Figure 9. Simplified process flowsheet for fructose production.

In the whole-cell process, the microbial cell containing intracellular enzyme is recovered from the fermentation broth and treated to preserve enzymatic activity and maintain particle integrity. In one process (48), culture broth is centrifuged, and the concentrated cells are disrupted by homogenization and cross-linked with glutaraldehyde. The material is then diluted and flocculated with a cationic floc-culant, and a final product is prepared by extrusion, drying, and sieving. Another method (49) involves fixing the cells in gelatin and cross-linking with glutaraldehyde, followed by washing, particle size classification, and drying.

In the soluble-enzyme process, enzyme is separated from the cells and purified before immobilization. Since glucose isomerase is an intracellular enzyme, the cell wall is first disrupted by physical (Bonification, homogenization) or enzymatic methods. The solubilized glucose isomerase is then separated by centrifugation and/or filtration and concentrated by ultrafiltration. In one method of immobilization (50), binding takes place by simply contacting the soluble enzyme with a particle containing a combination of DEAE cellulose, titanium dioxide, and polystyrene. Other supports for glucose isomerase include anion-exchange resin, anion-exchange cellulose, porous ceramics, and porous alumina.

Glucose isomerase enzymes have been isolated from a variety of microbial sources (51,52). However, only a few bacterial organisms have been used to produce glucose isomerase for commercial use. These include Streptomyces olivochromogen.es, S. murinus, S. rubiginosas, Bacillus coagulans, Actinoplanes missouriensis, and Microbacter-ium arborescens. Enzyme properties vary depending on the source, but all are similar in terms of operational pH and temperature.

HFCS is produced from dextrose hydrolysate that has been clarified, refined (including demineralization), and evaporated to 40 to 50 wt % dry substance (ds), as shown in Figure 9. Magnesium is added as a cofactor to maintain isomerase stability and to prevent inhibition by trace amounts of residual calcium. If the calcium level is below 1 ppm, a magnesium level (added as MgS04) of 0.4 mM is sufficient, although a higher calcium level requires additional magnesium. Hydrolysate is passed through a fixed bed of immobilized isomerase at a controlled flow rate. Process conditions depend on the particular enzyme system used but are generally 55 to 65°C (131 to 149°F), pH 7.5 to 8.5, and an initial reaction time of 1 h or less.

Maximum fructose content at equilibrium is 50 to 55% db; however, residence time is adjusted to attain 42 to 45% db fructose since a greatly increased reaction time is required to attain higher levels. The enzyme can be used for as long as several months, and compensation for loss in activity during operation is made by regulating the residence time, ie, flow rate through the column. Enzyme reactors are operated in parallel or in series until activity is reduced to about 10% of the initial level. Isomerized hydrolysate containing about 42% db fructose is adjusted to pH 4 to 5, refined to remove color and salts using resins either alone or in combination with activated carbon, and concentrated by evaporation to about 71 wt % solids. Product shipment is by tank trucks or by rail. Since the dextrose content in the HFCS product is more than 50% db, storage at 32 °C (90°F) is required to prevent crystallization. If crystallization occurs, the syrup is heated to 38°C (100°F) to dissolve crystals before unloading.

Products containing higher levels of fructose are produced by chromatographic separation of HFCS42 and were first commercially available in limited quantities in 1976. Enrichment is accomplished by passing HFCS42 through a column of absorbent (usually a strong-acid cation-exchange resin) containing calcium or other cation groups acting as a counter ion. Fructose is retained to a greater degree than dextrose or oligosaccharides, and therefore a stream containing most of the nonfructose is collected first in a raffinate stream, followed by elution of a fructose-enriched extract with water. Separation can be achieved using batchwise, semicontinuous, or continuous operation; commercial operations favor continuous processes. The continuous procedure involves a simulated moving bed in which feed and desorbent enter the column at different points while fructose and raffinate streams are withdrawn at others. Points of entry and withdrawal are changed periodically to correspond to flow through the column, and hence separation efficiency is maximized. Typical operation involves the addition of HFCS42 at a dry substance content of 50 to 60% to a column at 50 to 70°C (122 to 158°F). Dextrose-rich raffinate is recycled to isomerization columns for additional production of HFCS42. Enriched HFCS is blended with HFCS42 to produce a product containing 55% db fructose. A solids level of 77% ds is suitable for shipment at 27°C (81°F) with minimal dextrose crystallization problems. In addition, enriched HFCS at about 90% db fructose is evaporated to 80% ds for shipment as an essentially noncrystallizable syrup at normal room temperature.

Fructose of >99% purity is produced by crystallization to the /?-d-fructopyranose form. In one process, chromato graphic separation of 42% HFCS is used to produce a fraction containing 97% fructose. The material is evaporated to 70% solids, and 50% of the fructose is recovered by crystallization in 80 to 100 h (53).

Economic Aspects

Published U.S. wholesale prices of 42 and 55% HFCS since 1980 are listed in Table 6. The 1989 price for 90% fructose was about $l/kg (45 cents/lb) on a commercial basis. The price of HFCS has not been intimately tied to the price of sucrose for a number of years. Supply and demand seem to be the most important factors influencing price.

During the early 1970s, the price of refined sugar increased dramatically, resulting in a concomitant increase in the price of HFCS and the construction of new production facilities. When sugar prices fell during 1975 to 1978, HFCS prices also dropped, falling to a level of about 30 to 35% below sugar rather than the 15 to 20% discount that had existed previously. Excess production capacity also lowered HFCS prices, delaying the start-up of some new plants. However, during the late 1970s through the early 1980s, demand for HFCS increased significantly in the soft-drink industry, and the discount to sucrose decreased, especially for the sweeter HFCS55 product.

As can be seen from Table 7, the new sweetener also took market share from existing starch sugars in some segments, especially the more expensive dextrose. Dextrose consumption in the United States actually fell for a time before rebounding in the late 1980s.

Because of the increased demand and higher sucrose prices, processing capacity was again increased throughout the industry. From 1980 to 1985, per capita consumption of HFCS increased from 8.7 to 20.5 kg (19 to 45 lb) due primarily to 100% substitution for sugar in many soft drinks. Because of this near maximum penetration of the soft drink market, HFCS growth slowed to 2 to 4% per year through the end of the 1990s, and prices relative to sucrose fell again.

Then, in 1991, consumption accelerated to a level of 5 to 6% annual growth, and prices firmed until the industry once more made substantial capacity increases that caused prices relative to sucrose to fall. This was particularly painful in 1996 when corn prices increased dramatically, averaging nearly $4.00/bushel ($160/metric ton) for the year. Prices in 1997 reached lows not seen in 20 years but have begun to firm as demand continues to grow by about 1 billion pounds per year. HFCS prices in the United States are expected to continue to be influenced primarily by factory utilization and to a lesser degree by sugar prices and the cost of corn.

Analysis and Specifications

International (including U.S.) specifications for HFCS are the same as those for corn syrup. Fructose content is determined by high-performance liquid chromatography; dry substance, by refractive index; and color, by spectroscopy.

High-fructose corn syrup is used as a partial or complete replacement for sucrose or invert sugar in food applications to provide sweetness, flavor enhancement, ferment-ables, or humectant properties. It is used in soft drinks, baking, canned fruit, dairy products, and confections (Table 7). HFCS is used in combination with sucrose as well as other corn sweeteners. The main application of HFCS55 is in soft drinks. HFCS containing 90 wt % fructose is used in low calorie or specialty foods because of its high sweetness and, therefore, reduced usage level and lower caloric value. Other uses are as a liquid tabletop sweetener or as a honey-flavored product for use in baked goods and confections. Crystalline fructose is essentially pure and is used at a level that provides sweetness at a lower caloric level than that in other sweeteners. Uses include health foods and medicines.

Homemade Pet Food Secrets

Homemade Pet Food Secrets

It is a well known fact that homemade food is always a healthier option for pets when compared to the market packed food. The increasing hazards to the health of the pets have made pet owners stick to containment of commercial pet food. The basic fundamentals of health for human beings are applicable for pets also.

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