Amylopectin structure of heat–moisture treated starches

The effects of heat–moisture treatment (HMT; moisture content of 25%, at 100°C for 24 h) on starch chain distribution and unit chain distribution of amylopectin in normal rice, waxy rice, normal corn, waxy corn, normal potato, and waxy potato starches were investigated. After HMT, starch chain distribution (amylose and amylopectin responses) of waxy corn and potato starches were identical to those of untreated starches, whereas the chromatographic response of waxy rice starch showed a slight decrease, but with a slight increase in peak tailing. This result indicated that HMT had no (or very limited) effect on the degradation of amylopectins. Analysis of unit chain distribution of amylopectins revealed that waxy characteristics affected the molecular structure of amylopectin in untreated starches, i.e., the CL of normal‐type starches was greater than that of waxy‐type starches. After HMT, the CL and unit chain distribution of all starches were no different than those of untreated starches. The results implied that changes in the physico‐chemical properties of HMT starches would be due to other phenomena rather than the degradation of amylopectin molecular structure. However, the thermal degradation of amylopectin molecules of waxy starches could occur by HMT at higher treatment temperatures (120 and 140°C).     

Gel and Molecular Properties of Waxy Rice Starch

The differences in the physicochemical properties of starch (amylopectin) from waxy rices from the Philippines, Japan, and Thailand differing in processed rice quality were investigated. Samples of waxy rice starch showed final birefringence end-point temperature (BEPT) between 58 and 78°C. None of the samples showed BEPT values between 70 and 72°C. The gel viscosity values (measured with a Wells-Brookfield viscometer) of samples with BEPT values above 70°C were higher than those of samples with BEPT values below 70°C. Sedimentation coefficient and intrinsic viscosity were positively correlated and showed a U-shaped relationship with BEPT with minima at a BEPT of about 68°C. Differences in viscosity properties were mainly due to differences in the molecular weight of amylopectin, since the samples studied had similar mean chain lengths. BEPT was a useful index of amylopectin molecular weight in the waxy rice starch samples studied.     

SENSORY AND INSTRUMENTAL EVALUATION OF TEXTURE OF COOKED AND RAW MILLED RICES WITH SIMILAR STARCH PROPERTIES

Three pairs of milled rices with similar starch properties (low gelatinization temperature waxy, and low gelatinization temperature low amylose, and intermediate gelatinization temperature intermediate amylose) were assessed for cooked rice properties by two industry taste panels and for raw and cooked rice properties by 30-member Filipino consumer panels. Only slight differences in texture within pairs were noted by the two industry taste panels who had not been trained to assess boiled raw rice or waxy rice. The Filipino consumer panel gave significantly higher ranked scores for one low-amylose variety in both raw and cooked forms. Malagkit Sungsong suman sa antala was ranked higher than modern waxy rices. Instrumental methods for translucency and whiteness of raw rice and Instron hardness and stickiness of cooked rice were not able to detect differences perceived by the Filipino consumer panels.     

稻米淀粉及其级分的凝胶色谱分析

对糯稻、粳稻和籼稻的天然淀粉及其支链淀粉、直链淀粉进行凝胶色谱分析，以确定不同来源淀粉的组成、淀粉级分的特性。结果表明，籼稻淀粉和粳稻淀粉主要由支链淀粉、中间级分和直链淀粉组成，糯稻淀粉主要由支链淀粉和中间级分组成。采用正丁醇反复结晶法分离得到的直链淀粉和支链淀粉有较高的纯度。支链淀粉的分子量分布比直链淀粉的宽，粳米直链淀粉的分子量分布比籼米的宽，三种稻米支链淀粉的分子量分布差异不大。     

The Effect of Environmental Temperature on Distribution of Unit Chains of Rice Amylopectin

The effects of environmental temperature during the early development of seeds on the structural characteristics of the endosperm starch were investigated using near‐isogenic lines of rice plants (Taichung 65, waxy), grown under temperature controlled conditions. High performance gel permeation chromatography (HPLC) demonstrated that Pseudomonas isoamylase‐debranched amylopectins of rice plants grown at lower temperature (25°C) contain increased amounts of short chains and decreased amounts of long chains as compared with amylopectins obtained from rice plants grown at higher temperature (30°C). By high performance anion exchange chromatography with pulsed amperometric detection (HPAEC‐PAD) of isoamylase‐debranched amylopectins it was detected that the amount of unit chains with degree of polymerization (DP) 6 and 11‐13, in the amylopectin of rice plants grown at lower temperature (25°C) had significantly increased and the amount of unit chains with DP 8, 22‐24 and 29 had significantly decreased, as compared with the amylopectin of rice plants grown at higher temperature (30°C). It was confirmed that the environmental temperature between 5 and 10 d after pollination strongly influenced the structure characteristics of the endosperm starch of rice plants.     

Starch Biosynthesis. II. The Statistical Model for Amylopectin and Its Precursor Plant Glycogen

A modified Meyer model as well as a model containing all possible randomly branched structures (a statistical model) were used for both a precursor glycogen and its amylopectin and were modified by placing short A-chains into the interior part of the structure and thus eliminating some of the longer chains. Debranching of the exterior A-chains of the glycogen model produced amylopectin plus 25% amylose with the assumption that only those A-chains removed from the glycogen were converted into amylose. A comparison of the debranched amylopectin model with debranched wheat and barley amylopectins showed the polymodal behavior of debranched amylopectins can be duplicated with a model system that has inner A-chains and a Poisson size distribution. Branching of external chains of glycogen without chain extension after synthesis has stopped plus inner A-chains can explain the increase (from glycogen to amylopectin) in the A/B chain ratio, the existance of cluster structures, and the observed decrease in branching (8% to 4%) in going from dent, waxy and sweet corn glycogens to their respective amylopectins (or 6.3% to 2.0% for glycogen to amylopectin in ae corn). Disperseable (as in waxy) or indispersable high molecular weight aggregates may be due to different amylopectin-protein complexes.     

Amylopectin: Structural, gelatinisation and retrogradation studies

Amaranth, waxy corn, and commercial corn amylopectins were enzymically debranched and their fractions separated by gel filtration. In all cases a bimodal distribution of chain lengths was found, containing a high proportion of short chains. Amaranth, waxy corn starches and commercial corn amylopectin displayed an A-type X-ray diffraction pattern, which is characteristic of cereal starches, whereas amaranth amylopectin did not show a well-defined pattern, suggesting that the former samples have granular structure. Gelatinisation and retrogradation data, by differential scanning calorimetry, showed a good agreement between starches and amylopectins of the same source. Amaranth starch and its amylopectin presented a lower tendency to undergo these changes compared to the remaining tested materials. The temperature effiect on retrogradation was more drastic for amaranth and waxy corn amylopectins.     

Eating quality indicators for waxy rices

A study of the properties of raw and cooked waxy milled rices from the Republic of Korea, the Philippines and Thailand verified that the hardness and stickiness values of cooked rices, as measured by an Instron food tester, tended to be related to final gelatinisation or birefringence end-point temperature (BEPT), neutral gel consistency or both properties of raw rices. Actual texture determination of cooked rice is required among the low final BEPT rices that have similar gel consistency and alkali test values. Intermediate final BEPT waxy rices as cooked rice had hardness and stickiness properties similar to those of high final BEPT rices.     

Starch and Amylopectin — Rheological Behavior of Gels

Rheological behavior of starch and amylopectin gels was evaluated by small amplitude oscillatory testing using the storage modulus (G′), loss modulus (G″) and the complex viscosity (n*). It was found for the three starches (normal and waxy corns, and amaranth) that at low frequency the viscous component G″ had a major contribution on the gel structure than the elastic G′ and that the complex viscosity (n*) diminished when the frequency was increased. Amaranth amylopectin showed G″ values higher than those of G′. Corn commercial and waxy corn amylopectins presented a similar behavior in the G′ values. Normal corn amylopectin gave the highest complex viscosity values.     

Effect of pH on aqueous structure of maize starches analyzed by HPSEC-MALLS-RI system

Molecular conformation of maize starches (waxy, normal and high amylose) was examined at different pH values (5–10) using an aqueous medium-pressured size exclusion column chromatography (SEC) connected to multi-angle laser light scattering (MALLS) and refractive index (RI) detectors. The starch molecules were partially degraded at pH 5 and 10, resulting in lower values for molar size and radius of gyration than those in neutral condition. The specific volume data revealed that the structural changes under an alkaline condition such as pH 10 was more significant for amylose than that for amylopectin. Logarithmic ratios between molar size and radius of gyration were similar (0.2–0.3) for the amylopectins in waxy and normal maize starches, but higher (0.4–0.5) for the amylopectin in high amylose starch, indicating that the amylopectins in waxy or normal maize starches had sphere forms whereas that in high amylose starch had a random coil shape.     

CONSUMER PREFERENCE AND PROPERTIES OF RAW AND COOKED MILLED RICE

Consumer preference tests for raw and cooked rices were run on representative consumers 16 years and older in a selected Philippine village. For four sets of samples, major criteria for selecting raw milled rice were grain whiteness and hardness, and aroma and flavor for boiled rice. Actual preference ranks suggested partiality to white raw rice and low-amylose, intermediate-amylose and high-amylose boiled rice in order of decreasing preference. Soft texture due to low amylose content probably contributed to better flavor of boiled rice.
Selection criteria for one set of waxy rices were aroma and whole, big grains for raw rice, and aroma and cohesiveness for rice cake suman sa antala . Properties disliked in suman were flakiness, and coarse, hard, and soft textures. Among five low-gelatinization temperature, waxy milled rices, the traditional, aromatic, coarse-grained Malagkit Sungsong was preferred over newer rices with less aroma and with longer grains in both raw and suman forms.     

The Fine Structure of Corn Starches of Various Amylose-Percentage: Waxy,Normal and Amylomaize

The fine structure of high-amylose corn starches has been studied after dispersion of the starch and fractionation into their components amylose and amylopectin. The resulting amylopectin fraction reported in the literature possesses anomalous properties with regard to the waxy and normal amylopectin. However, the experimental results obtained by different authors for determining the structure lead to controversal explanations. Therefore, using an enzymic method, which permits the direct examination of the constitutive chains of the starch, the fine structure of the amylopectin of an amylomaize starch (64% amylose) has been investigated and compared with those of waxy and normal starches. The pullulanase – debranched chains are fractionated by gel permeation and their linearity are checked under the action of β-amylase. The inner chains of the amylopectin fraction are studied after debranching of the β-limit dextrins. The results show the identity between amylopectins from waxy and normal starches. The amylopectin fraction of amylomaize has its own structure with longer inner chains than those of waxy-maize amylopectin.     

TEXTURE CHANGES AND STORAGE OF RICE

Monthly texture assessments of seven milled rices, differing in amylose content and stored at 28–30°C, verified that three months was the minimum storage period for major changes to occur in hardness of cooked rice, gel consistency, and amylograph viscosity values. Therefore, texture measurements should be done on samples aged at least three months after harvest. Texture changes tend to be greatest for high-amylose rice with hard gel consistency and least for waxy rice. Free fatty acids were highest in stored, waxy, milled rice. Storage under nitrogen instead of air had a slight retarding effect on storage changes of five rices in another study. Surface defatting with petroleum ether had little effect on storage change in cooked rice hardness and stickiness, but reduced the changes in gel consistency and amylograph setback and consistency.     

Characteristics of Gel-chromatographic Fractions of Starch in Relation to Rice and Expanded Rice-Product Qualities

Starch from waxy and nonwaxy rices was separated on Sepharose. In nonwaxy rice, the major (void volume) fraction stained a varying shade of blue with iodine depending on the sample. The water-insoluble amyolose content as estimated in milled rice flour was highly positively correlated with the λ_max of the iodine colour as well as with the „amylose”︁ content of the fraction. Debranching with pullulanase showed that the fraction had the dual character of being both amylopectin and amylose. A second fraction was for the most part true amylose. The volume of expanded rice product seemed to increase with average molecular weight of starch. The highest average molecular weight of starch corresponded to analytical values of water-insoluble amylose as estimated in rice flour and the same corresponded to the greatest expansion volume.     

Structural Aspects of Native and Acid or Enzyme Degraded Amylopectins - a 13C NMR Study

¹³C NMR signal assignments were achieved for amylopectin (from waxy maize starch) dissolved in dimethylsulfoxide mainly by comparison with the corresponding amylose spectrum and chemical shift arguments. From these data a branching degree of amylose and amylopectin of 1.4±0.5% and 6.0±0.7% could be estimated. Investigation of acid and enzyme degraded amylopectins by means of this method revealed that cleavage by these methods proceeded in an analogous manner. Thus, viewed from the standpoint of structural aspects they yielded virtually identical products.     

Chain Length Distribution of Amylopectins of Double- and Triple-Mutants Containing the Waxy Gene in the Inbred Oh43 Maize Background

Starch granules were isolated from mature kernels of double- and triple-mutant combinations of the waxy (wx) gene with other starchmodifying genes in the inbred Oh43 maize background. The amylose content and the distribution of unit chain-length of amylopectin were determined by enzymatic-chromatographic methods. Starches of the mutants containing the wx gene comprised 100% amylopectin. Amylopectin of the amylose-extender;waxy (ae wx) mutant had an increased proportion of long B chains and decreased proportion of short B chains, compared with wx amylopectin, whereas amylopectin of the dull;waxy (du wx) mutant had a decreased proportion of long B chains and an increased proportion of short B chains. Therefore, the ae wx and du wx mutants amylopectins were novel. The A:B chain ratios for amylopectins examined, namely for ae wx, amylose-extender;waxy;floury-2 (ae wx fl₂), amylose-extender;waxy;sugary-1 (ae wx su₁), amylose-extender;waxy;sugary-2 (ae wx su₂), brittle-1;waxy (bt₁wx). dull;waxy (du wx), and sugary-2;waxy (su₂wx) amylopectins, were in a range of 1.1 to 1.4 and similar to the wx amylopectin. Thus, starches of double-mutant combinations of the wx gene with other starch-modifying genes are good sources for elucidating the fine structure of amylopectin, in regards to long- and short-B chains, which is affected by a single recessive gene coupled with the wx gene.     

Physicochemical characteristics of waxy rice starch influencing the in vitro digestibility of a starch gel

Starches were isolated from three waxy rice varieties: Koganemochi (Kog), Hakuchomochi (Hak), and Kantomochi 172 (K172). Forty percent starch gels were prepared and the extent of starch gel digestibility was determined by an in vitro method. The distribution of chain lengths of amylopectin was analyzed and differential scanning calorimetry was used to analyze gelatinization and retrogradation of waxy rice starch. The K172 gel had significantly higher resistance to hydrolysis than had the other gels. The K172 starch contained lower proportions of the short chains of amylopectin and showed higher gelatinization temperature and enthalpy. The retrogradation peak was measured using waxy rice starch gels stored for 1 and 7 days at 5 °C. The K172 gel was observed to retrograde more quickly and to have a greater extent of retrogradation than the other gels. The difference in amylopectin chain length distribution and recrystallinity contributed to the variation in the starch gel digestibility of waxy rice.     

Starch and Amylopectin - Effects of Solutes on Clarity of Pastes

The effect of sucrose, glucose and sodium chloride at different concentrations on clarity of starch and amylopectin pastes was studied. It was found that clarity of amaranth, waxy corn and normal corn starch pastes tended to increase by increasing carbohydrate concentrations. The percentage of transmittance (%T) values for the same starch sample with sucrose and glucose did not present significantly differences (α=0.05). The starches with sodium chloride did not show a defined pattern. The %T for amaranth and waxy corn amylopectin pastes with all solutes tended to increase by increasing solute concentration. Interestingly, the %T values among all amylopectins at a given solute concentration were significantly different (α=0.05) probably due to different chain length proportion in such amylopectins. The same amylopectin in presence of sucrose and glucose did not show %T significantly different (α=0.05) but with sodium chloride those values were different (α=0.05).     

Molecular Structure of Starches from Cassava Varieties having Different Cooked Root Textures

Starches from 12 cassava varieties with different cooked root texture; i.e. mealy, firm and mealy and firm, were investigated with a particular focus on aspects of molecular structures of amylose and amylopectin. Structural elements of amylopectin were essentially constant in terms of unit chain distributions and chain lengths. All cassava amylopectins displayed two distinct chain length peaks, at DP 40–46 and at DP 11–13, with a shoulder at DP 17–19, and average chain length (CL) of amylopectins was 17–20. A fraction of extra‐long chains in the range of 0.24–1.78% was found. Amylose and amylopectin from four varieties with different textures of cooked root were isolated. Data from C‐chain distributions indicated that the molecular size of amylopectin from M‐hanatee (Hanatee), a locally adapted cassava variety, was 2.5–2.9 times smaller than those of the other varieties. Three of the four amylose samples, except that from M‐hanatee, were very similar in average DP (4120–4390), chain length (530–550) and number of chains (7.1–7.5), and composed of nearly equal numbers of linear and branched molecules. The amylose from the M‐hanatee variety showed a unique characteristic: it had smaller size (2050), shorter chain length (450), fewer chains (4.7) and a higher content of linear fraction (58%), when compared with other amyloses.     

Stufenweise Elutionsanalyse der Fraktionen von thermisch dispergierter Amylose-, Kartoffel- und Wachsmaisstärke

Stepwise Elution Analysis of Fractions of Thermically Dispersed High Amylose, Potato and Waxy Corn Starch. Changes in the starch constituents - the amylose and the amylopectin — from dispersions of high amylose, potato- and waxy corn starch were studied by stepwise elution analysis and determination of molecular weight. The dispersions were prepared by dispersing the pastes 1 and 3 h at 120 °C and the amyloses and amylopectins separated by means of n-butanol and methanol, resp. With the exeption of a partial separation in waxy corn starch no separation of pastes into amylose and amylopectin could be observed, probably due to the mild pasting conditions in the Brabender Viscograph. By stepwise elution analysis it could be stated that after prolonged thermic dispersing of the pastes of high amylose starch the amylose and amylopectin do no longer change, which is in good agreement with the values of molecular weight. By analogous treatment of the pastes of potato starch, however, a decomposition of amylose and amylopectin could be stated. In the dispersions of waxy corn starch the amylose molecules decompose to a degree whereafter thermic dispersing of 3 h practically no complex with n-butanol could be observed. Relatively great losses were stated at the isolation of the precipitated constituents. It was stated that the isolated amyloses of potato starch are suitable substrates for activity measurements of α-amylase in human serum and urine as well as in other biologic materials.