Oxidation of amylose

Exhaustive studies on well-defined systems are rather scarce (4) nevertheless 3 systems thoroughly analyzed by independant research groups are of outstanding interest a) the quaternization of polyvinylpyridines by alkyl halogenides (20-25) b) the chlorination of polyethylene (13,26-28) c) the basic or acid hydrolysis of PMMA (29-31). On the other hand, neighbouring groups effects have been quantitatively taken into account for the kinetic analysis of periodate oxidation of amylose (32,33). 

Selective oxidation of amylose at C3 has been achieved with dimethyl sulfoxide/phosphorus pentaoxide [119]. In contrast, the oxidation of unprotected cellulose with dimethyl sulfox-ide/acetic anhydride [120] or dicyclohexylcarbodiimide/dimethyl sulfoxide [121] produced a product containing modified 8-D-glucopyranosyl units - some with a carbonyl function at C2, some with a carbonyl function at C3, and some with carbonyl functions at both C2 and C3[122],... 

T. 1. Painter and B. Larsen, Kinetic evidence for inter-residue hemiacetal formation during the oxidation of amylose by periodate ion, Acta Chem. Scand., 24 (1970) 2724-2736 O. Smidsrod, B. Larsen, and T. (1. ) Painter, Monte-Carlo investigation of nearest-neighbor auto-inhibitory effects in the oxidation of amylose by periodate ion, Acta Chem. Scand, 24 (1970) 3201-3212. 

The Michaelis constant and maximal velocity of a-amylase-free glucoamylase from Rhizopus delemar have been shown to decrease with increasing periodate oxidation of amylose.These kinetic features have been explained on the basis of competitive inhibition by the oxidized non-reducing end of the (1 4)-o -D-... 

Table I shows the results of periodate oxidation and methylation applied to amylopectins from various sources. If the percentage of amylose in a whole starch is known, the length of unit chain of the amylopectin component can be calculated from the results of periodate oxidation of the whole starch (see Table II). The length of unit chain appears to depend on the botanical species, but not the variety, from which the starch wras isolated. In the case of tapioca and corn amylopectins, sub-fractionation of these by precipitation with methanol, followed by periodate oxidation, showed the sub-fractions had the same degree of branching as the original amylopectins.71 The action of periodate on whole starches and amylopectins is now so well established and accurate, that it may well completely supersede the methylation technique for pure starches, in view of its many advantages.

Periodate oxidation has also been applied to this component.7 81 108 Theoretically, this method should be more satisfactory than methylation, as formation of derivatives is not necessary. However, recent work suggests that the chain length of amylose comprises several thousands of D-glucose units rather than hundreds (see Section V, 2), and the accuracy of such... 

Malto-oligosaccharide aldonolactones react with ethylenediamine to give Ar-(2-aminoethyl)aldonamides (113-115), which have been successfully grafted onto carriers via amide linkages. The malto-oligosaccharides were produced by degradation of amylose with alpha amylase. After purification of the oligosaccharides, they were converted into the lactones by hypoiodite or electrolytic oxidation. 

For the oxidation of primary hydroxyl groups, three times the amount of nitrite is required when compared with nitrate, and three times as much of the toxic NO would be formed. This oxidation procedure has been applied to the glucans cellulose, amylose, and pullulan. A study of this system with cyclomaltoheptaose (/J-cyclodextrin) showed that the reaction is autocatalytic. 

A minimum temperature of 88°C is required for paste storage of thermally oxidized starch in order to prevent retrogradation. Various retrogradation control agents have been recommended for stabilizing. The addition of 0.5 to 1.0% calcium stearate prevents the build up of viscosity, but could actually lead to the precipitation of amylose due to gradual stearate dissolution (ionization) and complex formation with... 

Oxidation with chlorine or sodium hypochlorite reduces the tendency of amylose to associate or retrograde. Oxidized starches are used where intermediate viscosity and soft gels are desired, and where the instability of acid-converted starches is unacceptable.76 Oxidized starches are reported to give batters improved adhesion to meat products and are widely used in breaded foods.76 Fuller77 reported that candies made with hypochlorite-oxidized starches gel and dry faster and have increased clarity, longer shelf life and better taste than those made with acid-thinned counterparts. 

The helical structure of amylose also serves as the basis for an interesting and useful reaction. The inside of the helix is just the right size and polarity to accept an iodine (I2) molecule. When iodine is lodged within this helix, a deep blue starch-iodine complex results (Figure 23-19). This is the basis of the starch-iodide test for oxidizers. The material to be tested is added to an aqueous solution of amylose and potassium iodide. If the material is an oxidizer, some of the iodide (I-) is oxidized to iodine (I2), which forms the blue complex with amylose. 

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