Donald B. Thompson

On the non-random nature of amylopectin branching

The cluster model of amylopectin (AP) provides a useful conceptual basis for understanding of the structure of the molecule, and this model guides current thinking related to AP biosynthesis and physical behavior. The chain length profile of constituent linear regions of the molecule is commonly determined, and the cluster model guides the interpretation of results with an emphasis on the clustering of the linear regions of these chains. Less attention has been given to the related but distinct question of the clustering of the branch points in AP, perhaps because this work is methodologically more difficult than for determination of the chain length profile and interpretation of the results is less straightforward. However, the unique aspect of AP is that its branching is non-random, and the physical properties of AP may be considered to result from this unique structure. This review addresses the available information on the distribution of branch points in AP. Emphasis on this aspect of the cluster model has ramifications for future research on AP biosynthesis and AP physical behavior.

STRATEGIES FOR THE MANUFACTURE OF RESISTANT STARCH

Abstract Starch not hydrolyzed in the small intestine is considered to be enzyme-resistant starch (RS). Because individuals differ in their ability to digest starch, there is no absolute distinction between RS and digestible starch. A method for in vitro determination of RS should be validated using a human population average value. In any starch material, the constituent molecules will have a range of susceptibility to amylolytic activity in vitro . For a starch or starch-containing ingredient it is possible to alter this range by judicious selection of processing conditions to increase the proportion that tests as RS. The starch material will also have a range of thermal stabilities before and after processing, which may or may not reflect the range of susceptibility to hydrolysis. The manufacture of RS may be thought of as enhancement of the proportion of the starch that tests as RS. To compare the effect of different processing schemes, it is critical to stipulate the method used to estimate RS content. This review focuses on strategies for increasing the proportion of types 2 and 3 RS in a starch-containing ingredient. Special emphasis is given to increasing RS levels of granular starch.

Fractionation of high-amylose maize starches by differential alcohol precipitation and chromatography of the fractions

ABSTRACT Three high-amylose maize starches (HAS) and a common corn starch (CCS) were subjected to differential alcohol precipitation using isoamyl alcohol and 1-butanol to obtain fractions designated as amylose (AM), amylopectin (AP), and intermediate material (IM). For each starch, IM had a blue value and an iodine binding wavelength maximum (λmax) between the λmax of the respective AM and AP. Size-exclusion chromatography (SEC) showed similarities in the AM from CCS and HAS. HAS AP had higher blue values and iodine binding λmax values than CCS AP. SEC of the intact HAS AP and IM both showed large proportions of material eluting after the void volume (45–85%) when compared to CCS AP and IM. Chain length (CL) distributions of debranched AP and IM indicated that these fractions from each starch were highly branched, and that AP had a shorter average chain length than IM. Consequently, the differential precipitation behavior of the HAS AP and IM appears dependent on general branching structure rather than s...

Production of Boiling-Stable Granular Resistant Starch by Partial Acid Hydrolysis and Hydrothermal Treatments of High-Amylose Maize Starch

ABSTRACT The purpose of the present work was to examine whether partial acid hydrolysis (PAH) of a high-amylose maize starch (ae-VII) would enhance the effects of hydrothermal treatments to produce granular resistant starch (RS) that is stable to further heat treatment at atmospheric pressure. PAH ae-VII starches were prepared by heating 35% (w/v) suspensions with 1% (w/w) HCl at 25°C for 6, 30, and 78 hr. Native and PAH starches were then treated by annealing (ANN) or heat-moisture treatment (HMT). ANN was done at 70% moisture at 50, 60, or 70°C for 24 hr, and HMT was done at 30% moisture at 100, 120, or 140°C for 80 min. RS that survives boiling during analysis was determined by a modification of the AOAC method for determining total dietary fiber. RS was also determined by the Englyst method. Little change in the gelatinization enthalpy was found for ae-VII starch after PAH, ANN, or HMT as individual treatments. After PAH, either ANN or HMT led to decreased gelatinization enthalpy. HMT and ANN alone in...

Effects of moisture content and different gelatinization heating temperatures on retrogradation of waxy-type maize starches

Abstract The effect of moisture content on retrogradation of wx, du wx, ae wx, and su2 wx maize starches was studied by differential scanning calorimetry (DSC). All starches showed maximum retrogradation enthalpy at an intermediate moisture content, but the precise relationship between moisture content and retrogradation enthalpy varied for each starch. The ae wx starch was least affected by moisture content, showing measurable retrogradation (2–3 J/g) after only 1 day for the 95% moisture sample. Retrogradation of the su2 wx starch was exceptionally slow even at intermediate moisture contents, and the retrogradation enthalpy was particularly sensitive to moisture content. The effect of varied moisture content was also investigated in combination with initial heating to a wide range of temperatures. Retrogradation of wx, du wx, and su2 wx starches, but not ae wx starch, was strongly influenced by both initial heating temperature and moisture content, with development of enthalpy consistently in the order of du wx>wx>su2 wx. The chain length profiles for the four starches were unique. The exceptionally rapid retrogradation and relatively small concentration dependence of ae wx starch may be related to a greater proportion of longer chains, whereas the very slow retrogradation of su2 wx starch may be related to a population of exceptionally short chains. The more rapid retrogradation of du wx starch than wx starch may be related to the high number and concentration of branch points in a cluster.

Amylose and amylopectin interact in retrogradation of dispersed high-amylose starches

ABSTRACT Retrogradation of three high-amylose starches (HAS: ae du, ae V, and ae VII) and common corn starch (CCS) was examined by dynamic oscillatory rheometry (7.5% [w/w] starch in 20% [v/v] dimethyl sulfoxide [DMSO]), differential scanning calorimetry (DSC; 30% [w/w] starch in water), and turbidity (0.5% [w/w] starch in 20% [v/v] DMSO). Nongranular lipid-free starch and starch fractions (amylose [AM], amylopectin [AP], and intermediate material [IM]) were studied. Gels were prepared by dispersing starches or fractions in 90% DMSO and diluting with water, followed by storage for seven days at 4°C. For AM from each starch, the elastic modulus (G′) was similar when heated from 6 to 70°C. The G′ of HAS AP gels at 6°C was higher than for CCS AP gels. For nongranular CCS and ae du gels, G′ dropped dramatically (≈100×) when heated from 6 to 70°C, less (≈10×) for ae V gels, and least (≈5×) for ae VII gels. By DSC, each AM endotherm had a peak temperature of ≈140°C, whereas all AP endotherms were complete befor...

Maize starch-branching enzyme isoforms and amylopectin structure. In the absence of starch-branching enzyme IIb, the further absence of starch-branching enzyme Ia leads to increased branching

Previous studies indicated that the deficiency of starch-branching enzyme (SBE) Ia in the single mutant sbe1a∷Mu (sbe1a) has no impact on endosperm starch structure, whereas the deficiency of SBEIIb in the ae mutant is well known to reduce the branching of starch. We hypothesized that in maize (Zea mays) endosperm, the function of SBEIIb is predominant to that of SBEIa, and SBEIa would have an observable effect only on amylopectin structure in the absence of SBEIIb. To test this hypothesis, the mutant sbe1a was introgressed into lines containing either wx (lacking the granule-bound starch synthase GBSSI) or ae wx (lacking both SBEIIb and GBSSI) in the W64A background. Both western blotting and zymogram analysis confirmed the SBEIa deficiency in sbe1a wx and sbe1a ae wx, and the SBEIIb deficiency in ae wx and sbe1a ae wx. Using zymogram analysis, no pleiotropic effects of sbe1a genes on SBEIIa, starch synthase, or starch-debranching enzyme isoforms were observed. High-performance size exclusion chromatography analysis shows that the chain-length profiles of amylopectin as well as β-limit dextrin were indistinguishable between wx and sbe1a wx, whereas significant differences for both were observed between ae wx and sbe1a ae wx, suggesting an effect of SBEIa on amylopectin biosynthesis that is observable only in the absence of SBEIIb. The amylopectin branch density and the average number of branches per cluster were both higher in endosperm starch from sbe1a ae wx than from ae wx. These results indicate possible functional interactions between SBE isoforms that may involve enzymatic inhibition. Both the cluster repeat distance and the distance between branch points on the short intracluster chains were similar for all genotypes however, suggesting a similar pattern of individual SBE isoforms in cluster initiation and the determination of branch point location.

Expression of Escherichia coli glycogen synthase in the tubers of transgenic potatoes (Solanum tuberosum) results in a highly branched starch

A chimeric gene containing the patatin promoter and the transit-peptide region of the small-subunit carboxylase gene was utilized to direct expression of Escherichia coli glycogen sythase (glgA) to potato (Solanum tuberosum) tuber amyloplasts. Expression of the glgA gene product in tuber amyloplasts was between 0.007 and 0.028% of total protein in independent potato lines as determined by immunoblot analysis. Tubers from four transgenic potato lines were found to have a lowered specific gravity, a 30 to 50% reduction in the percentage of starch, and a decreased amylose/amylopectin ratio. Total soluble sugar content in these selected lines was increased by approximately 80%. Analysis of the starch from these potato lines also indicated a reduced phosphorous content. A very high degree of branching of the amylopectin fraction was detected by comparison of high and low molecular weight carbohydrate chains after debranching with isoamylase and corresponding high-performance liquid chromatography analysis of the products. Brabender viscoamylograph analysis and differential scanning calorimetry of the starches obtained from these transgenic potato lines also indicate a composition and structure much different from typical potato starch. Brabender analysis yielded very low stable paste viscosity values (about 30% of control values), whereas differential scanning calorimetry values indicated reduced enthalpy and gelatinization properties. The above parameters indicate a novel potato starch based on expression of the glgA E. coli gene product in transgenic potato.

Resistance to α-Amylase Digestion in Four Native High-Amylose Maize Starches

ABSTRACT Native and processed high-amylose maize starch (HAMS) is an important source of resistant starch (RS). The objectives of this work were to use an in vitro procedure to estimate the RS content of native granules from a series of ae-containing HAMS genotypes, and to examine the nature of the α-amylase resistant starch (ARS). By the method of Englyst et al (1992), RS for ae V, ae VII, ae su2, and ae du were estimated to be 66.0, 69.5, 69.5, and 40.6%, respectively. By transmission electron microscopy, most of the residual granules from ae V, ae VII, and ae su2 showed little evidence of digestion. Partially digested granules had a radial digestion pattern in the interior and an enzyme-resistant layer near the surface. Size and chain-length profile of constituents of ARS were similar to those of the native HAMS (unlike type 3 RS), consistent with complete hydrolysis in susceptible granule regions. Between crossed polarizers, many iodine-stained native and residual HAMS granules had blue centers and pi...

Retrogradation of Maize Starch After Thermal Treatment Within and Above the Gelatinization Temperature Range

ABSTRACT Studies of starch retrogradation have not considered the initial thermal treatment. In this article, we explore the effect of heating to temperatures within and above the gelatinization range on maize starch retrogradation. In the first experiment, 30% suspensions of waxy (wx) starch were initially heated to final temperatures ranging from 54 to 72°C and held for 20 min. On reheating in the differential scanning calorimeter immediately after cooling, the residual gelatinization endotherm peak temperature increased, the endotherm narrowed, and enthalpy decreased. Samples stored for seven days at 4°C showed additional amylopectin retrogradation endotherms. Retrogradation increased dramatically as initial holding temperature increased from 60 to 72°C. In a second experiment, wx starch was initially heated to final temperatures from 54 to 180°C and rapidly cooled, followed by immediate reheating or storage at 4°C. Maximum amylopectin retrogradation enthalpy after storage was observed for initial heat...