Carbohydrates large-scale

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. 

Other Processes. Isopropyl alcohol can be prepared by the Hquid-phase oxidation of propane (118). It is produced iacidentaHy by the reductive condensation of acetone, and is pardy recovered from fermentation (119). Large-scale commercial biological production of isopropyl alcohol from carbohydrate raw materials has also been studied (120—123). 

Fermentative Manufacture. Throughout the years, riboflavin yields obtained by fermentation have been improved to the point of commercial feasibiUty. Most of the riboflavin thus produced is consumed in the form of cmde concentrates for the enrichment of animal feeds. Riboflavin was first produced by fermentation in 1940 from the residue of butanol—acetone fermentation. Several methods were developed for large-scale production (41). A suitable carbohydrate-containing mash is prepared and sterilised, and the pH adjusted to 6—7. The mash is buffered with calcium carbonate, inoculated with Clostridium acetohutylicum and incubated at 37—40°C for 2—3 d. The yield is ca 70 mg riboflavin/L (42) (see Fermentation). 

A conceptually new direct oxidative glycosylation with glycal donors, employing a reagent combination of triflic anhydride and diphenyl sulfoxide, has recently been reported by Gin [83], This new 3-glycosylation method works very well with hindered hydroxy nucleophiles, including sterically shielded carbohydrate hydroxy systems, and can be run on large scales. 

One feature of this oxidation system is that it can selectively oxidize primary alcohols in preference to secondary alcohols, as illustrated by Entry 2 in Scheme 12.5. The reagent can also be used to oxidize primary alcohols to carboxylic acids by a subsequent oxidation with sodium chlorite.34 Entry 3 shows the selective oxidation of a primary alcohol in a carbohydrate to a carboxylic acid without affecting the secondary alcohol group. Entry 5 is a large-scale preparation that uses NaC102 in conjunction with bleach as the stoichiometric oxidant. 

Much of the research on the l.c. of carbohydrates has focused on analytical, rather than preparative, aspects. In reality, however, the conditions found in the majority of l.c. methods, namely, no sample derivatization, high-resolution separations, and nondestructive detection-techniques, are ideal for the preparation of pure molecules. Thus, most of the analytical l.c. methods previously described can also be used to isolate small quantities of pure compounds. This Section will cover the use of analytical-scale equipment for preparative applications, as well as the use of large-scale and dedicated preparative instruments for this purpose. Prior to discussion of these applications, a general overview of the preparative l.c. of carbohydrates will be given. 

Isolation of Carbohydrates on Large-Scale Columns, and Instrumentation... 

For large-scale oxidations of secondary alcohols and of carbohydrates by RuO cf 2.3.7. 

Large-Scale Oxidations of Alcohols, Carbohydrates and Diols... 

For large-scale oxidations of carbohydrates (> Ig) cf. the first column of Table 2.3. For synthesis of carbohydrates by alkene cyclisation cf. 3.1.3.3. 

In addition to enhancement with essential vitamins, amino acids, and proteins, plants can also be metabolically engineered to produce nutritionally superior carbohydrates and lipids. The relative inexpensiveness as well as the capability to grow large-scale quantities make plant production an attractive feature. In the case of carbohydrates such as starch and sucrose, many products or modifications of these products can be produced on a large scale and at much lower costs than are currently available. For example, trehalose, a food additive, was in the past too costly for large-scale production however, it has now been produced in transgenic tobacco tissue at a much reduced cost. 

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