Fermentation Processing

Because of the small scale of enzyme production, laboratory 

Enzymes are proteins with molecular weights in the range of 15,000-1,000,000 or so. In 1968, for instance, about 1300 were known, but only a few are of industrial significance. They are named after the kinds of reactions that they promote rather than to identify the structure which often is still unknown. Some kinds of enzymes are  

Amylase, which converts polysaccharides (starch or cellulose) to sugars. 

Glucose oxidase, which converts glucose to dextrose and levulose. Isomerase, which converts glucose to fructose. 

Lipase, which splits fats to glycerine and fatty acids. 

It has been mentioned already that only a few inorganic and organic electrochemical processes have made it to commercial scale, but the potential may be there and should not be ignored. Recent surveys of the field and of the literature have been made by Fline (1985), Fletcher (1982), and Roberts et al. (1982). 

Microorganisms (microbes) are living cells, single or in multiples of the same kind, including bacteria, yeasts, fungi, molds, algae and protozoa. Their metabolic products may be of simple or complex structure. 

Fermentation is a metabolic process whereby microorganisms grow in the presence of nutrients and oxygen, sometimes in the absence of oxygen. The terms used are aerobic (in the presence of oxygen) and anaerobic (in the absence of oxygen) 

Substrate consists of the nutrients on which a microorganism subsists orthe chemicals upon which an enzyme acts Enzymes are made by living cells, and are proteins with molecular weights ranging from about 15,000 to 1,000,000. 

Enzymes, immobiiized, are attached to a solid support by adsorption or chemical binding or mechanical entrapment in the pores of a gel structure, yet retain most of their catalytic powers -ase is a suffix identifying that the substance is an enzyme. The main part of the name describes the nature of the chemical reaction that can be catalyzed, as in cellulase, an enzyme that catalyzes the decomposition of cellulose 

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Manufactured by the liquid-phase oxidation of ethanal at 60 C by oxygen or air under pressure in the presence of manganese(ii) ethanoate, the latter preventing the formation of perelhanoic acid. Another important route is the liquid-phase oxidation of butane by air at 50 atm. and 150-250 C in the presence of a metal ethanoate. Some ethanoic acid is produced by the catalytic oxidation of ethanol. Fermentation processes are used only for the production of vinegar. 

H2N-CH2 [CH2j3.CH(NH2) COOH. Colourless needles, m.p. 224 C (decomp.), very soluble in water, insoluble in alcohol. L-(-H)-Lysine is one of the basic amino-acids occurring in particularly large quantities in the protamine and histone classes of proteins. It is an essential amino-acid, which cannot be synthesized by the body and must be present in the food for proper growth. It can be manufactured by various fermentation processes or by synthesis. 

With the proper ratio of nutrients and oxygen feed, a water-soluble polymer is produced and accompanied by growth in the microorganism population. Both contribute to the viscosity of the medium and this limits the production process. Fermentation processes require more strenuous mixing and control conditions. 

Careful records must be kept to enable verification of compHance. Each lot of wine must be traceable back to the grapes and vineyard. Tanks must be carefully gauged and the capacities recorded on them. If the wine is to be labeled "estate botded," not only must the wine be fermented, processed, and bottled by the state winery at thein Hsted address, but the vineyard must also be owned or controlled by that winery. Other label terrninology, subject to some further intricacies, are "produced," ie, fermented 75% or made into a different class of wine "prepared," "vinted," or "cellared," ie, subjected to ceUar processing or aging without changing the class of wine "blended," ie, combined at the stated address, wines (probably purchased) of the same class and type and "botded" or "packed" by the stated winery. 

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). 

Fig. 2. Schematic representation of a fermentation process for an extracellular product.

Generally, for most fermentation processes to yield a good quality product at a competitive price, at least six key criteria must be met. (/) Fermentation is a capital intensive business and investment must be minimised. (2) The raw materials should be as cheap as possible. (J) Only the highest yielding strains should be used. (4) Recovery and purification should be as rapid and as simple as possible. (5) Automation should be employed to minimise labor usage. (6) The process must be designed to minimise waste production and efftciendy use all utilities (26,27). 

Lactic acid-producing bacteria associated with fermented dairy products have been found to produce antibiotic-like compounds caUed bacteriocins. Concentrations of these natural antibiotics can be added to refrigerated foods in the form of an extract of the fermentation process to help prevent microbial spoilage. Other natural antibiotics are produced by Penicillium wqueforti the mold associated with Roquefort and blue cheese, and by Propionibacterium sp., which produce propionic acid and are associated with Swiss-type cheeses (3). 

Biological—Biochemical Processes. Fermentation is a biological process in which a water slurry or solution of raw material interacts with microorganisms and is enzymatically converted to other products. Biomass can be subjected to fermentation conditions to form a variety of products. Two of the most common fermentation processes yield methane and ethanol. Biochemical processes include those that occur naturally within the biomass. 

Some of the economic hurdles and process cost centers of this conventional carbohydrate fermentation process, schematically shown in Eigure 1, are in the complex separation steps which are needed to recover and purify the product from the cmde fermentation broths. Eurthermore, approximately a ton of gypsum, CaSO, by-product is produced and needs to be disposed of for every ton of lactic acid produced by the conventional fermentation and recovery process (30). These factors have made large-scale production by this conventional route economically and ecologically unattractive. 

Certain bacterial species produce polymers of y-hydroxybutyric acid and other hydroxyalkanoic acids as storage polymers. These are biodegradable polymers with some desirable properties for manufacture of biodegradable packaging materials, and considerable effort is being devoted by ICI Ltd. and others to the development of bacterial fermentation processes to produce these polymers at a high molecular weight (66). 

In the 1950s, a group of coryneform bacteria which accumulate a large amount of L-glutamic acid in the culture medium were isolated (21). The use of mutant derivatives of these bacteria offered a new fermentation process for the production of many other kinds of amino acids (22). The amino acids which are produced by this method are mostiy of the T.-form, and the desired amino acid is singly accumulated. Therefore, it is very easy to isolate it from the culture broth. Rapid development of fermentative production and en2ymatic production have contributed to the lower costs of many protein amino acids and to their availabiUty in many fields as economical raw materials. 

Xyhtol (Fig. Ig) is found in the primrose (38) and in minor quantity in mushrooms (39). It can be obtained from glucose in 11.6% overall yield by a sequential fermentation process through D-arabinitol and D-xylulose (28). 

Carbon dioxide generated by the fermentation process must be removed to help maintain the pH of the solution at pH 7.6—8.0. Carbon dioxide also inhibits the activity of the bacteria. The oxidation reduction potential is kept at 100—200 mV. The ideal temperature in the reactor varies with different strains in the bacteria but generally is 25—35°C. 

Fermentabihty of com symps by yeast is important in certain food appHcations, eg, baking and brewing. The fermentable sugars present in corn symp are dextrose, maltose, and maltotriose. Fermentabihty of maltose or maltotriose depends on the specific fermentation process and organism. In general, greater fermentabihty is obtained at higher DE levels. 

FIa.VOnoIOxida.tlon, The fermentation process is initiated by the oxidation of catechins (1) to reactive catechin quinones (13), a process catalyzed by the enzyme polyphenol oxidase (PPO) (56). Whereas the gaHocatechins, epigaHocatechin, and epigaHocatechin gaHate, are preferred, polyphenol oxidase can use any catechin (Table 2) as a substrate. This reaction is energy-dependent and is the basis of the series of reactions between flavanoids that form the complex polyphenoHc constituents found in black and oolong teas. 

Dlterpenes. Diterpenes contain 20 carbon atoms. The resin acids and Vitamin A are the most commercially important group of diterpenes. GibbereUic acid [77-06-5] (110), produced commercially by fermentation processes, is used as a growth promoter for plants, especially seedlings. 

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