Fermentation organic acids

Bailly, M., Roux-de Balmann, H., Aimar, P., Lutin, F., and Cheryan, M. 2001. Production processes of fermented organic acids targeted around membrane operations Design of the concentration step by conventional electrodialysis. J. Membr. Sci. 191, 129-142. 

Figure 7.1 Electrodialytic production of fermented organic acids (Adapted from M. Bailly (2002). Desalination 144 157-162). With permission.

Figure 7.1 Electrodialytic production of fermented organic acids. 172...

Food preservatives are yet another product of industrial fermentation. Organic acids, particularly lactic and citric acids, are extensively used as food preservatives. Some of these preservatives (such as citric acid) are used as flavoring agents. A mixture of two bacterial species (Lactobacillus and Streptococcus) is usually used for industrial production of lactic acid. The mold Asper Uus niger is used for citric acid manufacturing. Another common preservative is the protein nisin. Nisin is produced via fermentation by the bacterium Lactococcus lactis. It is employed in the dairy industry especially for production of processed cheese. 

The downstream domain of the microbial production of FA has imposed a major economical barrier to entry into commercial trade for this multifaceted organic acid. As compared to the well-established downstream strategies for different fermented organic acids such as lactic acid, succinic acid, and citric acid, separation techniques for FA from the fermented broth have not met the conditions for scaling up in both economical and technical aspects. 

Citric Acid Separation. Citric acid [77-92-9] and other organic acids can be recovered from fermentation broths usiag the UOP Sorbex technology (90—92). The conventional means of recovering citric acid is by a lime and sulfuric acid process ia which the citric acid is first precipitated as a calcium salt and then reacidulated with sulfuric acid. However, this process generates significant by-products and thus can become iaefficient. 

Although a tremendous number of fermentation processes have been researched and developed to various extents, only a couple of hundred ate used commercially. Fermentation industries have continued to expand in terms of the number of new products on the market, the total volume (capacity), and the total sales value of the products. The early 1990s U.S. market for fermentation products was estimated to be in the 9-10 x 10 range. The total world market is probably three times that figure, and antibiotics continue to comprise a primary share of the industry. Other principal product categories are enzymes, several organic acids, baker s yeast, ethanol (qv), vitamins (qv), and steroid hormones (qv). 

Lactic acid [50-21-5] (2-hydroxypropanoic acid), CH CHOHCOOH, is the most widely occurring hydroxycarboxylic acid and thus is the principal topic of this article. It was first discovered ia 1780 by the Swedish chemist Scheele. Lactic acid is a naturally occurring organic acid that can be produced by fermentation or chemical synthesis. It is present ia many foods both naturally or as a product of in situ microbial fermentation, as ia sauerkraut, yogurt, buttermilk, sourdough breads, and many other fermented foods. Lactic acid is also a principal metaboHc iatermediate ia most living organisms, from anaerobic prokaryotes to humans. 

Cultured buttermilk is that which is produced by the fermentation (qv) of skimmed milk often with some cream added. The principal fermentation organisms used are l ctococcus lactis suhsp. cremoris l ctococcus lactis suhsp. lactis and l euconostoc citrovorum. The effect of the high processing temperature and the lactic acid provide an easily digestible product. 

In the acid hydrolysis process (79—81), wood is treated with concentrated or dilute acid solution to produce a lignin-rich residue and a Hquor containing sugars, organic acids, furfural, and other chemicals. The process is adaptable to all species and all forms of wood waste. The Hquor can be concentrated to a molasses for animal feed (82), used as a substrate for fermentation to ethanol or yeast (82), or dehydrated to furfural and levulinic acid (83—86). Attempts have been made to obtain marketable products from the lignin residue (87) rather than using it as a fuel, but currently only carbohydrate-derived products appear practical. 

Organic acids, including carbon dioxide, lower the wort pH during fermentation. The principal acids formed are lactic, pymvic citric, malic, and acetic acids, at concentrations ranging from 100—200 ppm. The main sulfur compounds formed during fermentation and thek perception thresholds are as follows H2S (5—10 ppb) ethanethiol (5—10 ppb) dimethyl sulfoxide (35—60 ppb) and diethyl sulfide (3—30 ppb). At low levels, these may have a deskable flavor effect at higher levels they are extremely undeskable. Sulfur dioxide also forms during fermentation, at concentrations of 5—50 ppm its presence can be tasted at levels above 50 ppm. 

Candida utilis is grown on sulfite waste Hquor in Western Europe and North America, on sugar cane molasses in Cuba and Taiwan and on ceUulose acid hydrolysates in Eastern Europe and the former Soviet Union. C. ///i/if utilizes hexoses, pentoses, and many organic acids. Sulfite Hquor from hardwoods contains 2—3% fermentable sugars of which 20% are hexoses and 80% pentoses in softwood Hquors the proportions are reversed. The SO2 must be stripped out to allow yeast growth, which is carried out in large, highly-aerated fermentors. Eor continuous fermentations, carried out at pH 4 and 30°C, the dilution rate is 0.27—0.30 (34). 

Salts of Organic Acids. Calcium salts of organic acids may be prepared by reaction of the carbonate hydroxide and the organic acid (9). Calcium lactate [814-80-2] is an iatermediate ia the purification of lactic acid from fermentation of molasses. Calcium soaps, soaps of fatty acids, ate soluble ia hydrocarbons, and are useful as waterproofing agents and constituents of greases (9). 

Some products are precipitated from the fermentation broth. The insoluble calcium salts of some organic acids precipitate and are col-lec ted, and adding sulfuric acid regenerates the acid while forming gypsum (calcium sulfate) that constitutes a disposal problem. An early process for recovering the antibiotic cycloserine added silver nitrate to the fermentation broth to precipitate an insoluble silver salt. This process was soon obsolete because of poor economics and because the silver salt, when diy, exploded easily. 

Fermentation An anaerobic bioprocess. An enzymatic transformation of organic substrates, especially carbohydrates, generally accompanied by the evolution of gas as a byproduct. Fermentation is used in various industrial processes for the manufacture of products (e.g., alcohols, organic acids, solvents, and cheese) by the addition of yeasts, moulds, and bacteria. 

A feed concentration of 15 g glucose and 15 g xylose per litre was used over a feed rate of 20-200 ml/hr. Samples were taken at successive points along the reactor length, and the usual analysis for glucose and xylose consumption, organic acid production and cell density were done. A kinetic model for the growth and fermentation of P. acidipropionici was obtained from these data. 

Najafpour, G., Organic Acids for Biomass by Continuous Fermentation , Resour. Consent. 17, 187 (1987). (Riley, et al, 1996) (Senthuran, etal, 1997). 

Based on the practical history of scale-up, most fermentation processes for alcohol and organic acid production have followed the concepts of geometric similarity and constant power per unit volume. From the above concept, and as a strong basis for translation of process criteria, only physical properties of the process were considered in the scale-up calculation. For power consumption in an agitated vessel, there is a fixed relation between impeller speed, N, and impeller diameter, l)t. The constant power per unit volume, for a mechanical agitated vessel is given by ... 

---