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An accurate characterization of the fine molecular structure of starch in terms of the chain length distribution (CLD) of amylopectin requires complete dispersion of the starch in a solvent, either buffer or water and the non-interference of this on the subsequent enzymatic debranching of starch with isoamylase (pretreatments before determining the CLD). In this study, the HYLON V and HYLON VII starches (commercial high-amylose corn starches) were selected, since high-amylose starches typically present difficulties in their dispersion and, therefore, the study of their fine structure can commonly present errors. The goal of this research was to study two water dispersion treatments (1. boiling water for 1 h and 2. autoclaving at 120 °C and 15 Psi for 15 min) to achieve a fast and reliable method of the fine structure of two high-amylose corn starches using high-performance size exclusion chromatography coupled with a refractive index detector (HPSEC-RID) and high-performance anion-exchange chromatography coupled a pulsed amperometric detector (HPAEC-PAD). The HPSEC-RID chromatograms of both starches showed better resolution using autoclaving than boiling water treatment. The two starches tested had higher amylose and degree of polymerization (DP) values utilizing the autoclaving than the boiling water treatment. However, no appreciable differences were observed in the CLD values employing HPAEC-PAD for either of the two water dispersion treatments. Lastly, the water dispersion treatment by autoclaving before enzymatic debranching is recommended to obtain a more accurate quantification of the amylose content of high-amylose starches. [ABSTRACT FROM AUTHOR]

The chalkiness, starch fine structure, and physiochemical properties of rice starch were analyzed and their correlations were investigated under different nighttime temperatures during the early grain-filling stage. Compared to MT, medium temperature (MT) and low (LNT) and high (HNT) nighttime temperatures resulted in an increased chalky grain rate (CGR) and chalkiness degree (CD). LNT mainly affected the chalkiness by increasing peak1 (short branch chains of amylopectin), the branching degree, and the proportion of small starch granules but decreasing peak2 (long branch chains of amylopectin) and peak3 (amylose branches). This altered the pasting properties, such as by increasing the peak viscosity and final viscosity. However, HNT mainly affected the chalkiness by increasing peak2 and the crystallinity degree but decreasing peak1 and peak3. Regarding the thermal properties, HNT also elevated peak and conclusion temperatures. The CGR and CD were significantly and positively correlated with the proportions of small and medium starch granules, peak1, branching degree, gelatinization enthalpy, setback viscosity, and pasting time but markedly and negatively correlated with the proportion of large starch granules, amylose content, peak3, peak viscosity, and breakdown viscosity. These findings suggest that LNT and HNT disrupted the starch structure, resulting in increased chalkiness. However, their mechanisms of action differ. [ABSTRACT FROM AUTHOR]

Grain quality indicates rice commodity value. This research compared grain quality and physicochemical properties of premium japonica rice from three production regions, Yangtze River downstream of China (YRDCN), Northeast region of China (NECN) and Japan. Results showed that there were distinct quality and physicochemical characteristics variance among the three groups of japonica rice, while CVs of most quality parameters from low to high was Japan, YRDCN and NECN. YRDCN rice presented obvious lower apparent amylose content (AAC) and ratio of each chain-length sections of amylopectin, and showed higher protein contents especially glutelin and ratio in short and intermediate amylopectin molecules. Among three rice groups, YRDCN rice presented weaker appearance, whereas did not show inferior cooking and eating properties, which was primarily linked to lower AAC. Rice AAC and starch fine structure significantly correlated with pasting parameters, swelling power and solubility, while protein content had close relation with taste analyzer parameters. Results of this study indicated improvement direction for japonica rice of YRDCN, and also provided reference for consumers' rice purchasing selection in accordance with individual taste preference. [ABSTRACT FROM AUTHOR]

Elevated ripening temperature (ET) impacts rice grain quality. In this study, two rice varieties were investigated to evaluate the characterization of starch fine structure and grain eating quality under ET conditions. Rice exposure to ET increased the proportion of large-sized granules and starch granule average size, regardless of grain position. Compared to normal temperature (NT), the amylose content (AM) in the upper grain position (UP) exhibited a significant increase under ET, whereas the contrary results showed a decrease in the lower grain position (LP), and the proportion of shorter amylopectin chains increased under ET in UP or LP, whereas the proportion of long amylopectin chains decreased, resulting in a higher starch gelatinization temperature and enthalpy under ET. For grain position, compared to LP, UP had higher AM and a higher proportion of long amylopectin chains, leading to higher gelatinization enthalpy under ET. For eating quality, we found that ET deteriorated the eating quality of rice compared to NT, and UP had higher eating quality than LP under NT; however, there was a comparable eating quality between UP and LP under ET. Hence, elevated grain filling temperature mitigated the eating quality deterioration of rice grain in LP due to the lower AM and gelatinization enthalpy and the higher proportion of shorter amylopectin chains. [ABSTRACT FROM AUTHOR]

Straw return can improve rice eating quality by modifying starch formation from long-term field trials, whereas the relevant mechanisms are still unknown. A long-term field experiment, including straw removal (CK), straw burning return (SBR), and straw return (SR) was conducted to investigate the starch structure, physicochemical properties, and cooked rice textures of indica early- and late-rice. Compared with CK, SBR and SR enhanced relative crystallinity, amylopectin long chains in both rice seasons, and gelatinization temperatures in late rice. Compared to SBR, SR decreased protein content and amylopectin short chains but increased starch branching degree, breakdown, and stickiness, ultimately contributing to improved starch thermal and pasting properties. Meanwhile, SR decreased hardness, cohesiveness, and chewiness, resulting in cooked texture meliorated, which was mainly attributed to amylopectin chain length and starch granule size. The results suggest that SR increased cooked texture of indica rice by altering starch structural and physicochemical properties.

The chalkiness, starch fine structure, and physiochemical properties of rice starch were analyzed and their correlations were investigated under different nighttime temperatures during the early grain-filling stage. Compared to MT, medium temperature (MT) and low (LNT) and high (HNT) nighttime temperatures resulted in an increased chalky grain rate (CGR) and chalkiness degree (CD). LNT mainly affected the chalkiness by increasing peak1 (short branch chains of amylopectin), the branching degree, and the proportion of small starch granules but decreasing peak2 (long branch chains of amylopectin) and peak3 (amylose branches). This altered the pasting properties, such as by increasing the peak viscosity and final viscosity. However, HNT mainly affected the chalkiness by increasing peak2 and the crystallinity degree but decreasing peak1 and peak3. Regarding the thermal properties, HNT also elevated peak and conclusion temperatures. The CGR and CD were significantly and positively correlated with the proportions of small and medium starch granules, peak1, branching degree, gelatinization enthalpy, setback viscosity, and pasting time but markedly and negatively correlated with the proportion of large starch granules, amylose content, peak3, peak viscosity, and breakdown viscosity. These findings suggest that LNT and HNT disrupted the starch structure, resulting in increased chalkiness. However, their mechanisms of action differ.

Sensory deterioration exists in marketed cooked rice. The migration and interaction of intrinsic components occur under multiple conditions in each industrial production process and cause relevant physicochemical changes in cooked rice. This review aims to establish a scientific knowledge system of intrinsic component transition and migration in cooked rice kernel during processing to solve qualitative deficiencies in cooked rice products. The main influencing factors of intrinsic component structural change in cooked rice and the quality control points that should be considered are summarized. Further studies are needed to establish proper evaluation standards for cooked rice products to meet the growing consumer demands. • Changes in intrinsic components cause sensory deterioration in cooked rice. • Influences of water in cooked rice occur throughout the entire production process. • Recent researches focus on starch structure, content interaction, and leachates. • The quality control points and future perspectives are summarized. [ABSTRACT FROM AUTHOR]

The fine structures of pumpkin, potato, wheat, cassava, and pea starches were determined, followed by an evaluation of how these structures affected the properties of starch films. The structures significantly influenced film properties. Starches with larger molecular weights exhibited greater thermal stability. The tensile strength of starch film was negatively associated with the amylose chain length (r = −0.88, p < 0.05). The chain length distributions of amylose and amylopectin affected the mechanical properties of starch films by influencing structure ordering, supported by the positive correlation between the double helix content and the tensile strength (r = 0.95, p < 0.05). The amylopectin B1, B2, and B3 chains increased film mechanical strength. Conversely, amylopectin A-chains reduced the mechanical strength. The water contact angle was negatively correlated with the B3 chain proportion (r = −0.93, p < 0.05). The pumpkin starch exhibited the highest tensile strength (14.29 MPa), while the wheat starch film showed the highest water contact angle (112°). This study offers valuable insights into the structure-function relationships of starch films, thereby facilitating the acquisition of starch films with enhanced strength and stability through screening or designing starch structures. Consequently, this will expand the application of starch films as packaging materials in various food products. Graphical abstract [Display omitted] [ABSTRACT FROM AUTHOR]

The non‐conventional starch isolated from unripe fruits is an alternative to obtain this raw material with improved or different functionality and digestibility. The starch isolated from Pouteria campechiana pulp (SIP) and seeds (SIS) of unripe fruits shows similar average granule sizes and A‐type X‐ray diffraction pattern. The digestibility characteristics are related to the hierarchical structure, since the amylopectin of the SIS sample has the highest crystallinity percentage and degree of polymerization (DP). These long amylopectin chains produce a thermally stable helical structure. Resistant starch (RS) in the SIP and SIS samples remains after cooking, and the cooked SIS show an increase in slowly digestible starch (SDS) content. In contrast, cooked SIP has an increased content of rapidly digestible starch (RDS). The SIP sample also shows interesting β‐carotene content values (15.4 µg g−1 dry starch) for the manufacture of potentially health‐promoting food additives in terms of anti‐inflammatory and antioxidant activities. The supramolecular structure–in vitro digestibility relationship of the SIS sample yields interesting results as a novel, low‐cost, and underutilized alternative starch source for the manufacture of potential health‐promoting starchy food additives. [ABSTRACT FROM AUTHOR]

Amylose content, fine structure, and protein content affect the hardness and stickiness of cooked rice. However, the mechanisms of those effects have not been fully understood especially the fine structure of amylose. Here, 22 rice varieties with large ranges of both starch chain‐length distributions and protein content are examined, and the starch structural results are parameterized using biosynthesis‐based models. The ratios of the activities of branching enzyme and starch synthase for amylose showed positive and negative correlations with rice hardness (coefficient 0.556 and 0.838) and stickiness (coefficient −0.498 and −0.639), respectively. Protein content is strongly positively correlated with hardness, with nitrogen application up to the panicle development stage (coefficient 0.640). New findings could be obtained from these correlations, which reveal that in the whole region of amylose, the shorter the amylose is, the harder and less sticky the cooked rice is, which has not been reported previously. In addition, protein is found to influence rice hardness significantly, while rice stickiness is less affected by it. Therefore, a comprehensive mechanism of protein effects on rice texture is proposed. This work provides information for breeders to develop improved rice varieties. [ABSTRACT FROM AUTHOR]

BackgroundSimulated oral processing can be used to evaluate the palatability of cooked rice. Previously, we established a simulated oral processing method using a texture analyzer equipped with a multiple extrusion cell probe (TA/MEC). However, the relationship between oral processing and starch fine structure remains unknown.MethodsIn this study, we analyzed the oral processing properties using TA/MEC and characterized the starch fine structure of japonica rice by size-exclusion chromatography (SEC) and fluorophore-assisted capillary electrophoresis (FACE). The relationship between starch fine structure and oral processing of cooked japonica rice was further investigated.ResultsCooked rice structure contains fast-breakdown (Type I structure), slow-breakdown (Type II structure) and unbreakable structures (Type III structure). Fast-breakdown and slow-breakdown structure were positively correlated with the content of amylose and shorter amylopectin branches. The content of longer amylopectin branches was positively correlated with the contribution of unbreakable structure.ConclusionThe results indicated that cooked japonica rice varieties with more amylose and shorter amylopectin branches tend to form a harder texture and need more work to break down the fast and slow breakdown structures related to rice kernel fragmentation. Meanwhile, cooked japonica rice varieties possess stronger molecular entanglements due to their longer amylopectin branches and contribute more to the breakdown of unbreakable structures. These results can guide breeders to select rice varieties with desirable eating qualities for cultivation.

Nitrogen fertilizer is essential for rice growth and development, and topdressing nitrogen fertilizer at panicle stage has a huge impact on rice grain quality. However, the effect of panicle nitrogen fertilizer (PNF) on starch physicochemical properties and fine structure remain unclear. In this study, four PNF levels (0, 60, 120, 180 kg N ha−1) were grown with the same basal and tiller fertilizer (150 kg N ha−1). The starch physicochemical properties, fine structure, texture properties and eating quality of two japonica rice were determined. We found that the content of total protein, crude fat and amylose between superior and inferior grains were significantly different. Compared with inferior grains, superior grains had low relative crystallinity, good pasting characteristics and outstanding eating quality. With the increase of nitrogen application rates, the starch volume mean diameter was lower; the average chain length of amylopectin was longer; and the relative crystallinity of starch was higher. The changes above in starch structure resulted in an increase in starch solubility, swelling power and gelatinization enthalpy, and led to a decrease in retrogradation enthalpy, retrogradation percentage and pasting viscosity, consequently contributing to the increase in hardness and stickiness of rice and the deterioration of taste value. These results indicated that topdressing PNF lengthened the amylopectin chain, decreased starch granule size, enhanced crystallization stability and increased gelatinization enthalpy, which were the direct reasons for the deterioration of cooking and eating quality. [ABSTRACT FROM AUTHOR]

Abstract Background ALK is the key gene controlling rice gelatinization temperature (GT), which is closely associated with the eating and cooking quality (ECQ) in rice (Oryza sativa L.). To date, at least three ALK alleles are thought to be responsible for the diversity of GT among rice cultivars. The ALK c /SSIIa i allele with high activity of the soluble starch synthase IIa (SSIIa) controls high GT, but the accurate functional difference between ALK a and ALK b alleles, both controlling low GT, is not clearly elucidated. Thus, we generated rice near-isogenic lines (NILs) by introducing different ALK alleles into the japonica cultivar Nipponbare (Nip) to clarify the discrepant effects of the two low-GT ALK alleles. Results The results showed that the function of two low-GT alleles (ALK a and ALK b ) was different, and a much lower GT was observed in NIL(ALK b ) rice grains compared with that of Nip(ALK a ). Moreover, the starches of NIL(ALK b ) grains had a higher degree of branching, higher setback, consistence and higher cool pasting viscosity than those of Nip(ALK a ). The lower expression level of ALK b , compared with ALK a , resulted in depleted intermediate chains and increased short chains of amylopectin, thus affected the thermal and pasting properties of NILs’ grains. Also, the data revealed both low-GT alleles were mainly found in temperate japonica, but more ALK b was found in other subpopulations such as indica as compared to ALK a . Conclusions Overall, all the results suggested that the function between two low-GT alleles was different, and the distribution of ALK b was much wider than that of ALK a among the subpopulations of cultivated rice.

The retrogradation of starch is crucial for the texture and nutritional value of starchy foods products. There is mounting evidence highlighting the significant impact of starch's fine structures on starch retrogradation. Because of the complexity of starch fine structure, it is a formidable challenge to study the structure-property relationship of starch retrogradation. Several models have been proposed over the years to facilitate understanding of starch structure. In this review, from the perspective of starch models, the intricate structure-property relationship is sorted into the correlation between different types of structural parameters and starch retrogradation performance. Amylopectin B chains with DP 24–36 and DP ≥36 exhibit a higher tendency to form ordered crystalline structures, which promotes starch retrogradation. The chains with DP 6–12 mainly inhibit starch retrogradation. Based on the building block backbone model, a longer inter-block chain length (IB-CL) enhances the realignment and reordering of starch. The mathematical parameterization model reveals a positive correlation between amylopectin medium chains, amylose short chains, and amylose long chains with starch retrogradation. The review is structured according to starch models; this contributes to a clear and comprehensive elucidation of the structure-property relationship, thereby providing valuable references for the selection and utilization of starch. [ABSTRACT FROM AUTHOR]

The processing quality of indica rice must undergo ripening after harvest to achieve stability and improvement. However, the mechanism underlying this process remains incompletely elucidated. Starch, the predominant component in indica rice, plays a crucial role in determining its properties. This study focused on analyzing the rheological properties and starch fine structure, as well as the related biosynthetic enzymes of indica rice during the after-ripening process. The results showed that after-ripened rice exhibited increased elastic modulus (G′) and viscous modulus (G″), accompanied by a decrease in the loss tangent (Tan δ), indicating an enhancement in viscoelasticity and the gel network structure. Moreover, the proportions of amylopectin super long chains (DP 37–60) decreased, while those of medium chains (DP 13–24 and DP 25–36) or short chains (DP 6–12) of amylopectin increased. Additionally, the activities of starch branching enzyme (SBE) and starch debranching enzyme (DBE) declined over the after-ripening period. Pearson correlation analysis revealed that the rheological properties of after-ripened rice were correlated with the chain length distribution (CLD) of starch, which, in turn, was associated with its related endogenous enzymes. These findings provied new insights into understanding the quality changes of after-ripened indica rice. [Display omitted] • The elastic modulus and viscous modulus of rice increased during after-ripening. • The chain length distribution of amylopectin undergoed changes during after-ripening. • The activities of starch branching enzyme and starch branching enzyme decreased during after-ripening. • The starch biosynthesis enzymes changed the starch structure and thus affected the rheological properties of rice. [ABSTRACT FROM AUTHOR]

Nitrogen fertilizer is essential for rice growth and development, and topdressing nitrogen fertilizer at panicle stage has a huge impact on rice grain quality. However, the effect of panicle nitrogen fertilizer (PNF) on starch physicochemical properties and fine structure remain unclear. In this study, four PNF levels (0, 60, 120, 180 kg N ha−1) were grown with the same basal and tiller fertilizer (150 kg N ha−1). The starch physicochemical properties, fine structure, texture properties and eating quality of two japonica rice were determined. We found that the content of total protein, crude fat and amylose between superior and inferior grains were significantly different. Compared with inferior grains, superior grains had low relative crystallinity, good pasting characteristics and outstanding eating quality. With the increase of nitrogen application rates, the starch volume mean diameter was lower; the average chain length of amylopectin was longer; and the relative crystallinity of starch was higher. The changes above in starch structure resulted in an increase in starch solubility, swelling power and gelatinization enthalpy, and led to a decrease in retrogradation enthalpy, retrogradation percentage and pasting viscosity, consequently contributing to the increase in hardness and stickiness of rice and the deterioration of taste value. These results indicated that topdressing PNF lengthened the amylopectin chain, decreased starch granule size, enhanced crystallization stability and increased gelatinization enthalpy, which were the direct reasons for the deterioration of cooking and eating quality.

Background: ALK is the key gene controlling rice gelatinization temperature (GT), which is closely associated with the eating and cooking quality (ECQ) in rice (Oryza sativa L.). To date, at least three ALK alleles are thought to be responsible for the diversity of GT among rice cultivars. The ALKc/SSIIai allele with high activity of the soluble starch synthase IIa (SSIIa) controls high GT, but the accurate functional difference between ALKa and ALKb alleles, both controlling low GT, is not clearly elucidated. Thus, we generated rice near-isogenic lines (NILs) by introducing different ALK alleles into the japonica cultivar Nipponbare (Nip) to clarify the discrepant effects of the two low-GT ALK alleles. Results: The results showed that the function of two low-GT alleles (ALKa and ALKb) was different, and a much lower GT was observed in NIL(ALKb) rice grains compared with that of Nip(ALKa). Moreover, the starches of NIL(ALKb) grains had a higher degree of branching, higher setback, consistence and higher cool pasting viscosity than those of Nip(ALKa). The lower expression level of ALKb, compared with ALKa, resulted in depleted intermediate chains and increased short chains of amylopectin, thus affected the thermal and pasting properties of NILs' grains. Also, the data revealed both low-GT alleles were mainly found in temperate japonica, but more ALKb was found in other subpopulations such as indica as compared to ALKa. Conclusions: Overall, all the results suggested that the function between two low-GT alleles was different, and the distribution of ALKb was much wider than that of ALKa among the subpopulations of cultivated rice. [ABSTRACT FROM AUTHOR]

The evolution of the starch fine structure during growth and its impact on the gelatinization behavior of cassava starch (CS) was investigated by isolating starch from South China 6068 (SC 6068) cassava harvested from the 4th to 9th growth period. During growth, the short-range ordered structure, crystallinity as well as particle size distribution of starch were increased. Meanwhile, the starch molecular size and amylopectin (AP) proportion increased, while the proportion of amylose (AM) exhibited a decreasing tendency. The chains of short-AM (X ~ 100–1000) were mainly significantly reduced, whereas the short and medium-AP chains (X ~ 6–24) had the most increment in AP. The solubility, thermal stability, shear resistance, and retrogradation resistance of starch were enhanced after gelatinized under the influence of the results mentioned above. This study presented a deeper insight into the variation of starch fine structure during growth and its influence on gelatinization behavior, which would provide a theoretical basis for starch industrial applications. [Display omitted] [ABSTRACT FROM AUTHOR]

In this study, the effect of buckwheat polyphenols (rutin and quercetin) on in vitro digestion of cooked starch was analyzed from view of the grain source, fine structure of starch and enzymatic inhibition. The results showed no significant difference in the inhibition of rutin on tartary buckwheat starch digestion as compared with common buckwheat and wheat starches. However, their inhibitory effects were negatively correlated with the content of long amylose chains (2000 < DP < 20000) but positively correlated with that of short amylose chains (100 < DP < 500) and amylopectin (13 < DP < 24) chains (p < 0.05). There was a significant difference in the digestive inhibition of rutin on starches obtained from different tartary buckwheat varieties, and the optimal ratio of rutin (2%) addition for TS1 (tartary buckwheat starch, Heifeng No.1). Quercetin showed stronger inhibition on the digestion of tartary buckwheat starch, which was attributed to the following fact: quercetin can significantly change the structure of enzymatic molecular, thereby inhibiting enzyme activity. Overall, the inhibition of rutin on starch digestion was mainly determined by starch fine structure, and 2% of rutin could show optimal inhibition on the digestion of tartary buckwheat starch. [Display omitted] • Short starch chain enhanced the inhibition effect of rutin on starches digestion. • Starch-polyphenols interaction played important roles in starch digestion inhibition. • Cereal species cannot affect the inhibition effect of rutin on starch digestion. • Quercetin strongly changed the structure of digestive enzyme than rutin. • Rutin was more likely to induce the aggregation of starch chains. [ABSTRACT FROM AUTHOR]

Differences in cooked rice and starch and protein physicochemical properties of three japonica rice were compared systematically. Cultivars of japonica rice, Daohuaxiang2, from Northeast China (NR) and two semiglutinous japonica rice (SGJR), Nangeng46 and Nangeng2728, from the Yangtze River Delta (YRD) were investigated. Both Daohuaxiang2 and Nangeng46 achieved high taste values, but there were great differences in starch and protein physicochemical properties. Daohuaxiang2 showed higher apparent amylose content (AAC), lower protein content (PC), and longer amylopectin (especially fb2 and fb3) and amylose chain lengths, resulting in thicker starch lamellae and larger starch granule size. Its cooked rice absorbed more water and expanded to larger sizes. All of these differences created a more compact gel network and harder but more elastic cooked rice for Daohuaxiang2. Nangeng46 produced a lower AAC, a higher PC, shorter amylopectin and amylose chain lengths, thinner starch lamellae, and smaller starch granule sizes, creating a looser gel network and softer cooked rice. The two SGJR, Nangeng46 and Nangeng2728, had similar low AACs but great differences in taste values. The better-tasting Nangeng46 had a lower PC (especially glutelin content) and higher proportion of amylopectin fa chains, which likely reduced the hardness, improved the appearance, and increased the adhesiveness of its cooked rice. Overall, both types of japonica rice from the NR and YRD could potentially have good eating qualities where Nangeng46’s cooked rice was comparable to that of Daohuaxiang2 because of its lower AC. Moreover, its lower PC and higher proportion of amylopectin fa chains likely improved its eating quality over the inferior-tasting SGJR, Nangeng2728. This research lays a foundation for the improvement of the taste of japonica rice in rice breeding.

• Starch degradation during rice ageing happens at branching points of amylopectin. • Starch degradation during rice ageing occurs from short amylose chains. • Rice ageing can cause decrease of starch gelatinization temperature and enthalpy. The eating and cooking quality (ECQ) of stored rice grains is significantly affected by ageing, but the molecular mechanisms for this are not well understood. In the present study, changes of starch hierarchical structures and thermal properties of starch were investigated for rices with up to 12 months storage. For the first time, it was seen that storage resulted in molecular degradation of starch. This mainly involved shorter amylose chains and around (1 → 6)-α glycosidic branching points of amylopectin, which altered the crystalline structure. This resulted in lower gelatinization temperatures and enthalpy but higher crystalline heterogeneity. The ageing effect was varietally-dependent. The information obtained from this study offers improved molecular-level understanding of the effects of ageing process on rice cooking and eating qualities. [ABSTRACT FROM AUTHOR]

BACKGROUND: High temperature during the grain‐filling stage is an important factor that can affect grain quality by altering the composition and structure of starch in rice. Therefore, it is important to study the regulatory mechanism of high temperature on rice starch biosynthesis. RESULTS: Two japonica cultivars, the waxy rice Taihunuo and non‐waxy Nangeng 5055 were used to examine the effect of high temperature on the fine structure of starch during the grain‐filling stage. Analysis of starch chain length distribution indicated that exposure to a high temperature increased the content of starch with medium‐long chains and decreased the starch with short chains in both rice varieties. The differences of amylopectin synthesis responding to high temperature between waxy and non‐waxy rice can shed light on the interactions of amylose and amylopectin synthesis under high temperature conditions. In the non‐waxy variety, the amylose biosynthesis may affect the short and medium‐long amylopectin biosynthesis under high temperature. A mathematical fitting model was used to interpret the fine structure of amylopectin and a series of parameters with enzymatical significance (β and γ) were obtained. The fitting results showed that the waxy and non‐waxy rice had similar responses to high temperature. The variations of the parameter response to high temperature was more remarkable in Taihunuo. Activity analysis of starch synthesis‐related enzymes during the grain‐filling stage demonstrated the reliability of model fitting results. CONCLUSION: The influences of high temperature on the fine structure of starch are similar between waxy and non‐waxy rice. Amylose biosynthesis may affect amylopectin biosynthesis under high temperature. © 2018 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

Abstract: The effects of variety and growth location on grain composition and starch structures were investigated using three rice (Oryza sativa L.) cultivars (Phka Romduol, Sen Pidao and IR66) with different amylose contents. All the three cultivars were planted in three different agro-climatic zones (Phnom Penh, Coastal and Plateau) of Cambodia. The protein content of polished grains increased when rice was planted at a location with higher average temperature, but their lipid content decreased. The amylose content and degree of branching were not greatly affected by the minor temperature differences among the growing locations. Starch fine structures characterized by the chain-length distribution were significantly different among the cultivars, but not significantly among different locations. The results suggested that protein and lipid biosyntheses were more sensitive to the environmental temperature than that of starch in rice grains. [Copyright &y& Elsevier]

The biochemical basis of modified kernel texture in Quality Protein Maize (QPM) is poorIy understood. Proteomic analysis of several QPM lines indic4ted increased levels of granule-bound starch synthase I in the soluble nonzein protein fraction of these geno-types. Increased extraction of this enzyme reflected a change in starch structure, which was manifested as shorter amylopectin branches and increased starch-granule swelling. In mature kernels, these alterations in starch structure were associated with inter-connections between starch granules that resulted in a vitreous kernel phenotype. Understanding the molecular basis for this previously uncharacterized starch structure will accelerate the development of QPM. [ABSTRACT FROM AUTHOR]

Differences in cooked rice and starch and protein physicochemical properties of three japonica rice were compared systematically. Cultivars of japonica rice, Daohuaxiang2, from Northeast China (NR) and two semiglutinous japonica rice (SGJR), Nangeng46 and Nangeng2728, from the Yangtze River Delta (YRD) were investigated. Both Daohuaxiang2 and Nangeng46 achieved high taste values, but there were great differences in starch and protein physicochemical properties. Daohuaxiang2 showed higher apparent amylose content (AAC), lower protein content (PC), and longer amylopectin (especially fb2 and fb3) and amylose chain lengths, resulting in thicker starch lamellae and larger starch granule size. Its cooked rice absorbed more water and expanded to larger sizes. All of these differences created a more compact gel network and harder but more elastic cooked rice for Daohuaxiang2. Nangeng46 produced a lower AAC, a higher PC, shorter amylopectin and amylose chain lengths, thinner starch lamellae, and smaller starch granule sizes, creating a looser gel network and softer cooked rice. The two SGJR, Nangeng46 and Nangeng2728, had similar low AACs but great differences in taste values. The better-tasting Nangeng46 had a lower PC (especially glutelin content) and higher proportion of amylopectin fa chains, which likely reduced the hardness, improved the appearance, and increased the adhesiveness of its cooked rice. Overall, both types of japonica rice from the NR and YRD could potentially have good eating qualities where Nangeng46's cooked rice was comparable to that of Daohuaxiang2 because of its lower AC. Moreover, its lower PC and higher proportion of amylopectin fa chains likely improved its eating quality over the inferior-tasting SGJR, Nangeng2728. This research lays a foundation for the improvement of the taste of japonica rice in rice breeding. [ABSTRACT FROM AUTHOR]

The ripening temperature is a critical factor impacting rice starch structure and properties. In this study, the starch fine structure and functional properties of two semi-waxy japonica rice cultivars were characterized under different dynamic ripening temperatures. Exposure of rice to dynamic high temperature during grain filling increased the relative crystallinity and the lamellar peak intensity of starch. Analysis of starch chain length distribution indicates, as rice grain filling temperature increased, the amylose content (AM) and the proportion of shorter amylopectin chains (DP 6–12 or AP1) decreased, and the proportion of long amylopectin chains (DP 37–76 or AP2) increased, resulting in higher starch gelatinization temperature and enthalpy, as well as pasting viscosities and pasting temperature. The above results imply that high temperature during grain filling can change starch fine structure, and degrade starch gelatinization and pasting properties. Dynamic high temperature during grain filling increased starch relative crystallinity, and changed starch fine structure with higher in the proportion of long amylopectin chains, which led to deterioration of starch gelatinization and pasting properties. [Display omitted] • Starch relative crystallinity and peak intensity were increased under high temperature during rice grain filling stage. • Starch fine structure was altered by high temperature during rice grain filling stage. • Starch gelatinization quality was degraded under high temperature during rice grain filling stage. [ABSTRACT FROM AUTHOR]

• The physical barrier caused by protein influences starch digestion in cooked rice. • Protein/starch hydrogen-bonding interactions are significant in uncooked rice. • The type of protein has negligible effect on in vitro rice starch digestion. Rices with higher protein contents are nutritionally desirable. This study investigates the effects of endosperm proteins on starch in vitro digestibility in cooked and uncooked rice, and the mechanisms underlying any changes. The composition of rice endosperm proteins and the morphologies of proteins and starch granules were determined by SDS-PAGE and confocal microscopy. Starch molecular fine structure was examined using size-exclusion chromatography. In vitro digestion showed that the digestion rate coefficients (k) of cooked rice flour were significantly lower than those of isolated starch or of a starch-protein mixture. (e.g for samples from SWR4, k is 9.6, 12.9 and 11.6 × 10-2 min−1 for cooked rice flour, isolated starch and starch-protein mixture, respectively). For uncooked samples, digestion rate coefficients were 1.4, 1.5 and 1.8 × 10-2 min−1 for flour, starch-protein mixture and starch, respectively. The digestion rates in cooked samples were higher than those in uncooked samples. This suggests that, in cooked samples, starch digestion rates are more affected by the protein physical barrier than by some chemical effect (e.g. hydrogen bonding between protein and starch), while in uncooked samples, a chemical effect from protein is more pronounced than a physical barrier from protein. [ABSTRACT FROM AUTHOR]

Composition and functionality of five waxy wheat (Triticum aestivum L.) genotypes were elaborately investigated and related to end-product attributes of extrudates. As such, the interaction between starch biopolymers and protein in extrusion processing could be studied. Furthermore, the effect of an increasing amylose-concentration was studied by the use of blends. Waxy genotypes absorbed more water, gave rise to stiffer doughs and had higher onset and peak gelatinization temperature. In contrast, a lower pasting temperature and final viscosity and higher peak viscosity and breakdown could be observed. The volume percentage of small starch granules showed to be negatively correlated with peak temperature and positively with final viscosity and holding strength as well as with extrudate hardness. This was also positively correlated with amylose concentration. Expansion index was highest at a slightly decreased amylose concentration of 16.6%. Markedly higher moisture content for all amylose-free extrudates was attributed to a combination of increased solubility of amylopectin and reduced water evaporation at die emergence. It was hypothesized that an interplay with protein content and composition was laying at the basis of the observed differences. Moreover, the altered pasting behavior of waxy wheat may enhance the extrudability of gluten containing wheat flour. Starch granule size distribution is related to extrudate texture. Amylose content affects expansion index, water absorption and texture of extrudates. Interaction between starch content and protein composition and quality was observed. Waxy genotypes are strongly varying in their protein composition and functionality. Maximum expansion was obtained for blends containing 25% waxy flour. Image 1 • Starch granule size distribution is related to extrudate texture. • Amylose content affects expansion index, water absorption and texture of extrudates. • Interaction between starch content and protein composition and quality was observed. • Waxy genotypes are strongly varying in their protein composition and functionality. • Maximum expansion was obtained for blends containing 25% waxy flour. [ABSTRACT FROM AUTHOR]

Consumers of Gluten Free Bread (GFB) seek soft, cohesive and resilient crumbs. However, the combined effect of amylose (AM) content and chain length, as opposed to only AM content, on crumb hardness have not been studied, neither the synergies of multiple starch molecular features (i.e., amylopectin, AP, and AM fine structures) are understood. In this work, kernels from 5 different rice varieties (Basmati, Thai, Waxy, Sushi and Bomba) were milled after tempering to result in rice flours with less than 8% starch damage varying in AM and AP fine structure, as measured by HPSEC. Dynamic rheology of rice flour gels revealed that Basmati flour exhibited a six-fold higher propensity to form internal Physical Junction Zones (PJZ), those that contribute to the food mechanical properties, than the rest of the starches. Frequency and temperature sweeps revealed AM-AM and AM-AP interactions, respectively, as the internal PJZ. Since Basmati and Bomba exhibited similar AM content and AP fine structure, the intermediate length amylose (699 DP) of Basmati is proved to be the responsible for a greater amount of AM-AM and AM-AP internal PJZ. Interestingly, GFB crumbs made with Bomba flour were 20% softer than those made with Basmati flour. For the first time, AM length is suggested to be a crucial parameter to attain breads with softer and more cohesive crumbs. In fact, results provide strong evidence that the AM length could play a major role than its content in the texture of GFBs crumbs. Image 1 • The effect of amylose and amylopectin fine structure on crumb texture was assessed. • Structure analysis of rice starch revealed amylose chains of different length. • Basmati flour was six-time more effective in forming internal Physical Junction Zones. • Intermediate length amylose (699 DP) of Basmati led to a more elastic gel network. • Amylose length was a crucial factor to attain softer and more cohesive crumbs. [ABSTRACT FROM AUTHOR]

The gelatinization temperature (GT) of endosperm starch influences rice eating and the cooking quality (ECQ). ALK encoding soluble starch synthase IIa (SSIIa) is the major gene determining grain GT in rice. Herein, we identified a spontaneous ALK mutant named ALK d , which resulted from a G/T single-nucleotide polymorphism (SNP) in exon 1 of the ALK c allele from the high-GT indica rice cultivar. Compared with grains from the ALK c near-isogenic line (NIL), NIL( ALK d ) grains exhibited a high GT (2.3 °C) and improved retrogradation properties. The NIL( ALK d ) grain starch contained an increased proportion of amylopectin intermediate chains (DP 13-24) at the expense of short chains (DP < 12), resulting in enhancements in both the crystallinity and the lamellar peak intensity compared with low-GT rice grains. Moreover, both NIL( ALK d ) and NIL( ALK c ) grains also featured a significantly lower apparent amylose content (AAC), harder gel consistency (GC), higher pasting curve, and poorer taste values in comparison to Nip( ALK a ) grains. Taken together, this work provides novel insights underlying the allelic variation of the ALK gene in rice.

OsGBSSI, encoded by the Waxy (Wx) gene, is the key enzyme in the synthesis of amylose chains. Transgenic rice lines with various GBSSI activities were previously developed via site-directed mutagenesis of the Wx gene in the glutinous cultivar Guanglingxiangnuo (GLXN). In this study, grain morphology, molecular structure, and physicochemical properties were investigated in four transgenic lines with modified OsGBSSI activity and differences in amylose content. A milky opaque appearance was observed in low- and non-amylose rice grains due to air spaces in the starch granules. Gel permeation chromatography (GPC) and high-performance anion-exchange chromatography (HPAEC) analyses showed that although OsGBSSI can synthesize intermediate and extra-long amylopectin chains, it is mainly responsible for the longer amylose chains. Amylose content was positively correlated with trough viscosity, final viscosity, setback viscosity, pasting time, pasting temperature, and gelatinization temperature and negatively with gel consistency, breakdown viscosity, gelatinization enthalpy, and crystallinity. Overall, the findings suggest that OsGBSSI may be also involved in amylopectin biosynthesis, in turn affecting grain appearance, thermal and pasting properties, and the crystalline structure of starches in the rice endosperm.

Temperature during the growing season is a critical factor affecting grain quality. High temperatures at grain filling affect kernel development, resulting in reduced yield, increased chalkiness, reduced amylose content, and poor milling quality. Here, we investigated the grain quality and starch structure of two japonica rice cultivars with good sensory properties grown at different temperatures during the filling stage under natural field conditions. Compared to those grown under normal conditions, rice grains grown under hot conditions showed significantly reduced eating and cooking qualities, including a higher percentage of grains with chalkiness, lower protein and amylose contents, and higher pasting properties. Under hot conditions, rice starch contained reduced long-chain amylose (MW 10(7.1) to 10(7.4)) and significantly fewer short-chain amylopectin (DP 5-12) but more intermediate- (DP 13-34) and long- (DP 45-60) chain amylopectin than under normal conditions, as well as higher crystallinity and gelatinization properties.