Unit Chains Of Amylopectin Research Articles

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.

Impact of mutations in starch synthesis genes on morphological, compositional, molecular structure, and functional properties of potato starch.

Morphology, composition and molecular structure of starch directly affect the functional properties. This study investigated the morphological, compositional, and molecular structure properties of starch from starch branching enzyme gene (SBE) and granule-bound starch synthase gene (GBSS) mutated potato, and their associations with thermal, pasting, and film-making properties. SBE mutations were induced in native variety Desiree while GBSS mutations were herestacked to a selected SBE mutated parental line. Mutations in SBE resulted in smaller starch granules and higher amylose content, while GBSS mutations in the SBE background reduced amylose content. Mutations in SBE, particularly with GBSS mutations, significantly increased total phosphorus content. 31P NMR spectroscopy revealed higher proportions of C6-bound phosphate than of C3-bound phosphate in all studied lines. Amylopectin unit chain and internal chain distributions showed higher proportions of long chains in mutated lines compared with Desiree. These amylopectin long-chains were positively correlated with gelatinizationand, pasting temperatures, and temperature at peak viscosity. Short amylopectin chains showed positive correlations with breakdown viscosity, but negative correlations with the crystal melting temperature of retrograded starch. Total phosphorus content was positively correlated with the crystal melting temperature of retrograded starch. Starch from different lines was used to produce a series of potato starch films that differed in morphology and functional properties. A negative correlation was observed between Young's modulus of films and the long amylopectin-chain fraction. Thermal gravimetric analysis revealed highest thermal stability of Desiree starch films, followed by films from SBE-mutated high-amylose lines. Oxygen transmission rate and oxygen permeability analyses showed that films made with starch from selected GBSS and SBEs mutated line maintained comparable oxygen barrier properties to Desiree film. These insights on the impact of genetic mutations on starch properties indicate potential applications of in-planta starch modification for specific end-uses including packaging.

Rice noodle quality is structurally driven by the synergistic effect between amylose chain length and amylopectin unit-chain ratio

Chewiness, slipperiness, and rapid rehydration are satisfactory qualities for rice noodles. These qualities are dependent on rice starch structure. However, the synergistic effect of fine structure of amylose (AM) and amylopectin (AP) on rice noodle quality remains unclear. In this work, six rice varieties, three from early indica and three from late indica, with similar amylose content for each pair were analyzed to assess the synergistic effects between AM and AP fine structures. The results showed that the combination of amylose long-chains and a low amylopectin unit-chain (APC) ratio favored the maintenance of relatively intact starch granules, resulting in a higher die expansion ratio and improvement of the mechanical properties of rice noodles (Hardness varied from 403 g to 1627 g). Meanwhile, higher die expansion was associated with a larger rehydration ratio. These results suggest that the synergistic effect between AM and AP fine structures significantly affects rice noodles' quality.

The molecular structure of starch from different Musa genotypes: Higher branching density of amylose chains seems to promote enzyme-resistant structures

Starch from bananas/plantains, belonging to the genus Musa spp, is gaining prominence given its great potential as a healthy food ingredient made from an inexpensive raw material. Recent works highlight the outstanding potential of Musa starch to develop enzyme-resistant structures upon retrogradation. However, despite the wide variety of Musa cultivars (due to both natural mutation and breeding selection), there is no comparative investigation of the starch molecular structure from the most commonly cultivated Musa genotypes. In this work, the starch from six Musa cultivars harvested during the same growing season from the same parcel, was purified and analyzed for amylose ratio, amylose chain length distribution, and amylopectin unit and internal chain length distribution. Results showed significant differences between the fine structure of all Musa amylopectin molecules, which were structurally categorized as type 4 (consisting of a high number of B3-chains, few BS- and Bfp-chains, and low S:L and BS:BL ratios). Moreover, the different Musa starches exhibited dramatic differences in amylose ratio (17.7–27.6%), amylose branching degree (as evidenced by differences in the population of short chains of approximately 260 glucose units, GU) and a shorter average length (approximately 1000 GU) of the population of long amylose unit chains. Remarkably, these differences in amylose structure resulted in the cultivar Manzano (Musa AAB, silk subgroup) to possess a dramatically lower extension of in vitro starch digestion (C90 = 4.70%) than the rest of the cultivars (C90 = 17–18%) after full gelatinization and retrogradation for 7 days.

Observations on the impact of amylopectin and amylose structure on the swelling of starch granules

Four different types of amylopectin structure have been reported in our earlier work based on the internal unit chain profile obtained from limit dextrins of amylopectin and data strongly suggested that chain length and organization of internal unit chains of amylopectin influence the gelatinization and retrogradation properties of the starch. Another important functional attribute is granule swelling that mainly contributes to the viscosifying property of starches. In this study, unmodified defatted amylose-containing starch granules possessing amylopectin of four types were subjected to swelling in warm water. The swelling pattern of the granules was related to the structural type of the amylopectin component. Granules having amylopectin of Type 1 structure started to swell at lower temperature (about 55 °C) and possessed more restricted swelling than most of the other starches. Type 1 starches lost their integrity at temperatures above 85 °C, whereas starch granules with Type 2 and 3 amylopectin were still intact at 95 °C. Starches with Type 4 amylopectin were heterogeneous with respect to their swelling: Lesser yam starch possessed comparatively restricted swelling between 75 and 95 °C, whereas canna and potato starch swelled extensively and disintegrated already before 95 °C. Some waxy samples were also included in the investigation and these were generally more sensitive to swelling than their non-waxy counterparts, showing that amylose restricts the swelling and stabilizes the granular structure, albeit there was no correlation between the apparent amylose content and the swelling of tested samples. Instead, the result suggested a correlation between the structure of amylopectin and the deposition of amylose in the starch granules.

Rheological properties in relation to molecular structure of quinoa starch

Quinoa starch granules are small (~0.5 – 3μm) with potentials for some food and other applications. To better exploit it as a new starch resource, this study investigates the steady shear and dynamic oscillatory properties of 9 quinoa starches varying in composition and structure. Steady shear analysis shows that the flow curves could be well described by 4 selected mathematic models. Temperature sweep analysis reveals that the quinoa starch encounters a 4-stage process including 2 phase transitions. Structure-function relationship analysis showed that composition as well as unit and internal chain length distribution of amylopectin have significant impact on the rheological properties (e.g., G′ at 90°C) of quinoa starch. The roles of some individual unit chains and super-long unit chains of amylopectin in determining the rheological properties of quinoa starch were revealed. This study may stimulate further interest in understanding the structural basis of starch rheology.

The cluster structure of barley amylopectins of different genetic backgrounds

The unit chains of amylopectin are organized into clusters. In this study, the cluster structure was analysed in detail in four different genotypes of barley, of which two possessed the amo1 genetic background. Amylose content of the barley starches differed from 0 to 32.6%. Isolated amylopectin was hydrolysed with α-amylase from Bacillus subtilis into domains, defined as groups of clusters, which were size-fractionated by methanol. The domain fractions were further treated with α-amylase to release single clusters. Amylopectin, domains and clusters were subsequently treated with phosphorylase and β-amylase to produce φ,β-limit dextrins and the detailed internal structures of these different structure levels were investigated. Analysis was performed with gel-permeation and anion-exchange chromatography. Equal amount of A-chains were detected in all barleys, but the distribution of B-chains differed. At least two types of domain structures were identified in all four barley varieties. Large domains were built up by large clusters and small domains by small clusters. In all four barley samples the number of long chains was small suggesting that shorter chains with a degree of polymerization of 25–35 also are involved in the interconnection of clusters. The cluster structure of the amylopectin correlated with the genetic background. The two barley samples with amo1 genetic background possessed a more dense structure. Internal chain lengths in these two barleys were shorter resulting in larger domains built up by larger clusters.

Barley Grain Constituents, Starch Composition, and Structure Affect Starch in Vitro Enzymatic Hydrolysis

The relationship between starch physical properties and enzymatic hydrolysis was determined using ten different hulless barley genotypes with variable carbohydrate composition. The ten barley genotypes included one normal starch (CDC McGwire), three increased amylose starches (SH99250, SH99073, and SB94893), and six waxy starches (CDC Alamo, CDC Fibar, CDC Candle, Waxy Betzes, CDC Rattan, and SB94912). Total starch concentration positively influenced thousand grain weight (TGW) (r(2) = 0.70, p < 0.05). Increase in grain protein concentration was not only related to total starch concentration (r(2) = -0.80, p < 0.01) but also affected enzymatic hydrolysis of pure starch (r(2) = -0.67, p < 0.01). However, an increase in amylopectin unit chain length between DP 12-18 (F-II) was detrimental to starch concentration (r(2) = 0.46, p < 0.01). Amylose concentration influenced granule size distribution with increased amylose genotypes showing highly reduced volume percentage of very small C-granules (<5 μm diameter) and significantly increased (r(2) = 0.83, p < 0.01) medium sized B granules (5-15 μm diameter). Amylose affected smaller (F-I) and larger (F-III) amylopectin chains in opposite ways. Increased amylose concentration positively influenced the F-III (DP 19-36) fraction of longer DP amylopectin chains (DP 19-36) which was associated with resistant starch (RS) in meal and pure starch samples. The rate of starch hydrolysis was high in pure starch samples as compared to meal samples. Enzymatic hydrolysis rate both in meal and pure starch samples followed the order waxy > normal > increased amylose. Rapidly digestible starch (RDS) increased with a decrease in amylose concentration. Atomic force microscopy (AFM) analysis revealed a higher polydispersity index of amylose in CDC McGwire and increased amylose genotypes which could contribute to their reduced enzymatic hydrolysis, compared to waxy starch genotypes. Increased β-glucan and dietary fiber concentration also reduced the enzymatic hydrolysis of meal samples. An average linkage cluster analysis dendrogram revealed that variation in amylose concentration significantly (p < 0.01) influenced resistant starch concentration in meal and pure starch samples. RS is also associated with B-type granules (5-15 μm) and the amylopectin F-III (19-36 DP) fraction. In conclusion, the results suggest that barley genotype SH99250 with less decrease in grain weight in comparison to that of other increased amylose genotypes (SH99073 and SH94893) could be a promising genotype to develop cultivars with increased amylose grain starch without compromising grain weight and yield.

Genotypic diversity in physico-chemical, pasting and gel textural properties of chickpea (Cicer arietinum L.)

Abstract Twenty chickpea cultivars were evaluated for genetic diversity in seeds (physical, hydration and cooking), flours (composition, pasting and gel textural) and starch (swelling, thermal, amylose content and amylopectin structure) properties. Frequency distribution and principal component analysis revealed significant differences among the cultivars studied. Pasting temperature, peak viscosity, breakdown, final viscosity and setback of flours ranged from 75.0 to 87.1 °C, 564 to 853 cP, 32 to 123 cP, 573 to 969 cP, and 84 to 185 cP, respectively. Amylose content of starch ranged from 28.26% to 52.82%. Amylopectin unit chains of DP 6–12, 13–18, 19–24 and 25–30 ranged from 36.2% to 43.25%, 36.44% to 38.68%, 14.86% to 18.22% and 4.95% to 6.9%, respectively. To establish the relationships between different properties Pearson correlation coefficients ( r ) were computed. Cluster analysis for grain and flour characteristics was also done to see the association between chickpea cultivars.

Diversity in amylopectin structure, thermal and pasting properties of starches from wheat varieties/lines

Structural, thermal and pasting diversity of starches from Indian and exotic lines of wheat was studied. Majority of the starches showed amylose content ranging between 22% and 28%. Endotherm temperatures ( T o, T p and T c) of the starches showed a range between 56–57, 60 –61 and 65.5–66.5 °C, respectively. Exotherms with T p between 87.0 and 88.2 °C were observed during cooling of heated starches, indicating the presence of amylose–lipid complexes. Exotherm temperatures were negatively correlated to swelling power. Amylopectin unit chains with different degree of polymerization (DP) were observed to be associated with pasting temperature, setback and thermal (endothermic T o, T p, and T c) parameters. Amylopectin unit chains of DP 13–24 showed positive relationship with endothermic T o, T p and T c. Pasting temperature showed positive correlation with short chains (DP 6–12) while negative correlation with medium chain (DP 13–24) amylopectins. Setback was positively correlated to DP 16–18 and negatively to DSC amylose–lipid parameters.

Granule-Bound Starch Synthase I is Responsible for Biosynthesis of Extra-Long Unit Chains of Amylopectin in Rice

A rice Wx gene encoding a granule-bound starch synthase I (GBSSI) was introduced into the null-mutant waxy (wx) rice, and its effect on endosperm starches was examined. The apparent amylose content was increased from undetectable amounts for the non-transgenic wx cultivars to 21.6-22.2% of starch weight for the transgenic lines. The increase was in part due to a significant amount of extra-long unit chains (ELCs) of amylopectin (7.5-8.4% of amylopectin weight), that were absent in the non-transgenic wx cultivars. Thus, actual amylose content was calculated to be 14.9-16.0% for the transgenic lines. Only slight differences were found in chain-length distribution for the chains other than ELCs, indicating that the major effect of the Wx transgene on amylopectin structure was ELC formation. ELCs isolated from debranched amylopectin exhibited structures distinct from amylose. Structures of amylose from the transgenic lines were slightly different from those of cv. Labelle (Wx(a)) in terms of a higher degree of branching and size distribution. The amylose and ELC content of starches of the transgenic lines resulted in the elevation of pasting temperature, a 50% decrease in peak viscosity, a large decrease in breakdown and an increase in setback. As yet undetermined factors other than the GBSSI activity are thought to be involved in the control of formation and/or the amount of ELCs. Structural analysis of the Wx gene suggested that the presence of a tyrosine residue at position 224 of GBSSI correlates with the formation of large amounts of ELCs in cultivars carrying Wx(a).

アミロペクチン単位鎖長分布による水稲糯品種の餅硬化性評価

Waxy rice is used for staple and processed foods, and for its effective breeding an evaluation/selection index has been required. Here, the chain-length distribution of amylopectin from japonica waxy rice varieties with different hardness of rice cake were analyzed by the fluorescent labeling/HPSEC method, and the relation of the unit chain-length distribution to the hardness was examined. The difference among varietals was found in the amylopectin structure. Waxy rice producing soft cake, such as Hakuchoumochi, has more short chains (A+B1), and fewer long chains (B2+B3), than that producing hard cake, such as Koganemochi. The molar ratio of short chains (A+B1)/long chains (B2+B3), which is considered to be the number of chains comprising a cluster of amylopectin, was 10.1-11.7, being different among the varieties tested. The molar ratio determined by fluorescent response was much more reliable than the weight ratio determined by IR response because of the stable base line during HPLC. A negative correlation was found between the molar ratio and the hardening of rice cake. Therefore, the molar ratio (A+B1)/(B2+B3) of amylopectin unit-chains seemed to be one of useful evaluation/selection indexes for breeding of waxy rice. An index, or molar ratio, lower than 11 appeared to be suitable for processing use, and one higher than 11.5 for principal food use.

登熟温度が米のアミロペクチン単位鎖長分布と超長鎖（ＬＣ）含量に及ぼす影響

アミロペクチン単位鎖長分布と超長鎖(LC)含量に及ぼす登熟温度の影響をHanashiroらの蛍光標識ゲル濾過HPLC法で調べた．北海道米の主要品種である「きらら397」のアミロペクチンLC含量は，低温(21/17°C)2.58%，中温(25/21°C)1.30%，高温(29/25°C)0.48%で登熟温度が低いほど多かった(Table 1)．アミロペクチン単位鎖の短鎖(A+B1)と長鎖(B2+B3)の重量比およびモル比(A+B1)/(B2+B3)は登熟温度が低いほど大きかった(Table 2)．これらの結果は，近年育成された北海道米5品種と4系統およびミルキークイーンを供試して確証された．登熟温度は22/16，26/20，30/24，34/28°C(昼/夜)で行った．アミロペクチンLC含量の平均登熟温度1°C当たりの変動量は，19-23°Cの範囲では0.542%，23-27°Cでは0.152%，27-31°Cでは0.037%で，低温ほど大きかった(Fig. 4)．見かけのアミロース含有率は登熟温度と負の相関があることが知られているが，アミロペクチンLC含量も同様に低温で増加することが明らかとなった．低アミロース品種はうるち品種に比べて見かけのアミロース含量に占めるアミロペクチンLC含量の割合が高かった(Fig. 6)．見かけのアミロース含量とアミロペクチンLC含量は品種よりも登熟温度の影響が大きかった(Table 4)．以上のことから，今後の良食味米の選抜において，アミロペクチンLC含量が低く，異なる登熟温度条件でも澱粉の構造が安定している品種の育成が目標である．これはアミロペクチンLCの生合成に関与する酵素の遺伝子分析によって達成できるかもしれない．

Structural, thermal and viscoelastic properties of potato starches

The starches separated from different Indian potato cultivars (Kufri Sindhuri, Kufri Jyoti, Kufri Pukhraj, Kufri Chipsona-1, Kufri Chipsona-2, Kufri Bahar and Kufri Chandermukhi) were evaluated for granule size, amylopectin structure, thermal and pasting properties. The changes in viscoelastic properties of cooked starch pastes during cooling and heating were also evaluated using a dynamic rheometer. Unit chains of amylopectin between DP 6 and 30 were analyzed by fluorophore-assisted capillary electrophoresis. Pearson correlation coefficients between different properties were also determined. Starches from all the cultivars showed peak DP 12–13. DP 6–7 content varied significantly among the starches studied; K. Chandermukhi showed the highest and K. Pukhraj showed the lowest. K. Chandermukhi starch showed significantly lower DP 14–30 content than starches from other potato cultivars. DP 14–30 content was in the order of K. Chipsona-1>K. Jyoti>K. Sindhuri>K. Pukhraj>K. Bahar>K. Chipsona-2>K. Chandermukhi. DP 6 was significantly and negatively correlated to peak gelatinization temperature ( T p) and conclusion temperature ( T c) ( r=−0.780 and −0.824, respectively, p⩽0.05). Pasting temperature, hot-paste viscosity and cold-paste viscosity showed significantly negative correlation with DP 6 ( r=−0.780, −0.824 and −0.808, respectively, p⩽0.05). However, pasting temperature, hot-paste viscosity and cold-paste viscosity showed positive correlation with DP 15–17. K. Pukhraj with the lowest amount of short-side-chain amylopectin fraction showed the highest moduli. K. Pukhraj starch with G′ much greater than G″ indicates its predominantly more elastic than viscous character. Chipsona-2 and K. Chandermukhi starches with a higher amount of short-chain amylopectin fractions (DP 6–12) showed a greater change in moduli during cooling of cooked paste and had more viscous character than other starches with lower amounts of these fractions.

Starches from different botanical sources II: Contribution of starch structure to swelling and pasting properties

Swelling and pasting properties of 15 starches from different plant origins were studied to elucidate their relationship with structural features using simple and multiple regression analyses. Avoidance of additional effects of starch minor components showed that swelling power and pasting parameters were associated with the ratio of the relative molar distribution of amylopectin branch-chains with a degree of polymerization (DP) of 6–12 to that of chains with DP 6–24 (amylopectin unit-chain (APC) ratio). Swelling power of starch granules increased with APC ratio. Multiple regression analysis revealed that the peak viscosity (PkV) of starch paste increased with low APC ratio, low amylose content (AC) and large average granule size (AGS). At a high starch concentration, pasting temperature (PT) was reduced by a high APC ratio and large AGS. Peak time (PkT) decreased with increasing APC ratio and AC. Percentage of breakdown viscosity (BD%) and setback viscosity (SB) were primarily affected by APC ratio. At a low concentration, AC and AGS had more profound effects on BD%. SB was also reduced by higher AC. Models of pasting profile, which is influenced by individual factors, were also proposed.

Structure function relationships of transgenic starches with engineered phosphate substitution and starch branching

Potato tuber starch was genetically engineered in the plant by the simultaneous antisense suppression of the starch branching enzyme (SBE) I and II isoforms. Starch prepared from 12 independent lines and three control lines were characterised with respect to structural and physical properties. The lengths of the amylopectin unit chains, the concentrations of amylose and monoesterified phosphate were significantly increased in the transgenically engineered starches. Size exclusion chromatography with refractive index detection (SEC-RI) indicated a minor decrease in apparent molecular size of the amylose and the less branched amylopectin fractions. Differential scanning calorimetry (DSC) revealed significantly higher peak temperatures for gelatinisation and retrogradation of the genetically engineered starches whereas the enthalpies of gelatinisation were lower. Aqueous gels prepared from the transgenic starches showed increased gel elasticity and viscosity. Principle component analysis (PCA) of the data set discriminated the control lines from the transgenic lines and revealed a high correlation between phosphate concentration and amylopectin unit chain length. The PCA also indicated that the rheological characteristics were primarily influenced by the amylose concentration. The phosphate and the amylopectin unit chain lengths had influenced primarily the pasting and rheological properties of the starch gels.

Starches from different botanical sources I: Contribution of amylopectin fine structure to thermal properties and enzyme digestibility

Fifteen starches from different botanical sources were selected to study the influence of structural features on thermal properties and enzyme digestibility. Morphological appearance, X-ray diffraction pattern, apparent amylose content, unit-chain length distribution of amylopectin, thermal properties and enzyme digestibility of starch varied with botanical source. It was demonstrated that the distribution of unit-chains of amylopectin significantly correlated with functional properties of the starches. Gelatinization temperature of native and retrograded starches decreased and increased with a relative abundance of unit-chains with an approximate degree of polymerization (DP) of 8–12 and 16–26, respectively ( P<0.01). Similar unit-chain lengths also affected the enzyme digestibility of starch granules ( P<0.01).

Structural Characterization of Long Unit-Chains of Amylopectin

Long chains (LC) were fractionated by 1-butanol precipitation from isoamylase-debranched amylopectins of rice, maize, wheat, buckwheat, and sweet potato. The structure of the precipitate (LCppt) was characterized by high-performance size-exclusion chromatography (HPSEC) with pre-column labeling with 2-aminopyridine. HPSEC showed that LCppt corresponded to the LC fraction of unit-chain distribution of amylopectin. LCppt had a number-average degree of polymerization of 330-490 and an average-number of chains of 1.2-1.4, indicating that the structure of LCppt is very similar irrespective of its botanical sources and is distinct from amylose. HPSEC revealed that size distribution of LCppt was also similar among the specimens examined. The distribution was distinct from and much narrower than that of amylose. Still, LCppt consisted of a significant amount (by weight) of chains as long as amylose. LCppt contained 5.1-9.4 mol% of branched molecules, which had ∼5 chains per molecule (except for 10 of indica rice IR36), indicating incomplete debranching of the side chains on LC by isoamylase. The structure of the isoamylase-resistant branches is unknown. In this respect, LCppt and amylose appear to have a common branched structure, which is unusual in starch α-glucans.

Characterization of potato leaf starch.

The starch accumulation-degradation process as well as the structure of leaf starch are not completely understood. To study this, starch was isolated from potato leaves collected in the early morning and late afternoon in July and August, representing different starch accumulation rates. The starch content of potato leaves varied between 2.9 and 12.9% (dry matter basis) over the night and day in the middle of July and between 0.6 and 1.5% in August. Scanning electron microscopy analyses of the four isolated starch samples showed that the granules had either an oval or a round shape and did not exceed 5 microm in size. Starch was extracted by successive washing steps with dimethyl sulfoxide and precipitated with ethanol. An elution profile on Sepharose CL-6B of debranched starch showed the presence of a material with a chain length distribution between that generally found for amylose and amylopectin. Amylopectin unit chains of low molecular size were present in a higher amount in the afternoon than in the morning samples. What remains at the end of the night is depleted in specific chain lengths, mainly between DP 15 and 24 and above DP 35, relative to the end of the day.

Effect of Cultivation Conditions on Retrogradation of Sweetpotato Starch

AbstractSweetpotatoes were grown under four cultivation conditions, i. e. early planting and early harvesting (I, E‐E), standard (II, STD), early planting and late harvesting (III, E‐L), and late planting and late harvesting (IV, L‐L). Retrogradation of the starch isolated from fresh roots was estimated by the hardness and syneresis rate after two weeks of storage at 5 °C. A significant difference in retrogradation among the cultivation conditions and cultivars was observed. The starch tended to exhibit slower retrogradation in late harvesting, where the temperature was low. The differences in amylose content and the proportion of short unit‐chains (DP 9‐11) of amylopectin among cultivation conditions were also significant. Starch retrogradation was positively correlated with the proportion of chains with DP 12‐14 but negatively correlated with the proportion of DP 9‐11. Moreover, there was no significant correlation between amylose content and retrogradation. These results indicate that the main factor for retrogradation under any cultivation condition is the proportion of short unit‐chains of amylopectin. The best performance of sweetpotato starch as a food ingredient would be achieved by selecting both the proper cultivar and cultivation conditions.