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.     

Pulsed Nuclear Magnetic Resonance (PNMR) Study of Rice Starch Retrogradation

Although pulsed NMR (PNMR) has been used for qualitative study of starch retrogradation in selected systems, validation is necessary for its application to new systems. PNMR was used to analyze the retrogradation of rice starches in purified form, in rice flour, and in cooked rice grains. The standard curves between the relative solid content (S′, %) by PNMR and the percentage of gelatinized starch (GS, %) were determined for common rice flour, common rice starch, and waxy rice starch at different moisture contents. The coefficients of linear regression for these curves (R²) were all >0.997. Starches with different amylose contents were tested for S′ values at the stages of freshly gelatinized, retrograded (4°C, 18 days), and reheated (90°C, 20 min). The S′ of reheated starch (S′_reheat) was similar to the S′ of freshly gelatinized starch (S′₀), so we concluded that the increase in S′ during storage corresponded to amylopectin retrogradation. The effect of moisture content on retrogradation of rice starch, rice flour, and cooked rice grains was studied by PNMR, and the data were interpreted using the Avami equation. Decreasing the moisture content increased the rate of retrogradation and led to a higher parameter k and a lower parameter n. For moisture content in the range studied, PNMR can be used to follow amylopectin retrogradation of different rice starch systems.     

Structural and Retrogradation Properties of Rice Endosperm Starch Affect Enzyme Digestibility of Steamed Milled-Rice Grains Used in Sake Production

Structural and physicochemical characteristics of endosperm starch from milled rice grains of seven Japanese cultivars used in sake production were examined. Amylose content was 15.2–20.2%, number-average degree of polymerization (DP_n) of amylose was 900–1,400, and the ratio of short-to-long chain amylopectin was 2.7–3.5, respectively. The degree of retrogradation of purified starch stored for seven days at 4°C after gelatinization was 20–31%. The degree of retrogradation correlated negatively with the ratio of short-to-long chain amylopectin. The effect of holding time after steaming on enzyme digestibility and starch retrogradation of steamed rice grains was investigated. The longer the holding time after steaming, the greater the extent of retrogradation, and the less the degree of enzymatic digestibility. The decreased rate of enzyme digestibility correlated with amylopectin chain length distribution. Samples with short-chain amylopectin exhibited a slow decrease in enzyme digestibility. It was determined that the structure and retrogradation properties of endosperm starch in Japanese rice cultivars affect the decreasing rate of enzyme digestibility of the steamed, milled rice grains.     

Molecular Characteristics Influencing Retrogradation Kinetics of Rice Amylopectins

The enthalpy changes (ΔH) for melting of crystallites formed during retrogradation of 60% (w/w) amylopectins (AP) aged at 4°C were investigated using AP from 13 rice cultivars with well‐known structural properties. According to the Avrami equation, the resultant kinetic parameters for AP retrogradation were obtained in relation to structural factors. Generally, the AP systems studied showed two stages of retrogradation behavior during early (≤7 days) and late (≥7 days) storage. The Avrami exponent for early‐stage kinetics (n₁, 1.04–5.54) was greater than the corresponding value for late‐stage kinetics (n₂, 0.28–1.52). While the Avrami K constant of the early‐stage kinetics (K₁, 1.0×10^‐5 to 2.3×10^‐1 day^‐n) was lower than the corresponding value of late‐stage kinetics (K₂, 4.4×10^‐2 to 1.4 day^‐n). The ΔH values for late and infinite retrogradation stages showed a significantly positive correlation with the proportions of short chain (chain length [CL] ≤ 15 glucose units) and long chain (CL = 16–100 glucose units) fractions, respectively. Retrogradation of AP with a higher number‐average degree of polymerization, greater proportion of short chain fractions, and shorter average chain lengths revealed significantly greater n₁ values and smaller K₁ values. Values for n₂ and K₂ showed little influence from the molecular properties except for the proportion of extra long (CL>100 glucose units) and long chain fractions on K₂. The negatively linear relationships between log K and n suggest the importance of some nonstructural factors for AP retrogradation mechanisms in various starch systems.     

Method for Determining the Rate and Extent of Accelerated Starch Retrogradation

A method to accelerate and quantitate retrogradation of starch pastes using a freeze-thaw cycle (FTC) process and turbidometric analysis has been developed. Using this method and differential scanning calorimetry (DSC), it was determined that the rate of retrogradation in 2.5% waxy maize pastes was inversely correlated to the rate of freezing, and that the thawing temperature affected perfection of the crystallites in retrograded amylopectin. DSC and X-ray diffraction were used to determine whether the crystallites formed during the FTC process were the same as those formed in starch pastes held isothermally at 4°C. Analysis of retrogradation of pastes of starches from various botanical sources indicated that the method reflects retrogradation in higher concentration pastes. Retrogradation rates were reduced by the addition of sodium dodecyl sulfate. Microstructures of freeze-thaw processed waxy maize and common corn starch pastes were examined.     

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 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.     

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.     

Effect of Sucrose on Glass Transition,Gelatinization, and Retrogradation of Wheat Starch

Differential scanning calorimetry (DSC) was used to study the effect of sucrose on wheat starch glass transition, gelatinization, and retrogradation. As the ratio of sucrose to starch increased from 0.25:1 to 1:1, the glass transition temperature (T_g, T_g′) and ice melting enthalpy (ΔH_ice) of wheat starch‐sucrose mixtures (with total moistures of 40–60%) were decreased to a range of −7 to −20°C and increased to a range of 29.4 to 413.4 J/g of starch, respectively, in comparison with wheat starch with no sucrose. The T_g′ of the wheat starch‐sucrose mixtures was sensitive to the amount of added sucrose, and detection was possible only under conditions of excess total moisture of >40%. The peak temperature (T_m) and enthalpy value (ΔH_G) for gelatinization of starch‐sucrose systems within the total moisture range of 40–60% were increased with increasing sucrose and were greater at lower total moisture levels. The T_g′ of the starch‐sucrose system increased during storage. In particular, the significant shift in T_g′ ranged between 15 and 18°C for a 1:1 starch‐sucrose system (total moisture 50%) after one week of storage at various temperatures (4, 32, and 40°C). At 40% total moisture, samples with sucrose stored at 4, 32, and 40°C for four weeks had higher retrogradation enthalpy (ΔH) values than a sample with no sucrose. At 50 and 60% total moisture, there were small increases in ΔH values at storage temperature of 4°C, whereas recrystallization of samples with sucrose stored at 32 and 40°C decreased. The peak temperature (T_p), peak width (δT), and enthalpy (ΔH) for the retrogradation endotherm of wheat starch‐sucrose systems (1:0.25, 1:0.5, and 1:1) at the same total moisture and storage temperature showed notable differences with the ratio of added sucrose. In addition, T_p increased at the higher storage temperature, while δT increased at the lower storage temperature. This suggests that the recrystallization of the wheat starch‐sucrose system at various storage temperatures can be interpreted in terms of δT and T_p.     

Utilization of Hydroxypropylated Waxy Rice and Corn Starches in Korean Waxy Rice Cake to Retard Retrogradation

A traditional waxy rice gel cake in Korea, Injulmi, was prepared with hydroxypropylated waxy rice and corn starches (molar substitutions 0.13 and 0.11, respectively), and the textural and retrogradation characteristics of the cake were compared with a conventional cake made of waxy rice flour. In the pasting viscogram, hydroxypropylated starches exhibited reduced pasting temperatures, but increased peak viscosities compared with the unmodified starches. Under differential scanning calorimetry, the T_g′ and ice melting enthalpy of the starch gel cakes were reduced by hydroxypropylation, which indicated that the modified starches had higher water‐holding capacity than the unmodified starches. The degree of retrogradation, as measured by the hardness of the gel cake and the melting enthalpy, was significantly reduced by hydroxypropylation and hydroxypropylated waxy rice starch was more effective in retarding the retrogradation than hydroxypropylated waxy corn starch     

Changes in Retrogradation Properties of Rice Starches with Amylose Content and Molecular Properties

The increases in storage modulus (G′), retrogradation enthalpy change (ΔH) and ΔH‐related Avrami kinetic parameters of gelatinized rice starch dispersions at 25% (w/w) were investigated with respect to storage period, amylose content (AC), and molecular properties. Three high‐AC and five low‐AC rice cultivars were compared for understanding the multiple influences of AC and molecular properties involved. After refining the results of correlation analysis, the G′ of just‐cooled samples changed positively, mainly with AC and additionally with the average chain length of amylose (CL_AM) and the weight ratio of extra‐long plus long chains to short chains of amylopectin (AP) (r_APchain). The developed ΔH on short‐term storage (10 days) elevated with increasing AC and CL_AM and decreasing degree of polymerization of AP (DP_AP), but after long‐term aging for one to three months with increasing r_APchain, especially for the low‐AC cultivars examined. Greater Avrami rate constants for retrogradation could be attributed to the combination of a lower DP_AP and r_APchain or AP chain length and a greater CL_AM. The polynomials using these critical factors to describe the retrogradation parameters were elucidated and could account for 85–99.6% of data deviations.     

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.     

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.     

Relationships Between Soybean 11S Globulin Content and Thermal and Retrogradation Properties of Nonwaxy Maize Starch

In the present study, the relationships of soybean 11S globulin content, thermal properties, and retrogradation properties of nonwaxy maize starch in starch–globulin mixtures were investigated by differential scanning calorimetry. The onset and peak temperatures of maize starch were positively related to soybean 11S globulin content, whereas the thermal enthalpy was negatively related to it. However, the onset temperature, peak temperature, and thermal enthalpy of soybean 11S globulin were negatively related to maize starch content of mixtures. On the other hand, the onset and peak temperatures of retrograded maize starch were positively related to soybean 11S globulin content, whereas the retrogradation enthalpy was negatively related to it during storage. Therefore, adding soybean 11S globulin was an effective method to control maize starch gelatinization and retrogradation properties, which will be helpful for the food industry to produce high‐quality products based on starch and soybean protein.     

Retrogradation of Rice Flour Gel and Dough: Plasticization Effects of Some Food Additives

Certain food additives commonly used in flour products also have a plasticization effect on product shelf life regarding retrogradation. Sucrose, sorbitol, glycerol, citric acid, and acetic acid at 25, 25, 25, 0.5, and 0.5%, respectively, were added to two different starch gel systems: slurry (high‐amylose rice flour gel) and dough (waxy rice flour dough). All plasticizers increased gelatinization temperature, decreased enthalpy (ΔH), and promoted a more homogeneous system. Sucrose had the greatest effect on gelatinization increase. Rice dough was more susceptible to plasticizers, resulting in higher moisture content and a more amorphous structure. Retrogradation was highly positively correlated with amylose content, moisture retention, ratio of protons of water/starch, and previous occurrence of retrogradation. Moisture retention was increased in plasticizer‐added samples, especially waxy rice dough. Over a longer storage period, sucrose and sorbitol showed an antiplasticization effect in waxy rice flour dough, but glycerol and acid caused higher retrogradation in high‐amylose rice flour gel.     

Physicochemical Properties of Starch in Extruded Rice Flours

The effects of extruding temperatures and subsequent drying conditions on X‐ray diffraction patterns (XRD) and differential scanning calorimetry (DSC) of long grain (LG) and short grain (SG) rice flours were investigated. The rice flours were extruded in a twin‐screw extruder at 70–120°C and 22% moisture, and either dried at room temperature, transferred to 4°C for 60 hr, or frozen and then dried at room temperature until the moisture was 10–11%. The dried materials were milled without the temperature increasing above 32°C. XRD studies were conducted on pellets made from extruded and milled flours with particle sizes of 149–248 μm; DSC studies were conducted from the same material. DSC studies showed that frozen materials retrograded more than the flours dried at room temperature. The LG and SG samples had two distinct XRD patterns. The LG gradually lost its A pattern at >100°C, while acquiring V patterns at higher temperatures. SG gradually lost its A pattern at 100°C but stayed amorphous at the higher extruding temperatures. DSC analysis showed that retrograded flours did not produce any new XRD 2θ peaks, although a difference in 2θ peak intensities between the LG and SG rice flours was observed. DSC analysis may be very sensitive in detecting changes due to drying conditions, but XRD data showed gradual changes due to processing conditions. The gradual changes in XRD pattern and DSC data suggest that physicochemical properties of the extruded rice flours can be related to functional properties.     

稻米抗性淀粉的研究进展

稻米抗性淀粉具有重要的生理功能及食品应用价值,受到研究者的广泛关注。本文简述了抗性淀粉的分类及测定方法,介绍了稻米中抗性淀粉的测定方法、理化特性、生理功能和稻米抗性淀粉产业研发的研究进展,以期为我国富含抗性淀粉水稻品种选育及稻米抗性淀粉产业发展提供一些参考。     

Modeling Starch Gelatinization Kinetics of Milled Rice Flour

Milled long‐grain rice samples were evaluated by differential scanning calorimetry (DSC) to determine the kinetics of starch gelatinization. The experiments were conducted with milled rice flour with a 10.6% degree of milling. DSC thermograms were obtained from 35 to 110°C using heating rates between 1°C/min and 15°C/min. The rate constants were evaluated, and two activation energies were found for different temperature ranges. At <70.1°C gelatinization was not completed. It was assumed that at <70.1°C gelatinization would only affect the amorphous regions. During the subsequent phase the crystalline regions destabilized by the amorphous component begin to gelatinize. For moisture content of 70%, wet basis, and a heating rate of 12°C/min, the enthalpy of gelatinization reaches a constant value of 7.3 J/g.     

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.