Amylose content in starches: Toward optimal definition and validating experimental methods

Recent advances in the impact of gelatinization degree on starch: Structure, properties and applications

During home cooking or industrial food processing operations, starch granules usually undergo a process known as gelatinization. The starch gelatinization degree (DG) influences the structural organization and properties of starch, which in turn alters the physicochemical, organoleptic, and gastrointestinal properties of starchy foods. This review summarizes methods for measuring DG, as well as the impact of DG on the starch structure, properties, and applications. Enzymatic digestion, iodine colorimetry, and differential scanning calorimetry are the most common methods for evaluating the DG. As the DG increases, the structural organization of the molecules within starch granules is progressively disrupted, the particle size of the granules is altered due to swelling and then disruption, the crystallinity is decreased, the molecular weight is reduced, and the starch-lipid complexes are formed. The impact of DG on the starch structure and properties depends on the processing method, operating conditions, and starch source. The starch DG affects the quality of many foods, including baked goods, fried foods, alcoholic beverages, emulsified foods, and edible inks. Thus, a better understanding of the changes in starch structure and function caused by gelatinization could facilitate the development of foods with novel or improved properties.

Insights into wheat-starch biosynthesis from two-dimensional macromolecular structure

Starch structure is often characterized by the chain-length distribution (CLD) of the linear molecules formed by breaking each branch-point. More information can be obtained by expanding into a second dimension: in the present case, the total undebranched-molecule size. This enables answers to questions unobtainable by considering only one variable. The questions considered here are: (i) are the events independent which control total size and CLD, and (ii) do ultra-long amylopectin (AP) chains exist (these chains cannot be distinguished from amylose chains using simple size separation). This was applied here to characterize the structures of one normal (RS01) wheat and two high-amylose (AM) mutant wheats (an SBEIIa knockout and an SBEIIa and SBEIIb knockout). Absolute ethanol was used to precipitate collected fractions, then size-exclusion chromatography for total molecular size and for the size of branches. The SBEIIa and SBEIIb mutations significantly increased AM and IC contents and chain length. The 2D plots indicated the presence of small but significant amounts of long-chain amylopectin, and the asymmetry of these plots shows that the corresponding mechanisms share some causal effects. These results could be used to develop plants producing improved starches, because different ranges of the chain-length distribution contribute independently to functional properties.

Insight into Rheological Properties and Structure of Native Waxy Starches: Cluster Analysis Grouping

Recent interest in the use of waxy starches in food production is due to the possibility of replacing chemically modified starches as texture-forming agents with native starch analogues. However, there is a lack of a coherent research comparing different varieties of commercially available waxy starches with respect to their molecular and functional properties. Therefore, the objective of this study was to compare native waxy starches from potatoes, corn, and rice, with particular attention to rheological characteristics in relation to molecular structure. The investigated potato, corn, and rice starch preparations were characterized by significantly different molecular properties due to both botanical origin of starch and variety. The molecular weights of waxy starches were significantly higher than those of their normal counterparts. This phenomenon was accompanied by a more loose conformation of the waxy starch macromolecule in solution. The presence of amylose confers the ability to coagulate starch sol into gel, resulting in substantial changes in the rheological properties of starch paste, and waxy starch pastes being characterized by more viscous flow and smoother texture. Hierarchical cluster analysis indicated that differences between functional properties are more notable for normal than for waxy preparations, in which potato starch, regardless of its variety, was characterized by the most unique characteristics.

Molecular Basis of the Granular Characteristics of Small-Granule Starch: A Comparative Study

Small-granule starches (SGSs) have technological advantages over starches of conventional sizes for many applications. The study compared the granular characteristics of three SGSs (from amaranth, quinoa, and taro) with those of maize and potato starches and revealed their molecular basis. The results indicated that the supramolecular architecture of starch granules was not necessarily correlated with granule size. Acid hydrolysis of amaranth and quinoa starches was fast due to not only their small granule sizes but also the defects in the supramolecular structure, to which short external and internal chain lengths of amaranth and quinoa amylopectins contributed. By comparison, the granular architecture of taro starch granules was more stable partly due to the longer external chain length of taro amylopectin. Comparison of the molecular composition of branched subunits (released by using α-amylase of Bacillus amyloliquefaciens) in amylopectins and that in lintnerized starches suggested a significant heterogeneous degradation of amaranth and quinoa starches at supramolecular levels.

The important role of starch fine molecular structures in starch gelatinization property with addition of sugars/sugar alcohols

The relationship between the fine structure of starch and its gelatinization properties is not well studied, particularly in relation to the influence of sugar or sugar alcohol. In this study, seven starches with distinct molecular structures were investigated to determine how different sugars and sugar alcohols affect their gelatinization properties. The inclusion of sugars and sugar alcohols resulted in a significant elevation of starch gelatinization temperatures (∼ 8 °C), especially with sucrose, isomaltose and isomalt. Nevertheless, the influence of these sugars/ sugar alcohols on the gelatinization temperature range and enthalpy change varied depending on the particular starch varieties. According to the correlation analysis, sugars and sugar alcohols mainly exert their impact on the starch gelatinization temperature range and enthalpy change by possibly interacting with amylose chains possessing a degree of polymerization ranging from 100 to 1000 (p < 0.05) and inhibiting the amylose leaching during gelatinization. These findings help a better understanding of the complex relationship between starch fine structure and gelatinization properties under the influence of sugars and sugar alcohols.

Structure and functional characteristics of starch from different hulled oats cultivated in China

This work aimed to evaluate the structure and functional characteristics of starch from ten hulled oat cultivars grown in different locations in China. The protein, phosphorus, amylose, and starch contents were 0.2-0.4 %, 475.7-691.8 ppm, 16.2-23.0 %, and 93.6-96.7 %, respectively. All the starches showed irregular polygonal shapes and A-type crystallization with molecular weights ranging from 7.2 × 107 to 4.5 × 108 g/mol. The amounts of amylopectin A (DP 6-12), B1 (DP 13-24), B2 (DP 25-36), and B3 (DP > 36) chains were in the ranges of 10.3-16.0 %, 54.5-64.8 %, 16.5-21.1 %, and 4.9-13.1 %, respectively. The starches differed significantly in gelatinization temperatures, pasting viscosity, solubility, swelling power, rheological properties, and digestion parameters. The results revealed that the larger particle size could increase the peak viscosity of the starch paste. The presence of phosphorus increased the gelatinization temperature and enhanced the resistant starch content. The starch granules with higher crystallinity contained a higher proportion of phosphate, which increased final viscosity and setback viscosity but decreased rapidly digestible starch. Overall, oat starch with a high phosphorus content could be used to prepare low-glycemic-index food for diabetes patients.

Subtle structural variations of resistant starch from whole cooked rice significantly impact metabolic outputs of gut microbiota

While cooked rice is widely consumed as a whole food, the specific characteristics and impact of its resistant starch (RS) on gut microbiota are largely unexplored. In this study, three rice varieties with distinct starch molecular structures were used to prepare RS from cooked rice. All three types of RS had a crystalline structure characterized as B + V type, with the V type being the predominant crystalline polymorph. Distinct differences in chain-length distributions were observed among different RSs, with rapidly fermentable starch fractions comprising short amylopectin and long amylose chains, while the degrees of polymerization (DPs) ∼ 10, 37, 65, and 105 fractions comprised the slowly fermentable starch. Jasmine rice RS showed the highest proportion of this slowly fermentable starch fraction, which appeared to be specifically utilized by Megasphaera_elsdenii_DSM_20460 OTU198. The fermentation of Jasmine RS resulted in the highest production of butyrate after 24 h, which was positively correlated with the relative abundance of Megasphaera_elsdenii_DSM_20460 OTU198. These findings collectively indicate that RS in cooked rice with a higher V type crystallinity and DPs ∼ 10, 37, 65, and 105 fractions promote butyrate production and stimulate the growth of butyrate-producing bacteria in the human gut, thereby conferring beneficial effects on gut health.

Importance of both leached and residual starch molecular structures in determining cooked rice texture at different rice-to-water cooking ratios

Although texture of cooked rice has been investigated with regard to its relation to starch structure, it remains unclear how starch molecular structure and water content together affect its texture. Thus, the texture, and starch molecular structure of 10 rice varieties and their leachates during cooking were studied with a range of rice-to-water ratios. Although hardness of cooked rice decreased, no trend for the alteration of stickiness observed over the increase of water content. Generally, more amylopectin with DP 12-36 and amylose with DP 5000-20,000 in leachate, less starch molecules with DP > 36 in residual materials resulted in a higher stickiness of cooked rice, which is rationalized by their slower retrogradation tendency and higher amount of non-reducing ends available for binding to textural probe. Rice-to-water ratio was another crucial factor in determining relations between starch structures and cooked rice texture. For example, more leached amylopectin with DP 12-100 resulted in a higher stickiness of cooked rice, while this was not the case for rice cooked at rice-to-water ratios of 1: 1.2 and 1: 1.4. These results give new insights on the effects of starch molecular structure and water content on the cooked rice texture.

Effects of nitrogen application on physicochemical properties of rice starch under elevated temperature

Nitrogen fertilization can mitigate the negative effects of high temperatures on rice. In this study, we simulated dynamic field temperature increases using a free-air temperature enhancement system. Changes in the physicochemical properties of starch were investigated under increasing nitrogen fertilization during the grain-filling stage. We observed that the application of nitrogen at elevated temperatures (ETN) did not change the chain length distribution compared with elevated temperatures (ET) alone; however, it did significantly increase the heights of the first and second amylose peaks. Specifically, ETN significantly decreased the height of fifth amylopectin and relative crystallinity, and the changes it introduced in the physicochemical properties of starch were greater than those of ET. Overall, these changes in starch properties may be associated with the ability of nitrogen to facilitate the maintenance of rice quality at high temperatures.

A comparative study of grain quality and physicochemical properties of premium japonica rice from three typical production regions

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.

Characterization of green banana starch from "Songkibab" species cultivated in the southern part of Korea

Resistant starch (RS) has advantages for regulating the colon health as prebiotics and dietary fibers, and green banana has interested due to containing high amounts of RS. Here, the structural, physicochemical, and digestible characteristics of green banana starch from newly bred Songkibab (SB) were determined to evaluate its suitability for application as a new crop in response to global warming and for obtaining genetic diversity. SB starch has structural similarities to the Cavendish (CD) banana, which is widely consumed in Southeast Asia, in its ratio of B3-chains (in high amounts), flattened shapes of smooth surfaces, and B-type crystallinity. Physiochemically, SB shows comparable swelling power, amylose content, and viscosity pattern but a higher RS content. Conclusively, this study suggests that SB banana may be a good resource for replacing CD species with novel varieties in East Asia because of the high degree of similarity in the various characteristics.

Supplementary Information

The online version contains supplementary material available at 10.1007/s10068-023-01331-z.

Unlocking the potential of pasting properties to predict extrudate characteristics of corn grits blends with high amylose corn starch, potato starch, or rice flour

The development of new production lines of extruded ready-to-eat (RTE) snacks often results in high losses of edible food due to the trial-and-error approach in industry. Being able to predict extrudate characteristics of new formulations before having to run trials on industrial scale would be beneficial for reducing waste and having a more efficient development process. With this study, the correlation between pasting properties of seven blends of flours/starches and extrudate characteristics was investigated (100% corn grits, 25% and 50% replacement of corn grits with high amylose starch, potato starch, and rice flour). The predictive power of pasting characteristics on extrudate's moisture content, water absorption and solubility index, sectional expansion index (SEI) and hardness was studied. Results indicated the potential of predicting SEI, water solubility index (WSI), and water absorption index (WAI) of RTE-snacks. WSI and WAI were, respectively, negatively correlated with peak temperature (R2  = 0.897), and positively with peak temperature and positively with trough viscosity (R2  = 0.855). One can conclude that the rheometer can be a useful tool to gain insight into the characteristics of the extrudate, although further research with enlargement of the dataset is necessary to make the rheometer effectively deployable for potentially other extrudate characteristics.

Exploration of unique starch physicochemical properties of novel buckwheat lines created by crossing Golden buckwheat and Tatary buckwheat

Buckwheat is considered as a healthy cereal food, and it is essential to cultivate new buckwheat lines with good starch physicochemical properties for both consumers and food producers. Six novel buckwheat (Duoku, Dk) were generated by crossing of Golden buckwheat and Tatary buckwheat, and their kernel appearance properties and starch physicochemical properties were analyzed together with one domestic line (Cimiqiao) and one wild line (Yeku). The results showed that Dk samples had better appearance properties than two control samples. The Dk samples showed lower amylose content, similar amylopectin molecular structure and chain length distributions, and larger starch granules compared with Cimiqiao. The digestion results showed that two Dk samples: Dk6 & Dk9 had high resistant starch content; while the other two Dk samples: Dk37 & Dk38 had a steady glucose releasing rate. The Dk samples also showed high gelatinization temperature, indicating they were good raw materials for producing glass noodle. This study proved that Dk buckwheat had unique starch physicochemical properties, and could be used as new food materials in the future.

High-pressure pasting performance and multilevel structures of short-term microwave-treated high-amylose maize starch

Microwave treatment is an environmentally friendly method for modification of high-amylose maize starch (HAMS). Here, the effects of short-time (≤120 s) microwave treatment on the structure and pasting of two types of HAMSs, Gelose 50 (HAMSI) and Gelose 80 (HAMSII), with apparent amylose content (AAC) of 45 % and 58 %, respectively, was studied using a multiscale approach including X-ray scattering, surface structures, particle size distribution, molecular size distributions and high temperature/pressure Rapid Visco Analysis (RVA)-4800 pasting. As compared to starch with no amylose (waxy maize starch, WMS) and 25 % amylose content (normal maize starch, NMS), HAMSI underwent similar structural and pasting changes as WMS and NMS upon microwave treatment, and it might primarily be attributed to the amylopectin fraction that was affected by cleavage of the connector chains between double helices and backbone chains, which decreased the crystallinity and thickness of the crystalline lamellae. However, the multi-scale structure of HAMSII was almost unaffected by this treatment. The pasting properties of fully gelatinized HAMSI starch showed a decrease in RVA-4800 peak and final viscosities after microwave treatment. In contrast, for HAMSII starch, the microwave treatment led to an increase in these viscosities. The combined results highlight the influence of varying AAC on the effects of microwave-mediated modification, leading to diverse alterations in the structure and functionality of starches.

Critical examination of the characterization techniques, and the evidence, for the existence of extra-long amylopectin chains

It has been suggested that amylopectin can contain small but significant amounts of extra-long chains (ELCs), which could affect functional properties, and also would have implications for the mechanism of starch biosynthesis. However, current evidence for the existence of ELCs is ambiguous. The amylose/amylopectin separation and the characterization techniques used for the investigation of ELCs are reviewed, problems in those techniques are examined, and studies of ELCs of amylopectin are discussed. A model for the biosynthesis of amylopectin chains in terms of conventional biosynthesis enzymes, which provides an excellent fit to a large amount of experimental data, is used to provide a rigorous definition of ELCs. In addition, current investigations of ELCs, involving separation, is hindered by the lack of a method to quantitatively separate all the amylopectin from starch without any traces of residual amylose (which would have long chains). Unambiguous evidence for the existence of ELCs can be obtained using two-dimensional (2D) characterization, these dimensions being the degree of polymerization of a chain and the size of the whole molecule. Available 2D data indicate that there are no ELCs present in currently detectable quantities in native rice starches. However, concluding this more rigorously requires improvements in the resolution of current 2D methods.

Importance of amylose chain-length distribution in determining starch gelatinization and retrogradation property of wheat flour in the presence of different salts

Although starch gelatinization and retrogradation properties of wheat flour have been studied with respect to their relations to starch structures, it remains less understood how starch structure and salt (a common food additive) together determine these properties. Gelatinization and retrogradation properties of seven wheat flours with distinct starch structures were thus investigated after adding different salts. NaCl most efficiently increased starch gelatinization temperatures, while KCl showed highest efficiency in retarding the retrogradation degree. Both gelatinization and retrogradation parameters were significantly affected by amylose structural parameters and types of salts. E.g., wheat flours with longer amylose long chains had more heterogeneous amylopectin double helices during gelatinization, while this relationship disappeared after adding NaCl. More amylose short chains increased the heterogeneity of retrograded short-range starch double helices, while the relationship was opposite after adding NaCl. These results help a better understanding of the complex relationship between starch structure and physicochemical property.

Physicochemical properties of starch in sodium chloride solutions and sucrose solutions: Importance of starch structure

The influences of sodium chloride (NaCl)/sucrose on starch properties as affected by starch structural characteristics are little understood. In this study, the effects were observed in relation to the chain length distribution (from size exclusion chromatography) and granular packing (inferred through morphological observation and determination of swelling factor and paste transmittance) of starches. Adding NaCl/sucrose dramatically delayed the gelatinization of starch that had a high ratio of short-to-long amylopectin chains and had loose granular packing. The effects of NaCl on the viscoelasticity of gelatinizing starch were related to the flexibility of amylopectin internal structure. Effects of NaCl/sucrose on starch retrogradation varied with starch structure, co-solute concentration, and analytical method. The co-solute-induced changes in retrogradation were highly associated with amylose chain length distribution. Sucrose strengthened the weak network formed by short amylose chains, while the effect was not significant on amylose chains that were capable of forming strong networks.

Physicochemical properties and molecular structure of lotus seed starch

Current understanding of physicochemical properties of lotus seed starch (LS) is scarce partly due to its largely unknown molecular structure. This study compared the physicochemical and molecular characteristics of LSs of a wide collection to those of conventional starches (potato (PS) and maize starches (MS)). Variations were found in the chemical composition, physicochemical properties, and molecular structure of LSs. Amylose content and weight-based ratio of short to long chains of amylopectin (APS:APL) were principal factors affecting the physicochemical properties of LSs from different origins. Compared with PS and MS, LSs had higher gelatinization temperatures, lower amylose leaching, and faster retrogradation. These unique properties of LSs were related to their molecular structure and chemical composition. LSs had higher amylose contents than PS and MS as evaluated by various methods. A majority of amylose chains in LS were longer than those in MS but were shorter than those in PS. The APS:APL of LSs were higher than that of MS but lower than that of PS. The results provided a structural basis for understanding the properties of LS and suggested that this unconventional starch may be complementary to conventional starches for industrial applications.

Efficient Accumulation of Amylopectin and Its Molecular Mechanism in the Submerged Duckweed Mutant

Large-scale use of fossil fuels has brought about increasingly serious problems of environmental pollution, development and utilization of renewable energy is one of the effective solutions. Duckweed has the advantages of fast growth, high starch content and no occupation of arable land, so it is a promising starchy energy plant. A new submerged duckweed mutant (sub-1) with abundant starch accumulation was obtained, whose content of amylopectin accounts for 84.04% of the starch granules. Compared with the wild type (Lemna aequinoctialis), the branching degree of starch in sub-1 mutant was significantly increased by 19.6%. Chain length DP 6-12, DP 25-36 and DP > 36 of amylopectin significantly decreased, while chain length DP 13-24 significantly increased. Average chain length of wild-type and sub-1 mutant starches were greater than DP 22. Moreover, the crystal structure and physical properties of starch have changed markedly in sub-1 mutant. For example, the starch crystallinity of sub-1 mutant was only 8.94%, while that of wild-type was 22.3%. Compared with wild type, water solubility of starch was significantly reduced by 29.42%, whereas swelling power significantly increased by 97.07% in sub-1 mutant. In order to further analyze the molecular mechanism of efficient accumulation of amylopectin in sub-1 mutant, metabolome and transcriptome were performed. The results showed that glucose accumulated in sub-1 mutant, then degradation of starch to glucose mainly depends on α-amylase. At night, the down-regulated β-amylase gene resulted in the inhibition of starch degradation. The starch and sucrose metabolism pathways were significantly enriched. Up-regulated expression of SUS, AGPase2, AGPase3, PYG, GPI and GYS provide sufficient substrate for starch synthesis in sub-1 mutant. From the 0H to 16H light treatment, granule-bound starch synthase (GBSS1) gene was inhibited, on the contrary, the starch branching enzyme (SBE) gene was induced. Differential expression of GBSS1 and SBE may be an important reason for the decrease ratio of amylose/amylopectin in sub-1 mutant. Taken together, our results indicated that the sub-1 mutant can accumulate the amylopectin efficiently, potentially through altering the differential expression of AGPase, GBSS1, SBE, and BAM. This study also provides theoretical guidance for creating crop germplasm with high amylopectin by means of synthetic biology in the future.

The textural properties of cooked convenience rice upon repeated freeze-thaw treatments are largely affected by water mobility at grain level

Brown rice (BR) is a promising source for convenience rice that are mostly stored frozen. However, freezing and thawing may cause deterioration in rice texture quality. To investigate how rice texture is influenced by freeze-thaw cycles, BR, the pretreated BR with partially ruptured bran layer (UER) and white rice (WR) were cooked and treated with repeated freeze-thaw cycles, with their textural properties, variations in moisture distribution and starch structure being measured. Results showed that the repeated freeze-thaw treatment induced a progressive reduction in hardness and stickiness of all cooked rice. The reduced hardness of rice could be explained by the enlarged pore size of starch inside rice under scanning electron microscopy. Moisture migration in WR was the fastest responding to multiply freeze-thaw cycles, followed by UER, while water mobility in BR was slowest. Moreover, WR, BR and UER resulted in a similar extent of amylopectin retrogradation and chains length distribution after repeated freeze-thaw cycles. It indicated similar and minor effect of starch variations on determining the texture of different rice samples against freeze-thawing. Water mobility tended to be a main factor leading to the textural difference of fully gelatinized rice samples. This study focused on the relationship between water distribution and starch retrogradation, providing a better understanding on influences of multiple freeze-thawing on textural quality of cooked rice maintaining different extents of surface layer.

Starch fine molecular structures: The basis for designer rice with slower digestibility and desirable texture properties

Development of whole rice with low glycaemic index has been achieved, however, these rices are frequently associated with a poor texture property. Recent advances in terms of understanding the importance of starch fine molecular structures on the starch digestibility/texture of cooked whole rice have shed new insights on mechanisms of starch digestibility and texture from molecular levels. With an extensive discussion on the correlative and causal relationships among starch molecular structure, texture and starch digestibility of cooked whole rice, this review identified desirable starch fine molecular structures contributing to both slow starch digestibility and preferable textures. For instance, the selection of rice variety having more amylopectin intermediate chains while less amylopectin long chains might help develop cooked whole rice with both slower starch digestibility and softer texture. The information could help rice industry transform cooked whole rice into a healthier food product with slow starch digestibility and desirable texture.

The Effects of Starch Molecular Fine Structure on Thermal and Digestion Properties of Rice Starch

Whole white rice is a major staple food for human consumption, with its starch digestion rate and location in the gastrointestinal tract having a critical role for human health. Starch has a multi-scale structure, which undergoes order-disorder transitions during rice cooking, and this structure is a major determinant of its digestibility. The length distributions of amylose and amylopectin chains are important determinants of rice starch gelatinization properties. Starch chain-length and molecular-size distributions are important determinants of nucleation and crystal growth rates, as well as of intra- and intermolecular interactions during retrogradation. A number of first-order kinetics models have been developed to fit starch digestograms, producing new information on the structural basis for starch digestive characteristics of cooked whole rice. Different starch digestible fractions with distinct digestion patterns have been found for the digestion of rice starch in fully gelatinized and retrograded states, the digestion kinetics of which are largely determined by starch fine molecular structures. Current insights and future directions to better understand digestibility of starch in whole cooked rice are summarized, pointing to ways of developing whole rice into a healthier food by way of having slower starch digestibility.

Relationship between starch fine structure and simulated oral processing of cooked japonica rice

Background

Simulated 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.

Methods

In 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.

Results

Cooked 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.

Conclusion

The 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.

Verification of autoclaving-cooling treatment to increase the resistant starch contents in food starches based on meta-analysis result

Autoclaving-cooling is a common starch modification method to increase the resistant starch (RS) content. The effect of this method varies depending on the type of crop and treatment condition used. The objectives of this study were to verify the autoclaving-cooling treatment based on a meta-analysis result and to evaluate the physicochemical properties of modified starches. The meta-analysis study used 10 articles from a total of 1,293 that were retrieved using the PRISMA approach. Meta-analysis showed that the optimal treatments of autoclaving-cooling process that increase the RS content significantly, was in starch samples from the cereal group (corn, oats, rice) (SMD: 19.60; 95% CI: 9.56–29.64; p < 0.001), with water ratio 1:4 (SMD: 13.69; 95% CI: 5.50–21.87; p < 0.001), using two cycles of autoclaving-cooling (SMD: 16.33; 95% CI: 6.98–25.67; p < 0.001) and 30 min of autoclaving heating (SMD: 12.97; 95% CI: 1.97–23.97; p < 0.001) at 121°C (SMD: 12.18; 95% CI: 1.88–22.47; p < 0.001). Verification using corn flour and corn starch showed a significant increase in RS contents from 15.84 to 27.78% and from 15.27 to 32.53%, respectively, and a significant decrease in starch digestibility from 67.02 to 35.74% and from 76.15 to 28.09%, respectively. Treated sample also showed the pasting profile that was stable under heating and stirring.

Combined effects of starch fine molecular structures and water content on starch digestibility of cooked white rice

Although the starch digestibility of cooked white rice has been investigated with regard to its relation to starch structure, it is not yet clear how starch molecular structure and water content affect its digestion rate. To investigate this, the in vitro starch digestibility and molecular structure of 10 rice varieties with a range of rice-to-water cooking ratios were investigated. As expected, starch digestibility varied with different conditions. Typically, a higher amylose content resulted in a lower maximum digestion extent for a given water content. Having relatively more and longer amylopectin intermediate chains caused a slower starch digestion rate, but only with rice-to-water ratios between 1:1 and 1:1.2. These results could prove useful to find combinations of starch fine molecular structures and water contents to produce cooked rice with low glycemic index.

Starch molecular structural differences between chalky and translucent parts of chalky rice grains

Chalky rice has an undesirable appearance and reduced commercial value. To understand the relationship between starch structural characteristics and chalkiness, a comprehensive investigation was conducted of molecular structural differences between starch in chalky and translucent parts of the same chalky grains (three Japonica and two Indica rices), this strategy being such as to minimize genetic and environmental effects. Compared to translucent parts, chalky parts had a larger ratio of large to small branched molecules and more short amylopectin chains (degree of polymerization < 35), but fewer longer chains, which affect higher-level starch structures, such as crystallinity. No significant differences in amylose structure were observed. White-belly and white-core chalky grains showed distinguishable starch characteristics, suggesting studying different chalkiness types separately. These findings extend understanding of chalkiness from the perspective of starch structure, and control of this structure can in the future help breeders to develop strategies against the formation of chalkiness.

Diurnal changes in starch molecular structures and expression profiles of starch biosynthesis enzymes in rice developing seeds

The diurnal changes in the expression profiles of starch synthesis related enzymes (SSREs) has been previously studied in transitory starches, while its influences on storage starch molecular structures in the rice endosperm during seed development have not been elucidated. In this study, the changes in the transcript levels of starch synthesis related genes (SSRGs), the protein abundances and enzyme activities of SSREs as well as starch molecular structures in rice endosperm at 10 days after flowering (DAF) over the diurnal cycle were analyzed. It was found that the expression profiles of SSRG and the protein contents of SSREs displayed different diurnal patterns between two indica rice varieties with medium- and high-amylose content (AC), respectively. The expression levels of SSRGs were higher in the light time, and most SSREs also accumulated during this period except debranching enzymes. Amylose synthesis displayed distinct diurnal patterns in two rice varieties, which is attributed to the diurnal changes in the protein content of granule-bound starch synthase I (GBSSI), but amylopectin chain-length distributions (CLDs) remained unaltered due to its vast numbers of branches. The results provide the first step to understand the roles of each enzyme isoform involved in starch synthesis in response to diurnal regulation in rice endosperm.

Amylose Inter-Chain Entanglement and Inter-Chain Overlap Impact Rice Quality

Retrogradation of cooked rice happens in two ways: one is by the formation of ordered structures, and the other is through intra- and inter-chain entanglement and inter-chain overlap, which in turn are affected by the amylose chain-length distribution. Both entanglement and overlap could affect rice texture. Here, four amylose samples were isolated from starch by precipitation from a dimethyl sulfoxide solution with butan-1-ol and isoamyl alcohol. Following enzymatic debranching, they were then characterized using size-exclusion chromatography. Amylose solutions (10%, m/v) were made by dissolving amylose in 90% (v/v) DMSO. Amylose gels (10%, w/v) were made by dissolving amylose powders into hot water, followed by cooling. The rigidity of the amylose gels and the structural order were measured using a texture analyzer and X-ray diffractometer, respectively. In the amylose solution, for a given mass of polymer in a fixed amount of solvent, the total occupied volume was reduced when the polymer molecular weight was smaller, resulting in less inter-chain overlap and a lower viscosity of the amylose solution. The overall mobility and diffusion of the molecules were inversely related to the square of the molecular weight until the gelation concentration. Thus, amylose gels in which amylose had a lower molecular weight had a greater chance to permeate into other molecules, which counterintuitively led to more inter-chain entanglement and more rigid amylose gels during retrogradation. This information could help rice breeders improve rice quality by using the molecular structure of starch as a guide.

Relative importance of branching enzyme isoforms in determining starch fine structure and physicochemical properties of indica rice

Down-regulation of starch branching enzymes alters fine structure and starch properties, especially the B-type crystalline pattern and extremely high amylose content identified in the BEIIb-deficiency mutant in the indica rice. The relative importance of the starch branching enzymes in determining the molecular fine structure and starch functional properties were uncovered in this study. An indica rice, Guangluai 4 with high amylose content (AC) and high gelatinization temperature (GT) was used to generate the clustered regularly interspaced short palindromic repeats (CRISPR)/associated protein-9 (Cas9) knockout lines. Five mutant lines were identified including be1-1, be1-2, be2a-1, be2a-2 and be2b-1, and analysis of western blot showed the CRISPR/Cas9 system was successful in inducing mutations in the targeted genes. AC of be2b-1 (34.1%) was greater than that of wild type (WT) (27.4%) and other mutants. Mutations of either BEI or BEIIa did not alter the starch crystallite pattern (A-type). The BEIIb deficiency caused an opaque endosperm phenotype, changed the crystallite pattern from A- to B-type, and dramatically increased the degree of ordered structure, the relative proportion of amylose chains and intermediate to long amylopectin chains, average chain length of amylopectin molecules as well as GT. The BEIIa deficiency had no effect on the proportion of amylose chains, the length of amylopectin intermediate-long chains, conclusion temperature and enthalpy of gelatinization. Down-regulation of BEI increased the proportion of shortest amylopectin chains (fa) but decreased the proportion of long amylopectin chains (fb2 and fb3), leading to a lower GT. It is concluded that the relative importance in determining starch fine structures and functionality was in the order of BEIIb > BEI > BEIIa. Our results provide new information for utilizations of BE-deficient mutants in rice quality breeding.

The role of different Wx and BEIIb allele combinations on fine structures and functional properties of indica rice starches

This study examined the effects of the combinations of Waxy (Wx) and starch branching enzyme IIb (BEIIb) alleles on starch fine structure and functional properties in indica rice cultivars. The results showed that be2b mutant starches with BEIIb deficiency had higher amylose content, shorter amylose long chains, a higher proportion of amylopectin long chains and molecular order, but a lower proportion of amylopectin short chains and relative crystallinity, resulting in higher gelatinization temperature but lower enthalpy and paste viscosity. Compared with the rice lines carrying Wx^b allele, Wx^a allele contributed to relatively higher amylose content, longer amylopectin chains, less short-range ordered structure and lower relative crystallinity, leading to a little lower gelatinization enthalpy. This study provides new insight into structure-function relations among rice lines with different allele combinations of starch synthesis related genes, which is a useful strategy for rice quality breeding.

Functional Interactions between Enzymes Involved in Amylose and Amylopectin Biosynthesis in Rice Based on Mathematical Models

Starch biosynthesis is controlled by multiple enzymes, including granule-bound starch synthase I (GBSSI), soluble starch synthases (SSs), branching enzymes (BEs), and debranching enzymes (DBEs). Although the role of individual isoforms has been primarily elucidated, the precise information about how they work together in the synthesis of specific amylose and amylopectin chains is still unclear. In this study, starch molecular chain-length distributions (CLDs) of five rice varieties with different amylose contents were measured by fluorophore-assisted carbohydrate electrophoresis and size-exclusion chromatography and fitted with two mathematical models, and the protein abundance of 11 starch synthesis-related enzymes was measured by western blotting. The correlation between model fitting parameters of amylose and amylopectin CLDs demonstrated that amylose and amylopectin syntheses are closely dependent. GBSSI could interact with BEI, BEIIb, SSIIa, SSIVb, ISA1, PUL, and PHO1 to synthesize the amylopectin intermediate and long chains as well as amylose chains. In addition, the interaction among SSIVb and SSI, SSIIa, BEI, BEIIb, ISA1, and PUL possibly suggests that SSIVb assists them to synthesize the amylopectin chains. The results can help understand the mechanisms about the functional interaction of different enzyme isoforms in starch biosynthesis.

Mutual interactions between α‑amylase and amyloglucosidase on the digestion of starch with distinct chain-length distributions at fully gelatinized state

Amyloglucosidase (AMG) and α-amylase (AMY) are involved in the human small intestine for starch digestion, whereas their mutual interactions with starch molecules of distinct structures are still unknown. In current...

Molecular brewing: The molecular structural effects of starch adjuncts on barley malt brewing performances

In this study, the effects of starch adjuncts with different fine molecular structures obtained by size-exclusion chromatography on the mashing and fermentation efficiencies of barley malts were investigated. Following fermentation, violate compounds of freshly-fermented beer samples were determined by headspace-solid-phase microextraction coupled with gas chromatography-mass spectrometry analysis (HS-SMPE-GC-MS). High performance liquid chromatography results showed that depending on their molecular structures, starch adjuncts addition significantly increased wort maltose and maltotriose content, whereas reducing the glucose content and thus both the ratios of glucose and maltotriose to that of the maltose. The whole fermentation by dry beer yeast was finished within the first 48 h and reached to equilibrium for the rest 72 h, represented by the stable soluble protein content. Results also showed that the addition of starch adjuncts resulted into increased alcohol content, which was mainly attributed to the altered glucose/maltose ratio. The HS-SPME-GC-MS results showed that whether or not with starch adjuncts addition, the composition of violate compounds were not significantly influenced, their content, on the contrary, were altered, represented by different peak heights. This study provides important information concerning the molecular effects of starch adjuncts on brewing performances of barley malts, and also provides a new pathway for choosing suitable types of adjuncts for making beer with better quality.

Development of Starch-Based Materials Using Current Modification Techniques and Their Applications: A Review

Starch is one of the most common biodegradable polymers found in nature, and it is widely utilized in the food and beverage, bioplastic industry, paper industry, textile, and biofuel industries. Starch has received significant attention due to its environmental benignity, easy fabrication, relative abundance, non-toxicity, and biodegradability. However, native starch cannot be directly used due to its poor thermo-mechanical properties and higher water absorptivity. Therefore, native starch needs to be modified before its use. Major starch modification techniques include genetic, enzymatic, physical, and chemical. Among those, chemical modification techniques are widely employed in industries. This review presents comprehensive coverage of chemical starch modification techniques and genetic, enzymatic, and physical methods developed over the past few years. In addition, the current applications of chemically modified starch in the fields of packaging, adhesives, pharmaceuticals, agriculture, superabsorbent and wastewater treatment have also been discussed.

Starch molecular fine structure is associated with protein composition in chickpea seed

Chickpea (Cicer arietinum L.) seed is a nutritional food high in starch and protein. This study aims to find the relationships between the molecular fine structure of starch and the composition of storage proteins and metabolic enzymes, using different chickpea varieties. It is found that storage proteins and starch biosynthetic enzymes influence each other. The initial formation of amylopectin molecules is affected by storage proteins, as suggested by the positive correlation (p < 0.01) between the average molecular size of amylopectin and total protein content. In addition, a higher amount of seed globulin could be an indication of higher amylose content and more short - medium amylose chains (degree of polymerization, DP, 118-2000). This study might assist selection of chickpea varieties with desirable qualities, such as low starch digestibility.

Starch granule size: Does it matter?

Nature has developed starch granules varying in size from less than 1 μm to more than 100 μm. The granule size is an important factor affecting the functional properties and the applicability of starch for food and non-food applications. Within the same botanical species, the range of starch granule size can be up to sevenfold. This review critically evaluated the biological and environmental factors affecting the size of starch granules, the methods for the separation of starch granules and the measurement of size distribution. Further, the structure at different length scales and properties of starch-based on the granule size is elucidated by specifying the typical applications of granules with varying sizes. An amylopectin cluster model showing the arrangement of amylopectin from inside toward the granule surface is proposed with the hypothesis that the steric hindrance for the growth of lamellar structure may limit the size of starch granules.