Amylopectin Clusters Research Articles

High-Resistant Starch Based on Amylopectin Cluster via Extrusion: From the Perspective of Chain-Length Distribution and Structural Formation.

Resistant starch (RS) has the advantage of reshaping gut microbiota for human metabolism and health, like glycemic control, weight loss, etc. Among them, RS3 prepared from pure starch is green and safe, but it is hard to achieve structural control. Here, we regulate the crystal structure of starch with different chain-length distributions (CLDs) via extrusion at low/high shearing levels. The change in CLDs in extruded starch was obtained, and their effects on the fine structure (Dm, dBragg, dLorentz, degree of order and double helix, degree of crystal) of RS and its physicochemical properties were investigated by SAXS, FTIR, XRD and 13C NMR analyses. The results showed that the RS content under a 250 r/min extrusion condition was the highest at 61.52%. Furthermore, the crystalline system induced by high amylopectin (amylose ≤ 4.78%) and a small amount of amylose (amylose ≥ 27.97%) was favorable for obtaining a high content of RS3-modified products under the extruding environment. The control of the moderate proportion of the A chains (DP 6-12) in the starch matrix was beneficial to the formation of RS.

Starch Characteristics and Amylopectin Unit and Internal Chain Profiles of Indonesian Rice (Oryza sativa).

Indonesia is arguably a major player in worldwide rice production. Though white rice is the most predominantly cultivated, red, brown, and red rice are also very common. These types of rice are known to have different cooking properties that may be related to differences in their starch properties. Investigating the starch properties, especially the fine structure of their amylopectin, can help understand these differences. This study aims to investigate the starch characteristics of some Indonesian rice varieties by evaluating the starch granule morphology and size, molecular characteristics, amylopectin unit and internal chain profiles, and thermal properties. Starches were extracted from white rice (long grain (IR-64) and short grain (IR-42)), brown rice, red rice, and black rice cultivated in Java Island, Indonesia. IR-42 had the highest amylose content of 39.34% whilst the black rice had the least of 1.73%. The enthalpy of gelatinization and onset temperature of the gelatinization of starch granules were between 3.2 and 16.2 J/g and 60.1 to 73.8 °C, respectively. There were significant differences between the relative molar amounts of the internal chains of the samples. The two white rice and black rice had a significantly higher amount of A-chains, but a lower amount of B-chains and fingerprint B-chains (Bfp) than the brown and red rice. The average chain length (CL), short chain length (SCL), and external chain length (ECL) were significantly longer for the red rice and the black rice in comparison to both the white rice amylopectins. The long chain length (LCL) and internal chain length (ICL) of the sample amylopectins were similar. Rice starches were significantly different in the internal structure but not as much in their amylopectin unit chain profile. These results suggest the differences in their amylopectin clusters and building blocks.

Development and applications of enzymatic modified starch with high water solubility providing a continuous supply of glucose

Amylopectin clusters (APCs) are produced by cyclodextrin glucanotransferase (EC 2.4.1.19). Their solubility rate in aqueous solution was found to be 16.7 %. The weight-average molecular weight of APCs is ∼105 Da, as determined by multiangle laser light scattering analysis. Side chain length analysis indicated that the relative proportions of side chains with a degree of polymerization in the ranges of 2–8 and 25–50 decreased and increased, respectively, during preparation of APCs. In the exercise experiment, the blood glucose level of rats was higher in the APC-treated group than in the groups treated with commercial carbohydrate supplement (CCD) and glucose. In the forced swimming test, the swimming time in the APC and CCD groups increased by 22.6 % and 31.1 %, respectively, compared with the glucose administration group. The insulin levels were also similar between the APC and CCD groups. However, the glycogen levels in the liver and muscles of mice were significantly higher in the APC group than control group. These results suggest that APCs could potentially enhance endurance when added to sports drinks.

A model for the reproduction of amylopectin cluster by coordinated actions of starch branching enzyme isoforms.

Amylopectin is a highly branched glucan which accounts for approximately 65-85% of starch in most plant tissues. It is crucially important to understand the biosynthetic process of this glucan in regulating the structure and functional properties of starch granules. Currently, the most accepted ideas of structural feature and biosynthesis of amylopectin are that amylopectin is composed of a branched element called "cluster" and that the essential process of amylopectin biosynthesis is to reproduce a new cluster from the existing cluster. The present paper proposes a model explaining the whole process of amylopectin biosynthesis as to how the new cluster is reproduced by concerted actions of multiple isoforms of starch biosynthetic enzymes, particularly by combinations of distinct roles of starch branching enzyme (BE) isoforms. This model proposes for the first time the molecular mechanism as to how the formation of a new cluster is initiated, and the reason why BEI can play a major role in this step. This is because BEI has a rather broad chain-length preference compared to BEIIb, because a low preference of BEI for the substrate chain-length is advantageous for branching a couple of elongated chains that are not synchronously formed and thus these chains having varied lengths could be safely attacked by this isoform. On the contrary, it is unlikely that BEIIb is involved in this reaction because it can react to only short chains having degree of polymerization of 12-14. BEIIa is possibly able to complement the role of BEI to some extent, because BEIIa can attack basically short chains but its chain-length preference is lower compared with BEIIb. The model implies that the first branches mainly formed by BEI to construct the amorphous lamellae whereas the second branches predominantly formed by BEIIb are located mainly in the crystalline lamellae. This paper provides new insights into the roles of BEI, BEIIb, and BEIIa in amylopectin biosynthesis in cereal endosperm.

Effect of Shearing and Heat Milling Treatment Temperature on the Crystallinity, Thermal Properties, and Molecular Structure of Rice Starch.

Rice flour is produced by various methods for use in the food industry, but little is known about how the structure of starch is affected during rice flour production. In this study, the crystallinity, thermal properties, and structure of starch in rice flour were investigated after treatment with a shearing and heat milling machine (SHMM) at different temperatures (10-150 °C). Both the crystallinity and gelatinization enthalpy of starch showed an inverse relationship with the treatment temperature; rice flour treated with the SHMM at higher temperatures showed lower crystallinity and gelatinization enthalpy than that treated at lower temperatures. Next, the structure of undegraded starch in the SHMM-treated rice flour was analyzed by gel permeation chromatography. A significant reduction in the molecular weight of amylopectin was observed at high treatment temperatures. Chain length distribution analysis showed that the proportion of long chains (degree of polymerization (DP) > 30) in rice flour decreased at temperatures ≥ 30 °C. By contrast, the molecular weight of amylose did not decrease. In summary, the SHMM treatment of rice flour at high temperatures resulted in starch gelatinization, and the amylopectin molecular weight decreased independently, due to the cleavage of amorphous regions connecting the amylopectin clusters.

Effect of new type extrusion modification technology on supramolecular structure and in vitro glycemic release characteristics of starches with various estimated glycemic indices.

Nowadays, the highly effective modified technology to starch with various digestibility is gaining interest in food science. Here, the interactions between glycemic release characteristics and fine supramolecular structure of cassava (ECS), potato (EPS), jackfruit seed (EJFSS), maize (EMS), wheat (EWS), and rice starches (ERS) prepared with improved extrusion modification technology (IEMS) were investigated. The crystalline structures of all extruded cooking starches changed from the A-type to V-type. IEMS-treated cassava, potato, and rice starches had broken α-1.6-glycosidic amylopectin (long chains). The others sheared α-1.4-glycosidic amylopectin. The molecular weight, medium and long chain counts, and relative crystallinity decreased, whereas the number of amylopectin short chains increased. The glycemic index (GI) and digestive speed rate constant (k) of ECS, EPS, EJFSS, and EWS were improved compared to those of raw starch. Although EMS and ERS had degraded molecular structures, their particle morphology changed from looser polyhedral to more compact with less enzymolysis channels due to the rearrangement of side chain clusters of amylopectin, leading to enzyme resistance. The starch characteristics of IEMS-treated samples significantly differed. EPS had the highest amylose content, medium chains, long chains, and molecular weight but lowest GI, relative crystallinity, and k. ERS showed the opposite results. Thus, IEMS may affect starches with different GIs to varying degrees. In this investigation, we provide a basis for wider applications of conventional crop starch in the food industry corresponding to different nutrition audience.

Multi-scale supramolecular structure of Pouteria campechiana (Kunth) Baehni seed and pulp starch

Study of non-conventional under-utilized starch sources is gaining interest in food science. Here, the multi-scale supramolecular structure of starch from Pouteria campechiana seed (PCSS) and pulp (PCPS) was analyzed. Amylopectin free side chain, α-1,6 glycosidic bond, and double helix content of PCSS and PCPS were similar to those of wheat, pea, and rice starch, respectively. Average semi-crystalline lamellae thickness (d) and PCSS and PCPS weight-average molar mass (Mw) were similar to those of jackfruit starch. Short-range order and blocklet size (Rq) were similar to those of corn and wheat starch. Fractal dimensions of PCSS and PCPS were lower than those of potato starch. PCSS showed higher α-1,6 content (9.98%), free side chain (11.14%), double helix content (44.70%), Mw (3.64 × 107 g/mol), and V-type polymorphism (4.78%), lower d (8.858 nm), gyration radius (Rg) (82.1 nm), fractal dimension (2.06), Fwhm at 480 cm−1 (13.19), and Rq (8.5 nm) than PCPS (8.75%, 9.88%, 39.24%, 2.79 × 107 g/mol, 3.33%, 9.074 nm, 89.4 nm, 2.23, 16.11 and 18.00 nm, respectively). Compared to PCPS, denser nano nodules of amylopectin clusters were formed in PCSS resulting from the relatively stronger intermolecular hydrogen forces among numbers of double helix or V-polymorph arrangements. This led to the higher molecular density in the amorphous and crystalline layer, the smaller Rg, Rq and higher Mw in PCSS. We provide a basis for further applications of P. campechiana starches in the food industry.

Development of Freeze-Thaw Stable Starch through Enzymatic Modification.

The use of unmodified starch in frozen foods can cause extremely undesirable textural changes after the freeze-thaw process. In this study, using cyclodextrin glucanotransferase (CGTase) and branching enzymes, an amylopectin cluster with high freeze-thaw stability was produced, and was named CBAC. It was found to have a water solubility seven times higher, and a molecular weight 77 times lower, than corn starch. According to the results of a differential scanning calorimetry (DSC) analysis, dough containing 5% CBAC lost 19% less water than a control dough after three freeze-thaw cycles. During storage for 7 days at 4 °C, bread produced using CBAC-treated dough exhibited a 14% smaller retrogradation peak and 37% less hardness than a control dough, suggesting that CBAC could be a potential candidate for clean label starch, providing high-level food stability under repeated freeze-thaw conditions.

Structure and Properties of Starch in Rice Double Mutants Lacking Starch Synthase (SS) IIa and Starch Branching Enzyme (BE) IIb.

Starch biosynthetic enzymes form multi-protein complexes consisting of starch synthase (SS) I, SSIIa, and starch branching enzyme (BE) IIb, which synthesize amylopectin clusters. This study analyzed the starch properties in two double mutant rice lines lacking SSIIa and BEIIb, one of which expressed an inactive BEIIb protein. The ss2a be2b lines showed similar or greater seed weight than the be2b lines, and plant growth was not affected. The ss2a line showed increased short amylopectin chains resulting in a lower gelatinization temperature. Starch granule morphology and A-type crystallinity were similar between the ss2a line and the wild type, except for a mild chalky seed phenotype in the ss2a line. However, the starch phenotype of the ss2a be2b lines, which was similar to that of be2b but not ss2a, was characterized by increased long amylopectin chains, abnormal starch granules, and B-type crystallinity. The similarity in phenotype between the ss2a be2b and be2b lines may be attributed to the inability of the be2b mutants to generate short amylopectin branches, which serve as primers for SSIIa. Therefore, the presence or absence of SSIIa hardly affected the amylopectin structure under the be2b background. The amylose content was significantly higher in the ss2a be2b lines than in the be2b lines. Starch crystallinity was greater in ss2a be2b lines than in be2b lines, despite the fact that starch crystallinity is generally negatively correlated with amylose content. This suggests that the formation of a double helix between long amylopectin chains and amylose affects starch crystallinity in the ss2a be2b mutants.

Effects of BEIIb-Deficiency on the Cluster Structure of Amylopectin and the Internal Structure of Starch Granules in Endosperm and Culm of Japonica-Type Rice.

It is known that one of starch branching enzyme (BE) isoforms, BEIIb, plays a specific role not only in the synthesis of distinct amylopectin cluster structure, but also in the formation of the internal structure of starch granules in rice endosperm because in its absence the starch crystalline polymorph changes to the B-type from the typical A-type found in the wild-type (WT) cereal endosperm starch granules. In the present study, to examine the contribution of BEIIb to the amylopectin cluster structure, the chain-length distributions of amylopectin and its phosphorylase-limit dextrins (Φ-LD) from endosperm and culm of a null be2b mutant called amylose-extender (ae) mutant line, EM10, were compared with those of its WT cultivar, Kinmaze, of japonica rice. The results strongly suggest that BEIIb specifically formed new short chains whose branch points were localized in the basal part of the crystalline lamellae and presumably in the intermediate between the crystalline and amorphous lamellae of amylopectin clusters in the WT endosperm, whereas in its absence branch points which were mainly formed by BEI were only located in the amorphous lamellae of amylopectin. These differences in the cluster structure of amylopectin between Kinmaze and EM10 endosperm were considered to be responsible for the differences in the A-type and B-type crystalline structures of starch granules between Kinmaze and EM10, respectively. The changes in internal structure of starch granules caused by BEIIb were analyzed by wide angle X-ray diffraction, small-angle X-ray scattering, solid state 13C NMR, and optical sum frequency generation spectroscopy. It was noted that the size the amylopectin cluster in ae endosperm (approximately 8.24 nm) was significantly smaller than that in WT endosperm (approximately 8.81 nm). Based on the present results, we proposed a model for the cluster structure of amylopectin in WT and ae mutant of rice endosperm. We also hypothesized the role of BEIIa in amylopectin biosynthesis in culm where BEIIb was not expressed and instead BEIIa was the major BE component in WT of rice.

Solubility, stability, and bioaccessibility improvement of curcumin encapsulated using 4-α-glucanotransferase-modified rice starch with reversible pH-induced aggregation property

Curcumin is a polyphenolic compound with anti-cancer, anti-inflammatory and anti-oxidant effects. However, its application in the food industry is very limited owing to its low water solubility and chemical stability. In the present study, 4αGTase-treated rice starch (GS) was prepared by treating rice starch with 4-α-glucanotransferase (4αGTase) for 1 h (1 GS) and 96 h (96 GS), and the physicochemical properties of GS were analyzed. Moreover, the capability of GS to improve the encapsulation efficiency and stability of curcumin by forming complexes was investigated in comparison with maltodextrin (MD) and β-cyclodextrin (CD). GS is known to contain cyclic glucans and amylopectin clusters that contribute to its complex forming capability with bioactive compounds. Upon encapsulation with 1 GS and 96 GS, curcumin solubility increased by 2,241- and 2,846-fold, respectively. UV stability of the encapsulated curcumin with 96 GS also improved by 1.83-fold. GS was effective under all pH conditions except for 96 GS under acidic condition, as well as curcumin encapsulated with 1 GS and 96 GS exhibited 11.53- and 11.27-fold increase in bioaccessibility. The increased stability of curcumin within GS may be attributed to the unique molecular structure of GS interacting with curcumin, as suggested by chromatography and Fourier transform infrared spectroscopy. Also, the improved bioaccessibility of curcumin encapsulated with 96 GS even with lower pH stability at acidic pH seems to be partly attributed to reversible pH-induced aggregation of 96 GS. These results suggest that GS could act as a novel food-grade host material to improve the chemical stability of curcumin.

Digestion properties of corn starch modified by α-D-glucan branching enzyme and cyclodextrin glycosyltransferase

Corn starch was modified using α-D-glucan branching enzyme (GBE) and cyclodextrin glucosyltransferase (CGTase), and their in vitro digestibility were investigated. Compared to native corn starch and single-enzyme treated starch, dual-enzyme modified starch had higher amount of slowly digestible starch (SDS) and resistant starch (RS) contents. The chain length distributions and the ratio of α-1,6 linkages of the dual-enzyme modified starch indicated an increase in short side-chains (DP < 13) as well as branching degree, compared with control starch (corn starch treated without enzyme). Cyclodextrins formed in starch modified reaction was found to complex with branched amylopectin clusters by hydrogen bonding and other intermolecular forces, showing V-type X-ray diffraction pattern. The presence of the crystalline regions of dual-enzyme modified starch favored digestion rate reduction, which may give some useful reference for the development of modified starch with slow digestion property.

Starch Synthase IIa-Deficient Mutant Rice Line Produces Endosperm Starch With Lower Gelatinization Temperature Than Japonica Rice Cultivars.

The gelatinization temperature of endosperm starch in most japonica rice cultivars is significantly lower than that in most indica rice cultivars. This is because three single nucleotide polymorphisms in the Starch synthase (SS) IIa gene in japonica rice cultivars (SSIIaJ) significantly reduce SSIIa activity, resulting in an increase in amylopectin short chains with degree of polymerization (DP) ≤ 12 compared to indica rice cultivars (SSIIaI). SSIIa forms a trimeric complex with SSI and starch branching enzyme (BE) IIb in maize and japonica rice, which is likely important for the biosynthesis of short and intermediate amylopectin chains (DP ≤ 24) within the amylopectin cluster. It was unknown whether the complete absence of SSIIa further increases amylopectin short chains and reduces gelatinization temperature and/or forms altered protein complexes due to the lack of a suitable mutant. Here, we identify the SSIIa-deficient mutant rice line EM204 (ss2a) from a screen of ca. 1,500 plants of the rice cultivar Kinmaze (japonica) that were subjected to N-methyl-N-nitrosourea mutagenesis. The SSIIa gene in EM204 was mutated at the boundary between intron 5 and exon 6, which generated a guanine to adenine mutation and resulted in deletion of exon 6 in the mRNA transcript. SSIIa activity and SSIIa protein in developing endosperm of EM204 were not detected by native-PAGE/SS activity staining and native-PAGE/immunoblotting, respectively. SSIIa protein was completely absent in mature seeds. Gel filtration chromatography of soluble protein extracted from developing seeds showed that the SSI elution pattern in EM204 was altered and more SSI was eluted around 300 kDa, which corresponds with the molecular weight of trimeric complexes in wild type. The apparent amylose content of EM204 rice grains was higher than that in its parent Kinmaze. EM204 also had higher content of amylopectin short chains (DP ≤ 12) than Kinmaze, which reduced the gelatinization temperature of EM204 starch by 5.6°C compared to Kinmaze. These results indicate that EM204 starch will be suitable for making foods and food additives that easily gelatinize and slowly retrograde.

Effect of diurnal photosynthetic activity on the fine structure of amylopectin from normal and waxy barley starch

The impact of diurnal photosynthetic activity on the fine structure of the amylopectin fraction of starch synthesized by normal barley (NBS) and waxy barley (WBS), the latter completely devoid of amylose biosynthesis, was determined following the cultivation under normal diurnal or constant light growing conditions. The amylopectin fine structures were analysed by characterizing its unit chain length profiles after enzymatic debranching as well as its φ,β-limit dextrins and its clusters and building blocks after their partial and complete hydrolysis with α-amylase from Bacillus amyloliquefaciens, respectively. Regardless of lighting conditions, no structural effects were found when comparing both the amylopectin side-chain distribution and the internal chain fragments of these amylopectins. However, the diurnally grown NBS and WBS both showed larger amylopectin clusters and these had lower branching density and longer average chain lengths than clusters derived from plants grown under constant light conditions. Amylopectin clusters from diurnally grown plants also consisted of a greater number of building blocks, and shorter inter-block chain lengths compared to clusters derived from plants grown under constant light. Our data demonstrate that the diurnal light regime influences the fine structure of the amylopectin component both in amylose and non-amylose starch granules.

Biophysical features of cereal endosperm that decrease starch digestibility

The influence of the physical structure of cereal endosperm on the natural structural integrity (intact cells) and starch bioaccessibility of the resultant flours was studied using maize as example. Endosperm hardness, defined by its intracellular (protein matrix) and extracellular (cell walls) constituents, affected the granular and molecular damage of the starch of the resultant flours leading to higher digestibility of raw hard than soft endosperm flours, but comparatively lower digestibility after cooking. After milling, hard endosperm possessed more damaged starch (radial splitting of amylopectin clusters) in the periphery of the resultant particles that increased in vitro starch digestibility of raw flours. Conversely, the hard endosperm plant tissue matrix significantly limited water availability and heat transfer on starch gelatinisation, thereby decreasing the digestion rate after hydrothermal processing (in particle size flours >80μm). This study provides a unique mechanistic understanding to obtain cereal flours with slow digestion property for commercial utilisation.

High‐pressure homogenization induced degradation of amylopectin in a gelatinized state

An investigation of the degradation mechanism of a highly branched polymer during a high‐pressure homogenization (HPH) process was performed using gelatinized waxy maize starch as a substrate. The degradation mechanism was studied using high‐performance size‐exclusion chromatography equipped with multi‐angle laser‐light scattering and refractive index detectors. The HPH induced an exponential molecular degradation trend that was a function of HPH pressure/cycles. The results revealed that HPH preferentially disrupted larger molecules and caused their size distribution (or molecular weight) to a narrow range, resulting in a maximum stable size (or molecular weight). A final z‐average radius of gyration of about 20 nm for amylopectin was observed after HPH for eight cycles at 100 MPa or two cycles at 150 MPa, which was due to the midpoint scission mechanism during the HPH treatment. The increase in molecular density after HPH verified the breakdown of the α‐1,4‐glycosidic bonds among the clusters of (midpoint scission) amylopectin.

Cyclodextrin Glucanotransferase를 이용한 아밀로펙틴 클러스터의 생산

선행연구에서 얻은 alkalophilic Bacillus I-5 유래의 CGTase wild-type과 가수분해능이 강화된 mutant 효소를 활용하여 waxy rice starch로부터 아밀로펙틴 클러스터를 제조하였다. SEC-MALLS-RI 분석법으로 CGTase wild-type과 mutant 효소가 처리된 시료의 평균 분자량을 확인한 결과 10분가량의 효소반응으로 두 반응 모두 평균 분자량은 104 ∼105 Da으로 급격히 감소하였음을 확인하였으며, 일정 반응 시간이 경과한 이후에는 더 이상 분자량의 감소가 일어나지 않음으로 미루어 시료가 아밀로펙틴 클러스터 단위로 분해되었으며 그 분자량은 104∼105 Da 정도임을 알 수 있다. 또한 MALDI-TOF/MS 분석을 통하여 CGTase wild-type은 다양한 종류의 cyclic 형태의 maltodextrin을 생성하고 있으며 mutant 효소는 주로 소량의 maltooligosaccharide들을 생산함을 확인하였다.

Deficiencies in both starch synthase IIIa and branching enzyme IIb lead to a significant increase in amylose in SSIIa-inactive japonica rice seeds.

Starch synthase (SS) IIIa has the second highest activity of the total soluble SS activity in developing rice endosperm. Branching enzyme (BE) IIb is the major BE isozyme, and is strongly expressed in developing rice endosperm. A mutant (ss3a/be2b) was generated from wild-type japonica rice which lacks SSIIa activity. The seed weight of ss3a/be2b was 74-94% of that of the wild type, whereas the be2b seed weight was 59-73% of that of the wild type. There were significantly fewer amylopectin short chains [degree of polymerization (DP) ≤13] in ss3a/be2b compared with the wild type. In contrast, the amount of long chains (DP ≥25) connecting clusters of amylopectin in ss3a/be2b was higher than in the wild type and lower than in be2b. The apparent amylose content of ss3a/be2b was 45%, which was >1.5 times greater than that of either ss3a or be2b. Both SSIIIa and BEIIb deficiencies led to higher activity of ADP-glucose pyrophosphorylase (AGPase) and granule-bound starch synthase I (GBSSI), which partly explains the high amylose content in the ss3a/be2b endosperm. The percentage apparent amylose content of ss3a and ss3a/be2b at 10 days after flowering (DAF) was higher than that of the wild type and be2b. At 20 DAF, amylopectin biosynthesis in be2b and ss3a/be2b was not observed, whereas amylose biosynthesis in these lines was accelerated at 30 DAF. These data suggest that the high amylose content in the ss3a/be2b mutant results from higher amylose biosynthesis at two stages, up to 20 DAF and from 30 DAF to maturity.

Enzymatic modification of corn starch with 4-α-glucanotransferase results in increasing slow digestible and resistant starch

In this study, partial 4-α-glucanotransferase (4αGT) treatment was used to modulate the fine structure responsible for the slow digestion and resistant property of starch. Normal corn starch modified using 4αGT for 4h showed an increase of slowly digestible starch from 9.40% to 20.92%, and resistant starch from 10.52 to 17.63%, respectively. The 4αGT treatment decreased the content of amylose from 32.6% to 26.8%. The molecular weight distribution and chain length distribution of 4αGT-treated starch showed a reduction of molecular weight and a great number of short (DP<13) and long (DP>30) chains through cleaving and reorganization of starch molecules. Both the short and long chain fractions of modified amylopectin were attributed to the low in vitro digestibility. The viscosity was inversely related to the digestibility of the 4αGT-treated starch. These results suggested that the 4αGT modified starch synthesized the novel amylopectin clusters with slow digestible and resistant character.

Physicochemical Characteristics of Starches in Rice Cultivars of Diverse Amylose Contents

Through the sampling four rice cultivars with differing amylose contents, the relationship between the structural and gelatinization properties of endosperm starches was analyzed. These rice varieties exhibited different chain length distribution ratio within the amylopectin cluster as well as varing amylose levels. The proportion of amylopectin short chains of in Goami cutlivars was higher than the other varieties, whereas the Goami 2 which shows amylose extender mutant properties in the endosperm showed the highest proportion of long chains. In X-ray diffraction analysis of rice starches, the Goami 2 variety displayed a B-type pattern whereas the other varieties were all A-type. Among the cultivars with high and normal rice starch levels, those with the higher amylose contents showed distinctly lower swelling. Goami 2 rice was found to have the highest onset and peak gelatinization temperature from the differential scanning calorimetry results. The four rice cultivars under analysis also showed different rates of hydrolysis by amyloglucosidase. These findings suggest that the composition and chemical structure of the starch content is a major determinant of both the gelatinization and functional properties of rice.