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.     

Effect of Cultural Management Practices on Grain Quality of Two Rice Cultivars

To reduce fuel and labor costs and increase profits, farmers are trying new ways of growing rice (Oryza sativa L.). This includes changing crop rotations, tillage systems, and fertilization levels. There is little information on how these changes affect the cooking quality of rice. We therefore looked at the parameters associated with cooking and processing quality (apparent amylose, gelatinization temperature, lipid and protein contents, and pasting properties) of two U.S. long grains (Cybonnet and Wells) that were grown using two different tillage systems, standard rate and high rates of fertilization, and different crop rotations (continuous rice R‐R, rice after soybeans R‐SB, and rice after corn R‐C). No differences in quality traits were observed among any of the tillage systems. Rice grown in continuous rice rotation had the lowest protein content of brown and milled rice (8.6 and 8.1%, respectively) as compared to the highest levels observed in the rice‐soybean rotation (9.3 and 8.6%, respectively). Rice grown in continuous rice rotation also had higher peak viscosity than other crop rotations. Increasing the fertilization rate increased the protein content of brown rice and decreased peak, trough, and final viscosities. Apparent amylose content, gelatinization temperature, and lipid content were not affected by crop rotation or fertility; however, they were influenced by cultivar. Although the results indicated statistical differences for some quality parameters, the differences were small enough that they are unlikely to have a major impact on processing quality of long grain rice if co‐mingled.     

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).     

Impact of Elevated Nighttime Air Temperatures During Kernel Development on Starch Properties of Field‐Grown Rice

The structural features of starch were examined to better understand the causes of variability in rice quality resulting from nighttime air temperature (NTAT) incidence during kernel development. Starch samples were isolated from head rice of four cultivars (Bengal, Cypress, LaGrue, and XL723) field‐grown in four Arkansas locations (Keiser, Pine Tree, Rohwer, and Stuttgart) in 2009 and 2010. Average NTATs recorded during the grain‐filling stages of rice reproductive growth in the four locations were 3.0–8.4°C greater in 2010 than 2009. Elevated NTATs altered the deposition of starch in the rice endosperm. Means pooled across cultivars and locations showed that amylose content was 3.1% (percentage points) less for the 2010 sample set. The elevated NTATs in 2010 resulted in a decrease in the percentage of amylopectin short chains (DP ≤ 18) and a corresponding increase in the percentage of long chains (DP ≥ 19) by an average of 1.3% (percentage points). The greater NTATs in 2010 also produced greater starch paste peak, final, and breakdown viscosities, whereas setback and total setback viscosities decreased. Changes in paste viscosity were highly correlated with the changes in the proportion of amylose and amylopectin. Onset gelatinization temperature was greater by 3.5°C, gelatinization enthalpy by 1.3 J/g, and relative crystallinity by 1.5% (percentage points) for the 2010 sample set. Changes in gelatinization parameters and granule relative crystallinity were highly correlated with the changes in amylopectin chain‐length distribution. Year × cultivar × location interaction effects were statistically insignificant, indicating that the four cultivars evaluated all showed some degree of susceptibility to the effects of temperature incidence during kernel development, regardless of the growing location.     

Classification of Rice Based on Statistical Analysis of Pasting Properties and Apparent Amylose Content: The Case of Oryza glaberrima Accessions from Africa

The diversity of 1,020 Oryza glaberrima rice accessions being kept at the Genetic Resources Unit of the Africa Rice Center with a varied range of apparent amylose content (AAC) and pasting properties was explored with cluster analysis. Rice cultivars are usually characterized according to grain dimensions, AACs, and gelatinization temperatures; however, this work focused on grouping African rice accessions based on their pasting properties and AAC. Using the Ward method of hierarchical cluster analysis, 1,020 rice accessions were initially distributed into five major clusters and further into 23 subclusters. The distribution pattern indicated that clusters I, II, III, IV, and V formed 27.6, 10.2, 15.8, 23.7, and 22.6% of the entire population, respectively. Although some of the groups had similar AAC, their pasting properties were very different, making it imperative for further investigations. Peak viscosity highly correlated (P < 0.01) with trough, breakdown, and final viscosities in all five clusters, whereas correlation between peak viscosity and AAC was not significant within clusters II and IV. Additionally, this categorization serves as a tool for exploring materials that can be employed in the development of rice cultivars for specific end uses.     

Relationships Between Some Structures and Functionalities of Starches from Wheat Cultivars Grown in East China

Starches separated from 30 wheat cultivars grown in East China were studied for granule size, amylose content, degree of crystallinity, thermal, pasting, and gel textural properties. Average granule size and amylose content of wheat starches were 15.08–20.8 μm and 29.43–34.19%, respectively. The degree of crystallinity and enthalpy of gelatinization of samples was 29.54–42.12% and 5.2–9.95 J/g, respectively. The gelatinization temperature and pasting temperature were 59.45–62.2°C and 75.40–83.95°C, respectively. There was a wide range of gel hardness values (208.5–426 g). Various significant correlations between functionality and structural parameters were observed. Highly positive correlations were found between the gelatinization temperatures. Gelatinization peak temperature was significantly correlated to hardness of starch gels (r = –0.374, P < 0.05). Significant correlations were observed between amylose content and breakdown viscosity (r = –0.483, P < 0.01), hardness (r = 0.373, P < 0.05), and cohesiveness (r = 0.378, P < 0.05). Many significant correlations between the various pasting parameters were observed. The average granule size was positively correlated to peak viscosity, trough viscosity, and final viscosity (r = 0.369, 0.381, and 0.398, respectively, P < 0.05).     

Genetic Diversity in Physical Properties of Starch from a World Collection of Amaranthus

Physical and functional properties of starches isolated from 93 noncultivated genotypes of nine Amaranthus species from a world germ plasm collection and an additional 31 cultivated Amaranthus genotypes obtained from China were tested. A wide variation was found in the properties tested among the Amaranthus species and among genotypes within the same species. When comparing starches from cultivated and noncultivated genotypes, it was generally found that amylose was lower; starch pasting profiles were more consistent with higher peak viscosity, lower breakdown, and lower setback; the gelatinization temperature was lower; and energy of enthalpy was higher. Under cool storage, the hardness of cultivated starch pastes was lower and the adhesiveness was higher. As expected, amylose content was a primary factor affecting the physical and functional properties of Amaranthus starch. Compared with reference maize, rice, and wheat starches, Amaranthus starch tended to have lower hot paste viscosity and lower cool paste viscosity; and higher gelatinization temperatures and higher energy of enthalpy. Furthermore, Amaranthus starch pastes showed less change of gel hardness and adhesiveness after cold storage. The environmental effect on the different properties of starch varied among Amaranthus species. It is suggested that Amaranthus starches can be developed for a wide range of food uses.     

辐照改良水稻淀粉特性的研究

以相似AAC的不同类型水稻 (籼稻、粳稻和杂交稻 )和不同AAC早籼稻品种为材料 ,研究了辐照对淀粉粘滞性、理化品质和淀粉颗粒的影响。研究表明 ,最高粘度 (PKV)、热浆粘度 (HPV)、冷胶粘度 (CPV)、消减值 (SBV)和回复值 (CSV)等 5个RVA谱特征参数随剂量增加均显著下降。辐照明显降低了低AAC品种、糯稻和中等AAC品种的AAC ,但对高AAC品种的AAC影响不显著。辐照对碱消值 (ASV)无影响 ,但最高粘度时间 (PKT)随剂量增加而下降。胶稠度尤其是高AAC的胶稠度 (GC)随剂量增加明显提高。胚乳内淀粉颗粒经辐照处理也有所变形。结果表明 ,辐照可提高稻米食用和蒸煮品质。     

Functional Characteristics of Bread Wheat (Triticum aestivum L.) Near‐Isogenic Lines Differing at the Waxy (Wx) Locus

The Waxy (Wx) gene in hexaploid wheat (Triticum aestivum L.) encodes granule‐bound starch synthase (GBSS1), which is involved in the synthesis of amylose, a mostly linear glucan polymer that makes up ∼25% of wheat starch. A null mutation of the Wx gene in each of the three genomes is associated with starch almost entirely consisting of the branched glucan polymer amylopectin (waxy starch), with corresponding changes in functionality. However, the rheological behavior of partially waxy starch remains unclear. The objective of this study was to characterize flour and baking quality in 16 near‐isogenic lines, null at the Wx locus on zero, one, two, or all three genomes, grown in four different environments. Across allelic groups, significant variations in amylose concentrations, flour paste viscosity, loaf structure and texture, dough stability, and proximate variables were observed. Because waxy wheat starch has greater water absorbance and resistance to retrogradation than normal starch, its inclusion in flour blends has been suggested as a means of improving the texture and appearance of bakery products and noodles. The results indicate that wheat encoding <3 functional homeologs of GBSS1 produces starch that has potential in the production of certain food items, such as Asian noodles. However, further research is necessary to determine the optimal amylose‐to‐amylopectin ratio to improve baking quality.     

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.     

Properties of Starches from Several Low‐Amylose Rice Cultivars

The starch properties of five low‐amylose rice cultivars, Yawarakomachi, Soft 158, Hanabusa, Aya, and Snow Pearl, were compared with those of two normal amylose rice cultivars, Nipponbare and Hinohikari. There were no large differences in the distributions of the amylopectin chain length determined by high‐performance anion‐exchange chromatography, and the starch gelatinization properties determined by differential scanning calorimetry, between normal and low‐amylose rice cultivars. Results obtained using rapid viscosity analysis indicated that low‐amylose rice starches had lower peak viscosity, breakdown, and setback values than normal amylose rice starches. Starch granules from low‐amylose rice cultivars had a higher susceptibility to glucoamylase than those from normal amylose rice cultivars. The results of this study showed some differences between normal and low‐amylose rice starches in pasting properties and enzymatic digestibility.     

Genotype and Environmental Influences on Pasting Properties of Rice Flour

The pasting behavior of flour from several Australian rice (Oryza sativa L.) cultivars, differing in amylose content and grown in three different locations and three seasons, were determined using the Rapid Visco Analyser. Genotype, growth season, and growth location all affected the pasting behavior of rice flour. The amylose content of the same cultivar was significantly higher in the coolest growing season, resulting in RVA traces with lower peak viscosity and higher setback than samples with lower amylose content. When the same cultivar of rice was grown in different locations in the same season, there were no significant differences in the total starch, protein, lipid, and amylose content of the flour, but there were significant differences in the pasting behavior. This indicates that environmental as well as genetic factors influence the pasting behavior of rice flour. Flour from parboiled and quick‐cooking rice did not paste and had low viscosities compared with unprocessed rice. Results from this study showed that the pasting behavior of rice flour was related to genotype and was influenced by environmental factors that brought about subtle changes in the grains that were not picked up by chemical analyses.     

Kernel and Starch Properties of U.S. and Imported Medium‐ and Short‐Grain Rice Cultivars

The production of medium‐ and short‐grain rice in the mid‐Southern U.S. rice‐growing region is increasing. This work aimed to identify the quality traits of importance to the markets for these grain types. Twenty‐five medium‐ and short‐grain milled rice samples were collected and analyzed for physical, gelatinization, pasting, and starch structural properties. Six samples were from Arkansas (AR), five from California (CA), and 14 imported (IM). Cluster and principal component analyses showed that the AR samples had greater gelatinization temperature, enthalpy, and percentages of amylopectin long chains (B2 and B3 chains) but lesser kernel whiteness, total setback viscosity, and percentage of amylopectin short chains (A chains) than the CA samples. With the exception of one sample from Taiwan, chemometrics indicated that the IM samples differed from the AR samples (cluster A) in some properties and were grouped into three clusters (clusters B, C, and D). Cluster B samples had properties that were similar to the CA samples; cluster C samples had lower gelatinization temperature and peak viscosity but greater percentages of amylose and A chains than the AR samples; and cluster D samples had lesser paste breakdown but greater final viscosity and percentage of B1 chains than the AR samples. Kernel width, color, and chalk were the primary sources of variation in milled rice appearance. In relation to structure and functionality, the percentages of amylopectin A and B3 chains and amylose content were the major sources of variation.     

A Better Understanding of Factors That Affect the Hardness and Stickiness of Long‐Grain Rice

Eight U.S. long‐grain rice cultivars were studied for chemical compositions, physicochemical properties, and leaching characteristics in relation to hardness and stickiness of rice flour paste and cooked rice. There were differences in the chemical composition of rice kernels among the eight rice cultivars, including crude protein (6.6–9.3%), crude fat (0.18–0.51%), and apparent amylose content by iodine colorimetry (19.6–27.0%). Differences were also observed in gelatinization temperatures and enthalpies, pasting temperatures and viscosities, leached/insoluble amylose, soluble solids, and hardness and stickiness of rice flour pastes and cooked rice kernels. The quantity and molecular size distribution of the leached starch molecules varied greatly among the samples. Protein and crude lipid contents negatively correlated with hardness of rice flour paste and cooked rice, but positively correlated with stickiness. Apparent amylose content correlated with gel properties but not cooked rice texture, whereas the ratio of A and short B chains to long B chains of amylopectin correlated significantly with cooked rice texture.     

Composition Dependencies of the Rheological Properties of Rice Starch Blends

The gelatinization, pasting, and dynamic rheological parameters of rice starch dispersions from Kaoshiung Sen 7 (KSS7), Taichung Waxy 70 (TCW70), and their blends were examined in relation to total starch concentration (C_t) and the property of starch components. Mixing the rice starches, especially at equivalent ratios, resulted in decreasing onset temperature for gelatinization or developing viscosity and in cold‐paste viscosity, accompanied by a synergistically increased peak viscosity. The logarithmic of storage moduli, G′, for all starch dispersions except the retrograded systems of C_t = 20–30 wt%, showed two linear dependencies on the weight‐average amylose content (AC) of the blends separating at a critical AC of 20 wt% (i.e., TCW70 = 25 wt%). Interestingly, the temperatures at which G′ started to increase drastically maximized on heating, and the exponent n of G′ ∝ C_tⁿ also maximized at the same TCW70 starch concentration Generally, the elasticity of the systems after complete gelatinization and retrogradation followed the isostress models of Takayanagi's blending laws at C_t = 10 wt%, but changed to the intermediates of isostress and isostrain at C_t = 20–30 wt%. The changes in these parameters can be explained by competitive swelling behavior, the strengthening effect of swollen granules, and shear disintegration.     

Categorizing Rice Cultivars Based on Cluster Analysis of Amylose Content,Protein Content and Sensory Attributes

Presently, rice cultivars are categorized according to grain dimensions, amylose content, and alkali spreading value (gelatinization temperature type). Categorization of rice cultivars based on total sensory impact is needed. This work endeavors to divide world rices into groups based on amylose, protein, flavor, and texture properties. Ninety‐one rice samples representing 79 different cultivars and seven growing locations were separated into seven groups with Ward's Cluster Analysis. Cluster 1 included a third of the rice samples and had cultivars with a large diversity of grain shapes and amylose contents. Mean attribute scores for this cluster were near the grand mean for the collective rice samples for nearly every sensory attribute. Cluster 2 included conventional U.S. short‐ and medium‐grain cultivars. Cluster 3 included conventional U.S. medium cultivars that were produced in Louisiana. Mean sensory scores for this cluster characterized these cultivars as having relatively undesirable flavor and texture attributes. Cluster 4 included Japanese premium quality cultivars and U.S. medium‐grain cultivars developed for the Japanese market. Cluster 5 included high‐amylose, indica types that had relatively firm textural properties. Cluster 6 included relatively soft cooking, aromatic cultivars. Cluster 7 included waxy cultivars and other soft cooking grains. In several cases, the production environment (location, weather effects, etc.) influenced flavor and texture characteristics and resulted in the cultivar falling into an unexpected cluster. This categorization serves as a catalyst for indexing rice cultivars for cooking and processing qualities.     

Effect of Aging on the Quality of Glutinous Rice Crackers

The experiment was conducted to study the effects of aging on the physicochemical properties of two Thai cultivars of milled glutinous rice (RD6 and RD8). The amylose and protein content of rice samples did not change when stored from 0 to 4 months. Amylograph curves from samples of milled rice stored from 0 to 8 months were analyzed. Both cultivars gave constant gelatinization temperature during aging. The values for peak viscosity, final viscosity on cooking at 94°C, viscosity on cooling to 50°C and breakdown decreased significantly for RD6 cultivar, whereas the setback value and consistency were not changed significantly. For RD8 cultivar, no significant difference was observed for viscosity on cooling to 50°C and consistency during aging up to 8 months. Peak viscosity and breakdown value were reduced during storage, whereas the final viscosity on cooking at 94°C and setback value increased with time. Raw milled rice of both RD6 and RD8 cultivars have similar water uptake rates. Stored rice tended to have a lower water uptake rate which increased proportionately with soaking time. Samples from both rice cultivars were used to make rice crackers to study the effects of aging on quality. Volume expansion of rice crackers made from RD6 and RD8 cultivars tended to decrease during storage which resulted in an increase in the hardness of the crackers.     

Heat Treatments of Milled Rice and Properties of the Flours

The effects of autoclave and oven treatments on the gelatinization of rice flour and on the rheological characteristics of its pastes were studied by differential scanning calorimetry (DSC), rapid viscoanalysis (RVA), and rotational viscometry. Flours from autoclave‐treated rice (ATR) and oven‐treated rice (OTR) were prepared, respectively, by heating at 120°C for 60 min and 160°C for 60 min followed by drying (ATR sample), and grinding at 2.2–12.9% moisture content. The rice flour dispersions were adjusted between pH 6.3 and 2.8 using 0.2M citrate buffer. The retort processing of rice flour in water pastes were done at 120°C for 20 min either once or twice. The gelatinization peak temperature (PT and T_o) and the peak temperature corresponding to the amylose‐lipid complexes (T_p3) of ATR increased at pH 6.3 and 2.8 compared with OTR and UTR flour. This indicates that the internal structures of the starch granules in ATR became more stable to heat and acid, even though the damaged starch content of ATR was 23% compared with 16 and 7%, respectively, for untreated rice flour (UTR) and OTR. The OTR flour pastes showed a gel‐like behavior at pH 4.5 after retort processing in water at 120°C for 20 min; however, the ATR mixture behaved more like a liquid paste. Decreases in the reducing sugar content of OTR and ATR pastes suggested that enzymes in the heat‐treated rice were denatured, which retarded the hydrolysis of glucose chains and the rupture of starch granules during pasting.     

不同地区再生季稻米蒸煮食味品质及淀粉结构与性能差异研究

为探究再生季稻米蒸煮食味品质在不同生态区的差异,并从淀粉结构与性能角度揭示其差异机理,本试验以杂交稻甬优4149、晶两优1468为供试材料,按再生稻栽培模式分别种植于肇庆、长沙、信阳3个生态区,研究了再生季齐穗后温光条件对稻米蒸煮食味品质、RVA 谱特性及淀粉热性能和晶体结构的影响。结果表明,肇庆试验地区的再生季稻米蒸煮食味品质优于长沙、信阳,其直链淀粉含量适中,胶稠度长,糊化温度较低,总淀粉含量较高。再生季齐穗后温光条件与稻米胶稠度、糊化特性以及淀粉热性能和相对结晶度具有显著相关性。籽粒灌浆初中期的温度和光照对再生季稻米淀粉的糊化性能与热性能影响较大;淀粉的相对结晶度受中后期的日均温度影响最为显著。本研究将有助于绿色农业的可持续发展和优质稻米的生产。