Химия и химические технологии/6.Органическая химия.

Podganiyk E. V.

Shulga O. S.

Vlasova I. A.

Donetsk National University of Economics and Trade

Named after Mikhailo Tugan-Baranovsky

Modified starches in Ukrainian products

Wheat starch paste was used by Egyptians to stiffen cloth and during weaving linen and possibly to glue papyrus. Romans used it also in cosmetic creams, to powder the hair and to thicken sauces. Persians and Indians used it to make dishes similar to gothumai wheat halva. In China, with the invention of paper, rice starch was used as a surface treatment of the paper. Starch is the most important carbohydrate in the human diet and is contained in many staple foods. The major sources of starch intake worldwide are rice, wheat, maize (corn), potatoes and cassava. Widely used prepared foods containing starch are bread, pancakes, cereals, noodles, pasta, porridge and tortilla. The predominant commercial starches are those from field corn, potato, cassava, wheat, rice, and arrowroot. Field cornstarch (27 percent amylose and 73 percent amylopectin) is the major commercial starch worldwide. Genetic variants of field corn include waxy maize, which produces a starch with 98 to 100 percent amylopectin, and high-amylose starches, which have amylose contents of 55 percent, 70 percent, and higher. Waxy starch does not form gels and does not retrograde readily. High-amylose starches retrograde more extensively than normal starches and are less digestible. Their linear structure enables them to form films.

From the 1940s on the demand for convenience foods, dry mixes, and various processed foods has led to the modification of starches for food use and for other commercial products. These modified starches improve the textural properties of food products and may be more suitable for use in modern processing equipment. The Food and Drug Administration regulates use of the various modified food starches by stipulating the types of modification allowed, the degree of modification, and the reagents used in chemical modification. However, the food label is required only to state that "modified starch" is present. Only a small fraction of the sites available for modification of the food starches are actually modified. Although the degree of modification is small, the properties of the starches are significantly improved. This small degree of modification is sufficient to give a more soluble and stable starch after cooking. The clarity of the gelatinized starch as well as the stability of the cooked starch and starch gels are improved. The modification procedures are carried out under mild conditions that do not cause gelatinization of the native starch granules, and therefore the functional properties of the granule are preserved. The emulsifying properties of starch also may be improved by proper modification, improving the stability of salad dressings and certain beverages.

Physically modified starches include a pregelatinized starch that is prepared by heat-gelatinization and then dried to a powder. This instant starch is water-soluble and doesn't require further cooking. Because of its lower viscosity resulting from loss of granule structure, the starch can be used at higher concentrations. Certain confectionaries require high levels of starch to give structure to their products. These gelatinized instant starches serve this role. Cold water swelling starches represent a different type of instant starch. They are made by a proprietary process that retains the granule structure but lowers the granule strength. These cold water swelling starches give higher viscosities than the other instant starches. They are used in instant food mixes and for products such as low-fat salad dressings and mayonnaise.

Plant breeding has led to specialty starches with atypical proportions of amylose and amylopectin. Waxy maize starch with nearly 100 percent amylopectin is inherently stable to retrogradation. Chemically cross-linked waxy maize starch is a very high-quality modified starch. High-amylose starches have become available more recently and have led to lower caloric starches. Because of the crystallinity of these starches they are partially resistant to digestion by intestinal amylases and behave as dietary fiber when analyzed by the official methods of analysis for dietary fiber. Some of these high-amylose starches contain as high as 60 percent dietary fiber when analyzed.

The nutritional value of uncooked (ungelatinized) starchy foods (cereal grains, potato, peas, and beans) is relatively poor. Our digestive enzymes do not readily convert the native granular starch of uncooked fruits and vegetables into glucose that would be absorbed in the small intestine. Undigested starch passes into the large intestine where, along with dietary fiber, it is broken down to glucose and fermented to short-chain fatty acids. Some of these short-chain acids are absorbed from the large intestine resulting in recovery of some of the caloric value of the native starch.

Modified starches as described above were developed to improve starch functionality in foods as well as their ability to withstand the physical forces of modern food processing systems. In addition to the food applications of starches and modified starches, the native starches are also converted into other products that serve food and other industries. These products do not require the granular character of native starches, which is lost by chemical or enzymic action during processing of the starch.

Dextrinization, a process requiring high temperatures and acid that has been in use since the early 1800s, converts native starch into dextrins that are composed of amylose and amylopectin chains of smaller sizes and altered structure. Consequently, food and nonfood industries have access to a range of dextrin of varying molecular sizes, solubility, and viscosity, but without the granular characteristics described above. Corn syrups are made in the same way as the dextrin, but they are converted to a higher degree such that glucose is a major ingredient. The more recent availability of an enzyme that converts glucose into fructose has led to a new industry in high-fructose corn syrups, which have found a strong market in beverages.

As an additive for food processing, food starches are typically used as thickeners and stabilizers in foods such as puddings, custards, soups, sauces, gravies, pie fillings, and salad dressings, and to make noodles and pastas. But by far the most common starch based food ingredient are starch sugars used as sweetener in many drinks and foods. Gummed sweets such as jelly beans and wine gums are not manufactured using a mold in the conventional sense. A tray is filled with native starch and leveled. A positive mold is then pressed into the starch leaving an impression of 1000 or so jelly beans. The mix is then poured into the impressions and then put into a stove to set. This method greatly reduces the number of molds that must be manufactured. Starch is used as an excipient, a binder in medications to aid the formation of tablets. Resistant starch is starch that escapes digestion in the small intestine of healthy individuals.