Prevenció i tractament de les úlceres venoses

The raw materials to be discussed are used because of the properties mentioned above:

cheapness, ready availability, constancy of chemical quality, etc. A raw material which is

Left: Vitamin B¹². Please note that cobalt is highlighted. It must be present in the medium in which organisms producing the vitamin are grown

Right: Top; The general structure of tetracyclines. Bottom; The structure of 7-Chlortetracycline; a chlorine atom is present in position 7. Chlorine must be present in the medium for producing chlortetracyline; note that chlorine is highlighted in position 7 in chlortetracycline.

Fig. 4.1 Vitamin B¹² and Chlortetracycline Showing Location of Components Present as Precursors in the Medium

Industrial Media and the Nutrition of Industrial Organisms 59 cheap in one country or even in a different part of the same country may however not be cheap in another, especially if it has already found use in some other production process.

In such cases suitable substitutes must be found if the goods must be produced in the new location. The use of local substitutes where possible is advantageous in reducing the transportation costs and even creating some employment in the local population. Prior experimentation may however be necessary if such new local materials differ substantially in composition from those already being used. Some well-known raw materials will now be discussed. In addition, some of potential useability will also be examined.

(a) Corn steep liquor

This is a by-product of starch manufacture from maize. Sulfur dioxide is added to the water in which maize is steeped. The lowered pH inhibits most other organisms, but encourages the development of naturally occurring lactic acid bacteria especially homofermentative thermophilic Lactobacillus spp. which raise the temperature to 38-55°C. Under these conditions, much of the protein present in maize is converted to peptides which along with sugars leach out of the maize and provide nourishment for the lactic acid bacteria. Lactic fermentation stops when the SO₂ concentration reaches about 0.04% and the concentration of lactic acid between 1.0 and 1.5%. At this time the pH is about 4. Acid conditions soften the kernels and the resulting maize grains mill better while the gel-forming property of the starch is not hindered. The supernatant drained from the maize steep is corn steep liquor. Before use, the liquor is usually filtered and concentrated by heat to about 50% solid concentration. The heating process kills the bacteria.

As a nutrient for most industrial organisms corn steep liquor is considered adequate, being rich in carbohydrates, nitrogen, vitamins, and minerals. Its composition is highly variable and would depend on the maize variety, conditions of steeping, extent of boiling etc. The composition of a typical sample of corn steep liquor is given in Table 4.2. As corn steep liquor is highly acidic, it must be neutralized (usually with CaCO₃) before use.

(b) Pharmamedia

Also known as proflo, this is a yellow fine powder made from cotton-seed embryo. It is used in the manufacture of tetracycline and some semi-synthetic penicillins. It is rich in

Table 4.2 Approximate composition of corn steep liquor (%)

Lactose 3.0-4.0

60 Modern Industrial Microbiology and Biotechnology

protein, (56% w/v) and contains 24% carbohydrate, 5% oil, and 4% ash, the last of which is rich in calcium, iron, chloride, phosphorous, and sulfate.

(c) Distillers solubles

This is a by-product of the distillation of alcohol from fermented grain. It is prepared by filtering away the solids from the material left after distilling fermented cereals (maize or barley) for whiskey or grain alcohol. The filtrate is then concentrated to about one-third solid content to give a syrup which is then drum-dried to give distillers soluble. It is rich in nitrogen, minerals, and growth factors (Table 4.3).

Table 4.3 Composition of maize distillers soluble

%

Soya beans (soja) (Glycine max), is an annual legume which is widely cultivated throughout the world in tropical, sub-tropical and temperate regions between 50°N and 40°S. The seeds are heated before being extracted for oil that is used for food, as an anti-foam in industrial fermentations, or used for the manufacture of margarine. The resulting dried material, soya bean meal, has about 11% nitrogen, and 30% carbohydrate and may be used as animal feed. Its nitrogen is more complex than that found in corn steep liquor and is not readily available to most microorganisms, except actinomycetes. It is used particularly in tetracycline and streptomycin fermentations.

(e) Molasses

Molasses is a source of sugar, and is used in many fermentation industries including the production of potable and industrial alcohol, acetone, citric acid, glycerol, and yeasts. It is a by-product of the sugar industry. There are two types of molasses depending on whether the sugar is produced from the tropical crop, sugar cane (Saccharum officinarum) or the temperate crop, beet, (Beta alba).

Four stages are involved in the manufacture of cane sugar. After crushing, a clear greenish dilute sugar solution known as ‘mixed juice’ is expressed from the canes.

During the second stage known as clarification the mixed juice is heated with lime.

Addition of lime changes the pH of the juice to alkaline and thus stops further hydrolysis (or inversion) or the cane sugar (sucrose), while heating coagulates proteins and other undesirable soluble portions of the mixed juice to form ‘mud’. The supernatant juice is then concentrated (in the third stage) by heating under high vacuum and increasing low pressures in a series of evaporators. In the fourth and final stage of crystallization, sugar crystals begin to form with increasing heat and under vacuum, yielding a thick brown

Industrial Media and the Nutrition of Industrial Organisms 61 syrup which contains the crystals, and which is known as ‘massecuite’. (In the beet industry it is known as ‘fillmass’.) The massecuite is centrifuged to remove the sugar crystals and the remaining liquid is known as molasses. The first sugar so collected is ‘A’

and the liquid is ‘A’ molasses. ‘A’ molasses is further boiled to extract sugar crystals to yield ‘B’ sugar and ‘B’ molasses. Two or more boilings may be required before it is no longer profitable to attempt further extractions. This final molasses is known as

‘blackstrap molasses’.

The sugar yielded with the production of black strap molasses is low-grade and brown in color, and known as raw sugar, cargo sugar, or refining sugar. This raw sugar is further refined, in a separate factory, to remove miscellaneous impurities including the brown color (due to caramel) to yield the white sugar used at the table. The heavy liquid discarded from the refining of sugar is known in the sugar refining industry as ‘syrup’

and corresponds to molasses in the raw sugar industry.

The above description has been of cane sugar molasses. In the beet sugar industry the processes used in raw refined sugar manufacture are similar, but the names of the different fractions recovered during purification differ. Cane and beet molasses differ slightly in composition (Table 4.4). Beet molasses is alkaline while cane molasses is acid.

Table 4.4 Average composition of beet and cane molasses

Beet Molasses Cane Molasses

Materials, acids, gums, etc.) 19.0 10.0

Ash 11.5 8.0

Even within same type of molasses – beet or cane – composition varies from year to year and from one locality to another. The user industry selects the batch with a suitable composition and usually buys up a year’s supply. For the production of cells the variability in molasses quality is not critical, but for metabolites such as citric acid, it is very important as minor components of the molasses may affect the production of these metabolites.

‘High test’ molasses (also known as inverted molasses) is a brown thick syrup liquid used in the distilling industry and containing about 75% total sugars (sucrose and reducing sugars) and about 18% moisture. Strictly speaking, it is not molasses at all but invert sugar, (i.e reducing sugars resulting from sucrose hydrolysis). It is produced by the hydrolysis of the concentrated juice with acid. In the so-called Cuban method, invertase is used for the hydrolysis. Sometimes ‘A’ sugar may be inverted and mixed with ‘A’

molasses.

62 Modern Industrial Microbiology and Biotechnology (f) Sulfite liquor

Sulfite liquor (also called waste sulfite liquor, sulfite waste liquor or spent sulfite liquor) is the aqueous effluent resulting from the sulfite process for manufacturing cellulose or pulp from wood. Depending on the type, most woods contain about 50% cellulose, about 25% lignins and about 25% of hemicelluloses. During the sulfite process, hemicelluloses hydrolyze and dissolve to yield the hexose sugars, glucose, mannose, galactose, fructose and the pentose sugars, xylose, and arabinsoe. The acid reagent breaks the chemical bonds between lignin and cellulose; subsequently they dissolve the lignin. Depending on the severity of the treatment some of the cellulose will continue to exist as fibres and can be recovered as pulp. The presence of calcium ions provides a buffer and helps neutralize the strong lignin sulfonic acid. The degradation of cellulose yields glucose. Portions of the various sugars are converted to sugar sulfonic acids, which are not fermentable.

Variable but sometimes large amounts of acetic, formic and glactronic acids are also produced.

Sulfite liquor of various compositions are produced, depending on the severity of the treatment and the type of wood. The more intense the treatment the more likely it is that the sugars produced by the more easily hydrolyzed hemicellulose will be converted to sulfonic acids; at the same time the more intense the treatment the more will glucose be released from the more stable cellulose. Hardwoods not only yield a higher amount of sugar (up to 3% dry weight of liquor) but the sugars are largely pentose, in the form of xylose. Hardwood hydrolyzates also contains a higher amount of acetic acid. Soft woods yield a product with about 75% hexose, mainly mannose.

Sulfite liquor is used as a medium for the growth of microorganisms after being suitably neutralized with CaCO₃ and enriched with ammonium salts or urea, and other nutrients. It has been used for the manufacture of yeasts and alcohol. Some samples do not contain enough assaimilable carbonaceous materials for some modern fermentations. They are therefore often enriched with malt extract, yeast autolysate, etc.

(g) Other Substrates

Other substrates used as raw materials in fermentations are alcohol, acetic acid, methanol, methane, and fractions of crude petroleum. These will be discussed under Single Cell Protein (Chapter 15). Barley will be discussed in the section dealing with the brewing of beer (Chapter 12).