Fermentation industry malic acid

Poly(malic acid) is of pharmaceutical interest because its chemical derivatives may harbor both tissue-specific homing molecules and therapeutic effectors to be used for tissue (tumor) targeting in chemotherapy [2]. Because of its efficient production by fermentation, its biodegradability and nontoxicity, it is also considered as raw material in the industrial production of detergents, glues, and plastic materials. 

There are many organic acids that can be produced by microbial or biochemical means. However, at present, only acetic acid (as vinegar), citric acid, itaconic acid, gluconic acid, 2-keto-gulonic acid, and lactic acid are produced industrially by fermentation. Other organic acids, such as fumaric, gallic, malic, and tartaric acids, once produced by fermentation or enzyme processes, are now produced commercially, predominantly by the more economic means of chemical synthesis. 

Malolactic fermentation (MLF) is an important process, nowadays also conducted on an industrial scale, aimed at improving organoleptic characteristics and conferring microbiological stability to quality wines (Davis et al., 1985). The main transformation of the wine occurring in this process operated by lactic bacteria, is decarboxylation of L(—)-malic acid with formation of L(+)-lactic acid (Figure 1.5). 

Flavors of organic acids range from fresh acidic (citric acid) to salty and bitter (succinic acid). This characteristic plays an important role in the wine industry. The natural malolactic conversion causes major changes in fermented beverages, red wine, and cider, which results in a decrease in the acidity of red wine and cider, and the replacement of malic acid with lactic acid, which has a weaker taste (Gomis, 1992). 

Rhizopus oryzae is an indispensable microorganism in industrial fermentation, as it is widely employed to produce L-lactic acid as well as other organic acids. This organism is able to produce only one stereospecific product (L-lactic acid), rather than a racemic mixture and can, therefore, fulfill the need for producing a food additive to be used as both acidulant and preservative. During L-lactic acid fermentation many other metabolites can be produced as by-products. These include fumaric acid, malic acid, ethanol, and the like. However, these metabolites can greatly influence the downstream process and the quality of the L(+)-lactic acid produced. Fumaric acid is the main by-product, as a result of a special metabolic pathway in L-lactic acid production by R. oryzae (Wang et al., 2005). 

Although L-malic acid (1) can be isolated from a variety of fruits, it is manufactured industrially by the fermentation of fumaric acid with immobilized fumarase as the biocatalyst [1]. This process is capable of producing up to 30 tons of the acid per month. L-Malic acid is commercially available from many suppliers, and is relatively inexpensive. The current price is approximately 208/Kg. 

In succession to the L-aspartic acid production, in 1974 we succeeded in the third industrial application, i.e. the production of L-malic acid from fumarlc acid by immobilized microbial cells. L-Mallc acid is an essential compound in cellular metabolism, and is mainly used in pharmaceutical field. L-Malic acid can be produced by fermentative or enzymatic methods from fumarlc acid by the action of fumarase as follows. 

Lactobacillus plantarum is used in the wine industry, where it performs malo-lactic fermentation following the alcoholic fermentation by the wine yeast (Term, Engelbrecht, du Toit, 2011). This fermentation is important for the organoleptic properties of the wine because the relatively harsh malic acid is converted to the... 

The optically inactive citric acid (8-67) is the most important representative of tricarboxylic hydroxy acids. Citric acid, as well as malic acid, occurs in many fruits (especially in lemons). Industrially, it is obtained from lemon juice or produced by fermentation of molasses using fungi Aspergillus niger. Along with malic acid, citric acid is used as an additive in widely different canning products... 

Fumaric acid is used in the plastics industry, in the food industry and as a source of malic add. Although demand has increased rapidly over the last 30 years its production from fermentation has been totally replaced by a chemical method. It is now produced far more cheaply by the catalytic oxidation of hydrocarbons, particularly benzene. With the continuing uncertainties concerning the availability and cost of petroleum, however, fermentation may yet be a viable alternative. 

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