Properties and Structures of Flours and Starches from Whole,Broken, and Yellowed Rice Kernels in a Model Study

The objective of this study was to compare the structure and properties of flours and starches from whole, broken, and yellowed rice kernels that were broken or discolored in the laboratory. Physicochemical properties including pasting, gelling, thermal properties, and X‐ray diffraction patterns were determined. Structure was elucidated using high‐performance size‐exclusion chromatography (HPSEC) and high‐performance anion‐exchange chromatography with pulsed amperometric detection (HPAEC‐PAD). The yellowed rice kernels contained a slightly higher protein content and produced a significantly lower starch yield than did the whole or broken rice kernels. Flour from the yellowed rice kernels had a significantly higher pasting temperature, higher Brabender viscosities, increased damaged starch content, reduced amylose content, and increased gelatinization temperature and enthalpy compared with flours from the whole or the broken rice kernels. However, all starches showed similar pasting, gelling, thermal properties, and X‐ray diffraction patterns, and no structural differences could be detected among different starches by HPSEC and HPAEC‐PAD. α‐Amylase may be responsible for the decreased amylopectin fraction, decreased apparent amylose content, and increased amounts of low molecular weight saccharides in the yellowed rice flour. The increased amount of reducing sugars from starch hydrolysis promoted the interaction between starch and protein. The alkaline‐soluble fraction during starch isolation is presumed to contribute to the difference in pasting, gelling, and thermal properties among whole, broken, and yellowed rice flours.     

Investigation of Digestibility In Vitro and Physicochemical Properties of A‐ and B‐Type Starch from Soft and Hard Wheat Flour

In this study, the functional properties of A‐ and B‐type wheat starch granules from two commercial wheat flours were investigated for digestibility in vitro, chemical composition (e.g., amylose, protein, and ash content), gelatinization, retrogradation, and pasting properties. The branch chain length and chain length distribution of these A‐ and B‐type wheat starch granules were also determined using high‐performance anion exchange chromatography (HPAEC). Wheat starches with different granular sizes not only had different degrees of enzymatic hydrolysis and thermal and pasting properties, but also different molecular characteristics. Different amylose content, protein content, and branch chain length of amylopectin in A‐ and B‐type wheat starch granules could also be the major factors besides granular size for different digestibility and other functional properties of starch. The data indicate that different wheat cultivars with different proportion of A‐ and B‐type granular starch could result in different digestibility in wheat products.     

Properties of Starches from Near‐Isogenic Wheat Lines with Different Wx Protein Deficiencies

To determine the effect of amylose content on the starch properties, the amylose content, pasting properties, swelling power, enzymatic digestibility, and thermal properties of partial and perfect waxy types along with their wild‐type parent were analyzed. As expected, amylose content decreases differently in response to the loss of each Wx gene, showing the least response to Wx‐A1a. Most of the characteristics, except the thermal properties of the amylose‐lipid complex in differential scanning calorimetry (DSC), differed significantly among the tested types. Furthermore, the breakdown, setback, and pasting temperatures from the Rapid Visco Analyser (RVA) and the enzymatic digestibility, swelling power, peak temperature, and enthalpy of starch gelatinization from DSC showed a correlation with the amylose content. The relationships between the peak viscosity from the RVA and the onset temperature of starch gelatinization determined by DSC with amylose content of the tested materials were not clear. Waxy starch, which has no amylose, showed a contrasting behavior in starch gelatinization compared with nonwaxy starches. Among the nonwaxy starches, lower setback, lower pasting temperature, higher enzyme digestibility, higher peak temperature, higher enthalpy of starch gelatinization, and higher swelling were generally associated with low amylose starches.     

Significance of Starch Properties and Quantity on Sponge Cake Volume

We evaluated the qualitative and quantitative effects of wheat starch on sponge cake (SC) baking quality. Twenty wheat flours, including soft white and club wheat of normal, partial waxy, and waxy endosperm, as well as hard wheat, were tested for amylose content, pasting properties, and SC baking quality. Starches isolated from wheat flours of normal, single‐null partial waxy, double‐null partial waxy, and waxy endosperm were also tested for pasting properties and baked into SC. Double‐null partial waxy and waxy wheat flours produced SC with volume of 828–895 mL, whereas volume of SC baked from normal and single‐null partial waxy wheat flours ranged from 1,093 to 1,335 mL. The amylose content of soft white and club wheat flour was positively related to the volume of SC (r = 0.790, P < 0.001). Pasting temperature, peak viscosity, final viscosity, breakdown, and setback also showed significant relationships with SC volume. Normal and waxy starch blends having amylose contents of 25, 20, 15, and 10% produced SCs with volume of 1,570, 1,435, 1,385, and 1,185 mL, respectively. At least 70 g of starch or at least 75% starch in 100 g of starch–gluten blend in replacement of 100 g of wheat flour in the SC baking formula was needed to produce SC having the maximum volume potential. Starch properties including amylose content and pasting properties as well as proportion of starch evidently play significant roles in SC baking quality of wheat flour.     

Effects of Genotype and Environment on the Starch Properties and End‐Product Quality of Oats

Five Canadian oat genotypes were grown at six environments in Manitoba to assess the effects of genotype, environment, and genotype‐by‐environment interaction on oat starch properties and end‐product quality. Genotypic variation was significant for total starch, amylose content, starch swelling volume (SSV), Rapid Visco Analyser (RVA) pasting viscosities, differential scanning calorimetry (DSC) thermal properties, and starch gel texture as well as the quality of flakes and cooked oatmeal made by laboratory‐scale methodologies. Environment was the dominant factor contributing to the total variation of starch content, RVA pasting viscosities, SSV, and DSC thermal properties. Most measurements of starch gel and oatmeal texture were not affected by growing environment. Cross‐over analysis revealed that changes in the ranking of genotypes across environments occurred for starch RVA hot paste, breakdown and shear thinning viscosities, work of gel compression, flake hydration capacity, and the proportion of large flakes, indicating that breeding for these traits would require multiple testing sites. Trends were observed between oatmeal texture and several flake and starch gel properties, warranting further study. Results of this study indicated that there is a potential to breed Canadian oat cultivars with improved functional end‐product quality for use in the milling and food manufacturing industries.     

Bread Quality of Spelt Wheat and Its Starch

Flours from five spelt cultivars grown over three years were evaluated as to their breadbaking quality and isolated starch properties. The starch properties included amylose contents, gelatinization temperatures (differential scanning calorimetry), granule size distributions, and pasting properties. Milled flour showed highly variable protein content and was higher than hard winter wheat, with short dough‐mix times indicating weak gluten. High protein cultivars gave good crumb scores, some of which surpassed the HRW baking control. Loaf volume was correlated to protein and all spelt cultivars were at least 9–51% lower than the HRW control. Isolated starch properties revealed an increase in amylose in the spelt starches of 2–21% over the hard red winter wheat (HRW) control. Negative correlations were observed for the large A‐type granules to bread crumb score, amylose level, and final pasting viscosity for cultivars grown in year 1999 and to pasting temperature in 1998 samples. Positive correlations were found for the small B‐ and C‐type granules relative to crumb score, loaf volume, amylose, and RVA final pasting viscosity for cultivars grown in 1999, and to RVA pasting temperature for samples grown in 1998. The environmental impact on spelt properties seemed to have a greater effect than genetic control.     

Starch Pasting Properties and Amylose Content from 17 Waxy Barley Lines

Starch pasting properties and amylose content from 17 waxy barley lines (waxy gene originating from indigenous lines and an artificial mutant) were analyzed using rapid viscosity analysis (Rapid Visco Analyser [RVA]). Amylose contents varied from 0% (Shikoku‐hadaka 97) to 9.5% (Shikoku‐hadaka 96) compared with 30% for normal barley. Eight parameters were obtained from RVA profiles of these lines and correlation between each of these parameters and amylose content were evaluated. These parameters include pasting temperature (PT), peak viscosity (PV), temperature at PV, minimum viscosity (MV), final viscosity (FV), breakdown (BD), setback (SB), and time maintained at >80% PV (hot paste stability [HPS]). Significant correlations (0.64 and 0.61) were found between amylose content and FV and SB, respectively. High correlation (0.72) was found between amylose content and temperature at PV. HPS calculated from RVA profiles showed the highest correlation (0.79) to amylose content. Outer part of barley grains contained higher amounts of amylose than the inner part. There was a tendency that both PT and FV positively correlated to the amylose content of these parts.     

Fine Structures of Starches from Long‐Grain Rice Cultivars with Different Functionality

The structural features of rice starch that may contribute to differences in the functionality of three long‐grain rice cultivars were studied. Dried rough rice samples of cultivars Cypress, Drew, and Wells were analyzed for milling quality, grain physical attributes, and starch structures and physicochemical properties. Drew was lower in head rice yield and translucency and higher in percentage of chalky grains compared with Cypress and Wells. Apparent amylose content (21.3–23.1%), crude protein (8.3–8.6%), and crude fat (0.48–0.64%) of milled rice flours were comparable, but pasting properties of rice flours as measured by viscoamylography, as well as starch iodine affinity and thermal properties determined by differential scanning calorimetry were different for the three cultivars. Drew had higher peak, hot paste, and breakdown viscosities, and gelatinization temperature and enthalpy. Molecular size distribution of starch fractions determined by high‐performance size‐exclusion chromatography showed that the three samples were similar in amylose content (AM) (20.0–21.8%) but differed in amylopectin (AP) (64.7–68.3%) and intermediate material (IM) (10.9–13.5%). Drew had highest AP and lowest IM contents, whereas Cypress had the lowest AP and highest IM contents. High‐performance anion‐exchange chromatography of isoamylase‐debranched starch indicated that the AP of Drew was lower in A and B1 chains but higher in B2, B3, and longer chains.     

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.     

Molecular Structure and Some Physicochemical Properties of Buckwheat Starches

The molecular structure and pasting properties of starches from eight buckwheat cultivars were examined. Rapid viscograms showed that buckwheat starches had similar pasting properties among cultivars. The actual amylose content was 16–18%, which was lower than the apparent amylose content (26–27%), due to the high iodine affinity (IA) of amylopectin (2.21–2.48 g/100 g). Amylopectins resembled each other in average chain‐length (23–24) and chain‐length distributions. The long‐chains fraction (LC) was abundant (12–13% by weight) in all the amylopectins, which was consistent with high IA values. The amyloses were also similar among the cultivars in number‐average DP 1,020–1,380 with 3.1–4.3 chains per molecule. The molar‐based distribution indicated that all the amyloses comprised two molecular species differing in molecular size, although the weight‐based distribution showed a single species. A comparison of molecular structures of buckwheat starches to cereal starches indicated buckwheat amylopectins had a larger amount of LC, and their distributions of amylose and short chains of amylopectin on molar basis were similar to those of wheat and barley starches.     

Survey of White Salted Noodle Quality Characteristics in Wheat Landraces

The introduction of novel quality characteristics from wheat (Triticum aestivum L.) landraces can enhance the genetic diversity of current wheat breeding programs. The composition of starch and protein in wheat is important when determining the end‐product quality, particularly for white salted noodles (WSN). Quality characteristics that contribute to the production of improved WSN include high starch pasting peak viscosity, low amylose content, high proportion of A‐type granules, low protein content, soft grain texture, and high protein quality as measured by SDS sedimentation volume. A survey of 133 wheat landraces from Afghanistan, China, Egypt, Ethiopia, India, Iran, Syria, and Turkey was conducted to examine the genetic variability of starch and protein quality characteristics. Two wheat cultivars, Rosella and Meering, were used as the quality controls. The variation in starch pasting peak viscosities observed among the wheat landraces had a range of 175–295 Rapid Visco Analyser units (RVU), where 52 of the landraces were not significantly different from Rosella, a commercial soft grain wheat with high pasting properties. The amylose content of the landrace population was 23.4–30.2%, where 17 landraces had significantly lower values than Rosella. The proportion of A‐type granules was 60.5–73.9%, where 112 landraces had significantly higher values than Rosella. The grain texture hardness score was 28.0–99.3, the total protein content was 8.0–15.1%, and the adjusted SDS sedimentation volume (SDS/protein) was 1.6–7.0 mL/%P. The landrace AUS4635 had high starch pasting peak viscosity, high breakdown, low amylose content, low protein content, soft grain texture, and high protein quality flour. This wheat is an ideal parent to use in a breeding program that increases the genetic variation available to develop cultivars with high‐quality WSN characteristics.     

Increase in Apparent Amylose Content and Change in Starch Pasting Properties at Cool Growth Temperatures in Mutant Wheat

Some mutant wheat lines with low‐amylose content were grown in a field and greenhouse (15 or 20°C) to compare apparent amylose content and starch pasting properties. The apparent amylose content of flour and starch increased and starch pasting parameters as measured by a Rapid Visco Analyser (RVA) changed in the greenhouse (at cool temperatures) during seed maturation. Densitometric analysis of the protein band separated by electrophoresis suggested that the increase in amylose content by cool temperature was related to the amount of Wx‐D1 protein. This data suggests that the Wx‐D1 gene was responsible for these changes. In wheat starch from Tanikei A6099 and Tanikei A6598 at 15°C, the value of final viscosity and total setback was higher than that from the field. In wheat starch from Tanikei A6599‐4 (waxy mutant with stable hot paste viscosity), the peak viscosity temperature was higher and time maintained >80% of the peak was shorter at 15°C than that from the field. Genetic analysis using doubled‐haploid (DH) lines from a combination of Tanikei A6599‐4 and Kanto 118 (low‐amylose line) showed that apparent amylose content increased and the starch pasting curve and properties changed in waxy progenies similar to Tanikei A6599‐4.     

Comparison of Flour Starch Properties in Half‐Sib Families of Opaque‐2 Maize (Zea mays L.) from Argentina

Since the discovery of the o2 mutation in maize, many studies have reported the characterization of the protein quality of opaque‐2 genotypes. However, few have reported the properties of their starch. The objective of this study was to characterize flour starch properties of 12 half‐sib families of opaque‐2 maize from Argentina. Chemical composition and thermal and pasting properties of whole grain flour were determined. Nonopaque genotypes were used as a control. Starch content of opaque‐2 genotypes did not show significant differences compared with nonopaque genotypes, yet amylose content was significantly lower. A high variability in pasting and thermal properties was observed in genotypes. Opaque samples showed a significantly higher peak viscosity and a lower pasting temperature compared with nonopaque samples, probably owing to larger and less compact starch granules in the floury endosperm. The higher the gelatinization enthalpy of opaque‐2 genotypes was, the lower the amylose content in relation to nonopaque varieties. Two retrogradation endotherms were observed in DSC analysis: one corresponding to amylopectin crystallization and the other to melting of amylose‐lipid complex. Both enthalpies were considered total starch retrogradation (ΔH _RT). A wide range of variation was obtained in ΔH _RT in opaque‐2 genotypes, but no significant differences between opaque and nonopaque genotypes were observed. The differences in starch properties found in this study would make it possible to identify opaque‐2 families with particular characteristics for the development of starchy food items adapted to specific processing traits.     

Rice amylopectin fine structure variability affects starch digestion properties

The possibility to identify or develop new rice cultivars with low glycemic response was investigated. Twelve rice cultivars with a narrow range of amylose contents were selected based on their wide variation in rapid viscoanalyzer (RVA) pasting breakdown to study the relationship between starch digestibility and amylopectin fine structure and pasting properties. Rice flour samples were cooked for in vitro digestibility analysis using the standard Englyst assay. RVA was performed for pasting properties of starches. Results showed that rapidly digestible starch (RDS) was highly and negatively correlated (r = -0.86, p < 0.01; r = -0.81, p < 0.01) with FrI long and FrII intermediate/short debranched amylopectin linear chains, respectively, and positively correlated (r = 0.79; p < 0.01) with FrIII very short linear chains. Slowly digestible (SDS) starch was positively correlated (r = 0.80, p < 0.01; 0.76, p < 0.01) with FrI and FrII, respectively, and negatively correlated (r = -0.76, p < 0.01) with FrIII. RVA breakdown viscosity was positively correlated (r = 0.88, p < 0.01) with RDS and negatively correlated (r = -0.89, p < 0.01) with SDS. Thus, the RVA method potentially could be used as a screening tool for starch digestion properties. This study reveals a molecular basis in amylopectin fine structure variability for starch digestion properties in rice cultivars and could have value in identifying slowly digesting cultivars as well as developing a breeding strategy to produce low glycemic rice cultivars. Keywords: Rice; starch; RVA; amylopectin; digestibility.     

Molecular and Gelatinization Properties of Rice Starches from IR24 and Sinandomeng Cultivars

The differences in pasting properties involving gelatinization and retrogradation of rice starches from IR24 and Sinandomeng cultivars during heating‐cooling processes were investigated using a Rapid Visco Analyser (RVA)and a dynamic rheometer. The results were discussed in relation to the molecular structure, actual amylose content (AC), and concentration of the starches. Generally, both starches possessed a comparable AC (≈11 wt%), amylose average chain length (CL), iodine absorption properties, and dynamic rheological parameters on heating to 95°C at 10 wt% and on cooling to 10°C at higher concentrations. In contrast to Sinandomeng, IR24 amylose had a greater proportion of high molecular weight species and number‐average degree of polymerization (DP_n). IR24 amylopectin possessed a lower DP_n and greater CL, exterior CL (ECL), and interior CL (ICL). Comparing the results of RVA analysis and dynamic rheology, the gelatinization properties and higher retrogradation tendencies of IR24 starch can be related to the structural properties and depend on starch concentration. In addition, the exponent n of starch concentration for storage moduli at 25°C (G′₂₅ ∝ Cⁿ) increased linearly with increasing AC.     

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.     

Use of Mixolab in Predicting Rice Quality

Mixolab is a new instrument with capability to measure starch pasting properties on actual dough. It characterizes dough rheological behavior using a dual constraints of mixing and temperature. Rice samples (183) collected from 15 provinces across China were tested to determine the possibility of using Mixolab in predicting rice quality. Mixolab measurements, torque (Nm) at different mixing and heating stages (C1 to C5) were compared with rice quality characteristics (gelatinization temperature and consistency, amylose and protein contents), Rapid Visco‐Analyser (RVA) parameters and sensory assessments scores of cooked rice. Our results showed that Mixolab parameters were good indicators of amylose and protein content and quality suggested by significant correlations among Mixolab parameters, and between Mixolab and RVA measurements. Based on a subsample of 30 rice cultivars, correlation coefficients between the Mixolab parameter C4 and sensory assessment characteristics of palatability and total sensory score was negatively significant (P < 0.05). C_b (C3 – C4) was also significantly correlated with flavor (P < 0.05). The rice samples that gave high palatability and total sensory scores had low C4 values and low amylose contents. The cooked rice with high flavor had high values of C_b and GT but low protein content. It is possible to determine physicochemical properties of rice flour and sensory characteristics of cooked rice using Mixolab parameters.     

Physicochemical Properties and In Vitro Starch Digestibility of Cooked Rice from Commercially Available Cultivars in Canada

The influence of amylose content, cooking, and storage on starch structure, thermal behaviors, pasting properties, and rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) in different commercial rice cultivars was investigated. Long grain rice with high‐amylose content had a higher gelatinization temperature and a lower gelatinization enthalpy than the other rice cultivars with intermediate amylose content (Arborio and Calrose) and waxy type (glutinous). The intensity ratio of 1047/1022 cm^–1 determined by Fourier Transform Infrared (FT‐IR), which indicated the ordered structure in starch granules, was the highest in glutinous and the lowest in long grain. Results from Rapid ViscoAnalyser (RVA) showed that the rice cultivar with higher amylose content had lower peak viscosity and breakdown, but higher pasting temperature, setback, and final viscosity. The RDS content was 28.1, 38.6, 41.5, and 57.5% in long grain, Arborio, Calrose, and glutinous rice, respectively, which was inversely related to amylose content. However, the SDS and RS contents were positively correlated with amylose content. During storage of cooked rice, long grain showed a continuous increase in pasting viscosity, while glutinous exhibited the sharp cold‐water swelling peak. The retrogradation rate was greater in rice cultivars with high amylose content. The ratio of 1047/1022 cm^–1 was substantially decreased by cooking and then increased during storage of cooked rice due to the crystalline structure, newly formed by retrogradation. Storage of cooked rice decreased RDS content and increased SDS content in all rice cultivars. However, no increase in RS content during storage was observed. The enthalpy for retrogradation and the intensity ratio 1047/1022 cm^–1 during storage were correlated negatively with RDS and positively with SDS (P ≤ 0.01).     

Structural Characteristics,Properties, and In Vitro Digestibility of Rice

Using rice samples derived from normal rice cultivars and endosperm starch mutant, we investigated key factors contributing to the enzyme digestibility of steamed rice grains. The chemical composition of polished rice grains, structural features of endosperm starch, and enzyme digestibility of steamed rice grains were examined. The protein content of polished rice grains was 4.6–9.1%, amylose content was 4–27%, the DP_n of purified amylose was 900–1,600, the amylopectin short/long chain ratio was 1.2–5.9, and the enzyme digestibilities of steamed polished rice grains were 0.9–12.6 °Brix. Amylose content and RVA parameters (viscosity, breakdown, and setback) correlated significantly with enzyme digestibility of steamed rice grains. Multiple regression formulas were constructed to predict digestibility of steamed rice grain as a function of the molecular characteristics of the starch. When both amylose content and the short/long chain amylopectin ratio were used as predictor variables, they accounted for >80% of the observed variance in digestibility of steamed rice grains. Multiple regression revealed that the more digestible rice samples had starch with a lower amylose content and more short‐chain amylopectin. Reassociation of amylose‐lipid complex and recrystallization of amylopectin in the stored steamed rice grains was monitored by differential scanning calorimetry (DSC), and the observed retrogradation properties were related to the structural characteristics of starch and to the enzyme digestibility of steamed rice grains.     

Wheat Tortilla Quality: Impact of Amylose Content Adjustments Using Waxy Wheat Flour

Amylose content is closely related to wheat flour pasting or thermal properties, and thus affects final food qualities. Fourteen flour blends with amylose content ranges of <1 to 29% were used to study tortilla production and quality parameters. Reduced amylose contents decreased dough stickiness and pliability; low amylose doughs were also very smooth in appearance. Very low flour amylose content was associated with earlier tortilla puffing and poor machinability during baking, darker color, low opacity, larger diameters, and reduced flexibility after storage. Tortilla texture analysis indicated that lowering amylose content gave fresh tortillas higher extensibility; after three or more days storage, however, low amylose flours required more force to break the tortillas and the rupture distances became shorter. These results, as reflected in covariate analysis, were not significantly affected by the flour blend's protein content, swelling volume/power, SDS‐sedimentation volume, mixograph dough development time, or mixograph tolerance score. Based on our observation of an initial increase in extensibility with reduced‐amylose tortillas, adding 10–20% waxy flour into wild‐type flours should be ideal for restaurant (on‐site) tortilla production or circumstances where tortillas are consumed shortly (within a day) after production. The optimal flour amylose content for hot‐press wheat tortilla products is 24–26%.