High-fructose corn syrup and

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. 

Microbacteruim arborescens, Streptomyces rubiginosus var., or Streptomyces murinus) Produced as an off-white to tan, brown, or pink, amorphous powder, granules, or a liquid by controlled fermentation using any of the above-named organisms. The products may be soluble in water but practically insoluble in alcohol, in chloroform, and in ether, or if immobilized, may be insoluble in water and partially soluble in alcohol, in chloroform, and in ether. Major active principle glucose (or xylose) isomerase. Typical applications manufacture of high-fructose corn syrup and other fructose starch syrups. 

These significant barriers are largely responsible for the lack of substantial commercial impact of enzyme and microbial catalysts on the chemicaIs-related industries. High fructose corn syrup and amino... 

Fructose (CjHi20j) Monosaccharide or simple sugar naturally occurring in fruits and honey. Chemically, it is a 3-d-fructofuranose molecule. Fructose is a major sugar in high-fructose corn syrups and is sweeter than glucose. 

In 2002, approximately 2.2 billion bushels of corn were processed in the United States for the production of food, fuel, and industrial products. Of that 2.2 billion bushels, 19.22 million tonnes (757 million bushels) were used for high fructose corn syrup (HFCS), glucose and dextrose, 6.34 million tonnes (250 million bushels) for pearl starch, 26.69 million tonnes (1051 million bushels) for fuel and beverage alcohol, and 4.75 million tonnes (187 million bushels) for cereals and other products (Corn Refiners Association, 2003). More than 50% of the com processed in the United States is done so using the corn wet milling process. 

Honey and maple syrup are complex products of high market price (813C — 23%o). The main source of adulteration is cheap high fructose corn syrup (813C — 13%o) or cane sugar (813C —ll%o) and the adulterated product is easily detected at levels as low as 10% or so of added sugar. 

A critical consideration in the development of biocatalytic systems is the form in which the enzyme or enzyme system is going to be used. There are two general approaches. One is to use isolated enzymes. If these are inexpensive, they can be used as disposable biocatalysts, as is the case for glucose isomerase, ° which is the key biocatalyst in the production of high-fructose corn syrups from starch, or the lipases and proteases that are present in detergents. Alternatively, if enzymes are expensive to produce, they can be immobilized and used repeatedly by recovering the enzyme particles after each use. 

Xylose isomerases (EC 5.3.1.5), often referred to as glucose isomerase, have been studied extensively, in large part because of their use in the conversion of glucose to fructose for high-fructose corn syrup (HFCS). The world market for HFCS is expected to reach a total of 7.9 million metric tons in 1990 which, at a cost of 0.20/LB, would amount to 3.2 billion (i), and sales of xylose isomerase is expected to be about 15 million (T. Wallace, International Biosynthetics, personal communication). Research on xylose isomerase has produced DNA sequences of the gene from a number of bacterial strains, including the detailed structure of the xylose operon (2-7). In addition, x-ray crystallographic studies (8), kinetic measurements (9), and the use of inhibitors (10,11) have led to descriptions of the location of the active site and mechanistic models of its activity. 

High fructose corn syrup (MFCS) has emerged In recent years as an alternative nutritional sweetener to sucrose. However, the use of HFCS has been confined to those applications suited to liquid syrups, In particular the beverage and canning sectors of the market. The manufacture of fructose as a crystalline product would open up further market opportunities for the sweetener. One company In the USA Is producing crystalline fructose In commodity quantities (1), but at a higher price than sucrose. 

The highest-volume chemicals made by biocatalysis are ethanol ( 70 metric tons), high-fructose corn syrup (1.5-2 metric tons), L-lysine (850,000 tons) and... 

About ten percent of the calories contained in the Western diet are supplied by fructose (approximately fifty g/day). The major source of fructose is the disaccharide sucrose, which, when cleaved in the intestine, releases equimolar amounts of fructose and glucose (see p. 86). Fructose is also found as a free monosaccharide in high-fructose corn syrup (55 percent fructose/45 percent glucose, which is used to sweeten most cola drinks), in many fruits, and in honey. Entry of fructose into cells is not insulin-dependent (unlike that of glucose into certain tissues, see p. 95), and, in contrast to glucose, fructose does not promote the secretion of insulin. 

Milk fat and milk solids-not-fat (MSNF) are most commonly obtained from cream and condensed skim milk, but may also be obtained from a combination of fluid milk, condensed whole milk, frozen cream, frozen condensed milk, nonfat dry milk, dry whole milk, and butter. Sweeteners used in the mix normally include a combination of liquid or dry sucrose, corn sweetener, high-fructose corn sweetener, and corn syrup solids. Ice cream stabilizers are formulated to contain one or more polysaccharide hydrocolloids, e.g., carboxymethyl cellulose, locust bean gum, carageenin, alginate, and other gums. Ice cream emulsifiers normally contain monoglycerides and diglycerides of palmitic and stearic... 

In recent years, the conversion of starch to fructose has become a very important commercial process. High-fructose corn syrup (HFCS) is approximately twice as sweet as sucrose. It is used in soft drinks, canned fruits, lactic acid beverages, juice, bread, ice cream, frozen candies, and so on. HFCS can be obtained from a variety of cereals and vegetables, such as corn, wheat, rice, potatoes, and cassava. Corn is the most important source of HFCS because of low costs and excellent utilities of its by-products, corn meal, oil, gluten, germ, and fiber. 

The food industry is a fertile area for biocatalysis applications high-fructose corn syrup (HFCS) from glucose with glucose isomerase, the thermolysin-catalyzed synthesis of the artificial sweetener Aspartame , hydrolysis of lactose for lactose-intolerant consumers, and the synthesis of the nutraceutical i-camitine in a two-enzyme system from "ybutyrobetaine all serve as examples. 

---