI: 10./jbb.101.9
López-Garzón, C. S., and Straathof, A. J. J. (). “Recovery of carboxylic acids produced by fermentation,” Biotechnol. Adv. 32(5), 873-904. DOI: 10./j.biotechadv..04.002
Lu, Z., Wei, M., and Yu, L. (). “Enhancement of pilot scale production of L(+)- lactic acid by fermentation coupled with separation using membrane bioreactor,” Process Biochem. 47(3), 410-415. DOI: 10./j.procbio..11.022
Lunelli, B. H. (). Produção e Controle da Síntese do Éster de Ácido Acrílico Através da Fermentação do Ácido Láctico, Ph.D. Dissertation, University of Campinas, Campinas, Brazil.
Lunelli, B. H., Andrade, R. R., Atala, D. I. P., Wolf Maciel, M. R., Maugeri Filho, F., and Maciel Filho, R. (). “Production of lactic acid from sucrose: Strain selection, fermentation and kinetic modeling,” Appl. Biochem. Biotech. 161(1), 227-237. DOI: 10./s-009--0
Madzingaidzo, L., Danner, H., and Braun, R. (). “Process development and optimisation of lactic acid purification using electrodialysis,” J. Biotechnol. 96(3), 223-239. DOI: 10./S-(02)-4
Malmary, G., Albet, J., Putranto, A., Hanine, H., and Molinier, J. (). “Recovery of aconitic and lactic acids from simulated aqueous effluents of the sugar-cane industry through liquid-liquid extraction,” J. Chem. Technol. Biot. 75(12), -. DOI: 10./-()75:12<::AID-JCTB334>3.0.CO;2-F
Marques, S., Santos, J. A. L., Gírio, F. M., and Roseiro, J. C. (). “Lactic acid production from recycled paper sludge by simultaneous saccharification and fermentation,” Biochem. Eng. J.41(3), 210-216. DOI: 10./j.bej..04.018
Matsumoto, M., Takahashi, T., and Fukushima, K. (). “Synergistic extraction of lactic acid with alkylamine and tri-n-butylphosphate: Effects of amines, diluents and temperature,” Separ. Purif. Technol. 33(1), 89-93. DOI: 10./S-(03)-9
Min, D., Choi, K. H., Chang, Y. K., and Kim, J. (). “Effect of operating parameters on precipitation for recovery of lactic acid from calcium lactate fermentation broth,” Korean J. Chem. Eng. 28(10), -. DOI: 10./s-011--9
Nakano, S., Ugwu, C. U., and Tokiwa, Y. (). “Efficient production od D-(-)-lactic acid from broken rice by Lactobacillus delbrueckii using Ca(OH)2 as a neutralizing agent,” Bioresour. Technol. 104, 791-794. DOI: 10./j.biortech..10.017
Narayanan, N., Roychoudhury, P. K., and Srivastava, A. (). “L (+) lactic acid fermentation and its product polymerization,” J. Biotechnol. 7(2), 167-179. DOI: 10./vol7-issue2-fulltext-7
Nguyen, C.M., Kim, J-S., Hwang, H.J., Park, M.S., Choi, G.J., Choi, Y.H., Jang, K.S., Kim, J-C. (). “Production of L-lactic acid from a green microalga, Hydrodictyon reticulum, by Lactobacillus paracasei LA 104 isolated from the traditional Korean food, makgeolli. Bioresource Tehcnology 110, 552-559.
Ohleyer, E., Blanch, H. W., and Wilke, C. R. (). “Continuous production of lactic acid in a cell recycle reactor,” Appl. Biochem. Biotech. 11(4), 317-332. DOI: 10./BF
Okano, K., Tanaka, T., Ogino, C., Fukuda, H., and Kondo, A. (). “Biotechnological production of enantiomeric pure lactic acid from renewable resources: Recent achievements, perspectives, and limits,” Appl. Microbiol. Biot. 85(3), 413-423. DOI: 10./s-009--5
Ou, M. S., Ingram, L. O., and Shanmugam, K. T. (). “L(+)-Lactic acid production from non-food carbohydrates by thermotolerant Bacillus coagulans,” J. Ind. Microbiol. Biot. 38(5), 599-605. DOI: 10./s-010--4
Ouyang, J., Ma, R., Zheng, Z., Cai, C., Zhang, M., and Jiang, T. (). “Open fermentative production of L-lactic acid by Bacillus sp. strain NL01 using lignocellulosic hydrolyzates as low-cost raw material,” Bioresour. Technol. 135, 475-480. DOI: 10./j.biortech..09.096
Padee, S., Thumsorn, S., On, J. W., Surin, P., Apawet, C., Chaichalermwong, T., Kaabbuathong, N., O-Charoen, N., and Srisawat, N. (). “Preparation of poly(lactic acid) and poly(trimethylene terephthalate) blend fibers for textile application,” Energy Procedia 34, 534-541. DOI: 10./j.egypro..06.782
Pal, P., and Dey, P. (). “Process intensification in lactic acid production by three stage membrane integrated hybrid reactor system,” Chem. Eng. Process. Intens. 64, 1-9. DOI: 10./j.cep..12.006
Pal, P., Sikder, J., Roy, S., and Giorno, L. (). “Process intensification in lactic acid production: A review of membrane based processes,” Chem. Eng. Process. Intens. 48(11-12), -. DOI: 10./j.cep..09.003
Panesar, P. S., Kennedy, J. F., Gandhi, D. N., and Bunko, K. (). “Bioutilisation of whey for lactic acid production,” Food Chemistry 105, 1-14.
Perry, R. H., and Chilton, C. H. (). Perry’s Chemical Engineers’ Handbook, McGraw-Hill, New York, NY.
Pivsa-Art, S., Tong-Ngok, T., Junngam, S., Wongpajan, R., and Pivsa-Art, W. (). “Synthesis of poly(D-lactic acid) using a 2-steps direct polycondensation process,” Energy Procedia 34, 604-609. DOI: 10./j.egypro..06.791
PR Newswire (). “Lactic acid market and derivatives forecasts (global, China) in new research report,” (http://www.prnewswire.com/news-releases/lactic-acid-market-and-derivatives--forecasts-global-china-in-new-research-report-.html), accessed 25 February January .
Prückler, M., Lorenz, C., Endo, A., Kraler, M., Dürrschmid, K., Hendriks, K., Da Silva, F.S., Auterith, E., Kneifel, W., and Michlmayr, H. (). “Comparison of homo- and heterofermentative lactic acid bacteria for implementation of fermented wheat bran in bread,” Food Microbiology 49, 211-219.
Ramchandran, L., Sanciolo, P., Vasiljevic, T., Broome, M., Powell, I., and Duke, M. (). “Improving cell yield and lactic acid production of Lactococcus lactis ssp. cremoris by a novel submerged membrane fermentation process,” J. Membrane Sci. 403-404, 179-187. DOI: 10./j.memsci..02.042
Rauch, M., Gerner, F., and Wecker, A. M. (). Ullmann’s Encyklopädie der technischen Chemie [Ullman’s Encyclopedia of Industrial Chemistry], Verlag Chemie, Weinheim, Germany.
Saito, K., Hasa, Y., and Abe, H. (). “Production of lactic acid from xylose and wheat straw by Rhizopus oryzae,” J. Biosci. Bioeng. 114(2), 166-169. DOI: 10./j.jbiosc..03.007
Sasson, Y., Toledano, O., and Levi-Ruso, G. (). “Pesticidal composition comprising a lactate ester as crystal growth inhibitor,” U.S. Patent A1.
Shi, D., Hua, J., Zhang, L., and Chen, M. (). “Synthesis of bio-based poly(lactic acid-co-10-hydroxy decanoate) copolymers with high thermal stability and ductility,” Polymers 7(3), 468-483. DOI: 10./polym
Sikder, J., Roy, M., Dey, P., and Pal, P. (). “Techno-economic analysis of a membrane-integrated bioreactor system for production of lactic acid from sugarcane juice,” Biochem. Eng. J. 63, 81-87. DOI: 10./j.bej..11.004
Silveira, M. S. (). Utilização do Suco de Caju Clarificado para Produção de Ácido Lático pelo Lactobacillus casei B-442, MSc Thesis, Universidade Federal do Ceará, Ceará, Brazil.
Sreenath, H. K., Moldes, A. B., Koegel, R. G., and Straub, R. J. (). “Lactic acid production by simultaneous saccharification and fermentation of alfalfa fiber,” J. Biosci. Bioeng. 92(6), 518-523. DOI: 10./s-006--4
Tang, J., Wang, X., Hu, Y., Zhang, Y., Li, Y. (). “Lactic acid fermentation from food waste with indigenous microbiota: Effects of pH, temperature and high OLR,” Waste Management. 52, 278-285. DOI: 10./j.wasman..03.034
Tashiro, Y., Matsumoto, H., Miyamoto, H., Okugawa, Y., Pramod, P., Miyamoto, H., and Sakai, K. (). “A novel production process for optically pure L-lactic acid from kitchen refuse using a bacterial consortium at high temperatures,” Bioresour. Technol. 146, 672-681.
Tejayadi, S., and Cheryan, M. (). “Lactic acid from cheese whey permeate. Productivity and economics of a continuous membrane bioreactor,” Appl. Microbiol. Biotechnol. 43, 242-248.
The Essential Chemical Industry Online (). “Biotechnology in the chemical industry,” (http://www.essentialchemicalindustry.org/materials-and-applications/biotechnology-in-the-chemical-industry.html), accessed 25 February .
Trindade, M. C. (). Estudo da Recuperação de Ácido Lático Proveniente Do Soro De Queijo pela Técnica de Membranas Líquidas Surfactantes, MSc Thesis, Universidade Federal de Minas Gerais, Minas Gerais, Brazil.
Vaidya, A.N., Pandey, R.A., Mudliar, S., Suresh Kumar, M., Chakrabarti, T., and Devotta, S. (). “Production and recovery of lactic acid for polylactide—An overview,” Crit. Rev. Env. Sci. Technol. 35, 429-467. DOI: 10./
Wang, C., Li, Q., Wang, D., and Xing, J. (). “Improving the lactic acid production of Actinobacillus succinogenes by using a novel fermentation and separation integration system,” Process Biochem. 49(8), -. DOI: 10./j.procbio..04.009
Wang, L., Zhao, B., Liu, B., Yu, B., Ma, C., Su, F., Hua, D., Li, Q., Ma, Y., and Xu, P. (). “Efficient production of L-lactic acid from corncob molasses, a waste by-product in xylitol production, by a newly isolated xylose utilizing Bacillus sp. strain,” Bioresour. Technol. 101(20), -. DOI: 10./j.biortech..05.031
Wang, Y., Meng, H., Cai, D., Wang, B., Qin, P., Wang, Z., and Tan, T. () “Improvement of L-lactic acid productivity from sweet sorghum juice by repeated batch fermentation coupled with membrane separation,” Bioresour. Technol. 211, 291-297. DOI: 10./j.biortech..03.095
Wankat P. C. (). Equilibrium Staged Separations, Prentice Hall, New York, NY.
Wasewar, K. L., Heesink, A. B. M., Versteeg, G. F., and Pangarkar, V. G. (). “Reactive extraction of lactic acid using alamine 336 in MIBK: Equilibria and kinetics,” J. Biotechnol.97(1), 59-68. DOI: 10./S-(02)-3
Wee, Y., Kim, J., and Ryu, H. (). “Biotechnological production of lactic acid and its recent applications,” Food Technol. Biotech. 44(2), 163-172.
Wee, Y., Yun, J., Park, D., and Ryu, H. (). “Biotechnological production of L(+) lactic acid from wood hydrolyzate by batch fermentation of Enterococcus faecalis,” Biotechnol. Lett. 26(1), 71-74. DOI: 10./B:BILE...e0
Wei, Q., Han, Z. W., Bai, D. M., Yan, Z. H., and Zhao, X. M. (). “Study on recovery and purification of l-lactic acid,” in: 4th International Conference on Separation Science and Technology: Frontiers on Separation Science and Technology, Nanning, Guangxi, China, pp. 717-723.
Wu, X., Jiang, S., Liu, M., Pan, L., Zheng, Z., and Luo, S. (). “Production of L-lactic acid by Rhizopus oryzae using semicontinuous fermentation in bioreactor,” J. Ind. Microbiol. Biot. 38(4), 565-571. DOI: 10./s-010--8
Xu, S., Zheng, T., and Xu, S. (). “The study of refining L-Lactic acid by molecular distillation,” J. Chem. Eng. Chin. Univ. 18, 246-249.
Yankov, D., Molinier, J., Albet, J., Malmary, G., and Kyuchoukov, G. (). “Lactic acid extraction from aqueous solutions with tri-n-octylamine dissolved in decanol and dodecanol,” Biochem. Eng. J. 21, 63-71.
Yin, P., Nishina, N., Kosakai, Y., Yahiro, K., Park, Y., and Okabe, M. (). “Enhanced production of L(+)-lactic acid from corn starch in a culture of Rhizopus oryzae using an air-lift bioreactor,” J. Ferment. Bioeng. 84(3), 249-253. DOI: 10./s-338x(97)-6
Yin, H., Zhang, C., Yin, H., Gao, D., Shen, L., and Wang, A. (). “Hydrothermal conversion of glycerol to lactic acid catalyzed by Cu/hydroxyapatite, Cu/MgO, and Cu/ZrO2 and reaction kinetics,” Chemical Engineering Journal 288, 332-343.
Yin, P., Yahiro, K., Ishigaki, T., Park, Y., and Okabe, M. (). “L(+)-lactic acid production by repeated batch culture of Rhizopus oryzae in air-lift bioreactor,” J. Ferment. Bioeng. 85(1), 96-100. DOI: 10./S-338X(97)-3
Yu, M., Wang, R., Wang, C., Duan, K., and Sheu, D. (). “Enhanced production of L(+)-lactic acid by floc-form culture of Rhizopus oryzae,” J. Chin. Inst. Chem. Eng. 38(3-4), 223-228. DOI: 10./j.jcice..02.005
Zhou, Y., Domínguez, J., Cao, N., Du, J., and Tsao, G. (). “Optimization of L-lactic acid production from glucose by Rhizopus oryzae ATCC ,” Appl. Biochem. Biotech. 77-79, 401-407. DOI: 10./ABAB:78:1-3:401
Article submitted: August 22, ; Peer review completed: December 29, ; Revised version received: January 26, ; Accepted: January 29, ; Published: February 6, .
DOI: 10./biores.12.2.Komesu
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