Fermentation glucose syrups used

By-products of starch refining and HFCS prodnction are significant and rednce HFCS production costs by 30 5% (Table 4.2). This is because the com is 70% starch on a dry weight basis, it also contains 10% protein, 4.5% fat and 2.7% erode fibre. In addition much of the glucose syrup produced is fermented to produce ethanol for fuel use. 

An additional feature is that the glucose syrups can also be fermented to produce ethanol for use in fuels. Obviously HFCS is a more valuable product, but power ethanol production does generate significant revenues. 

Starches may be used directly as feedstocks, or in more technical uses in modified form (typically as starch esters and ethers), or simply converted to glucose syrups for use in industrial fermentation processes or for onward conversion to isoglucose (fructose). After use of unmodified starches in ethanol production, the largest industrial user of both unmodified and modified starches is the papermaking... 

Maltodextrin solutions are not evaporated to as low a solids level as is typical of most glucose syrups because the viscosity of the latter is extremely high (see Table 21.9). At the higher solids level of 43 or 44 Baume typical for com syrups, maltodextrin solutions would be extremely difficult to pump. It should also be noted that, since the water activity of maltodextrins at a given solids level is so much higher than that of other syrups, some care must be exercised in the handling of these products to prevent microbial fermentation. Commercial maltodextrins, as shown in Table 21.1,15 are used in applications where high viscosity coupled with a bland, neutral taste is desirable. 

Major biotechnological uses of the biomass carbohydrate moiety have attracted worldwide attention. Controlled cellulose degradation by cellulases may produce materials for important multifarious applications carbohydrates that can be used in the food and beverage industries, cellulose microfibril fragments for non-caloric food additives, hyperabsorbent cellulose fibers from fragmented cellulose microfibrils which can be used in biomedical, commercial and house-hold absorbent materials. Biomass-derived glucose syrups can also be used as carbon source in industrial fermentations for the production of antibiotics, industrial enzymes, amino-acids, and bulk chemicals. 

Starch-Modifying Enzymes Starch is one of the most abundant carbohydrates in terrestrial plants and the most important polysaccharide used by humankind. This polymer is normally processed and used in a variety of products such as starch hydrolysates, starch or maltodextrin derivatives, fructose, glucose syrups, and cyclodextrins [148, 149]. In addition, starch is widely used as a raw material in the paper industry, in polyol production, and as economic substrate for many microbial fermentations [149]. Starch consists of a large number of glucose units that can be linearly attached as hehcal amylose [ 99% a-(l-4) and 1% a-(l-6) bonds] or branched as amylopectin [ 95% a-(l-4) and 5% a-(l-6) bonds] [69]. In nature, four types of starch-converting enzymes exist (i) endoamylases (ii) exoamylases (iii) debranching enzymes and (iv) transferases. 

Glucose syrups are also used as fermentables in beer and alcohol production. Finally, modified starches are used to encapsulate vitamins that are frequently added to juices. 

In starch-based bioplastics, starch is fully utilized with a yield very close to 100%, whereas in starch-derived bioplastics, synthesized from monomers resulting from fermentation of glucose syrup, the yield is generally less than 45%, and more complex processes and a less efficient use of resources are involved. 

The emerging glucose syrup has a wide variety of uses. In the United States, large quantities, equivalent to some 4 million tonnes of glucose, are fermented each year to ethanol. A further 6 million tonnes (7.8 million tonnes world-wide) are treated with glucose isomerase. This enzyme inter-... 

Use of Low-Cost and Nonedible Substrates. Whereas production of lactic acid from sucrose or glucose syrup is well established, crude sources (starches, sugars, or future fignoceUulose hydrolysates) will form the next hurdle as they contain much more impurities and possible fermentation inhibitors. 

Often, microbial fermentation media for biochemicals or enzyme production (Figure 1.10) contain cheap complex ingredients such as corn steep liquor, starch, glucose syrup, yeast extract, or other complex compounds that are not fully defined. The source of such raw materials is critical and will greatly impact growth and production. In either case, the medium, transfer lines, and bioreactor vessels are sterilized prior to use. 

All feeds are added as sterile solutions. Two tanks are used for the glucose feed for the entire fermentation, one in operation and one under maintenance (washing, loading, etc.). The glucose feed, that is, 161 of 65-66% glucose solution, is prepared from 74 to 75% glucose syrup by dilution with water. The feed tanks are equipped with agitators and jackets to maintain the syrup at 50-60 C to reduce viscosity and avoid crystallization or lump formation. The steam-heated jacket ensures temperature control. 

One of the more recent innovative approaches was to look for new micro-organisms and novel carbohydrate substrates. The early fermentations used sugar beet or cane molasses, various syrups, sweet potato starch or glucose itself and the micro-organism was always an Aspergillus spp. In the early 1930 s it was found that yeasts would produce dtric add from acetate. Since then a variety of yeasts, prindpally Candida spp., has been shown to convert glucose, w-alkanes or ethanol to dtric add with great effidency. 

Interest in the bacterial ens me xylose/glucose isomerase has been driven by its use in the isomerization of ucose to fructose to produce high>fructose corn syrups, and in the isomerization of xylose to xylulose for the conversion of the more fermentable xylulose to ethanol In this work, a brief historical perspective is presented, followed by a summary of the current understanding of the enzyme s major features. Also, a useful compilation of available xylose isomerase DNA sequences is presented with annotation of some of the major areas identified as being of functional significance. The extent of homology between the xylose isomerases is discussed with reference to differences in their function. 

The simultaneous bioconversion of mixed sugar syrups is one of the most ambitious challenges in the field of bioethanol production. Different productivities and ethanol-tolerance of the yeasts used in the fermentation of glucose and xylose (the most abundant biomass sugars) have led... 

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