Phase transitions of pea starch over a wide range of water content

The phase transitions of pea starch over a wide range of water content were investigated by differential scanning calorimetry (DSC). Swelling of starch granules increased progressively with increasing water content. The main endotherm G broadened progressively with increasing water content up to 94.5 wt % (water:starch ratio 15:1), above which it became too broad to define. The corresponding peak and conclusion temperatures and enthalpy change increased with increasing water content. Scanning electron microscopy (SEM) showed that, at a water:starch ratio of 2:1 (water content of 70.7 wt %), starch granules only swelled partially with discernible granular contours still clearly evident. The results of swelling power tests and SEM images revealed that the endotherm G obtained at a water:starch ratio of 2:1 represented only partial swelling of starch granules. The transition from a narrow to broad endotherm G was interpreted to reflect the thermal transition behavior progressing from limited swelling to maximum swelling and then partial dissolution and leaching of starch polymers from the granules.     

Partial Characterization of Buckwheat (Fagopyrum esculentum) Starch

Laboratory-isolated buckwheat (Fagopyrum esculentum) starch was compared to commercial corn and wheat starches. Buckwheat starch granules (2.9–9.3 μm) were round and polygonal with some holes and pits on the surface. Buckwheat starch had higher amylose content, waterbinding capacity, and peak viscosity, and it had lower intrinsic viscosity when compared with corn and wheat starches. Buckwheat starch also showed restricted swelling power at 85–95°C and lower solubility in water at 55–95°C and was more susceptible to acid and enzymatic attack. Gelatinization temperatures, determined by differential scanning calorimetry, were 61.1–80.1°C for buckwheat starch compared to 64.7–79.2°C and 57.1–73.5°C for corn and wheat starches, respectively. A second endotherm observed at 84.5°C was an amylose-lipid complex attributed to the internal lipids in buckwheat starch, as evidenced by selective extraction. The retrogradation of buckwheat, corn, and wheat starch gels was examined after storage at 25, 4, and -12°C for 1–15 days. In general, buckwheat starch retrogradation was slower than that of corn and wheat starch, but it increased as storage time increased, as did that of the other starch pastes. When the values of the three storage temperatures were averaged for each storage period analyzed, buckwheat starch gels showed a lower percentage of retrogradation than did corn and wheat starch gels. Buckwheat starch also had a lower percentage of water syneresis when stored at 4°C for 3–10 days and had better stability to syneresis after three freeze-thaw cycles at -12 and 25°C.     

Musings on the Architecture and Molecular Arrangement of Polymers in Starch Granules Based on Iodine

The molecular architecture of starch has been the focus of research for over two centuries. However, studies toward understanding the granular architecture of starch have been limited to the crystalline lamellae, and the composition, structure, and organization of polymers in the amorphous background still remain unclear. This essay summarizes some recent results based on novel experiments with iodine vapor–granular starch interactions that occur in the amorphous regions of the granule. In combination with atomic force microscopy, light microscopy, powder spectrophotometry, and X‐ray diffractometry, iodine binding was used to explore the amorphous structures and the architecture of the granule. Results based on heating starch granules in the presence of iodine and their implications are also presented.     

Effect of Moisture Content on Thermomechanical Behavior of Concentrated Wheat Starch-Water Preparations

The rheological behavior of wheat starch preparations at intermediate moisture contents (25–60%, w/w) was studied by dynamic mechanical thermal analysis (DMTA). Differential scanning calorimetry (DSC) and electron spin resonance (ESR) experiments were also performed in parallel. Upon heating wheat starch preparations from 25 to 85°C, DMTA showed first a slight decrease in storage modulus (G′) to 45–60°C, then an increase of the shear modulus (predominant effect of swelling) to 68–74°C, followed by a decrease (predominant effect of melting-softening) to 85°C. In this 25–85°C temperature range, the initial swelling and subsequent softening were less pronounced with decreasing moisture content. The 45% moisture content level appeared critical, since there was a radical change in the thermomechanical behavior below this concentration. DSC showed that gelatinization did not appear as a single endotherm but as two endotherms. Whatever the moisture content, the melting started within a quite narrow temperature range, while the end of melting shifted progressively to higher temperatures as moisture content was decreased. ESR showed first a slight decrease in the water-soluble probe (Tempol) mobility as temperature was increased to 47–50°C, followed by a pronounced decrease to 57–60°C. Then, a progressive increase in probe mobility was observed to 85°C. These changes in probe mobility suggest some modifications of the kinetic and thermodynamic properties of the aqueous phase associated with changes in the starch physical state. For the lowest moisture contents, the probe mobility was quite stable during heating.     

Effect of Lime on Gelatinization of Corn Flour and Starch

Analysis of swelling power, water retention capacity, and degree of gelatinization of corn flour cooked in water with and without lime indicated, over a concentration range of 0–1% (w/v), that at low concentrations, lime increases swelling and digestibility of starch granules. Measurement of starch solubility revealed an increase in the amount of starch dissolved by lime cooking. Swelling, retention, and gelatinization exhibited maxima at or near 0.2% (w/v) lime, and then decreased as lime concentration increased. Hot-stage polarized light microscopy and differential scanning calorimetry of isolated starch revealed increasing gelatinization temperatures with increasing lime concentrations. It is hypothesized that the high pH of the system causes starch hydroxyl groups to ionize, thereby creating binding sites for Ca⁺⁺/CaOH⁺ and producing Ca-starch crosslinks. It is also suggested that, at low lime levels (<0.4%, w/v), granule crystalline regions are disrupted and the granule matrix is stretched by exchange of protons for calcium ions; when the lime level surpasses 0.4% (w/v), the granule shell becomes stabilized by Ca⁺⁺-starch interactions, producing stronger, more rigid granules.     

Effect of Steeping Corn with Lactic Acid on Starch Properties

Pasting and thermal properties of starch from corn steeped in the presence of lactic acid and at different steeping times (8, 16, 24, 32, and 40 hr) were investigated. Corn kernels were steeped at 52°C with 0.2% (w/v) SO₂ and with and without 0.5% (v/v) lactic acid. The isolated starch obtained by corn wet‐milling was characterized by determining starch recoveries, retrogradation, and melting transition properties of the lipid‐amylose complex by differential scanning calorimetry (DSC), and pasting properties by the Rapid Visco Analyser (RVA). Damaged granules and the starch granule size were determined by using microscopic techniques. Starches from corn steeped in the presence of lactic acid (LAS) were compared with control starch (CS) steeped without lactic acid. Greater starch recoveries were obtained for LAS samples than for CS samples, and practically no damaged starch was present in the former preparations. The presence of lactic acid affected the RVA profiles and steeping time affected the viscosities of the starch suspensions. In general, the RVA parameters of LAS suspensions were lower than those of CS suspensions. No great modification of the thermal properties was observed; only a slight decrease in amylopectin retrogradation and in the melting enthalpy of the amylose‐lipid complex was observed. Hydrolysis of the starch during steeping seems the most probable explanation to the starch modifications produced by lactic acid addition.     

Thermomechanical Behavior of Concentrated Starch-Water Preparations

The rheological behavior of concentrated starch preparations from various origins was studied by dynamic mechanical thermal analysis (DMTA). Four types of starch were used: wheat, potato, normal, and waxy corn adjusted to moisture contents in the 42–49% (w/w) range. The thermal treatments of the starch-water mixtures consisted of heating to 85°C and cooling to room temperature, both at a rate of 1°C/min. During heating, the storage modulus (E′) appearance was first characterized by an increase with a maximum at ≈70°C (or potato starch at 63°C) followed by a decrease to 85°C. During cooling, storage modulus increased steadily down to room temperature. The magnitude of these variations depended on the starch type. Despite some differences, all the loss tangent curves showed a decrease during heating from 60–70°C to 85°C, followed by a plateau during cooling. To propose an interpretation for the DMTA results, we measured, by laser-light diffraction, the influence of heating (up to the maximum E′ peak) on the distribution of the granule sizes of the different starches. Moreover, differential scanning calorimetry (DSC) was used to measure the temperature range where the melting of starches ordered regions occurred. Partial melting enthalpies were plotted against temperature. The hypothesis of a relationship between swelling and an increase in rigidity during heating seemed to be confirmed by laser-light diffraction, whereas DSC indicated the decrease in rigidity was caused predominantly by order-disorder transitions. During cooling, amylose gelation plays a major role in the rigidity increase, but a contribution of amylopectin is not excluded.     

Molecular Structure and Organization of Starch Granules from Developing Wheat Endosperm

Wheat starches isolated from seeds harvested between 7 and 49 days after anthesis (DAA) were fractionated into large (>8 μm) and small (<8 μm) granules and studied for starch structure and architecture. Starch granules at 7 DAA possessed unimodal size distribution, whereas it was bimodal at later maturity stages. The apparent amylose fraction of starch granules at early maturity (7 and 14 DAA) consisted of intermediate‐type materials, whereas starch at later maturity stages (28 and 49 DAA) contained branched amylose. Wide‐angle X‐ray scattering (WAXS) revealed a well‐developed polymorphic structure already at 7 DAA. Although the presence of a small proportion of B‐type crystallites mixed with A‐type crystallites was observed in the X‐ray diffractogram of starches at early maturation (7 and 14 DAA), it was masked by the A‐type crystallites at later maturity stages. However, the large granules had a higher proportion of B‐type crystallites and lower relative crystallinity (RC) than their small‐granule counterpart. The iodine absorption properties of the starch granules demonstrated different levels of mobility of the starch polymers at different stages of maturity and the mobility of more glucan polymers in the large granule population compared with the small granules at the same maturity stage. Iodine did not change the characteristic A‐type crystalline pattern of starch, but it increased RC. Changes in peak width at half height based on WAXS data further suggested the possible interaction of iodine with amylopectin intercluster chain segments and branch chains in formation of inclusion complexes.     

Gelatinization Profiles of Triticale Starch in Cookies as Influenced by Moisture and Solutes

Starch physicochemical parameters and phase transitions were determined in flours of 10 advanced lines and cultivars of triticale (Cananea, Currency, Eronga, LA 24 Bve, LA 20 FCA, LA 83 FCA, Tatú, Tehuelche, Quiñé, and Yagan). Starch behavior was also analyzed during the baking of cookies prepared with triticale flours. Starch granule size, crystal type patterns, and size distribution were determined by light microscopy, X-ray diffraction, and gel-permeation chromatography, respectively. Two types and sizes of starch granules with characteristic A-form crystals were obtained in all samples tested. The Quiñé cultivar showed the lowest extent of starch crystallinity. Only a monophasic endotherm was found by differential scanning calorimetry for water content >50–60%. Gelatinization temperature and enthalpy values varied significantly among samples. A biphasic endotherm was detected for water contents between 35 and 60%, and no endothermic transitions were observed for water levels <35%. Only one endotherm corresponding to starch gelatinization was detected in baked cookies prepared with five triticale flours. In all samples, the highest enthalpy of gelatinization of starch was detected for the cookie surface, whereas the highest gelatinization temperature was observed for the center. These differences may be attributed to the presence and content of the solutes in cookie dough and also to the degree of starch gelatinization during the cooking process.     

Amyloglucosidase hydrolysis of high-pressure and thermally gelatinized corn and wheat starches

The study of glucose production using amyloglucosidase as a biocatalyst was carried out using high-pressure and thermally gelatinized corn and wheat starches. For corn starch, the measured initial rate of glucose production obtained from thermal gelatinization is faster than that obtained from the two high-pressure treatments, but the equilibrium yield of glucose was found to be similar for the three treatments. High-pressure treatments of wheat starch significantly improve the equilibrium yield of glucose compared with those obtained from the thermally gelatinized wheat starch. This difference has been related to the formation of amylose-lipid complexes during heating and could also explain previous physicochemical differences observed between high-pressure and thermally gelatinized starch.     

Effects of Growing Environment on Properties of Starch from Five Australian Wheat Varieties

The effects of growing conditions on properties of starch from wheat grain were examined. Growing conditions affected starch and amylose content, granule size distribution, protein associated with starch granules, and starch swelling power in grains from five commercial Australian milling wheat varieties grown at multiple locations in two years in crop production systems. Soil nitrogen and meteorological conditions were major contributors to variability in grain yield and grain protein and starch contents. The volume proportion of B‐granules was positively affected by warmer temperatures before flowering but negatively correlated with high temperatures during grain filling. Genotype was the main source of variability in the proportion of B‐granules and granule dimensions, starch‐granule proteins, and starch swelling power, although there were also significant contributions to variability from the growing conditions. Seasonal effects and interactions between genotype and season and location were significant sources of variability in amylose content, proportion of short chains of amylopectin, and flour swelling power. The positive relationships between starch content and the number of clear days and atmospheric temperatures before flowering indicate that conditions that enhance accumulation of assimilates before anthesis influence the deposition of reserves in developing grain.     

Physical Properties of Poly(Lactic Acid) and Starch Composites with Various Blending Ratios

Two‐phase polymer blends of poly(lactic acid) (PLA) and corn or wheat starches at various ratios were prepared by using a laboratory‐scale twin‐screw extruder and compression molding. The blends were characterized for thermal transitions, mechanical properties, and water absorption. Starch and PLA were immiscible polymers, and the thermal behavior of PLA was not affected by starch. Crystallinity of the blends decreased in some degree as starch content increased 20–40%. Tensile strength and elongation of the blends decreased as starch content increased, but modulus increased as starch content increased up to 70%. As starch content increased to >60%, the PLA phase became discontinuous, and water absorption of the blends increased sharply. Blends made from wheat starch gave slightly better mechanical properties than those made from corn starch, and no differences in other properties were observed.     

Characteristics of Granular Cold‐Water Gelling Starches of Cereal Grains and Legumes Prepared Using Liquid Ammonia and Ethanol

Starches of wheat, corn, smooth and wrinkled peas, and chickpeas were modified to a free‐flowing powder of granular cold‐water gelling (GCWG) starch using liquid ammonia and ethanol at 23°C and atmospheric pressure. Amylose content of starches was 26.3% in wheat, 27.1% in corn, 35.4% in chickpeas, 43.2% in smooth peas, and 79.9% in wrinkled peas. The modified starches remained in granular form with an increased number of grooves and fissures on the surface of the granules compared with native starch, while the crystallinity was mostly lost, as shown by X‐ray diffractograms and DSC endothermic enthalpies. Pasting viscosity of modified starches at 23°C was 171 BU and 305 BU in wheat and corn, respectively, and much higher in legume starches, ranging from 545 BU to 814 BU. Viscosities of modified legume starches at 23°C were at least twice as high as those of native starches determined at 92.5°C. Swelling power of modified starches at 23°C ranged from 8.7 g/g to 15.3 g/g, while swelling power of native starches heated to 92.5°C ranged from 4.8 g/g to 16.0 g/g. GCWG starches exhibited higher dextrose equivalent (DE) values of enzymatic hydrolysis, ranging from 25.2 to 27.0 compared with native starches (1.5–2.9). Modified starches from wheat, corn, smooth peas, and chickpeas formed weak gels without heat treatment and experienced no changes in gel hardness during storage, while native starch gels formed by heat treatment showed an increase in hardness by 1.1–7.5 N during 96 hr of storage at 4°C.     

Functional Properties of Cross-Linked and Hydroxypropylated Waxy Hull-less Barley Starches

Waxy hull-less barley (HB) starches containing 0 or 5% amylose were cross-linked with phosphorus oxychloride and the cross-linked starches were hydroxypropylated with propylene oxide. For comparison, waxy corn and potato starches were similarly modified. For all starches, cross-linking inhibited granule swelling and prevented swollen granules from disintegration, resulting in dramatic improvement in pasting properties and tolerance to cooking shear and autoclaving. Cross-linked waxy HB starches were more tolerant to cold storage and cooking shear than cross-linked waxy corn starch. Hydroxypropylation of the cross-linked starches reduced granule crystallinity and gelatinization temperature, and improved granule swelling, paste clarity, and freeze-thaw stability. The double-modified waxy HB starches showed higher cold tolerance than similarly modified waxy corn and potato starches, as judged by freeze-thaw stability and clarity after cold storage. These results indicated that the cross-linked and double-modified waxy HB starches together may have a wide range of food applications. This study indicated that the behavior of granule swelling and disintegration of swollen granules played an important role in governing paste viscosity, clarity, and freeze-thaw stability of waxy HB starches.     

Effect of sucrose on the thermomechanical behavior of concentrated wheat and waxy corn starch-water preparations

The rheological behavior of concentrated starch preparations from two different origins (wheat and waxy corn) was studied in the presence of sucrose by dynamic mechanical thermal analysis (DMTA). Moisture contents ranged from 30 to 60% (w/w wsb), and samples contained 0, 10, or 20 g of sucrose for 100 g of the starch-water mixture. The storage modulus (G') changes during heating depended strongly on water content (in the moisture range studied), and the importance of these variations was dependent upon the starch type. Sucrose addition resulted in a shift to higher temperatures of the increase in G' during heating. Differential scanning calorimetry (DSC) and electron-spin resonance (ESR) analyses were performed in parallel in order to relate the viscoelastic changes to water migrations and to structural disorganization of starch. Sucrose was found to increase the gelatinization temperature and enthalpy of both starches, implying a stabilization of the granular structure during heating. The sugar-water interactions do not appear to be the only way by which sucrose delays starch gelatinization. The obtained results suggest that sugar-starch interactions in the amorphous and/or the crystalline regions of the starch granules should be envisaged.     

Enthalpic Transitions in Native Starch Granules

Crystalline properties of native starch granule fractions that varied in apparent density and size were investigated using differential scanning calorimetry (DSC). Endotherms obtained at 80% hydration showed significant variations in enthalpy between the six fractions. Typical bi-phasic endotherms exhibiting significant variation in start temperature were obtained for the six fractions at 50% hydration. However, on annealing at 50°C/50% hydration for 48 hr, all fractions showed a single endotherm without any significant variability in endotherm characteristics. At 10% hydration, the six fractions exhibited single high-temperature endotherms with significant differences in their peak temperatures. It was observed that mechanically damaging starch, resulted in the disappearance of any enthalpic transition. These observations could not be satisfactorily explained on the basis of prevailing concepts about DSC enthalpic transitions.     

均质压力对玉米淀粉机械力化学效应的影响

为了研究均质压力对玉米淀粉微观结构及理化性质的影响,该文以玉米淀粉为原料,通过X-射线衍射(X-ray diffraction,XRD)、扫描电镜(scanning electron microscope,SEM)、快速黏性分析仪(rapid visco analyser,RVA)、偏光显微镜(polarizing microscope,PLM)、激光共聚焦显微镜(confocal laser scanning microscopy,CLSM)等手段研究不同压力(20、60、100、140 MPa)下淀粉结构及性质变化,并探究其相互关系,揭示均质压力对淀粉颗粒机械力化学效应。结果表明:均质压力处理对玉米淀粉结构及性质产生显著影响。经20~140 MPa处理后,与原淀粉相比,中央腔及孔道结构模糊,粒径、糊化黏度减小,结晶度下降,水溶指数和透光率呈上升趋势。20~100 MPa范围内,随均质压力增大,淀粉颗粒形貌逐渐破坏,球状凸起结构增加,100 MPa处理时中心球体最为明显,且与60 MPa相比,结晶度变大,膨胀度显著下降。当140 MPa处理时,颗粒内部球状凸起、碎片及孔洞结构显著减少,偏光十字破坏,糊化焓降低。可见不同均质压力对淀粉颗粒的无定形区、亚结晶区和结晶区产生不同程度的机械力化学作用,导致淀粉颗粒内部依次发生了聚集和团聚效应。该结果为研究淀粉化学活性及生产高性能变性淀粉提供理论支撑。     

Morphological, structural, thermal, and rheological characteristics of starches separated from apples of different cultivars

The starches were separated from unripe apples of five cultivars (Criterion, Ruspippum, Red Spur, Skyline Supreme, and Granny Smith) and evaluated using scanning electron microscopy (SEM), gel permeation chromatography (GPC), X-ray diffraction, differential scanning calorimetry (DSC), and dynamic viscoelasticity. SEM showed the presence of round granules as well as granules that had been partially degraded, probably by amylases. The starch granules in different apple starches ranged between 4.1 and 12.0 mum. Debranching of starch with isoamylase and subsequent fractionation of debranched materials by GPC revealed the presence of an apparent amylose, an intermediate fraction (mixture of amylose and amylopectin), long side chains of amylopectin, and short side chains of amylopectin in the range of 28-35.2, 3.6-4.4, 20-21.3, and 39.9-47.1%, respectively. The swelling power of starches ranged between 14.4 and 21.3 g/g. X-ray diffraction of apple starches showed a mixture of A- and B-type patterns. All apple starches showed peak intensities lower than that observed for normal corn and potato starch, indicating the lower crystallinity. The transition temperatures (onset temperature, T(o); peak temperature, T(p); and conclusion temperature, T(c)) and enthalpy of gelatinization (deltaH(gel)) determined using DSC ranged between 54.7 and 56.2 degrees C, between 57.1 and 59.1 degrees C, between 60.2 and 63.5 degrees C, and between 3.3 and 4.2 J/g, respectively. The viscoelastic properties of starch from different cultivars measured during heating and cooling using a rheometer differed significantly. Red Spur and Criterion starches with larger granule size showed higher G' and G' ' values, whereas those containing smaller size and amylolytically degraded granules showed lower G' and G' '.     

Assignments of proton populations in dough and bread using NMR relaxometry of starch, gluten, and flour model systems

Starch-water, gluten-water, and flour-water model systems as well as straight-dough bread were investigated with (1)H NMR relaxometry using free induction decay and Carr-Purcell-Meiboom-Gill pulse sequences. Depending on the degree of interaction between polymers and water, different proton populations could be distinguished. The starch protons in the starch-water model gain mobility owing to amylopectin crystal melting, granule swelling, and amylose leaching, whereas water protons lose mobility due to increased interaction with starch polymers. Heating of the gluten-water sample induces no pronounced changes in proton distributions. Heating changes the proton distributions of the flour-water and starch-water models in a similar way, implying that the changes are primarily attributable to starch gelatinization. Proton distributions of the heated flour-water model system and those of fresh bread crumb are very similar. This allows identifying the different proton populations in bread on the basis of the results from the model systems.     

Effects of β-amylolysis on the resistant starch formation of debranched corn starches

Retrograded amylose is resistant to digestion by amylolytic enzymes, which is known as resistant starch type III (RS3). In this study we investigated the effect of β-amylase hydrolysis on the formation and physicochemical properties of RS3 from debranched corn starches. Three types of corn starch (Hylon VII, Hylon V, and common corn) were first gelatinized and then hydrolyzed using β-amylase to varying degrees. The resultant hydrolyzed starch was debranched with isoamylase and then exposed to temperature cycling to promote RS formation. A broad endotherm from approximately 45 to 120 °C and a small endotherm above 150 °C were noted for all retrograded starches. All three corn starches had increased RS contents after moderate β-amylolysis, with Hylon V having the highest RS content at 70.7% after 4 h of β-amylolysis. The results suggest that RS3 formation is affected by the starch composition as well as the starch structure and can be increased by moderate β-amylolysis.