Relationship between the distribution of the chain length of amylopectin and the crystalline structure of starch granules

The distributions of chain lengths in the amylopectins of starches from 20 species (11 A-, 6 B-, and 3 C-type) were characterised by h.p.l.c. in terms of the relationship between the molecular structure of the amylopectin and the crystalline structure of the starch granule. The weight-average chain-lengths of the amylopectins of the A-, B-, and C-type starches were in the ranges 23–29, 30–44, and 26–29, respectively. Gel-permeation chromatograms of the amylopectins debranched with isoamylase showed bimodal distributions of fractions containing long and short chains for 17 specimens (including corn, rice, potato, etc.) and trimodal distributions, of which the fraction containing short chains had twin peaks, for wheat, tapioca, and tulip amylopectins. The correlation coefficients between the average chain-lengths of amylopectins and the fractions of long and short chains and the ratio of the fractions of short and long chains by weight were 0.90, 0.69, and ?0.95, respectively. In general, amylopectin molecules of A-type starches have shorter chains in both the long- and short-chain fractions and larger amounts of the short-chain fractions than those of the B-type starches. The chain lengths of amylopectins of the C-type starches were intermediate and it is inferred that these starches possibly yield any type of crystalline structure depending on the environmental temperature and other factors, whereas the A- and B-type starches are insensitive to temperature.     

Chain-length specificities of maize starch synthase I enzyme: studies of glucan affinity and catalytic properties

It is widely known that some of the starch synthases and starch-branching enzymes are trapped inside the starch granule matrix during the course of starch deposition in amyloplasts. The objective of this study was to use maize SSI to further our understanding of the protein domains involved in starch granule entrapment and identify the chain-length specificities of the enzyme. Using affinity gel electrophoresis, we measured the dissociation constants of maize SSI and its truncated forms using various glucans. The enzyme has a high degree of specificity in terms of its substrate-enzyme dissociation constant, but has a greatly elevated affinity for increasing chain lengths of alpha-1, 4 glucans. Deletion of the N-terminal arm of SSI did not affect the Kd value. Further small deletions of either N- or C-terminal domains resulted in a complete loss of any measurable affinity for its substrate, suggesting that the starch-affinity domain of SSI is not discrete from the catalytic domain. Greater affinity was displayed for the amylopectin fraction of starch as compared to amylose, whereas glycogen revealed the lowest affinity. However, when the outer chain lengths (OCL) of glycogen were extended using the phosphorylase enzyme, we found an increase in affinity for SSI between an average OCL of 7 and 14, and then an apparently exponential increase to an average OCL of 21. On the other hand, the catalytic ability of SSI was reduced several-fold using these glucans with extended chain lengths as substrates, and most of the label from [14C]ADPG was incorporated into shorter chains of dp < 10. We conclude that the rate of catalysis of SSI enzyme decreases with the OCL of its glucan substrate, and it has a very high affinity for the longer glucan chains of dp approximately 20, rendering the enzyme catalytically incapable at longer chain lengths. Based on the observations in this study, we propose that during amylopectin synthesis shorter A and B1 chains are extended by SSI up to a critical chain length that soon becomes unsuitable for catalysis by SSI and hence cannot be elongated further by this enzyme. Instead, SSI is likely to become entrapped as a relatively inactive protein within the starch granule. Further glucan extension for continuation of amylopectin synthesis must require a handover to other SS enzymes which can extend the glucan chains further or for branching by branching enzymes. If this is correct, this proposal provides a biochemical basis to explain how the specificities of various SS enzymes determine and set the limitations on the length of A, B, C chains in the starch granule.     

On the effect of surface active agents and their structure on the temperature-induced changes of normal and waxy wheat starch in aqueous suspension. Part II: A confocal laser scanning microscopy study

The location and penetration patterns of two fluorescently labelled, surface active molecules into normal and waxy wheat starch granules prior, during and after the temperature-induced gelatinization were studied by means of confocal laser scanning microscopy (CLSM). Amphiphilic dyes were found to have a tendency to penetrate wheat starch granules in aqueous suspension. The penetration patterns were however found to be dependent on the contact time, type of starch and the chain length (C₁₂ vs. C₁₆) of the amphiphilic dye. The penetration of amphiphilic dyes through the starch granule matrix proved to be less restricted in waxy than in normal wheat starch. For a given type of starch, the penetration of the longer chain dye was more constrained than that of the shorter chain one. The extent to which the dye diffuses into the granule matrix as it gelatinizes is also affected by the chain length of the dye, diffusion of the shorter chain dye occurring more profusely and at lower temperatures than for the longer chain one. These differences are suggested to be related to the dissociation temperature of the AM-amphiphilic dye complexes.     

Structural and physicochemical characterisation of rye starch

The gelatinisation, pasting and retrogradation properties of three rye starches isolated using a proteinase-based procedure were investigated and compared to those of wheat starch isolated in a comparable way. On an average, the rye starch granules were larger than those of wheat starch. The former had very comparable gelatinisation temperatures and enthalpies, but slightly lower gelatinisation temperatures than wheat starch. Under standardised conditions, they retrograded to a lesser extent than wheat starch. The lower gelatinisation temperatures and tendencies of the rye starches to retrograde originated probably from their higher levels of short amylopectin (AP) chains [degree of polymerisation (DP) 6–12] and their lower levels of longer chains (DP 13–24) than observed for wheat starch. The rapid visco analysis differences in peak and end viscosities between the rye starches as well as between rye and wheat starches were at least partly attributable to differences in the levels of AP short chains and in average amylose molecular weight. The AP average chain lengths and exterior chain lengths were slightly lower for rye starches, while the interior chain lengths were slightly higher than those for wheat starch.     

Relationship between branching density and crystalline structure of A- and B-type maize mutant starches

Amylopectin from two double maize mutant starches of A-crystalline (wxdu) and B-crystalline type (aewx) was subjected successively to hydrolysis involving alpha and beta amylases, which isolated clusters and all branching zones of clusters (BZC). Enzymatic analysis together with ionic and size-exclusion chromatography revealed the structural features of the clusters and BZC and their role in starch crystallization. A-type clusters were larger (dp(n) > 80) and contained more (but shorter) chains than B-type clusters. The BZC of A-type starch was also larger, but with a shorter distance between the branching points than in B-type BZC. A-type clusters had a densely packed structure and B-type a poorly branched structure. Models for the structure of A- and B-type clusters are presented, and a hypothesis for the influence of cluster geometry on crystallization is proposed.     

Crystallisation of malto-oligosaccharides as models of the crystalline forms of starch: minimum chain-length requirement for the formation of double helices

The multigram preparation of malto-oligosaccharides of average d.p. ∼11, by the debranching of glycogen using Cytophaga isoamylase is described. Debranched glycogen and fractions derived therefrom readily crystallise from hot, concentrated aqueous solution to give 40–70% of crystalline materials having sharp X-ray diffraction patterns characteristic of A-, B-, and C-type (intermediate) starch polymorphs. The polymorphic form obtained is dependent on chain length, concentration, and temperature, the A-type being favoured by shorter chain-length, higher concentration, and higher crystallisation temperature. For pure oligomers, the minimum chain-length required for crystallisation (formation of double helices) is 10. In the presence of longer chains, oligomers as short as maltohexaose can co-crystallise. These results explain the known differences in aggregation properties of glycogens and amylopectins.     

Influence of chain length of short monodisperse amyloses on the formation of A- and B-type X-ray diffraction patterns

Amyloses of uniform length were obtained by phosphorlytic synthesis (DP 20–35) and by preparative g.p.c. fractionation by an α-amylolytic digest of amylose on Bio-Gel P-4 (DP 3–20). Crystalline precipitates formed from pure aqueous solution on standing at ambient or lower temperatures gave the A-type X-ray pattern for malto-oligomers of DP 10–12 and the B-type pattern for DP 13 and all longer chains. With these carefully purified samples a mixture of the A- and B-amylose pattern was not observed. Malto-oligomers shorter than DP 10 did not crystallize. The findings support recent studies, indicating that the average chain length of amylopectin and the X-ray type of various starches are closely related. The reason for an influence of chain length on crystalline packing remains to be resolved.     

Amylopectin molecular structure reflected in macromolecular organization of granular starch

For lintners with negligible amylose retrogradation, crystallinity related inversely to starch amylose content and, irrespective of starch source, incomplete removal of amorphous material was shown. The latter was more pronounced for B-type than for A-type starches. The two predominant lintner populations, with modal degrees of polymerization (DP) of 13-15 and 23-27, were best resolved for amylose-deficient and A-type starches. Results indicate a more specific hydrolysis of amorphous lamellae in such starches. Small-angle X-ray scattering showed a more intense 9-nm scattering peak for native amylose-deficient A-type starches than for their regular or B-type analogues. The experimental evidence indicates a lower contrasting density within the "crystalline" shells of the latter starches. A higher density in the amorphous lamellae, envisaged by the lamellar helical model, explains the relative acid resistance of linear amylopectin chains with DP > 20, observed in lintners of B-type starches. Because amylopectin chain length distributions were similar for regular and amylose-deficient starches of the same crystal type, we deduce that the more dense (and ordered) packing of double helices into lamellar structures in amylose-deficient starches is due to a different amylopectin branching pattern.     

Spatial translational motions of base pairs in DNA molecules: Application of the extended matrix generator method

We have used the elementary generator matrices outlined in the preceding paper to examine the conformational plasticity of the nucleic acid double helix. Here we investigate kinked DNA structures made up of alternating B- and A-type helices and intrinsically curved duplexes perturbed by the intercalation of ligands. We model the B-to-A transition by the lateral translation of adjacent base pairs, and the intercalation of ligands by the vertical displacement of neighboring residues. We report a complete set of average configuration-dependent parameters, ranging from scalars (i.e., persistence lengths) to first- and second-order tensor parameters (i.e., average second moments of inertia), as well as approximations of the associated spatial distributions of the DNA and their angular correlations. The average structures of short chains (of lengths less than 100 base pairs) with local kinks or intrinsically curved sequences are essentially rigid rods. At the smallest chain lengths (10 base pairs), the kinked and curved chains exhibit similar average properties, although they are structurally perturbed compared to the standard B-DNA duplex. In contrast, at lengths of 200 base pairs, the curved and kinked chains are more compact on average and are located in a different space from the standard B- or A-DNA helix. While A-DNA is shorter and thicker than B-DNA in x-ray models, the long flexible A-DNA helix is thinner and more extended on average than its B-DNA counterpart because of more limited fluctuations in local structure. Curved polymers of 50 base pairs or longer also show significantly greater asymmetry than other DNAs (in terms of the distribution of base pairs with respect to the center of gravity of the chain). The intercalation of drugs in the curved DNA straightens and extends the smoothly deformed template. The dimensions of the average ellipsoidal boundaries defining the configurations of the intercalated polymers are roughly double those of the intrinsically curved chain. The altered proportions and orientations of these density functions reflect the changing shape and flexibility of the double helix. The calculations shed new light on the possible structural role of short A-DNA fragments in long B-type duplexes and also offer a model for understanding how GC-specific intercalative ligands can straighten naturally curved DNA. The mechanism is not immediately obvious from current models of DNA curvature, which attribute the bending of the chain to a perturbed structure in repeating tracts of A · T base pairs. © 1994 John Wiley & Sons, Inc.     

Molecular structure of amylopectin from Amaranth starch and its effect on physicochemical properties

The molecular structure of amylopectin and its varphi,beta-limit dextrins from starch of 13 amaranth cultivars was determined by HPAEC-PAD after debranching. Chain length profiles of amylopectins showed bimodal distributions. The molar-based ratios of the average chain lengths of amylopectins (CLap) ranged from 17.41 to 18.22. The molar-based average chain lengths (CLld) and average B-chain lengths (BCLld) of varphi,beta-limit dextrins varied from 7.68 to 8.05, and from 14.10 to 14.73, respectively. Correlation analysis indicated that most structural parameters were positively correlated with thermal properties with few exceptions, whereas the content of fraction fa' ("'" stands for molar-based chain length ratio) was negatively correlated with the thermal properties. Pasting properties of cold paste viscosity (CPV) and setback were also correlated with amylopectin structural parameters.     

The influence of various small plasticisers and malto-oligosaccharides on the retrogradation of (partly) gelatinised starch

Ageing of gelatinised and partly gelatinised potato starch and wheat starch were investigated in the presence of plasticisers with increasing size and number of OH groups (ethylene glycol, glycerol, threitol, xylitol, glucose, and for potato starch also maltose). The influences of these plasticisers and of granular remnants (ghosts) on recrystallisation were determined by using X-ray diffraction. Recrystallisation of potato starch samples in the presence of plasticisers resulted in crystallinity indices of 0.5. The largest reduction in potato starch recrystallisation is found for threitol (4 OH) and xylitol (5 OH). In the plasticiser range examined, the crystallisation inducing effect of granular potato starch remnants is reduced better when the plasticiser contains more OH groups. Wheat starch recrystallises to a lesser extent than potato starch, resulting in crystallinity indices of 0.4. The results for wheat starch do not show clear trends for the influences of plasticiser size and of ghosts. The difference in behaviour of the two starches is probably caused by wheat starch having shorter amylopectin chains. Resulting from these shorter amylopectin chains, the remaining structure in wheat starch ghosts may resemble A-type crystallinity, making it more difficult to form B-type crystals. Alternatively, the trends as found for potato starch may occur, but are less manifest for wheat starch, due to the lower total extent of recrystallisation. Solid state CP/MAS NMR spectra of the wheat starch samples containing ethylene glycol were obtained, in order to compare completely and partly gelatinised systems. The spectra were identical, confirming that the ghost structures do not influence wheat starch recrystallisation. Apparently, wheat starch ghosts do not act as nuclei for crystallisation.

Similarly, the influence of various malto-oligosaccharides in combination with granular remnants (ghosts) was investigated on wheat starch ageing. Gelatinised and partly gelatinised wheat starch were plasticised with maltose, maltotriose, maltotetraose, maltopentaose or maltohexaose. This resulted in crystallinity indices of 0.2, with the largest reduction in recrystallisation for maltotriose and maltotetraose. No trend was found for the influence of ghosts. The presence of ghosts did not influence the ¹³C solid state HP/DEC NMR spectra. Less recrystallisation took place than with the previously mentioned smaller plasticisers that resulted in crystallinity indices of 0.4. The finding that maltose was able to reduce retrogradation better than glucose could be of practical importance.     

Composition and Structure of Starch from Taproots of Contrasting Genotypes of Medicago sativa L

The objective of this study was to examine the composition and branch chain lengths of alfalfa (Medicago sativa L.) taproot starch during starch utilization and reaccumulation in response to defoliation. Genotypes were propagated vegetatively and well-established plants were sampled at defoliation and at weekly intervals thereafter. Starch granules from root tissues were dispersed in dimethyl sulfoxide and starch components separated using gel permeation chromatography. Root starches also were debranched enzymically, and branch chain lengths were examined. Results indicate that, irrespective of starch concentration, starch from taproots of the high starch genotype was composed of approximately 80% high molecular weight starch with I₂-Kl absorbance characteristics similar to amylopectin. The remaining 20% of the starch was low molecular weight with I₂-Kl absorbance characteristics similar to amylose. Starches of the low starch genotype contained approximately 85% high molecular weight polysaccharide at high root starch concentrations (>50 grams per kilogram). At low root starch concentrations (<10 grams per kilogram), starch from the low starch genotype had nearly equal proportions of low and high molecular weight polysaccharide. The I₂-Kl absorbance properties of the low molecular weight starches from roots of the low starch genotype indicated that some branching may be present. The distribution of chain lengths from amylopectin did not change during starch degradation and reaccumulation for the high starch genotype. In the low starch genotype, the proportion of low molecular weight branches having a degree of polymerization between 1 and 30 was decreased at the very low starch concentrations observed on the 14th day of regrowth. Higher concentrations and/or quantities of starch in roots of the high starch genotype were not associated with greater rate of herbage regrowth, when compared to the low starch genotype.     

The distribution of covalently bound phosphate in the starch granule in relation to starch crystallinity

Five selected starches with a 60-fold span in their content of monoesterified starch phosphate were investigated with respect to distribution of glucose 6-phosphate and glucose 3-phosphate residues, amylopectin chain length distributions and gelatinisation properties. The distribution of starch phosphate in the starch granules was determined by preparation of N?geli dextrins followed by quantitative 31P-nuclear magnetic resonance spectroscopy. Total starch phosphate content was positively correlated to the unit chain lengths of the amylopectin as well as to the chain lengths of the corresponding N?geli dextrins. The major part (68-92%) of the total starch phosphate content was partitioned to the hydrolysed (amorphous) parts. Starch-bound glucose 6-phosphate per milligram of starch was 2-fold enriched in the amorphous parts, whereas phosphate groups bound at the 3-position were more evenly distributed. The gelatinisation temperatures of the native starches as determined by differential scanning calorimetry were positively correlated (R(2)=0.75) to starch phosphate content, while crystallinity (gelatinisation enthalpy) and crystal heterogeneity (endotherm peak width) showed no correlations to starch phosphate content. The relations between starch molecular structure, architecture and functional properties are discussed.     

The polyisoprenoid chain length influences the interaction of ubiquinones with phospholipid bilayers

The interaction between ubiquinone homologues with polyisoprenoid chain lengths varying from 3 to 10 units and dipalmitoylphosphatidylcholine bilayers has been examined by differential scanning calorimetry and wide angle X-ray diffraction analysis. Decreasing the polyisoprenoid chain lengths of ubiquinone in mixed dispersions with phospholipid in mol ratios of about 10 mol% caused a decrease in the gel-liquid crystalline phase transition temperature of the phospholipid and a broadening of the transition. Enthalpy measurements showed that most of the phospholipid (greater than 92%) was involved in the transition endotherm and the formation of a gel phase was also confirmed by the presence of a sharp X-ray reflection of 0.42 nm. These results are consistent with a model in which all of the ubiquinone homologous ultimately undergo a phase separation from phospholipid molecules entering a gel phase on cooling below the phase transition temperature. Reducing the length of the polyisoprenoid chain alters the amphipathic balance of the ubiquinone molecules and is reflected in the tendency of shorter chain ubiquinones to intercalate between the phospholipid molecules upon reheating through the main phase transition.     

Starch-branching enzymes preferentially associated with A-type starch granules in wheat endosperm

Two starch granule-bound proteins (SGP), SGP-140 and SGP-145, were preferentially associated with A-type starch granules (>10 microm) in developing and mature wheat (Triticum aestivum) kernels. Immunoblotting and N-terminal sequencing suggested that the two proteins were different variants of SBEIc, a 152-kD isoform of wheat starch-branching enzyme. Both SGP-140 and SGP-145 were localized to the endosperm starch granules but were not found in the endosperm soluble fraction or pericarp starch granules younger than 15 d post anthesis (DPA). Small-size starch granules (<10 microm) initiated before 15 DPA incorporated SGP-140 and SGP-145 throughout endosperm development and grew into full-size A-type starch granules (>10 microm). In contrast, small-size starch granules harvested after 15 DPA contained only low amounts of SGP-140 and SGP-145 and developed mainly into B-type starch granules (<10 microm). Polypeptides of similar mass and immunologically related to SGP-140 and/or SGP-145 were also preferentially incorporated into A-type starch granules of barley (Hordeum vulgare), rye (Secale cereale), and triticale (x Triticosecale Wittmack) endosperm, which like wheat endosperm have a bimodal starch granule size distribution.     

Synthesis and properties of cationic oligopeptides with different side chain lengths that bind to RNA duplexes

A series of artificial peptides bearing cationic functional groups with different side chain lengths were designed, and their ability to increase the thermal stability of nucleic acid duplexes was investigated. The peptides with amino groups selectively increased the stability of RNA/RNA duplexes, and a relationship between the side chain length and the melting temperature (T_m) of the peptide–RNA complexes was observed. On the other hand, while peptides with guanidino groups exhibited a similar tendency with respect to the peptide structure and thermal stability of RNA/RNA duplexes, those with longer side chain lengths, such as l-2-amino-4-guanidinobutyric acid (Agb) or l-arginine (Arg) oligomers, stabilized both RNA/RNA and DNA/DNA duplexes, and those with shorter side chain lengths exhibited a higher ability to selectively stabilize RNA/RNA duplexes. In addition, peptides were designed with different levels of flexibility by introducing glycine (Gly) residues into the l-2-amino-3-guanidinopropionic acid (Agp) oligomers. It was found that insertion of Gly did not affect the thermal stability of the peptide–RNA complexes, but an alternate arrangement of Gly and Agp apparently decreased the thermal stability. Therefore, in the Agp oligomer, consecutive Agp sequences are essential for increasing the stability of RNA/RNA duplexes.     

Chemical and physical properties of ginkgo (Ginkgo biloba) starch

Starch isolated from mature Ginkgo biloba seeds and commercial normal maize starches were subjected to α-amylolysis and acid hydrolysis. Ginkgo starch was more resistant to pancreatic α-amylase hydrolysis than the normal maize starch. The chain length distribution of debranched amylopectin of the starches was analyzed by using high performance anion-exchange chromatography equipped with an amyloglucosidase reactor and a pulsed amperometric detector. The chain length distribution of ginkgo amylopectin showed higher amounts of both short and long chains compared to maize starch. Naegeli dextrins of the starches prepared by extensive acid hydrolysis over 12 days demonstrated that ginkgo starch was more susceptible than normal maize to acid hydrolysis. Ginkgo dextrins also demonstrate a lower concentration of singly branched chains than maize dextrins, and unlike maize dextrin, debranched ginkgo shows no multiple branched chains. The ginkgo starch displayed a C-type X-ray diffraction pattern, compared to an A-type pattern for maize. Ginkgo starch and maize starch contained 24.0 and 17.6% absolute amylose contents, respectively.     

HEMIFLAGELLOCHLORIS KAZAKHSTANICA GEN. ET SP. NOV.: A NEW COCCOID GREEN ALGA WITH FLAGELLA OF CONSIDERABLY UNEQUAL LENGTHS FROM A SALINE IRRIGATION LAND IN KAZAKHSTAN (CHLOROPHYCEAE,CHLOROPHYTA)1

A coccoid green alga, Hemiflagellochloris kazakhstanica S. Watanabe, S. Tsujimura, T. Misono, S. Nakamura et H. Inoue, gen. et sp. nov., was described from soil samples of a saline irrigation land in Ili River basin, Kazakhstan. This alga had a parietal chloroplast with a pyrenoid, which was covered with starch segments and penetrated with thylakoid membranes. Reproduction occurred by the formation of aplanospores and zoospores. The aplanospores frequently formed tetrad aggregations in a mother cell. The zoospores were covered by a single‐layered cell wall and lacked stigmata. The zoospores had two flagella of considerably unequal lengths; the longer flagellum was 17–19 lm in length and the shorter one was 9–10 lm. The flagellar apparatus architecture was of the clockwise orientation group type in the Chlorophyceae. Molecular phylogenetic analysis using 18S and 28S rDNA sequence data resolved this organism in a separate clade from the green algae that had flagella of slightly unequal lengths. It was suggested that features such as inequality in flagellar lengths, parallel exsertion of basal bodies, and subapical position of the flagellar apparatus were sporadically evolved.     

Characterization of Molecular Structure of Starch Granules in Suspension-cultured Cells from Ipomoea cordatotriloba Denn.

The molecular structure of starch granules formed in suspension-cultured cells of Ipomoea cordatotriloba Denn. was characterized by its chain length distribution, which was compared to those of the starches from the root and leaf of the original plant. The cultured cell starches were spherical and had a very small granule size (about 2 μm). The debranched starches roughly separated into three fractions during gel-permeation chromatography, and the fractions were defined as Fr.1, 2, and 3, respectively. The chain length distribution of the debranched cultured cell starch showed that the high molecular weight fraction (Fr.1), referred to as an amylose fraction, was much less than those of the root and leaf starches. The ratio of the two lower fractions (Fr.3/Fr.2) of the cultured cell starch, which was mainly derived from unit chains of amylopectin, was greatest among the starches, suggesting that the amylopectin from the cultured cell starch has much shorter unit chains. By X-ray diffraction analysis, it was found that both cultured cell and leaf starch granules have low crystallinity.     

Origin of the limited alpha-amylolysis of debranched maltodextrins crystallized in the A form: a TEM study on model substrates

The detailed ultrastructure of a new type of resistant starch and the way that it is modified during hydrolysis by alpha-amylases were studied by transmission electron microscopy (TEM) on model starch crystals. The selected substrates were waxy maize starch lintners and A-type crystals prepared from low degree of polymerization (DP) amylose. A model describing the stacking of double helices is proposed for A-type low DP amylose crystals. The enzymatic hydrolysis of both lintners and low DP crystals has been shown to occur by the side of double helices and not their ends. The results were transposed to a new type of resistant starch (RS) produced by debranching maltodextrins in concentrated solutions. This product presents A-type crystallinity contrary to all other known classified RS. Moreover it consists of low DP chains similar to the model crystals studied and yields similar electron diffraction patterns to those of A-type low DP crystals. The similarities in the morphology of these substrates with that of the studied RS led us to attribute its resistance to its particularly dense and compact morphology, resulting from the epitaxial growth of elementary crystalline A-type platelets. In the resulting structure, the accessibility of double helices to alpha-amylase is strongly reduced by aggregation.