Effect of Sucrose on Starch Conversion and Glass Transition of Nonexpanded Maize and Wheat Extrudates

Nonexpanded “half products” were prepared by twin‐screw extrusion of maize and wheat of fine and coarse particle size in three levels of sucrose, 0, 10, and 20% db. The degree of starch conversion in the extrudates was determined using X‐ray diffraction, differential scanning calorimetry, and rapid viscosity analysis. Starch conversion was greater in the fine material compared with the coarse material and greater for wheat compared with maize. Sugar addition decreased starch conversion in all cases, but the effect was greater for maize compared with wheat and for the coarse material compared with the fine material. The thermal mechanical properties were studied by dynamic mechanical thermal analysis to determine the effect of sugar on the glass transition temperature (T_g) in the four different materials. As expected, the mechanically determined T_g was reduced by sugar addition. Water plasticized wheat semolina less than the other three materials. It was suggested that this was because the extruded semolina was entirely amorphous, whereas Xray analysis showed some crystallinity in the other three materials. Die swell was much less for maize grits possibly because elasticity decreased with decreasing starch conversion. The implications for the role of both water and sugar on the behavior of directly expanded extrudates are discussed.     

Role of Phosphorus in Viscosity,Gelatinization, and Retrogradation of Starch

The effect of starch crystallinity and phosphorus on starch gelatinization and retrogradation were studied using wide-angle X-ray powder diffraction, cross polarization/magic angle spinning (CP/MAS) ¹³C nuclear magnetic resonance (NMR) spectroscopy, ³¹P NMR spectroscopy, Rapid Visco Analyzer (RVA) and differential scanning calorimetry (DSC). Two starches differing significantly in peak viscosity (cv. Stephens, 283 BU; cv. Crew, 560 BU) were comparable in amylose content and starch crystallinity, while differing significantly in phospholipids content. Starch of lower peak viscosity had a higher phospholipids content and showed a slower rate of retrogradation. Starch from Stephens (0.098% phosphorus) had an enthalpy value of retrograded starch of 2.2 J/g after 14 days of storage, while starch from Crew (0.062% phosphorus) had an enthalpy value as high as 4.4 J/g. Defatting with a hot n-propanol and water (3:1) mixture caused substantial changes in peak viscosity. Peak viscosity for starch from Crew decreased by 75 RVU due to defatting, while starch from Stephens decreased by as much as 125 RVU. After defatting with the hot n-propanol water mixture, the rate and extent of starch retrogradation were comparable between the prime starches, which differed significantly in peak viscosity.     

Effects of Starch Isolation,Drying, and Grinding Techniques on Its Gelatinization and Retrogradation Properties

The effects of two different methods of starch isolation, drying, and grinding on gelatinization and retrogradation properties were investigated. Starch was isolated from whole wheat and flour of four hard red spring wheat cultivars. Portions of each starch isolate were freeze-dried or air-dried and portions of each dried starch were ground using a mortar and pestle or a Wiley Jr. mill. Less starch damage was obtained for freeze-dried starch regardless of isolation method or grinding technique and for all starches derived from whole wheat. Highest starch damage was obtained for air-dried starch isolates. Wiley-milled starch isolates showed higher water-binding. Whole wheat starch isolates had higher peak, lower trough, and lower final viscosities, as determined by starch paste viscosity analysis, than did starch isolates derived from flour. Major effects of all treatments on differential scanning calorimetry gelatinization properties showed lower onset temperature for flour starch isolates, lower peak temperature for freeze-dried starches, and no effects due to grinding. Endotherms of all starches after refrigerated storage and freezethaw cycling were lower than those for gelatinization.     

Quality Characteristics of Waxy Hexaploid Wheat (Triticum aestivum L.): Properties of Starch Gelatinization and Retrogradation

The viscoelastic properties and molecular structure of the starch isolated from waxy (amylose-free) hexaploid wheat (WHW) (Triticum aestivum L.) were examined. WHW starch generally had lower gelatinization onset temperature, peak viscosity, and setback than the starch isolated from normal hexaploid wheat (NHW). Differential scanning calorimetry (DSC) showed that WHW starch had higher transition temperatures (T_o, T_p, and T_c) and enthalpy (ΔH) than NHW starch. However, when compared on the basis of amylopectin (AP) content, ΔH of WHW starch was almost statistically identical to that of its parental varieties. Typical A-type X-ray diffraction patterns were observed for the starches of WHW and its parental varieties. Somewhat higher crystallinity was indicated for WHW starch. WHW starch was also characterized by having greater retrogradation resistance. The high-performance size-exclusion chromatography (HPSEC) of amylopectin showed that each amylopectin yielded two fractions after debranching. Although WHW amylopectin had somewhat long B chains, little difference was observed in the ratio of Fr.III/ Fr.II between WHW and its parental varieties.     

Retrogradation of Maize Starch After Thermal Treatment Within and Above the Gelatinization Temperature Range

Studies of starch retrogradation have not considered the initial thermal treatment. In this article, we explore the effect of heating to temperatures within and above the gelatinization range on maize starch retrogradation. In the first experiment, 30% suspensions of waxy (wx) starch were initially heated to final temperatures ranging from 54 to 72°C and held for 20 min. On reheating in the differential scanning calorimeter immediately after cooling, the residual gelatinization endotherm peak temperature increased, the endotherm narrowed, and enthalpy decreased. Samples stored for seven days at 4°C showed additional amylopectin retrogradation endotherms. Retrogradation increased dramatically as initial holding temperature increased from 60 to 72°C. In a second experiment, wx starch was initially heated to final temperatures from 54 to 180°C and rapidly cooled, followed by immediate reheating or storage at 4°C. Maximum amylopectin retrogradation enthalpy after storage was observed for initial heating to 82°C. Above 82°C, retrogradation enthalpy decreased as initial heating temperature increased. A similar effect for ae wx starch was observed, except that retrogradation occurred more rapidly than for wx starch. These experiments show that heating to various temperatures above the range of gelatinization may profoundly affect amylopectin retrogradation, perhaps due to varying extents of residual molecular order in starch materials that are commonly presumed to be fully gelatinized. This article shows that studies of starch retrogradation should take into account the thermal history of the samples even for temperatures above the gelatinization temperature range.     

Gelatinization,Pasting, and Gelling Properties of Sweetpotato and Wheat Starch Blends

Sweetpotato starch is high yielding but has very limited uses. It is possible to expand its application by blending it with other starches to obtain novel properties. In this study, functional properties of the blends of native sweetpotato starch with native, acid‐thinned, and hydroxypropylated wheat starch were studied at different ratios (75:25, 50:50, 25:75). The swelling factor, extent of amylose leaching, pasting, and gel textural properties of the blends were nonadditive of their individual components, and could be mathematically modeled by quadratic equations in relation to the ratios. Two peaks during pasting were observed for some starch mixtures studied by Rapid ViscoAnalyser (RVA). The gelatinization and retrogradation enthalpies (ΔH) of the blends were additive of their individual components and could be modeled by linear equations. All starch mixtures exhibited two peaks during differential scanning calorimetry (DSC) scan for gelatinization, but a single peak for retrograded starches. This study may provide basis for formulation of mixtures using starch from diverse sources to develop more natural starch systems with a range of physicochemical properties.     

Effect of Amylose Content on Gelatinization,Retrogradation, and Pasting Properties of Starches from Waxy and Nonwaxy Wheat and Their F1 Seeds

We studied the effect of amylose content on the gelatinization, retrogradation, and pasting properties of starch using wheat starches differing in amylose content. Starches were isolated from waxy and nonwaxy wheat and reciprocal F1 seeds by crossing waxy and nonwaxy wheat. Mixing waxy and nonwaxy wheat starch produced a mixed starch with the same amylose content as F1 seeds for comparison. The amylose content of F1 seeds ranged between waxy and nonwaxy wheat. Nonwaxy‐waxy wheat had a higher amylose content than waxy‐nonwaxy wheat. Endothermic enthalpy and final gelatinization temperature measured by differential scanning calorimetry correlated negatively with amylose content. Gelatinization onset and peak temperature clearly differed between F1 and mixed starches with the same amylose content as F1 starches. Enthalpy for melting recrystallized starches correlated negatively with amylose content. Rapid Visco Analyser measurement showed that F1 starches had a higher peak viscosity than waxy and nonwaxy wheat starches. Mixed starches showed characteristic profiles with two low peaks. Setback and final viscosity correlated highly with amylose content. Some of gelatinization and pasting properties differed between F1 starches and mixed starches.     

Effect of Hydroxypropylation on Retrogradation and Water Dynamics in Wheat Starch Gels Using 1H NMR

The water dynamics in gels made from native wheat starch, control (alkali‐treated) starch, and hydroxypropylated starch were studied using ¹H NMR relaxometry. Transverse relaxation studies showed that at least two domains of water exist in the starch gel, one with a T₂ of 0.5–8 msec and one with a T₂ at 8–200 msec. For starch gels held at 5°C for up to 15 days, the peak T₂ of both regions decreased with time for gels made from native starch, but not for those made from hydroxypropylated starch. Changes in integrated signal in each region suggests that water migrates out of the lower T₂ domain during retrogradation. Gels made from isolated amylose had a single, relatively mobile water domain, with T₂ dependent on gel concentration. This fraction did not change during storage at 5°C. Granule‐rich gels showed two water domains, one with a T₂ range similar to that for amylose gels, which varied over time and were thermally reversible. During storage, most significant changes occurred in the relatively low T₂ region associated with granule remnants. These studies show that, in addition to changes in starch during retrogradation, water dynamics are also affected by recrystallization and chemical modification of starch molecules.     

Sources of Variation for Starch Gelatinization,Pasting, and Gelation Properties in Wheat

The starch of wheat (Triticum aestivum L.) flour affects food product quality due to the temperature-dependent interactions of starch with water during gelatinization, pasting, and gelation. The objective of this study was to determine the fundamental basis of variation in gelatinization, pasting, and gelation of prime starch derived from seven different wheat cultivars: Kanto 107, which is a partial waxy mutant line, and six near-isogenic lines (NILs) differing in hardness. Complete pasting curves with extended 16-min hold at 93°C were obtained using the Rapid Visco Analyser (RVA). Apparent amylose content ranged from 17.5 to 23.5%; total amylose content ranged from 22.8 to 28.2%. Starches exhibited significant variation in onset of gelatinization. However, none of the parameters measured consistently correlated with onset or other RVA curve parameters that preceded peak paste viscosity. Peak paste viscosity varied from 190 to 323 RVA units (RVU). Higher peak, greater breakdown, lower final viscosity, negative setback, and less total setback were associated with lower apparent and total amylose contents. Each 1% reduction in apparent or total amylose content corresponded to an increase in peak viscosity of about 22 and 25 RVU, respectively, at 12% starch concentration. Of the seven U.S. cultivars, the lower amylose cultivars Penawawa and Klasic were missing the granule-bound starch synthase (GBSS; ADPglucose starch glycosyl transferase, EC 2.4.4.21) protein associated with the Waxy gene locus on chromosome 4A (Wx-B1 locus). Kanto 107 was confirmed as missing both the 7A and 4A waxy proteins (Wx-A1 and Wx-B1 loci). The hardness NIL also were shown to be null at the 4A locus. Apparent and total amylose contents of prime starch generally corresponded well to the number of GBSS proteins; although the hardness NIL tended to have somewhat higher amylose contents than did the other GBSS 4A nulls. We concluded that reduced quantity of starch amylose due to decreased GBSS profoundly affects starch gelatinization, pasting, and gelation properties.     

Effects of Environmental Temperature on Structure and Gelatinization Properties of Wheat Starch

The effects of environmental temperature on gelatinization properties and amylopectin structures of wheat endosperm starch were examined by isolating starches from four wheat cultivars matured in growth chambers at daytime temperatures of 15, 20, 25, or 30°C. Kernel weight and starch content per kernel were reduced by high maturation temperature. Amylose content showed no significant change at high maturation temperature in some cultivars; in other cultivars, there was a slight increase. Principal component analysis of data on relative peak areas of debranched amylopectin showed that amylopectin from wheat grown at a lower temperature had a greater proportion of shorter chains. Amylopectin branch chains were classified into three groups based on the correlation coefficients between the data of branch chain length distribution and principal component scores, degree of polymerization (DP) of 6–12, DP 13–34, and DP ≥ 35. The gelatinization temperature of starches increased markedly at a higher maturation temperature, with increases exceeding 10°C at high maturation temperatures. Gelatinization properties correlated significantly with amylopectin chain length distribution.     

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.     

Gelatinization and Retrogradation Kinetics of High‐Fiber Wheat Flour Blends: A Calorimetric Approach

The impact of dietary fiber (DF) mixtures on dough thermal properties needs to be investigated when designing high‐fiber wheat bread. Effects of flour replacement at different levels (6–34%) by soluble (inuline [FN]), partially soluble (sugar beet [FX], pea cell wall [SW]), and insoluble (pea hull [EX]) DF on wheat dough thermal profiles have been investigated by simulating baking, cooling, and storage in differential scanning calorimetry (DSC) pans. In general, DF incorporation into water‐flour systems delayed endothermic transition temperatures for both gelatinization and retrogradation phenomena except for the peak temperature (T_p) of retrogradation. With some exception, the pattern of the enthalpy of amylopectin retrogradation was lower and slower (lower constant of proportion, k) over 10 days of storage in gelatinized hydrated flour‐fiber blends when compared with control without DF. FX, a partially soluble fiber, provided major effects on gelatinization (T_p decrease and ΔH increase) and retrogradation kinetics (the Avrami exponent, n, increase). Single presence of EX allowed a significant reduction in the Avrami exponent n leading to slower kinetics for amylopectin retrogradation when included in the blends.     

高压对玉米淀粉糊化度影响的研究

采用差热扫描量热法（ＤＳＣ）研究了不同压力及保压时间对玉米淀粉糊化度的影响。在７００ＭＰａ压力下，保压２ｍｉｎ即可使８６．８％玉米淀粉糊化，达到一般食品加工要求；保压５ｍｉｎ，可使玉米淀粉１００％糊化，这是高压食品加工的一大优点     

Retrogradation Mechanism of Rice Starch

The non‐Newtonian behavior and dynamic viscoelasticity of rice starch (Akihikari, 18.8% amylose content) solutions after storage at 25 and 4°C for 24 hr were measured with a rheogoniometer. The flow curves, at 25°C, of Akihikari starch showed plastic behavior >3.0% (w/v) after heating at 100°C for 30 min. The dynamic viscoelasticity of the starch increased after storage at 25 and 4°C for 24 hr and stayed at a constant value with increasing temperature. A small dynamic modulus of rice starch was observed upon addition of urea (4.0M) at low temperature (0°C), but it produced a sigmoid curve when plotted against increasing temperature. A small dynamic modulus was also observed in 0.05M NaOH solution. However, it increased rapidly after the temperature reached 70°C. Possible models of retrogradation mechanism of rice starch were proposed.     

压热-冻融循环处理对甘薯淀粉结构及物化特性的影响

为了探索压热冻融循环处理对甘薯淀粉结构及物化性质的影响,以甘薯淀粉为原料,并在不同淀粉乳浓度(5%、10%、20%,w/w)条件下进行重复的压热-冻融循环处理。结果表明,与甘薯原淀粉相比,经重复的压热-冻融处理后,甘薯淀粉颗粒形态消失,破裂熔融,最终呈不规则形状;甘薯淀粉衍射吸收峰强度减弱,晶型由A型向B型转化。随着淀粉乳浓度以及压热-冻融循环次数的增加,甘薯淀粉的膨胀势和溶解度均有所降低。在淀粉乳浓度为10%、压热-冻融循环1次处理后,甘薯淀粉中缓慢消化淀粉与抗性淀粉含量达到最高,分别为29.83%和39.82%。本研究为甘薯缓慢消化及抗性淀粉的制备提供了科学依据,为其在功能性食品领域中的应用提供了基础数据。     

Relationship of Gelatinization and Recrystallization of Cross‐Linked Rice to Glass Transition Temperature

Nonwaxy rice starch was cross‐linked with sodium trimetaphosphate and sodium tripolyphosphate to obtain different degrees of cross‐linking (9.2, 26.2, and 29.2%). The objective was to investigate the influence of cross‐linking on thermal transitions of rice starch. Starch suspensions (67% moisture) were heated at 2°C/min using differential scanning calorimetry (DSC) to follow melting transition of amylopectin. Biphasic transitions were observed at ≈60–95°C in all samples. Melting endotherms of amylopectin shifted to a higher temperature (≤5°C) with an increasing degree of cross‐linking, while there was no dramatic change in enthalpy. Recrystallization during aging for 0–15 days was significantly suppressed by cross‐linking. The delayed gelatinization and retrogradation in crosslinked starch were evident due to restricted swelling and reduced hydration in starch granules. Glass transition temperature (T_g) measured from the derivative curve of heat flow was ‐3 to ‐4°C. No significant change in T_g was observed over the storage time studied.     

Starch Retrogradation in Cooked Pasta and Rice

Effect of cooking time on starch retrogradation and water distribution was studied in pasta (spaghetti) and rice (parboiled and arborio) using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) Optimum cooking times (OCT) were 8, 16, and 18.5 min for spaghetti, parboiled, and arborio rice, respectively. Swelling was observed by image analysis. OCT spaghetti and rice showed various starch retrogradation rates at various aging times and temperatures. Based on the classical Avrami function, the retrogradation rate at 5°C followed the order spaghetti > parboiled rice > arborio rice, while extent was in the opposite order. At higher temperature (20°C), the rates decreased by 20× in all cases. Thermogravimetric analysis (TGA) investigations were undertaken to check the distribution of water within these products and its relationship to starch retrogradation. During heating, water was released in two distinguishable steps at ≈80 and 100°C. Results supported the conclusion that the more tightly bound water might not participate or facilitate starch retrogradation. In this study, the overall water content did not change during storage, and water appeared to migrate from sites of stronger binding to sites of weaker binding. The temperature dependence of the Avrami constant was described with the Vogel‐Tamman‐Fulcher empirical expression.     

Effects of Heat-Moisture Treatment and Lipids on Gelatinization and Retrogradation of Maize and Potato Starches

Effects of heat-moisture treatment (HMT) and lipids on the structure and gelatinization of maize and potato starches were studied, and the retrogradation process of 20% HMT starch gels was also investigated. Maize starch was physically modified by HMT or by defatting. Potato starch was physically modified by HMT or by adding monoglycerides. The X-ray pattern of the HMT maize starch was assigned to a combination of A and V patterns, which indicated that HMT formed crystallized amylose complexes and recrystallized amylose in maize starch granules. However, the X-ray pattern of defatted maize starch did not change for HMT, so the lipids originally existing in starch granules were important to the formation of new crystallites during this treatment. Differential scanning calorimetry (DSC) results suggested that weaker structures in amylopectin crystallites were more susceptible to degradation after HMT, while crystallized amylose complexes developed thermal stability after treatment. The amylose contents increased with increasing degree of HMT, which suggested that the newly created amylose arose from exterior linear chains of amylopectin degraded by the treatment. Investigation of retrogradation process showed that HMT significantly promoted retrogradation of starch gels, especially the initiation of recrystallization.     

Capillary Rheometry of Corn Endosperm: Glass Transition,Flow Properties,and Melting of Starch

A capillary rheometer was manufactured to study the properties of corn endosperm. Samples were tested at or near the pressures and temperatures encountered in high-temperature, short-time extrusion. The rheometer was designed to prevent moisture loss during testing. At a set pressure, raising the temperature caused corn endosperm particles to soften and change shape, resulting in a pressure drop as the voids in the sample were reduced. The temperature at which the pressure drop occurred was considered the glass transition temperature. Continued heating caused the pressure to rise and drop a second time as the sample softened and flowed through the capillary. Thermal analysis by differential scanning calorimetry showed that complete melting of starch crystals was not necessary to permit capillary flow. Pressure and temperature conditions sufficient to initiate flow were measured for opaque and vitreous corn flours and expressed as a boundary curve defining the flow region. The position of the curve shifted as a function of sample moisture content. The vitreous corn sample had a rough (unstable) flow that could be eliminated by addition of a small amount (2% w/w) of vegetable oil. When isolated corn starch was studied in the capillary rheometer, results showed that, under certain conditions, starch crystal melting was affected by pressure and time. A model was developed to account for the effects of pressure, temperature, time, and sample moisture on starch crystal melting.     

Effects of Rough Rice Storage Conditions on Gelatinization and Retrogradation Properties of Rice Flours

Changes in gelatinization and retrogradation properties of two rice cultivars, Bengal and Kaybonnet, during rough rice storage were studied using differential scanning calorimetry (DSC). The storage variables included two storage moisture contents (12 and 14%), three storage temperatures (4, 21, and 38°C), and four storage durations (0, 3, 9, and 16 weeks). Rough rice cultivar, storage temperature, moisture content, and duration affected (P < 0.05) the enthalpies and temperatures of gelatinization and retrogradation of rice flour. Bengal had a higher gelatinization enthalpy (P < 0.005) but lower gelatinization temperatures (P < 0.0001) than the long-grain Kaybonnet. Rice stored at 38°C exhibited higher gelatinization enthalpy and temperatures (P < 0.05) than those stored at 4 or 21°C. Storage duration affected the gelatinization and retrogradation properties through a higher order, rather than a linear, relationship.