Much attention has been paid on research to improve the microbial strains, and to maintain their production capacity. Citric acid is mainly used in food industry because of its pleasant acid taste an its high solubility in water. Table 1 presents main applications of citric acid. A large number of micro-organisms including bacteria, fungi and yeasts have been employed to produce citric acid.
Most of them, however, are not able to produce commercially acceptable yields. This fact could be explained by the fact that citric acid is a metabolite of energy metabolism and its accumulation rises in appreciable amounts only under conditions of drastic imbalances. Kubicek and Rohr reviewed the strains reported to produce citric acid.
Table 2 shows the micro-organisms used to produce citric acid. Among these, only A. However, the fungus A. The main advantages of using this micro-organism are: a its ease of handling, b its ability to ferment a variety of cheap raw materials, and c high yields. The two principal methods of selecting populations, namely, "the single-spore technique" and the "passage method" have been used for selecting citric acid producing micro-organisms The single-spore technique has the disadvantage that mineral acid or organic acids gluconic acid, oxalic acid simulate the presence of citric acid.
Rohr et al. The most employed technique to improve citric acid producing strains has been by inducing mutations in parental strains using mutagens. Among physical mutagens, g-radiation Bonatelli and Azevedo, ; Gunde-Cimerman, ; Islam et al. To obtain hyper-producer strains, frequently UV treatment could be combined with some chemical mutagens, e. By using a suitable selection technique on model medium with non-specific carbon sources, a strain yielding high amounts of citric acid from unusual substrates can be obtained from the mutants produced.
Another approach for strain improvement has been the para-sexual cycle, as first described by Pontecorvo et al.
According to Das and Roy , diploids displayed higher citric acid yields compared to their parent haploids, but tended to be less stable Bonatelli and Azevedo, Protoplast fusion appeared to be a promising tool to extend the range of genetic manipulation of A. Kirimura et al. They were able to obtain fusants with acid production capacities exceeding those of the parent strains in solid state fermentation, but not in submerged fermentation.
Some other aspects of strain improvement could be the resistance to detrimental constituents of fermentation raw materials, capability of utilizing raw materials starch, cellulose, pectin containing and other waste materials. However, there is no single effective technique to achieve hyper-producing mutants and much remains to be done in this area. Although citric acid is mostly produced from starch or sucrose based media using liquid fermentation, a variety of raw materials such as molasses, several starchy materials and hydrocarbons have also been employed.
The composition of molasses depends on various factors, e. Both, cane and beet molasses are suitable for citric acid production. However, beet molasses is preferred due to its lower content of trace metals. Generally, cane molasses contains calcium, magnesium, manganese, iron and zinc, which have a retarding effect on the synthesis of citric acid.
Despite that, cane molasses posses difficulties in achieving good fermentation yields. Various other agro-industrial residues such as apple pomace, cassava bagasse, coffee husk, wheat straw, pineapple waste, sugar beet cosset, kiwi fruit peel, etc. In fact, these residues are very well adapted to solid-state cultures due to their cellulosic and starchy nature.
However, despite the fact that these solid residues provide rich nutrients to the micro-organisms, and are good substrates for growth and activity of micro-organisms, much remains to be done for developing commercially feasible process utilizing these residues Pandey , , Pandey and Soccol Submerged fermentation: The submerged fermentation SmF process is the commonly employed technique for citric acid production.
Several advantages such as higher yields and productivity and lower labour costs are the main reasons for this. Two types of fermenters, conventional stirred fermenters and tower fermenters are employed, although the latter is preferred due to the advantages it offers on price, size and operation Rohr et al. Preferentially, fermenters are made of high-grade steel and require provision of aeration system, which can maintain a high dissolved oxygen level.
Fermenters for citric acid production do not have to be built as pressure vessels since sterilization is performed by simply steaming without applying pressure. Cooling can be done by an external water film over the entire outside wall of the fermenter.
In SmF, different kinds of media are employed such as sugar and starch based media Table 3. Molasses and other raw materials demand pre-treatment, addition of nutrients and sterilization. Inoculation is performed either by adding a suspension of spores, or of pre-cultivated mycelia. When spores are used, a surfactant is added in order to disperse them in the medium. Normally, submerged fermentation is concluded in 5 to 10 days depending on the process conditions.
It can be carried out in batch, continuous or fed batch systems, although the batch mode more frequently used. After that, other methods of fermentation, such as submerged fermentation were developed. Although this technique is more sophisticated, surface method required less effort in operation and installation and energy cost Grewal and Kalra, In the classical process for citric acid manu-facture, the culture solution is held in shallow trays capacity of L and the fungus develops as a mycelial mat on the surface of the medium.
The trays are made of high purity aluminium or special grade steel and are mounted one over another in stable racks. The fermentation chambers are provided with an effective air circulation in order to control temperature and humidity. Fermentation chambers are always in aseptic conditions, which might be conserved principally during the first two days when spores germinate. Frequent contamination are mainly caused by Penicilia, other Aspergilli, yeast and lactic bacteria Rohr et al, ; Morgant, Refined or crude sucrose, cane syrup or beet molasses are generally used as sources of carbon.
Solid-state fermentation SSF has been termed as an alternative method to produce citric acid from agro-industrial residues Pandey , , , Soccol , Pandey and Soccol Citric acid production by SSF the Koji process was first developed in Japan and is as the simplest method for its production. SSF can be carried out using several raw materials Table 4. The initial pH is normally adjusted to 4.
The most commonly organism is A. However there also have been reports with yeasts Maddox and Kingston, ; Tisnadjaja et al. One of the important advantages of SSF process is that the presence of trace elements may not affect citric acid production so harmfully as it does in SmF. Consequently, substrate pre-treatment is not required.
Different types of fermenters such as conical flasks, glass incubators and trays, etc. Vandenberghe et al. Higher yields were obtained in flasks without any aeration, and very little sporulation was observed. The same yields were found in column reactors only with variable aeration.
This showed great perspective to use SSF process for citric acid production in simple tray type fermenters. Carbon source: Citric acid accumulation is strongly affected by the nature of the carbon source. The presence of easily metabolized carbohydrates has been found essential for good production of citric acid. Hossain et al. Galactose contributed to a very low growth of fungi and did not favour citric acid accumulation. Other sources of carbon such as sorbose, ethanol, cellulose, manitol, lactic, malic and a -acetoglutaric acid, allow a limited growth and low production.
Starch, pentoses xyloses and arabinoses , sorbitol and pyruvic acid slow down growth, though the production is minimal Yokoya, According to Kovats , initial sugar concentration was critical for citric acid production and other organic acids produced by A.
Xu et al. Honecker et al. Maddox et al. Glucose, maltose, galactose, xylose and arabinose were tested. Better results were found for A. As presented previously, several raw materials can be employed successfully for citric acid production.
There are some critical factors costs, need of pretreatment , which should be considered for substrate determination. One another aspect is the presence of trace elements, which can act as inhibitors or stimulants. Consequently, sometimes it is necessary to conduce a pre-treatment, e.
Nitrogen source: Citric acid production is directly influenced by the nitrogen source. Physiologically, ammonium salts are preferred, e. Nitrogen consumption leads to pH decrease, which is very important point in citric acid fermentation Rohr et al. The Cosmetics Ingredient Review has deemed the ingredient safe for use in cosmetics.
Citric acid may be produced from fruits or other foods, through yeast fermentation, and by solvent extraction. Our obsession with natural cleaning performance is our profession, and we're here to share it with you. No returns necessary, never any hassles, and no questions asked. Learn more about our ingredients and why we call them natural and safe. Ingredient safety Environmental impact Privacy policy Terms of service.
Your Bag. Sign in Your Bag. Laundry Laundry Detergent Stain Remover. Shop best sellers. She has experience in food service management, nutrition counseling, and WIC.
You can see her writing work at www. Jennifer Purdie. She also served as a ghostwriter for U. Citrus fruits, such as lemons and limes, naturally contain citric acid. Video of the Day. Tip Most manufactured citric acid that you find in everyday commercial products comes from a fungus put through a fermentation process using a low-cost molasses. Citric Acid Production.
Oranges Limes Lemons Grapefruits Citrons a large fruit with a thick rind, similar in color to lemons. The solution is mixed with lime calcium hydroxide which causes citrate salt to come out of the solution precipitate. The citrate salt is then treated with sulfuric acid to make useable citric acid. The sugars that are used for the citric acid can be derived from cane sugar, corn or wheat.
In the United States, citric acid is most often derived from corn since it is a cheap, subsidized crop. In South America cane sugar is often used due to the low sugar prices, while in Europe wheat sweeteners are commonly used.
0コメント