Origins of B-type crystallinity in glycerol-plasticised, compression-moulded potato starches

The amount of B-type crystallinity in compression-moulded, glycerol-plasticised potato starches was strongly dependent on both the properties of the potato starch used and the applied processing conditions. The presence of amylose and the morphology of the potato starch used, but also processing parameters such as moulding temperature and water content during moulding affected the amount of B-type crystallinity in the materials and thus the ultimate mechanical properties of the plasticised starches. This indicated that the direct relation between composition and physical properties of processed starches is not always valid; processing parameters are important tools for controlling the physical properties of processed starches as they influence the amount of B-type crystallinity in the material. It was shown that the total amount of B-type crystallinity in the glycerol-plasticised potato starches should be considered as a summation of residual amylopectin crystallinity and recrystallisation of both amylose and amylopectin, being strongly dependent on the applied processing conditions. In order to explain the observed amount of B-type crystallinity in these starches, partial (co-)crystallisation of both amylose and amylopectin should occur at high moulding temperatures. The measured mechanical properties of the plasticised potato starches correlated well with the amount of B-type crystallinity observed in the materials.     

粉末X射线衍射图谱计算植物淀粉结晶度方法的探讨

植物淀粉有A-型、B-型和C-型3种晶体。以水稻(Oryza sativa)、马铃薯(Solanum tuberosum)、豌豆(Pisum sativum) 和莲藕(Nelumbo nucifera)淀粉为材料, 利用粉末X-射线衍射仪(XRD)调查了不同晶体类型淀粉的波谱特征, 探讨XRD波谱相对结晶度的计算方法。软件峰拟合法、软件曲线法、直线作图法和曲线作图法均可用于计算淀粉XRD波谱的相对结晶度, 以曲线作图法计算结果较为可靠。利用曲线作图法得出的结果表明, 稻米淀粉的结晶度与直链淀粉含量呈显著线性负相关, 酸解莲藕淀粉的结晶度与淀粉酸水解度呈显著线性正相关。酸水解使莲藕淀粉的C-型晶体转变为A-型晶体。上述研究结果为利用XRD分析植物淀粉晶体类型和计算相对结晶度提供了重要参考。     

Effect of heat–moisture treatment on the structure and physicochemical properties of tuber and root starches

Starch from tubers potato (Solanum tuberosum), taro (Alocassia indica), new cocoyam (Xanthosoma sagitifolium), true yam (Dioscorea alata), and root cassava, (Manihot esculenta) crops was isolated and its morphology, composition and physicochemical properties were investigated before and after heat–moisture treatment (HMT) (100 °C, for 10 h at a moisture content of 30%). Native starch granules were round to oval to polygonal with smooth surfaces. The granule size (diameter) ranged from 3.0 to 110 μm.The total amylose content ranged from 22.4 to 29.3%, of which 10.1–15.5% was complexed by native lipid. The phosphorus content ranged from 0.01 to 0.1%. The X-ray pattern of potato and true yam was of the ‘B’-type. Whereas, that of new cocoyam and taro was of the ‘A’-type. Cassava exhibited a mixed ‘A+B’-type X-ray pattern. The relative crystallinity, swelling factor (SF), amylose leaching (AML), gelatinization temperature range and the enthalpy of gelatinization of the native starches ranged from 30 to 46, 22 to 54, 5 to 23%, 13 to 19 °C and 12 to 18 J/g, respectively. Susceptibility of native starches towards hydrolysis by 2.2N HCl and porcine pancreatic -amylase were 60–86% (after 12 days), and 4–62% (after 72 h), respectively. Retrogradation was most pronounced in the B-type starches. Granule morphology remained unchanged after HMT. The X-ray pattern of the B-type starches was altered (B→A+B) on HMT. However, that of the other starches remained unchanged. HMT decreased SF, AML, gelatinization enthalpy and susceptibility towards acid hydrolysis, but increased gelatinization temperatures and enzyme susceptibility. Extent of retrogradation and relative crystallinity decreased on HMT of true yam and potato starches, but remained unchanged in the other starches. The foregoing data showed that changes in physicochemical properties on HMT are influenced by the interplay of crystallite disruption, starch chain associations and disruption of double helices in the amorphous regions.     

Crystallinity and morphology in films of starch, amylose and amylopectin blends

Films of potato starch, amylose, and amylopectin and blends thereof were prepared by solution casting and examined using X-ray diffraction, light microscopy, transmission electron microscopy, and differential scanning calorimetry. Amylose films had a relative crystallinity of about 30% whereas amylopectin films were entirely amorphous. Blending of amylose and amylopectin resulted in films with a considerably higher degree of crystallinity than could be predicted. This is explained by cocrystallization between amylose and amylopectin and possibly by crystallization of amylopectin. The crystallized material gave rise to an endotherm detected with differential scanning calorimetry. The enthalpy and peak temperature of the transition also increased as the water content decreased. When the amylose proportion in the blends was low, separate phases of amylose and amylopectin were observed by light microscopy. At higher amylose proportions, however, the phase separation was apparently prevented by amylose gelation and the formation of a continuous amylose network. The amylose network in the films, observed with transmission electron microscopy, consisted of stiff strands and open pores and became less visible as the amylose proportion decreased. The water content of the films was dependent on the microstructure and the crystallinity.     

In vitro digestibility of edible films from various starch sources

Banana, maize, potato and sagu starches were boiled in the presence or absence of plasticizer (glycerol), producing edible films. In vitro digestibility features, amylose content and amylopectin gel filtration behavior of films and parent starches were evaluated. Available starch contents were lower in glycerol-containing films, due to dilution by the plasticizer. Total resistant starch increased in the maize starch-based film but decreased markedly in those prepared from the other starches. Amylose content of banana starch (40%) was about double those of the other starches. Nonetheless, all starch films exhibited similar retrograded resistant starch content. Although film production led to increased -amylolysis rates, these were further augmented by additional film heating, thereby indicating that film-manufacture did not promote complete starch gelatinization. Gel filtration chromatography suggested amylopectin depolymerization after film-making, which may also increase digestion kinetics. The presence of glycerol in the films slowed down starch digestion, a feature of potential dietetic use.     

Fabrication and Characterization of Native and Oxidized Potato Starch Biodegradable Films

The need to replace conventional polymers due to environmental pollution caused by them has led to increased production of biodegradable polymers such as starch. Thus, the application possibilities of starch have increased. In this study, we produced and characterized biodegradable films derived from native and oxidized potato starch. The film-forming solution was prepared with different concentrations of extracted starch (native or oxidized) and a plasticizer (glycerol or sorbitol). Then, the mechanical, barrier, morphological, and structural properties of the films were characterized. The moisture content of the films varied from 15.35?±?1.31 to 21.78?±?0.49%. The elastic modulus of the films ranged from 219?±?14.97 to 2299?±?62.91 MPa. The film of oxidized starch plasticized with sorbitol in the lowest content was the most resistant and flexible; moreover, this film also presented lower water vapor permeability and low solubility in water. Fourier-transform infrared spectroscopic analysis of the biodegradable films indicated the presence of same functional groups as those of starch with bands in the same regions. The film thickness was lower for the films plasticized with glycerol whereas the color variation (Δ?) was lower for the ones plasticized with sorbitol. In case of both plasticizers, the increase in their content decreased the Δ? value. All the biodegradable films presented stability against water absorption owing to their low solubility in water. Morphological evaluation revealed the presence of partially gelatinized starch granules in the films. The roughness parameter (Rq) of the films varied from 3.39 to 10.9 nm, indicating that their surfaces are smooth. X-ray diffraction studies showed a B-type pattern for the starches, which is representative of tubers. Further, the films present higher relative crystallinity (RC) compared to the starches. The biodegradable starch films are uniform, transparent and with low solubility in water. The oxidation of starch and use of sorbitol as a plasticizer resulted in improved properties of the starch films, which is suitable for application.     

Influence of amylose content on starch films and foams

After extraction of smooth pea starch and waxy maize starch from pure amylose and amylopectin fractions, films with various amylose contents were prepared by casting in the presence of water or water with glycerol. For unplasticized films, a continuous increase in tensile strength (40–70 MPa) and elongation (4–6%) was observed as amylose increased from 0 to 100%. Discrepancies with values obtained for native starches with variable amylose content and different botanical origins were attributable to variations in the molecular weights of components. Taking cell wall properties into account, the values obtained in the laboratory were used to improve the relation between the flexural behavior of extruded foams and the model of cellular solids with open cavities.

The properties of plasticized films were not improved by the presence of glycerol and remained constant when amylose content was higher than 40%. Results are interpreted on the basis of topological differences between amylose and amylopectin.     

Structural and thermodynamic properties of starches extracted from GBSS and GWD suppressed potato lines

A combined DSC–SAXS approach was employed to study the effects of amylose and phosphate esters on the assembly structures of amylopectin in B-type polymorphic potato tuber starches. Amylose and phosphate levels in the starches were specifically engineered by antisense suppression of the granule bound starch synthase (GBSS) and the glucan water dikinase (GWD), respectively. Joint analysis of the SAXS and DSC data for the engineered starches revealed that the sizes of amylopectin clusters, thickness of crystalline lamellae and the polymorphous structure type remained unchanged. However, differences were found in the structural organization of amylopectin clusters reflected in localization of amylose within these supramolecular structures. Additionally, data for annealed starches shows that investigated potato starches possess different types of amylopectin defects. The relationship between structure of investigated potato starches and their thermodynamic properties was recognized.     

Preparation and characterization of new and improved soluble-starches, -amylose, and -amylopectin by reaction with benzaldehyde/zinc chloride

Seven different starches from potato, rice, maize, waxymaize, amylomaize-VII, shoti, and tapioca, and potato amylose and potato amylopectin have been reacted with benzaldehyde, catalyzed by ZnCl₂, to give new water-soluble starches and water soluble-amylose and soluble-amylopectin. In contrast to the native starches, aqueous solutions of the modified starches could not be precipitated with 2-, 3-, or 4-volumes of ethanol. β-Amylase gave no reaction with the modified starches, in contrast to the native starches, indicating that the modification occurred exclusively at the nonreducing-ends, giving 4,6-benzylidene-d-glucopyranose at the nonreducing-ends. Reactions of α-amylase with native and modified potato and rice starches gave a decrease in the triiodide blue color and an increase in the reducing-value that were similar for the native- and modified-starches, indicating the modified starches had not been significantly altered by the modification. The benzaldehyde-modified starches and benzaldehyde-modified potato amylose and potato amylopectin components, therefore, have a starch structure very much like their native counterparts, in contrast to the Lintner, Small, and the alcohol/acid-hydrolyzed soluble-starches that have undergone acid hydrolysis. The benzaldehyde-modified starches and starch components have significantly higher water solubility than their native counterparts even though the structures of the modified starches had only been slightly altered from the structures of their native counterparts. They all gave crystal-clear solutions that did not retrograde.     

Pisum sativum and vicia faba carbohydrates: Part IV — Granular structure of wrinkled pea starch

The granular structure of wrinkled pea starch, compared to two other B-type starches, potato and amylomaize, has been studied, using physical, chemical and enzymic methods both before and after lintnerisation (2·2n HCl, 35°C). Wrinkled pea starch, which was composed mainly (90%) of compound granules, had an apparent amylose content of 75·4% when measured at +2°C. Native granules showed weak B-type crystallinity. The fraction (27·4%) which was easily degraded during lintnerisation and which corresponded to the amorphous phase, was smaller than for other starches. The degradation rate of the more organised phase was low (6% in 17 days). The residue remaining after exposure to acid for 42 days presented a very high, B-type crystallinity but with the same sorption properties as native starch, which indicates that water is part of the crystallites. The crystalline phase is composed of linear chains of $\text{DP}$ 25, distributed asymmetrically. The native starch showed a single gelatinisation endotherm between 117 and 133°C and with a ΔH of 0·7 cal. g^?1 dry starch, which is somewhat lower than other B-type starches.     

Quantification of total iodine in intact granular starches of different botanical origin exposed to iodine vapor at various water activities

Iodine has been used as an effective tool for studying both the structure and composition of dispersed starch and starch granules. In addition to being employed to assess relative amylose contents for starch samples, it has been used to look at the molecular mobility of the glucose polymers within intact starch granules based on exposure to iodine vapor equilibrated at different water activities. Starches of different botanical origin including corn, high amylose corn, waxy corn, potato, waxy potato, tapioca, wheat, rice, waxy rice, chick pea and mung bean were equilibrated to 0.33, 0.75, 0.97 water activities, exposed to iodine vapor and then absorbance spectra and LAB color were determined. In addition, a new iodine quantification method sensitive to <0.1% iodine (w/w) was employed to measure bound iodine within intact granular starch. Amylose content, particle size distribution of granules, and the density of the starch were also determined to explore whether high levels of long linear glucose chains and the surface area-to-volume ratio were important factors relating to the granular iodine binding. Results showed, in all cases, starches complexed more iodine as water content increased and waxy starches bound less iodine than their normal starch counterparts. However, much more bound iodine could be measured chemically with waxy starches than was expected based on colorimetric determination. Surface area appeared to be a factor as smaller rice and waxy rice starch granules complexed more iodine, while the larger potato and waxy potato granules complexed less than would be expected based on measured amylose contents. Corn, high amylose corn, and wheat, known to have starch granules with extensive surface pores, bound higher levels of iodine suggesting pores and channels may be an important factor giving iodine vapor greater access to bind within the granules. Exposing iodine vapor to moisture-equilibrated native starches is an effective tool to explore starch granule architecture.     

Gel formation in mixtures of high amylopectin potato starch and potato starch

The effects of starch granules on the rheological behaviour of gels of native potato and high amylopectin potato (HAPP) starches have been studied with small deformation oscillatory rheometry. The influence of granule remnants on the rheological properties of samples treated at 90 °C was evident when compared with samples treated at 140 °C, where no granule remnants were found. The presence of amylose in native potato starch gave to stronger network formation since potato starch gave higher moduli values than HAPP, after both 90 and 140 °C treatments. In addition, amylose may have strengthened the network of HAPP because higher moduli values were obtained when native potato starch was added to the system. The moduli values of the mixtures also increased with increasing polysaccharide concentration in the system, which is due to an increment in the polysaccharide chain contacts and entanglements. Finally, it was found that a mixture of commercial amylose from potato starch and HAPP resulted in lower values of G′ compared to native potato starch. This indicates that the source of amylose is important for the properties in a blend with native amylopectin.     

Solid state NMR studies on the structural and conformational properties of natural maize starches

Natural maize starches having a range of amylose contents have been characterised by CP/MAS NMR spectroscopy. Chemical shifts, relative resonance intensities, line-widths and spectral shapes were compared at different moisture contents. At 10% moisture content, these parameters showed few significant differences across a range of apparent amylose levels from 0 to 84%. After hydration of the granules to ≈30% moisture, it was found that the amylose content significantly affected the relative signal intensities and line-widths especially of C-1 and C-4 resonances. Narrower line-widths after hydration were attributed to (i) an increased degree of crystallinity, and (ii) disappearance of the signals of amorphous material which, on becoming more mobile, became invisible to the CP/MAS experiment. The enhanced resolution at higher moisture levels revealed signals which were assigned to the amylose–lipid complex, i.e. V-type amylose. The amount of V-amylose detected by NMR increased with both amylose content and lipid content of the granule. Prolonged treatment of the granules with iodine vapour significantly increased the amount of V-type amylose in the high amylose samples, but caused a decrease in their degree of crystallinity. Waxy-maize starch was barely affected by iodination. The results provide evidence that amylose tends to disrupt the structural order within amylopectin crystallities. This effect is enhanced by the formation of the amylose–iodine complex, indicating that V-amylose could be a major crystallite-disrupting agent in native starch granules.     

Extraction of starches from tuber crops using ammonia

Ammonia solution (0·03 ) was used to extract starch from various tuber crops by the conventional settling method. It was found that there was noticeable improvement in the yield of starch from Colocasia (6–16%), while it fell for sweet potato starch and remained almost the same for the other starches. The various properties of starch, thus extracted, were compared with those for starch obtained by water extraction. It was found that total amylose of all starches were unaffected while the ‘soluble amylose’ was slightly suppressed for Colocasia starch extracted with ammonia solution. Peak viscosity was found to be increased to a large extent for Colocasia and Dioscorea esculenta starches by ammonia extraction, while it was lowered for sweet potato starch. The swelling volume of Colocasia starch extracted with ammonia was similarly enhanced by 25%, but the Dioscorea esculenta starch did not show such a tendency. Sweet Potato starch suffered a reduction in swelling volume. Phosphorus content was found to be independent of the extraction medium.     

Rate studies of the amylose–iodine reaction in unfractionated starch samples of various plant origin

The initial rate of the fast reaction among amylose, iodine, and iodide ions was studied in unfractionated corn, potato, rice, wheat, and arrowroot starches. It was found that the reaction followed the same rate equation as the one established in a previous study using pure amylose fractions containing no amylopectin. There were significant differences, however, among the rate constants of the various starches investigated. These variations were explained in terms of the different average molecular weights of the amylose fractions of these starches. Since whole potato starch indicated a rate constant well within the fange of those of pure amylose fraction (obtained from the same potato starch samples), it was concluded, that amylopectin did not interfere significantly with the rate of the complexation reaction.     

Extrusion processing of high amylose potato starch materials

Thermoplastic starch was prepared by mixing native high amylose potato starch and normal potato starch in a Buss co-kneading extruder at starch to glycerol ratios of 100:45 and 100:30. The materials were also conditioned to different moisture contents at different relative humidities at 23 °C. After the mixing, the compounds were extruded into sheets with a Brabender laboratory extruder. The thermoplastic high amylose materials exhibited a higher melt viscosity than the normal potato starch materials when conditioned at 53% relative humidity. Increasing the moisture content in HAP from 27% to 30% (by weight) lowered the melt viscosity to the same level as that of normal potato starch with a moisture content of 28%. In general, the high amylose materials were more difficult to extrude than the thermoplastic material based on normal starch. The main extrusion problems encountered with the high amylose starch were unstable flow, insufficient melt tenacity and clogging of the die. By increasing the moisture content, increasing the compression ratio of the screw and increasing the rotation rate of the screw, the problems were reduced or eliminated. However, only with a starch to glycerol ratio of 100:45 was an acceptable extrusion result obtained. Extruded sheets of such high amylose materials had a stress at break of about 5 MPa at room temperature and 53% relative humidity, whereas the corresponding value for normal potato (thermoplastic) starch was 3 MPa. The elongation at break was also higher in the case of the high amylose material. The results are discussed in terms of residual crystallinity of the starch materials.     

Susceptibility of annealed starches to hydrolysis by α-amylase and glucoamylase

The objective of this work was to determine if annealing altered the susceptibility of different starches to enzyme hydrolysis. Five commercial starches, including waxy corn, common corn, Hylon V, Hylon VII, and potato, were annealed by a multiple-step process, and their susceptibility to α-amylase and glucoamylase and the physicochemical properties of the hydrolyzed native and annealed starches were determined. During 36 h of enzyme hydrolysis, significant differences were noted between annealed starch and its native counterpart in the extent of α-amylolysis for Hylon V, Hylon VII, and potato, and in the extent of glucoamylolysis for potato. Waxy and common corn starches were hydrolyzed to a greater degree by both enzymes when compared with the other starches. The apparent amylose content of both native and annealed starches decreased during α-amylolysis for all starches, but increased for Hylon V, VII, and potato starches during glucoamylolysis. Most native and annealed starches exhibited comparable or increased peak gelatinization temperatures and comparable or decreased gelatinization enthalpy on hydrolysis with the exception of annealed potato starch, which showed a significant decrease in peak gelatinization temperature on hydrolysis. Annealed starches displayed significant higher peak gelatinization temperatures than their native counterparts. The intensity of main X-ray diffraction peaks of all starches decreased upon hydrolysis, and the changes were more evident for glucoamylase-hydrolyzed starches. The annealing process allowed for a greater accessibility of both enzymes to the amorphous as well as the crystalline regions to effect significant changes in gelatinization properties during enzyme hydrolysis.     

Preparation and characterization of gelatinized granular starches from aqueous ethanol treatments

In order to modify the properties of native starch granules, the formation of gelatinized granular forms (GGS) from normal, waxy, and high amylose maize, as well as potato and tapioca starches was investigated by treating granules with aqueous ethanol at varying starch:water:ethanol ratios and then heating in a rotary evaporator to remove ethanol. The modified starches were characterized using bright field, polarized and electron microscopy. Short/long range molecular order and enthalpic transitions on heating were also studied using infrared spectroscopy, X-ray diffractometry and differential scanning calorimetry respectively. A diffuse birefringence pattern without Maltese cross was observed for most GGS samples. Treatment with aqueous ethanol resulted in starch-specific changes in the surface of granules, most noticeably swelling and disintegration in waxy maize, surface wrinkling in normal maize and tapioca, swelling and opening-up in potato starches, and swelling and bursting in high amylose maize. The ratio of ethanol to water at which original granular order was disrupted also varied with starch type. GGS had less short range molecular order than native granules as inferred by comparing 1047/1022 wave number ratio from infrared spectroscopy. Similarly, A- and B-type diffraction reflections were either reduced or completely lost with evolution of V-type patterns in GGS.     

Determination of the maximum water solubility of eight native starches and the solubility of their acidic-methanol and -ethanol modified analogues

The maximum water solubilities of eight native starches from potato, shoti, tapioca, maize, waxy maize, amylomaize-7, wheat, and rice and their acid-methanol and acid-ethanol modified analogues have been determined. Maximum solubilities of 18.7 and 17.4 mg/mL were obtained for waxy maize and tapioca and 12.4 mg/mL for potato and maize starches by autoclaving 220 mg/10 mL at 121 degrees C; 8.7 mg/mL was obtained for shoti starch by stirring in 85:15 (v/v) Me(2)SO-H(2)O at 20 degrees C; and 7.0 and 5.2mg/mL for rice and amylomaize-7 starches by stirring in 1M NaOH at 20 degrees C. The acid-alcohol treated starches were 4-9 times more soluble than their native starches. The compositions of the solubilized starches had, in general, much higher ratios of amylose to amylopectin than the ratios in their native granules. A major exception to this was the acid-methanol treated potato, shoti, and rice starches that had much lower ratios of amylose to amylopectin than the ratios in their granules.     

Structural characteristics and physicochemical properties of oxidized corn starches varying in amylose content

The effects of amylose content on the extent of oxidation and the distribution of carboxyl groups in hypochlorite-oxidized corn starches were investigated. Corn starches including waxy corn starch (WC), common corn starch (CC), and 50% and 70% high-amylose corn starches (AMC) were oxidized with NaOCl at three concentrations (0.8%, 2%, and 5%). Carboxyl and carbonyl content of oxidized starches increased with increasing NaOCl concentration. High-AMC (70%) had slightly higher carboxyl and carbonyl contents at 0.8% NaOCl, whereas WC had significantly higher carboxyl and carbonyl contents at 2% and 5% NaOCl levels. Carbohydrate profiles by high-performance size-exclusion chromatography indicate that amylose was more susceptible to depolymerization than amylopectin. Degradation of amylopectin long chains (DP >24) was more pronounced in WC and CC than in AMCs. The crystalline lamellae of WC started to degrade at 2% NaOCl, but those of the other corn starches remained intact even at 5% NaOCl level according to X-ray crystallinity. By using anion-exchange chromatography for separation and size-exclusion chromatography for characterization, carboxyl groups were found to be more concentrated on amylopectin than on amylose, particularly in AMCs. Oxidation decreased gelatinization temperature and enthalpy with WC showing the most decrease and 70% AMC showing the least. The gelatinization enthalpy of 50% AMC decreased significantly faster than those of CC and 70% AMC after 0.8% oxidation. Retrogradation of amylopectin slightly increased after oxidation with increasing oxidation level. The peak viscosities of oxidized WC and CC were higher than those of their native counterparts at 0.8% NaOCl, but this increase was not observed in AMCs. The setback viscosities of 2% NaOCl-oxidized 50% and 70% AMCs were much higher than those of the unmodified counterparts. The extent of oxidation and physicochemical properties of oxidized starches varied greatly with the amylase:amylopectin ratio of corn starches. Amylose was suggested to play an important role in controlling the oxidation efficiency.