Robin Manelius

The substitution pattern in cationised and oxidised potato starch granules

The distribution pattern of substituents within the granules and the components of two cationised and two oxidised potato starches was studied. The level of crystallinity in wet-cationised (WC) and hypochlorite oxidised (HO) starch granules was similar to that of native starch granules but lower in dry-cationised (DC) and peroxide oxidised (PO) granules. However, the melting temperature of DC granules remained similar to native granules but was decreased in the other samples. With all modified starches, the initial rate of acid hydrolysis (lintnerisation) was increased compared to native granules. The degree of substitution decreased only slightly in WC granules after the lintnerisation, whereas virtually all the substituted glucosyl units in DC starch were hydrolysed already at initial stages. The decrease of substituents in the HO and PO starches was intermediate. The starches were partly resistant to the action of isoamylase and the successive beta-amylolysis, suggesting that substituents were found both close to the branches and near the nonreducing ends in the amylopectin component. It is suggested that the DC starch was preferentially cationised at the surface of the granules, whereas WC and oxidised starches were modified throughout the granules.

A method for the study of the enzymic hydrolysis of starch granules

Abstract A method for the study of the enzymic hydrolysis of starch granules is described. A solution of alpha-amylase was pumped through a bed of normal or waxy-maize starch in a column, and the eluate was passed through a column of ion-exchanger that retained the enzyme but not the solubilised dextrins which could be analysed further by gel-permeation chromatography. The material released first from the waxy-maize starch granules contained comparatively large proportions of dextrins of d.p. > 3000. Subsequently, maily dextrins were produced from each type of starch with d.p. 50–200 similar to those produced from the gelatinised starches. Dextrins with d.p. ∼6 were also solubilised in the later stages. The content and the lengths of amylose-like chains within the normal maize granules decreased notably when large concentrations of enzyme were used. These chains were probably not released from the granules and the reaction seemed to be correlated with the enzyme adsorbed on the granules, whereas the solubilised material originated from the amylopectin component.

Enzymatic and Acidic Hydrolysis of Cationized Waxy Maize Starch Granules

ABSTRACT A series of wet-cationized starch granules from waxy maize with different degrees of substitution (DS) were solubilized with either 2.2M HCl (lintnerization) or with the α-amylase of Bacillus amyloliquefaciens. The maximum rate of the enzymatic hydrolysis occurred in starches with intermediate DS. It appeared that the cationic substituents interfered with the binding to the active site of the enzyme at high levels of substitution. The DS remained fairly constant in the granular residues after the enzymatic attack. The rate of the acidic hydrolysis increased with increasing DS but the final level of solubilization slightly decreased. The DS of the residual starch material decreased to 40% of the original level, showing that a large part of the cationic groups was found within the amorphous parts of the granules. A dry-cationized sample with a high DS was also treated with the acid and lost a major part of its substituents at low levels of lintnerization. Probably most of the substituents were asso...

Effects of enzymically modified amylopectin on the rheological properties of amylose-amylopectin mixed gels

Branched α-dextrins with different molecular weights were prepared from waxy maize. A series of β-limit dextrins was prepared from α-dextrins and native amylopectin. The fine structure of the dextrin samples was investigated by debranching, and was found to be similar to the unit chain distribution of native amylopectin. The absolute molecular weights of α- and β-limit dextrins and commercial potato amy lose were determined by gel-permeation chromatography (GPC) and with a dual light-scattering detector. Solubilized potato amy lose and α- and β-limit dextrins were mixed at different ratios to give a total concentration of 8%. Dynamic viscoelastic measurements showed that gel formation of amylose was highly dependent both on the ratio of amylose to α-dextrin and on the molecular weight of α-dextrin. α-Dextrin caused an increase of storage modulus, G, when the amylose: α-dextrin ratio was low and the molecular weight of α-dextrin was high. The high-molecular-weight α-dextrin influenced amylose gelation in the same way as native waxy maize starch, but the medium- and low-molecular-weight α-dextrins weakened the gel formation, especially at a ratio of 25:75 (amylose: α-dextrin). When low-molecular-weight β-limit dextrins were mixed with amylose, the resulting gels were more rigid than those in which amylose was mixed with corresponding α-dextrins. When high-molecular-weight β-limit dextrins were mixed with amylose, the resulting gels were weaker.

Characterisation of Fractions Obtained by Isoamylolysis and Ion-exchange Chromatography of Cationic Waxy Maize Starch

Isoamylase hydrolysates of wet- (WC) and dry-cationised (DC) waxy maize starch were fractionated by ion-exchange chromatography on CM-Sepharose into an unbound and four bound fractions. The amount of bound dextrins was higher in the WC than in the DC sample. The fractions were characterised by gel-permeation chromatography and proton-NMR spectroscopy. The unbound fraction from the WC sample consisted mainly of linear chains formed from amylopectin. The dextrins in the bound fractions contained increased amounts, from 1.2-7.9, of cationic substituents per molecule and the degree of polymerisation increased with the density of substituents. Dextrins weakly bound to CM-Sepharose had a linear structure, whereas more tightly bound fractions were mixtures of linear and branched dextrins. In the latter, the debranching was incomplete because of sterical hindrance by substituents at or close to the branch points. Most of the dextrins were partly hydrolysed by β-amylase, but the more highly substituted fractions possessed also a population of β-amylase resistant dextrins, suggesting substituents at the non-reducing ends.

Observations on the α-Amylolysis Pattern of Some Waxy Maize Starches from Inbred Line Ia453

ABSTRACT Maize starches of the endosperm mutants waxy (wx), dull:waxy (duwx), and amylose-extender:dull:waxy (aeduwx) from inbred line Ia453 lack amylose. However, in addition to high molecular weight (HMW) amylopectin, the duwx and aeduwx starches contained 40 and 80%, respectively, intermediate branched material of low molecular weight (LMW). As gelatinized, the amylopectin of the wx starch was easily hydrolyzed into small dextrins by the α-amylase of B. amyloliquefaciens, but components of duwx and aeduwx possessed partial resistance to amylolytic attack. Residual material of intermediate size obtained by a 4-hr α-amylolysis could not be separated from LMW dextrins by fractional precipitation in methanol. It is suggested that this material possessed a more regularly branched structure, in which the d-glucosyl chain segments were too short to allow α-amylase action. The granular starches of duwx and aeduwx genotypes were initially considerably more resistant than the wx sample to α-amylase attack. This ...

Characterisation of Dextrins Solubilised by α-Amylase from Barley Starch Granules

α-Amylolysis of native granular starch represents a biochemical process, in which an enzyme in solution solubilises a highly organised, semicrystalline substrate. To study this process, which is very slow compared to the hydrolysis of gelatinised starch [1], it is necessary to use high concentrations of enzyme or very long incubation times. The solubilised dextrins are therefore easily hydrolysed further into small fragments, preventing a study of the products originally released from the granules. A method that enables a collection of the dextrins solubilised from starch granules by α-amylase was developed [1] and has made it possible to study the composition of the products at early stages of the process. In this method, the starch granules are packed as a thin layer in a two-compartment column [2] and a diluted enzyme solution is pumped through the starch. Before a secondary hydrolysis occurs, the enzyme is bound to an anionexchange matrix (DEAE-Sepharose) in the upper compartment of the column, whereas the solubilised dextrins are collected into fractions representing successive stages of the