Using starch molecular fine structure to understand biosynthesis-structure-property relations

Multi-scale structural insights on starch digestibility of instant rice

Multi-scale structures were investigated to understand starch digestibility of instant rice. A wide range of maximum starch digested ratio, up to about 20%, was observed among instant rice prepared from different rice varieties. Instant rice with a smooth and densely packed cross-section showed slower starch digestibility than those with a porous and loosely packed structure. All samples displayed B + V type crystallinity, with V-type crystallinity negatively correlating with maximum starch digested percentage. After digestion, starch chain-length distributions were significantly altered: rapidly digested starch comprised long amylose and short amylopectin chains, while slowly digested starch comprised chains with a peak degree of polymerization (DP) around 130. These results indicate that instant rice with a compact microstructure, high V-type crystallinity, and DP 130 fractions during digestion can reduce starch digestibility. This study provides insights for food industry to develop instant rice products with slow starch digestibility, potentially improving human health.

The effects of chain-length distributions on starch-related properties in waxy rices

Normal rice starch consists of amylopectin and amylose, whose relative amounts and chain-length distributions (CLDs) are major determinants of the digestibility and rheology of cooked rice, and are related to metabolic health and consumer preference. Here, the mechanism of how molecular structural features of pure amylopectin (waxy) starches affect starch properties was explored. Following debranching, chain-length distributions of seven waxy varieties were measured using size-exclusion chromatography, and parameterized using biosynthesis-based models, which involve breaking up the chain-length distribution into contributions from five enzyme sets covering overlapping ranges of chain length; structure-property correlations involving the fifth set were found to be statistically significant. Digestibility was measured in vitro, and parameters for the slower and longer digestion phase quantified using non-linear least-squares fitting. The coefficient for the significant correlation involving amylopectin fine structure for the fifth set was -0.903, while the amounts of amylopectin short and long chains were found to dominate breakdown viscosity (correlation coefficients 0.801 and - 0.911, respectively). This provides a methodology for finding or developing healthier starch in terms of lower digestion rate, while also having acceptable palatability. As rice breeders can to some extent control CLDs, this can help the development of waxy rices with improved properties.

The importance of starch chain-length distribution for in vitro digestion of ungelatinized and retrograded foxtail millet starch

The digestibility of ungelatinized, short-term retrograded and long-term retrograded starch from foxtail millet was investigated and correlated with starch chain length distributions (CLDs). Some variations in starch CLDs of different varieties were obtained. Huangjingu and Zhonggu 9 had higher average chain lengths of debranched starch and lower average chain length ratios of amylopectin and amylose than Dajinmiao and Jigu 168. Compared to ungelatinized starch, retrogradation significantly increased the estimated glycemic index (eGI), whereas significantly decreased the resistant starch (RS). In contrast, long-term retrograded starches have lower eGI (93.33-97.37) and higher RS (8.04-14.55%) than short-term retrograded starch. PCA and correlation analysis showed that amylopectin with higher amounts of long chains and longer long chains contributed to reduced digestibility in ungelatinized starch. Both amylose and amylopectin CLDs were important for the digestibility of retrograded starch. This study helps a better understanding of the interaction of starch CLDs and digestibility during retrogradation.

Insight to starch retrogradation through fine structure models: A review

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.

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.

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.

Structural and property changes of starch derivatives under microwave field: A review

Native starches are commonly modified for desired properties because of their limited applications. Among various modifications, microwave irradiation has been gaining strong interests and becoming a focal area to transform starch during the last few years. Such interests reside in microwave irradiation's high heating rates, lesser extent of loss in nutritional qualities, and so on when compared with other approaches. This review summaries the effects of microwave field on the structural (e.g. morphology characteristic, lamellae structure, crystallinity, and molecular structure) and physicochemical properties (e.g. pasting properties and gelatinization) of naturally existing starch derivatives. Different microwave-assisted chemical derivatizations can directly or indirectly affect starch structure from the macroscopic to the microscopic level, thereby resulting in various functionalities. Moreover, conventional starch modification processes can be optimized by applying microwave irradiation to obtain modified starch with high degree of substitution and low viscosity. The future research will help to better understand the structural changes of microwave-assisted starch chemical derivatization and thereby creating a wide range of functionalities.

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.

Starch chain-length distributions determine cooked foxtail millet texture and starch physicochemical properties

Starch chain-length distributions play an important role in controlling cereal product texture and starch physicochemical properties. Cooked foxtail millet texture and starch physicochemical properties were investigated and correlated with starch chain-length distributions in eight foxtail millet varieties. The average chain lengths of amylopectin and amylose were in the range of DP 24-25 and DP 878-1128, respectively. The percentage of short amylopectin chains (Ap1) was negatively correlated with hardness but positively correlated with adhesiveness and cohesion. Conversely, the amount of amylose intermediate chains was positively correlated with hardness but negatively correlated with adhesiveness and cohesion. Additionally, the amount of amylose long chains was negatively correlated with adhesiveness and chewiness. The relative crystallinity (RC) of starch decreased with reductions in the length of amylopectin short chains in foxtail millet. Pasting properties were mainly influenced by the relative length of amylopectin side chains and the percentage of long amylopectin branches (Ap2). Longer amylopectin long chains resulted in lower gelatinization temperature and enthalpy (ΔH). The amount of starch branched chains had important effects on the gelatinization temperature range (ΔT). These results can provide guidance for breeders and food scientists in the selection of foxtail millet with improved quality properties.

High fructan barley lines produced by selective breeding may alter β-glucan and amylopectin molecular structure

Six cross-bred barley lines developed by a breeding strategy with the target to enhance the fructan synthesis activity and reduce the fructan hydrolysis activity were analyzed together with their parental lines, and a reference line (Gustav) to determine whether the breeding strategy also affected the content and molecular structure of amylopectin and β-glucan. The highest fructan and β-glucan content achieved in the novel barley lines was 8.6 % and 12 %, respectively (12.3-fold and 3.2-fold higher than in Gustav). The lines with low fructan synthesis activity had higher starch content, smaller building blocks in amylopectin, and smaller structural units of β-glucans than the lines with high-fructan synthesis activity. Correlation analysis confirmed that low starch content was associated with high amylose, fructan, and β-glucan content, and larger building blocks in amylopectin.

Evaluation of altered starch mutants and identification of candidate genes responsible for starch variation in wheat

BACKGROUND

Induction of mutation through chemical mutagenesis is a novel approach for preparing diverse germplasm. Introduction of functional alleles in the starch biosynthetic genes help in the improvement of the quality and yield of cereals.

RESULTS

In the present study, a set of 350 stable mutant lines were used to evaluate dynamic variation of the total starch contents. A megazyme kits were used for measuring the total starch content, resistant starch, amylose, and amylopectin content. Analysis of variance showed significant variation (p < 0.05) in starch content within the population. Furthermore, two high starch mutants (JE0173 and JE0218) and two low starch mutants (JE0089 and JE0418) were selected for studying different traits. A multiple comparison test showed that significant variation in all physiological and morphological traits, with respect to the parent variety (J411) in 2019-2020 and 2020-2021. The quantitative expression of starch metabolic genes revealed that eleven genes of JE0173 and twelve genes of JE0218 had consistent expression in high starch mutant lines. Similarly, in low starch mutant lines, eleven genes of JE0089 and thirteen genes of JE0418 had consistent expression in all stages of seed development. An additional two candidate genes showed over-expression (PHO1, PUL) in the high starch mutant lines, indicating that other starch metabolic genes may also contribute to the starch biosynthesis. The overexpression of SSII, SSIII and SBEI in JE0173 may be due to presence of missense mutations in these genes and SSI also showed overexpression which may be due to 3-primer_UTR variant. These mutations can affect the other starch related genes and help to increase the starch content in this mutant line (JE0173).

CONCLUSIONS

This study screened a large scale of mutant population and identified mutants, could provide useful genetic resources for the study of starch biosynthesis and genetic improvement of wheat in the future. Further study will help to understand new genes which are responsible for the fluctuation of total starch.

Effects of the Molecular Structure of Starch in Foods on Human Health

Starch provides approximately half of humans' food energy, and its structural features influence human health. The most important structural feature is the chain length distribution (CLD), which affects properties such as the digestibility of starch-containing foods. The rate of digestion of such foods has a strong correlation with the prevalence and treatment of diseases such as diabetes, cardiovascular disease and obesity. Starch CLDs can be divided into multiple regions of degrees of polymerization, wherein the CLD in a given region is predominantly, but not exclusively, formed by a particular set of starch biosynthesis enzymes: starch synthases, starch branching enzymes and debranching enzymes. Biosynthesis-based models have been developed relating the ratios of the various enzyme activities in each set to the CLD component produced by that set. Fitting the observed CLDs to these models yields a small number of biosynthesis-related parameters, which, taken together, describe the entire CLD. This review highlights how CLDs can be measured and how the model-based parameters obtained from fitting these distributions are related to the properties of starch-based foods significant for health, and it considers how this knowledge could be used to develop plant varieties to provide foods with improved properties.

Investigation of the mechanism of different 3D printing performance of starch and whole flour gels from tuber crops

This study aims to reveal the variation in 3D printing performance of whole flour and starch gels as derived from different varieties of tuber crops including cassava, potato, and yam, along with its mechanism. The whole flour of the same tuber crops showed a higher branching degree, average molecular weight (R¯_h), and the proportion of AM chains for 100 < X ≤ 1000 than its starch. Due to the higher degree of branching, the crystallinity of whole flour reached a higher level. In this circumstance, G2' of the dispersion system decreased, which facilitated smooth extrusion of ink from the nozzle, thus improving the precision of printing for the final product. Besides, a higher R¯_h and the percentage of AM chains for 100 < X ≤ 1000 made it easier for the material to extrude, thus enhancing the printing accuracy of the product. The higher short-range ordered structure of whole flour also enhanced the printing performance of 3D printed products. This research contributes an effective solution to the selection of starch and whole flour for food 3D printing.

Structural changes of starch under different milling degrees affect the cooking and textural properties of rice

A long-term consumption of white rice increases the risk of T2D. Finding an appropriate milling degree (MD) of rice balancing nutrition and palatability benefits public health. This study investigated effects of MD-0 s, 5 s, 60 s on morphological, cooking and textural properties of rice. Texture profile analysis showed that milling decreased hardness, while increased adhesiveness of rice. SEM images showed that milling induced notches and structural damage, which facilitated gelatinization of rice determined by DSC. Leached starch was further analyzed by size exclusion chromatography and chain-length distribution. Pearson correlation analysis revealed that milling induced more leached shot-chain amylose and long-chain amylopectin, which decreased hardness and increased adhesiveness of cooked rice. Collectively, milling-induced changes of starch gelatinization and fine structure of leached starch were decisive factors of rice texture. Moderate processing improved the texture of brown rice and maintained nutrients. This would provide guidance for the health industry of whole grains.

A procedure for determining the number and pattern of digestible starch fractions in multiphasic food digestograms

BACKGROUND

Plant-based foods are frequently heterogenous systems, containing multiple starch fractions with distinct digestion rate constants. An unbiased determination of the number and digestion pattern of these fractions is a prerequisite for understanding the digestive characteristics of food.

RESULTS

A non-linear least-squares procedure based on a conditional selection of simple first-order kinetics or a combination of parallel and sequential kinetics models was developed. The procedure gave robust results fitting manually generated data, and was applied to in vitro experimental digestion data of retrograded rice starches. By correlating fitting parameters with starch structural parameters, it showed that rice starches with a lower amylose content, longer amylose chains, and amylopectin intermediate chains had more digestible starch fractions after long-term retrogradation.

CONCLUSION

This procedure enables the structural basis of starch digestibility and the development of food products with slow starch digestibility to be better understood. © 2022 Society of Chemical Industry.

Phenotypic differences in the appearance of soft rice and its endosperm structural basis

In view of the significant differences among genotypes in the appearance of soft rice, it is necessary to conduct research on the differences in the appearance quality of soft rice and their mechanisms. It can provide a theoretical basis for the selection and breeding of superior appearance varieties at a later stage. In order to clarify the differences in appearance phenotypes between different soft rice genotypes and structural basis of endosperm structures behind the differences, four soft rice varieties were selected in this study, including two varieties with good-appearance and two varieties with cloudy appearance. The differences in appearance phenotypes and endosperm structure in mature grains of soft rice with different appearance phenotypes were scientifically analyzed. The development process of their endosperm differences at the filling stage was investigated. The results show that the difference in the rice appearance of soft rice varieties mainly lay in the chalk-free seed transparency and chalkiness. These differences were caused by two completely different types of endosperm structure. Fewer and smaller starch grain cavities were responsible for higher chalk-free transparency of soft rice grains, denser starch granules arrangement caused lower chalkiness of soft rice grains. Ten days after flowering, the starch granules in the back and heart of good-appearance soft rice were already significantly fuller and more closely packed than those of cloudy soft rice. At the same time, the number and area of starch granule holes were significantly smaller than those of cloudy soft rice. This difference gradually increased until maturity. Therefore, based on appearance evaluation, soft rice with good-appearance should have higher transparency and lower chalkiness. The endosperm starch granules should be full and tightly arranged. The number of starch grain cavities and the area should be smaller. These differences develop in the early stages of grouting and gradually increase.

High-amylose maize starch: Structure, properties, modifications and industrial applications

High-amylose maize refers to a special type of maize cultivar with a 50 %-90 % amylose content of the total starch. High-amylose maize starch (HAMS) is of interest because it possesses unique functionalities and provides many health benefits for humans. Therefore, many high-amylose maize varieties have been developed via mutation or transgenic breeding approaches. From the literature reviewed, the fine structure of HAMS is different from the waxy and normal corn starches, influencing its gelatinization, retrogradation, solubility, swelling power, freeze-thaw stability, transparency, pasting and rheological properties, and even in vitro digestion. HAMS has undergone physical, chemical, and enzymatical modifications to enhance its characteristics and thereby broaden its possible uses. HAMS has also been used for the benefit of increasing resistant starch levels in food products. This review summarizes the recent developments in our understanding of the extraction and chemical composition, structure, physicochemical properties, digestibility, modifications, and industrial applications of HAMS.

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.

Multi-scale structures and physicochemical properties of waxy starches from different botanical origins

The multi-scale structures and physicochemical relationships of three different types of waxy starches (maize, tapioca, and potato) were investigated. The maize and tapioca starches exhibited A-type crystalline polymorph compared to potato starch (B-type). The WMS showed higher amorphous content (5.56 %) than other waxy starches. The WTS exhibited a low tendency of retrogradation with its high f_a (DP 6-12) and low f_b3 (DP ≥ 37) proportion of chains. Double helix content of WPS was observed highest with a high pasting viscosity (952.3 BU). Low f_a (DP 6-12) and high f_b3 (DP ≥ 37) chain proportions of the WPS retrograded easily. The compactness of the semi-crystalline aggregation structure influenced the retrogradation properties of waxy starches with a positive correlation. Furthermore, the peak viscosity of pastes was correlated with the proportion of f_b3 (DP ≥ 37) chains, mass fractal dimension, and double helix content. The results provide guidance to design the application of waxy starches in the production of clean-labels.

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.

High-amylose starch: Structure, functionality and applications

Starch with a high amylose (AM) content (high AM starch, HAS) has attracted increasing research attention due to its industrial application potential, such as functional foods and biodegradable packaging. In the past two decades, HAS structure, functionality, and applications have been the research hotspots. However, a review that comprehensively summarizes these areas is lacking, making it difficult for interested readers to keep track of past and recent advances. In this review, we highlight studies that benefited from rapidly developing techniques, and systematically review the structure, functionality, and applications of HAS. We particularly emphasize the relationships between HAS molecular structure and physicochemical properties.

Combined effects of starch fine molecular structures and storage temperatures on long-term rice amylopectin retrogradation property

Though the retrogradation property as affected by starch fine molecular structures has been widely investigated, it remains largely unexplored how concurrent starch structures and storage conditions e.g. temperature tailor the starch retrogradation property. The amylopectin long-term retrogradation for 8 different rice starches with a broad range of amylose content was thus investigated under different storage temperatures. Results showed that gelatinized starch stored at -20 °C generally had a narrower melting temperature range from differential scanning calorimetry, while larger cells and thicker cell walls in the gel matrix than that stored at 4 °C. Different linear correlations were found between starch fine molecular structures and amylopectin retrogradation parameters when starch was stored under different temperatures. For example, the melting enthalpy of retrograded starch double helices was negatively correlated with the amount of amylose intermediate chains at 4 °C, while positively correlated with the relative length of amylopectin short chains at -20 °C. Under both temperatures, rice starch R250 had the highest retrogradation enthalpy. These results could help the rice industry improve both the nutritional and textural attributes of cooked rice by selecting starch with desirable molecular structures and optimizing the storage conditions for rice after cooking.

Relations between starch fine molecular structures with gelatinization property under different moisture content

Although gelatinization property has been intensively investigated with its relation to starch structures, how a combination of starch molecular structures and moisture content affect the gelatinization remains unclear. The gelatinization of six rice starches with a wide range of amylose content was investigated under different moisture content in this study. Results showed that starch gelatinization temperatures increased and biphasic endothermic peaks appeared over the decreased moisture content. For the first time, amylose content was shown to have a parabolic relationship with gelatinization temperatures. Distinct linear relations among starch fine molecular structures with gelatinization parameters were observed under different moisture contents, which suggested that amylose short chains were involved in the first endothermic peak, while interactions among amylose intermediate chains and relatively shorter amylopectin trans-lamellar chains dominantly contributed to the second endothermic peak when gelatinized under limited moisture content. These results help in better understanding of starch structure-gelatinization relation.

Heat-induced conversion of multiscale molecular structure of natural food nutrients: A review

Thermal process is the most important way of treating foods. Heat energy inputted into the natural food system induces the depolymerization of multi-scale structures of matrix, and causes the intramolecular and intermolecular interactions of different nutrients. It attacks and breaks the original polymeric molecule structures and the functional properties of macronutrients such as carbohydrates, proteins and lipids. Micronutrients such as vitamins and other novel functional ingredients are also thermally converted. The heat-induced conversions of nutrients are slightly or totally with discrepancy in simple-, simulated- and real-food systems, respectively. Thus, this review aims to extensively summarize the heat-induced structural characteristics, thermal conversion pathways and pyrolysis mechanism of nutrients both in simple and complex food matrices. The structural change of each nutrient and its thermal reaction kinetics depend on the molecule structure and polymeric characteristic of the unit substances in the system.

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.

Methods for characterizing the structure of starch in relation to its applications: a comprehensive review

Starch is a major part of the human diet and an important material for industrial utilization. The structure of starch granules is the subject of intensive research because it determines functionality, and hence suitability for specific applications. Starch granules are made up of a hierarchy of complex structural elements, from lamellae and amorphous regions to blocklets, growth rings and granules, which increase in scale from nanometers to microns. The complexity of these native structures changes with the processing of starch-rich ingredients into foods and other products. This review aims to provide a comprehensive review of analytical methods developed to characterize structure of starch granules, and their applications in analyzing the changes in starch structure as a result of processing, with particular consideration of the poorly understood short-range ordered structures in amorphous regions of granules.

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.

Starch biosynthesis in cereal endosperms: An updated review over the last decade

Starch is a vital energy source for living organisms and is a key raw material and additive in the food and non-food industries. Starch has received continuous attention in multiple research fields. The endosperm of cereals (e.g., rice, corn, wheat, and barley) is the most important site for the synthesis of storage starch. Around 2010, several excellent reviews summarized key progress in various fields of starch research, serving as important references for subsequent research. In the past 10 years, many achievements have been made in the study of starch synthesis and regulation in cereals. The present review provides an update on research progress in starch synthesis of cereal endosperms over the past decade, focusing on new enzymes and non-enzymatic proteins involved in starch synthesis, regulatory networks of starch synthesis, and the use of elite alleles of starch synthesis-related genes in cereal breeding programs. We also provide perspectives on future research directions that will further our understanding of cereal starch biosynthesis and regulation to support the rational design of ideal quality grain.

Application of first-order kinetics modeling to reveal the nature of starch digestion characteristics

Mathematical modeling of in vitro starch digestograms is essential to understand starch structure-digestibility relationships as it covers all detailed information of the starch digestograms with only a few kinetics-based parameters. However, many assumptions exist for these mathematical models, which are frequently overlooked by researchers and lead to inappropriate or even wrong interpretations of the fitted parameters. This review presents a critical evaluation of four mostly applied empirical first-order kinetics models including single first-order kinetics (SK), logarithm of slope (LOS) transformed kinetics, parallel first-order kinetics (PK) and the combination of parallel and sequential (CPS) kinetics models. For homogeneous food systems, the SK model is perfectly suitable, whereas the LOS, PK and CPS models were suitably developed for food systems containing multiple digestible fractions. For the digestion of starch containing multiple digestible fractions, the LOS model assumed a sequential digestion pattern, whereas the PK model assumed a parallel pattern. In the current review, there is also emphasis on the recently developed CPS model, which is able to differentiate the sequential and parallel digestion patterns for different starch digestible fractions existing in food systems. Understanding these assumptions enables a better selection of an appropriate mathematical model for improving the understanding of in vitro starch digestion characteristics. This review meets the growing interest of the food industry in terms of developing a new generation of foods with slower starch digestibility.

Chemical components and chain-length distributions affecting quinoa starch digestibility and gel viscoelasticity after germination treatment

A germination treatment was explored in this study as a green strategy to reduce the in vitro starch digestibility of cooked quinoa. The alterations of chemical compositions, starch chain-length distributions (CLDs) and rheological characteristics of quinoa flours after the germination treatment were characterized. Results showed that a significant alteration of amylose CLDs and the starch digestibility was observed for cooked quinoa flours after different germination times. By fitting starch digestograms to the logarithm of slop (LOS) plot and the combination of parallel and sequential kinetics model (CPS), two starch digestible fractions with distinct rate constants were identified. Pearson correlation analysis further found that the observed starch digestive characteristics could be largely explained by the alterations of amylose CLDs caused by the germination treatment. More specifically, the rapidly digestible starch fraction mainly consisted of amorphous amylopectin molecules and amylose intermolecular crystallites. On the other hand, the slowly digestible starch fraction was largely formed by intramolecular interactions among amylose short chains (degree of polymerization (DP) < 500). These results suggest that germination may be a promising way to develop cereal products with slower starch digestibility.

Identification of Structure-Controlling Rice Biosynthesis Enzymes

The main enzymes controlling the chain-length distributions (CLDs) of starches are starch synthases (SSs), starch branching enzymes (SBEs), and debranching enzymes (DBEs), which have various isoforms, denoted as SSI, SSII-1, etc. Different isozymes dominate the CLD in different ranges of degrees of polymerization (DPs). Models have been developed for the CLDs in terms of the activities of isoforms of these enzymes, in terms of two parameters: β_i, which is the ratio of the activity of SBE to that of SS in set i, and h_i, which is the relative activity of SS in that set. These provide good fits to data but without specifying which isozymes are in set i. Here, CLDs for amylopectin and amylose synthesis in rice endosperm are explored. Molecular weight distributions of the different chains formed in 87 rice varieties were obtained using size-exclusion chromatography following enzymatic debranching (converting a complex branched macromolecule to linear polymers), and fitted by the biosynthesis-based models. The mutants of each isoform among tested rice varieties were identified by amino-acid mutations in coding sequences based on the extraction and analysis of whole gene sequences. The significant differences between mutant groups of different isoforms indicate that SSI, SSII-3, SSIII-1, SSIII-2, and SBEI as well as GBSSI (an isozyme of granule-bound starch synthase) belong to the enzymes sets that control amylose biosynthesis. Further, GBSSI is in the enzyme sets that control amylopectin chains. This enables specification of all isozymes and the DP range, which they dominate, over the entire DP range. As the CLD controls many functional properties of rice, this can help breeders target and develop improved rice species.

Relations between rice starch fine molecular and lamellar/crystalline structures

Starch lamellar and crystalline structures are important controller of its physicochemical and digestion properties. Here, starch lamellar/crystalline structures of 16 different rice starches were investigated and correlated with their chain-length distributions (CLDs) and molecular size distributions. Results showed that the thickness of amorphous lamellae was mainly correlated with the amount of amylose short and medium chains. Thickness of both amorphous and crystalline lamellae was negatively correlated with the amount of amylopectin medium chains and relative length of amylopectin short chains. The degree of crystallinity was negatively correlated with the amount of amylose short and long chains. The lamellar ordering, fractal nature and thickness polydispersity were also related to the starch CLDs. Whereas, starch molecular size distributions were shown to be lack of correlations with the starch lamellar/crystalline structures. This study helps a better understanding of the molecular nature of starch semi-crystalline lamellae.

Effects of acid hydrolysis on the evolution of starch fine molecular structures and gelatinization properties

Effects of acid hydrolysis on amylose molecular structures and their relations to starch gelatinization properties were investigated. First-order kinetics models were applied to fit the evolution curve of starch chain-length and molecular size by acid hydrolysis treatment. Results showed that a single hydrolysis phase was involved in the degradation of waxy maize starch chains, while two distinct phases existed for the degradation of maize, high amylose maize and sago starch chains. The fast hydrolysis phase involved degradation of amylose chains with DP > ~300 and amylopectin long intra-cluster branches, while amylose chains with DP < ~300 was involved in the slow hydrolysis phase. Amylose molecules with DP ~ 300 were proposed to impact starch gelatinization properties by interaction with cut-off amylopectin double helices and formation of amylose crystallites/entanglements. This study could help food industry precisely control amylose molecular structures by acid hydrolysis treatment to develop starchy foods with desirable properties.