Teorías Relacionadas al Tema

Burning of sugar in noncatalyzed processes results in formation of particularly high amounts of furan-2-aldehyde and its derivatives. They constitute the flavor and aroma typical for caramels. Many foodstuffs (meat, fish, dough, potato, cocoa, coffee, and tobacco) on thermal treatment (baking, frying, roasting, and smoking) develop spe-cific aromas. They are volatile derivatives of pyrazine, imidazole, pyrrole, and pyridine formed on thermal reactions of saccharides and proteins, nucleotides, and amino acids.

Saccharides and polysaccharides — starch and cellulose (B ˛aczkowicz et al., 1991), pectins (Sikora et al., 1998), and hemicelluloses (Tomasik and Zawadzki, 1998) — heated with amino acids develop scents specific for polysaccharide, amino acid, and reaction conditions. Thus, supplementation of saccharides and polysac-charides with amino acids and proteins, as well as supplementation of protein-con-taining products with saccharide, can be useful in generation, modification, and enrichment of flavor and aroma of foodstuffs and tobacco.

5.5.4 T^EXTURE

More concentrated aqueous solutions of carbohydrates form viscous liquids. This property is most commonly utilized in practice for texturizing foodstuffs. In such solutions sugar–sugar interactions (complexation) are responsible for this effect. It was found that although interactions in various monosaccharide–monosaccharide, disaccharide–disaccharide, and monosaccharide–disaccharide combinations brought no particularly promising texturizing result (Mazurkiewicz and Nowotny- , 1998), certain blends of either mono- or disaccharide with polysaccharides showed remarkable increase in viscosity and adhesiveness (Mazurkiewicz et al., 1993). On such, edible glues and adhesives could be prepared. Such interactions are commonly utilized in texturization of puddings, jellies, foams, and so on. Some oligosaccharides and the majority of polysaccharides form hydrocolloids, which build up their own macrostructure. They give an impression of jelly formation, thickening, smoothness, stabilization against temperature and mechanical shocks, aging, and resistance to sterilization and pasteurization. Plant gums, pectins, and alginates are particularly willingly utilized for this purpose. Recently, considerable attention was paid to textural properties of polysaccharide–polysaccharide interactions where both inter-acting polysaccharides were starches of various origins (Obanni and Bemiller, 1997;

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Lii et al., 2001a).One should note that the texturizing effect of a given saccharide or polysaccharide and its various blends is developed as a function of time necessary for the formation of a gel network (a physical cross-linking). The pH and temperature may also be essential factors. If protons (pH < 7) or hydroxyl anions (pH > 7) and temperature do not evoke any structural changes in interacting species, the textur-izing effect is reversible in pH and temperature. If retrogradation does not take place, texturization is also reversible in time.

Saccharides, oligosaccharides, and polysaccharides form also complexes with mineral salts, proteins, and lipids. Such complexes also contribute to foodstuff texture.

Apart from combinations of natural saccharides, oligosaccharides, and polysac-charides with involvement of lipids and proteins, chemically modified polysaccha-rides are also utilized for texturization. Cross-linked starches are important textur-izing agents. The degree of cross-linking is an important factor. It should not be higher than 0.2. Among cross-linked starches, those esterified with phosphoric acid are particularly favored. All starches can be cross-linked by esterification with phosphoric acid (in practice, either with salts of meta- or orthophosphates, as well as POCl₃ and PCl₅), but at the same degree of substitution, phosphorylated potato starch gives superior results, while cornstarch phosphate is the poorest.

Starch sulfate ester is used as a thickener and emulsion stabilizer. It is a typical anionic starch used as a component of anionic starch–protein complexes constituting meat substitutes (Tolstoguzov, 1991, 1995). Other anionic starches, as well as pec-tins, alginic acid, carrageenans, furcellaran, heparin, xanthan gum, and carboxym-ethyl cellulose, are anionic polysaccharides; their application in food texturization is now under study (Clark and Ross-Murphy, 1987; Schmitt et al., 1998; Zaleska et al., 2001a, 2001b). Anionic polysaccharides are particularly good texturizing agents in the presence of mineral salt cations (Na⁺, K⁺, Mg²⁺, and Ca²⁺).

Among many available modified polysaccharides, application of only few of them is legal in view of the food law of particular countries. Some restrictions are put on the method of their manufacture and the purity of such products.

The replacement of saccharide sweeteners (first of all sucrose) in food with various natural and synthetic sweeteners of very high RS (currently, mainly saccha-rine, aspartame, and cyclamates) is a task. It is also a demand of consumers looking for low-calorie food. Also, diabetics are looking for food free of insulin-requiring saccharides and polysaccharides. Following such demands, problems are encoun-tered in providing the anticipated texture of sweet products manufactured without saccharides (Mazurkiewicz et al., 2001).

5.5.5 ENCAPSULATION

Various foodstuffs loose their original, beneficial flavor, aroma, taste, and color on processing. It is a common result of evaporation of volatile components or decomposition of certain food components under the influence of oxygen or light.

In this manner the quality of foodstuffs decreases. In order to avoid such effects, volatile and unstable products are either protected in processed sources or, after processing, are supplemented by fragrances, colorants, and other components.

Such goals are met by encapsulation and supplementation of microcapsule closed additives. Saccharides are suitable for making such microcapsules. Compression of additives (guest molecules) with a saccharide forming the matrix of the micro-capsule (the host molecule) is a common practice. It is beneficial if there are some other-than-mechanical interactions between the guest and host that decrease the rate of evaporation or reaction of the guest from the microcapsule. Granular starch can encapsulate guests in capillaries between granules; gelatinized starch, amylose, and amylopectin can trap certain molecules inside helices generated in contact with guest molecules.

Coacervation or coprecipitation of host and guest and suspension of the guest molecule in polysaccharide gels, followed by drying, is another common procedure.

Microcapsules can be made on the formation of polysaccharide–protein complexes in the presence of a potential host. Preswelled granular starches are potential natural microcapsules (Lii et al., 2001b).

α-, β-, and γ-cyclodextrins are the most effective compounds for microen-capsulation of food components (Szejtli, 1984). Cyclodextrins take a form of toruses with cavities of 0.57, 0.78, and 0.95 nm in diameter, respectively. Their height is 0.78nm.

Upper and bottom edges of the toruses have secondary and primary hydroxyl groups, respectively. All hydroxyl groups reside on the external surface of toruses, making cyclodextrins hydrophilic. Simultaneously, their cavity interior is hydrophobic.

Cyclodextrins are water-soluble hosts for hydrophobic guests. The formation of inclusion complexes is controlled by the dimensional compatibility of the guest and host cavity. Commercially available dextrins are, in fact, inclusion complexes of cyclo-dextrins with two water molecules closing the entrance to the cavity. The formation of cyclodextrin inclusion complexes is reversible and, therefore, is governed by con-centration of guests competing for a place inside the cavity.

5.5.6 POLYSACCHARIDE C^ONTAINING BIODEGRADABLE M^ATERIALS

There is a growing concern about fully biodegradable plastic — packing and wrap-ping foils, containers, equipment of fast-food restaurants, and superabsorbents.

Currently, several products made of polyethylene modified into biodegradable mate-rial are in use throughout the world. Biodegradability of such matemate-rials was afforded by admixture of 6–15 w-% of natural components, such as starch, cellulose, wood, or proteins, into polyethylene. Polyurethane foams used as thermal insulators and packing materials contain up to 20% starch. The level of starch in copolymers of ethylene with either vinyl chloride, styrene, or acrylic acid may reach 50%. Of course, the effect of biodegradation of such material has more aesthetic significance than ecological. Although degradation of the finely pulverized synthetic portion of such materials is accelerated, it still takes several decades for depolymerization to come to its end.

Apparently, the simplest biodegradable plastics could be prepared of starch solely by compression of up to 10⁶ kPa, provided starch was moisturized up to its natural water-binding capacity (~20 w-%) ( and Tomasik, 1992).

Following the idea of full biodegradability of materials, attention has been paid to the compositions of plain carbohydrates with either unmodified or modified

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proteins and of modified carbohydrates with unmodified and modified proteins. Such compositions are processed to generate carbohydrate–protein complexes. The ther-modynamic and electrical compatibilities of components should be reached in order to afford the best functional properties of materials. Because of the chemical nature of proteins (cationic character), carbohydrates should be anionic, i.e., on dissociation the negative charge should be left on polysaccharide moiety. The COOH, PO₃H₂, and SO₃H groups provide such properties. Whenever modification of a carbohydrate is required to make it anionic, the degree of derivatization should not exceed 0.1. It should neither increase the hydrophilicity of the product nor, if possible, decrease its molecular weight.

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