Amyloses with fatty acids

It should be noted that the different structures of amylose and amylopectin confer distinctive properties to these polysaccharides (Table II). The linear nature of amylose is responsible for its ability to form complexes with fatty acids, low-molecular-weight alcohols, and iodine these complexes are called clathrates or helical inclusion compounds. This property is the basis for the separation of amylose from amylopectin when starch is solubilized with alkali or with dimethylsulfoxide, amylose can be precipitated by adding 1-butanol and amylopectin remains in solution. 

When the A-fraction from corn starch is potentiometrically titrated with iodine, its affinity for the latter is sharply reduced in the presence of small amounts of fatty acid. Thus the iodine adsorption of recrystallized A-fraction (originally 18.7%) is reduced to 12.4%, 3.5% and 0% by the addition respectively of 2%, 5% and 10% of palmitic acid. Raw corn starch contains approximately 0.66% of fatty acids, corresponding to approximately 2% on the basis of the linear A-fraction. Thus, a third of the linear component in raw com starch is inactivated. In a sense, Taylor and coworkers were correct in assuming an association between a-amylose and fatty acid, but they erred in presuming the combination to be an ester. 

Karkalas J., Ma S., Morrison W.R., Pethrick R.A., Some factors determining the thermal properties of amylose inclusion complexes with fatty acids, Carbohydr. Res., 268, 1995, 233-247. 

There are three types of crystallinity in starch as observed in the X-ray diffraction pattern (Fig. 6.5). They are the A type mainly cereal starches such as maize, wheat, and rice B type such as tuber starches (potato, sago) and finally the C type crystallinity which is the intermediate between A and B type crystallinity, normally found in bean and other root starches (Blanshard, 1987 French, 1984). Another type of crystallinity is the Vh-type, which is the characteristic of amylose complexed with fatty acids and monoglycerides. 

A. solutions are well suited to be cast to biodegradable films and fibers from the unmodified state, in which the functional properties are enhanced with increasing amylose content. After derivatization with fatty acid (DS >1) the esters are soluble in organic solvents and show properties similar to cellulose esters. 

Molecular Interactions. Various polysaccharides readily associate with other substances, including bile acids and cholesterol, proteins, small organic molecules, inorganic salts, and ions. Anionic polysaccharides form salts and chelate complexes with cations some neutral polysaccharides form complexes with inorganic salts and some interactions are stmcture specific. Starch amylose and the linear branches of amylopectin form inclusion complexes with several classes of polar molecules, including fatty acids, glycerides, alcohols, esters, ketones, and iodine/iodide. The absorbed molecule occupies the cavity of the amylose helix, which has the capacity to expand somewhat to accommodate larger molecules. The starch—Hpid complex is important in food systems. Whether similar inclusion complexes can form with any of the dietary fiber components is not known. 

Polycrystalline and well-oriented specimens of pure amylose have been trapped both in the A- and B-forms of starch, and their diffraction patterns84-85 are suitable for detailed structure analysis. Further, amylose can be regenerated in the presence of solvents or complexed with such molecules as alcohols, fatty acids, and iodine the molecular structures and crystalline arrangements in these materials are classified under V-amylose. When amylose complexes with alkali or such salts as KBr, the resulting structures86 are surprisingly far from those of V-amyloses. 

C-CP-MAS NMR produces a broad resonance with a chemical shift of 31.2 ppm,129 a characteristic of mid-chain methylene carbons of fatty acids in the V-amylose complex. The results showed that up to 43% of amylose in non-waxy rice starch, 33% in oat starch, and 22% in normal maize and wheat starch granules are complexed with lipids at a single helical conformation, and the remaining amylose is free of lipids and is in a random coil conformation.212 Up to 60% of apparent amylose in waxy barley starch is complexed with lipids.212... 

Other methods, alternative methods of producing lump-free CWS starch have been described. One employs heat-moisture treatment of a mixture of granular starch, a surfactant containing a fatty acid moiety and (optionally) a gum.214 A process for making a corn starch product giving a uniform viscous dispersion when added to boiling water employs heating a mixture of starch, surfactant and water, followed by microwave radiation.215 Compositions that gel at low solids concentrations were prepared by complexation of starches of moderate (20-30%) amylose content with emulsifiers.216... 

Inclusion complexes of amylose are rather well defined, and a consistent theory of such complexes is available that explains amylose complexes with iodine, fatty acids, alcohols, and other guest molecules.4,5 This subject is surveyed in this article because of the growing interest and importance of such complexes in pharmacology and in the food industry. It is probable that starch in its biological sources (tubers, granules) exists in the form of native complexes with proteins, lipids, mineral salts, and water. 

Fig. 45.—Decomposition to glucose by alpha amylase of complexes of starch with various fatty acids given as the function of time. 1, behenic acid 2, arachic acid 3, octadecanoic acid 4, hexadecanoic acid tetradecanoic acid decanoic acid 7, hexoctanoic acid 8, pure amylose. (By permission from Acker and Brauner-Glaesner.746)...

Szejtli and Banky-Eloed optimized conditions for the formation of amy-lose complexes with unsaturated fatty acids.753 The inhibiting effect of fatty acids on the blue reaction of amylose suggests that fatty acids are adsorbed by the amylose helix.751... 

X-ray diffraction analysis754 of a series of amylose complexes with lower and higher fatty acids revealed that the crystal structures depend on whether amylose was complexed in the dry or wet state. Both the 6, and 7i helical conformations of amylose were found in these complexes. The conformation appears to depend on the length of the hydrophobic moiety. Dry amylose forms crystalline complexes with a unit cell identical to that of the anhydrous 1-butanol-starch complex (lattice parameters a = b = 25.6 A). An orthorhombic unit cell was proposed for the 7i -helical structure of the wet complexes of monobasic acids (acetic, butanoic, pentanoic, hexanoic,... 

Inclusion protects unsaturated fatty acids from aging however, this protection is not perfect, as amylose itself also complexes oxygen753 756 (see Fig. 48). Unsaturated acids have a specific pattern of the carbon chain because at least two sp2-hybridized carbon atoms are present, causing geometrical isomerism. The frans-isomer does not fit perfectly into the cavity of amylose. Another report indicates that starch complexation with tannic acid has no effect on its activity against experimental ulcers in laboratory rats.757... 

Fic. 48.—Oxygen consumption of fatty acids complexed by amylose (1, 1 mg fatty acid 2, 16.4 mg fatty acid 3, 430 mg amylose). (Reprinted with permission from J. Szejtli and E. Banky-Eloed, Staerke, 27 (1975) 368-376.)... 

It is evident from stability-constant measurements that the monoglyceride of tetradecanoic acid forms the most stable complex. Enthalpies of melting of the complex increase proportionally with the length of the carbon chain of the fatty acid residue. Binding parameters (Table LII)717 show that the complexes are weak and they can be readily decomposed by other competing agents. As shown by Kim and Hill,863 cyclomaltoheptaose forms binary complexes with lysolecithin and ternary complexes with lysolecithin and amylose. The complex of lysolecithin with amylose is disrupted by cyclomaltoheptaose. 

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