Viscosity amylopectin

In a current rheological study [296], the galactoxyloglucan from Hymenia courbaril was mixed with starch containing 66% amylose and with waxy corn starch (amylopectin). The gel mixtures showed, under static rheological conditions, an increase in paste viscosity compared to those of the polysaccharides alone. Dynamic rheometry indicated that the interactions resulted in increased thermal stability of the gel formed in comparison to that of the starch alone. 

The viscosity of polymer solutions has been considered theoretically by Flory,130 but although this theory has been applied to cellulose esters,131 no applications have yet been made in the case of the starch components. Theoretical predictions of the effect, on [17], of branching in a polymer molecule have been made,132 and this may be of importance with regard to the viscometric behavior of amylopectin. 

Few measurements of the shape of the amylopectin component have been reported, although, from viscosity measurements on the jS-amylase limit... 

On cooking maize starch the viscosity increases when the starch begins to gelatinise. As the temperature rises towards 95°C the viscosity falls. When the paste is cooled the viscosity rapidly increases. The variation of viscosity with temperature is characteristic for each different origin of starch. Potato starch, for example, has a lower gelatinisation temperature than maize starch but has a higher maximum viscosity. When cooled the viscosity of potato starch rises less. Once again amylopectin starches do not show this behaviour as they do not gel. 

Figure 7.13 CLSM micrographs of heat-set gels of p-lactoglobulin + amy-lopectin (a) 6 vt% p-lactoglobulin (b) 6 wt% p-lactoglobulin + 0.75 wt% (high-viscosity) amylopectin (c) 6 wt% p-lactoglobulin + 2.0 wt% (low-viscosity) amylopectin. Images (d), (e) and (f) are for the same gels as (a), (b) and (c), respectively, but at a lower magnification. Reproduced from Olsson et al. (2002) with permission.

The investigations carried out by Professor French and his students were based on sound experimental approaches and on intuitive theoretical considerations. The latter often resulted in new experiments for testing a hypothesis. On the basis of theoretical considerations, Professor French proposed a model for the structure of the amylopectin molecule, and the distribution of the linear chains in this molecule. This model was tested by utilizing enzymes that selectively cleave the linear chains, and the results substantiated the theoretical deductions. He proposed a theory on the nature and types of reactions occurring in the formation of the enzyme - starch complex during the hydrolysis of starch by amylases. In this theory, the idea of multiple attack per single encounter of enzyme with substrate was advanced. The theory has been supported by results from several types of experiments on the hydrolysis of starch with human salivary and porcine pancreatic amylases. The rates of formation of products, and the nature of the products of the action of amylase on starch, were determined at reaction conditions of unfavorable pH, elevated temperatures, and increased viscosity. The nature of the products was found to be dramatically affected by the conditions utilized for the enzymic hydrolysis, and could be accounted for by the theory of the multiple attack per single encounter of substrate and enzyme. 

A further factor that causes the non-homogeneity of nitrostarch is the presence of the two components, amylose and amylopectin in starch. It has been demonstrated by nitrating each of these starch components separately that the nitration products differ from one another. Berl and Kunze [37] detected that amylopectin yields a product of a considerably higher viscosity than that resulting from the nitration of amylose. This effect may be attributable to the higher molecular weight of amylopectin. 

Fig. 6.—Variation of Staudinger index [ij] of potato amylose (a) and amylopectin (b) as a function of specific viscosity (from Ref. 46).

Species and/or cultivar differences are also observed in other starch properties and in the properties of isolated amylose and amylopectin. To illustrate, purified amylose samples have been shown to differ in (3-amylolysis limit and average DP.64,67,124 Purified amylopectin samples have also been shown to differ in (3-amylolysis limit, average length of unit chains and viscosity.64,66 67 124,125 Campbell et al.121 observed a range of amylose content from 22.5% to 28.1% in 26 maize inbreds selected for maturity, kernel characteristics and pedigree. Starches from these non-mutant genotypes also differed in thermal properties (DSC), paste viscosities and gel strengths. 

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