Formation of elongated starch granules in high-amylose maize

Heat-moisture treatment of freshly harvested high-amylose maize kernels improves its starch thermal stability and enzymatic resistance

The objective of this work was to study the effects of heat-moisture treatment (HMT) of freshly harvested mature high-amylose maize (HAM) kernels on its starch structure, properties, and digestibility. Freshly harvested HAM kernels were sealed in Pyrex glass bottles and treated at 80 °C, 100 °C, or 120 °C. HMT of HAM kernels had no impact on its starch X-ray diffraction pattern but increased the relative crystallinity. This result together with the increased starch gelatinization temperatures and enthalpy change indicated starch molecules reorganization forming long-chain double-helical crystalline structure during HMT of HAM kernels. The aggregation of starch granules were observed after HMT, indicating interaction of starch granules and other components. This interaction and the high-temperature crystalline structure led to reductions in the starch digestibility, swelling power, solubility, and pasting viscosity of the HAM flours. Some starch granules remained intact and showed strong birefringence after the HAM flours were precooked at 100 °C for 20 min and followed by enzymatic hydrolysis, and the amount of undigested starch granules increased with increasing HMT temperatures. This result further supported that HMT of HAM kernels with high moisture level could increase the starch thermal stability and enzymatic resistance.

Understanding resistant-starch formation during drying high-amylose maize kernels

Interests in using high-amylose maize (HAM) flour and starch for low glycemic index foods continue to grow. The objective of this work was to understand resistant-starch formation during drying the HAM kernels. Freshly harvested HAM kernels with 28.2 % initial moisture were subjected to sun drying (~30 °C) or hot-air drying at 50 °C, 70 °C, 90 °C, or 110 °C. The enzymatic digestibility of HAM flour decreased from 63.6 % to 41.1 % as the drying temperature increased from 30 °C to 110 °C. The swelling power, solubility, and overall viscosity of HAM flours milled from kernels dried at 110 °C decreased, whereas the peak and conclusion gelatinization temperatures, enthalpy change, and relative crystallinity increased compared to those of flours from kernels dried at 30 °C, 50 °C, 70 °C, and 90 °C. Light microscopic and scanning electron microscopic images showed that starch granule aggregation in HAM flour increased with increasing drying-temperatures. The aggregates remained after 16 h enzymatic hydrolysis of cooked HAM flours. These results suggested that the increase of enzymatic resistance of HAM flour resulted from the formation of high temperature-resistant ordered structures in starch granules and the starch aggregates less accessible to enzymatic hydrolysis.

Granular architecture of lotus seed starch and its impact on physicochemical properties

Lotus seed starch has high apparent amylose content (AAM). A representative definition of its granular architecture (e.g., lamellar structure) remained absent. This study defined the granular shape, crystalline and lamellar structures, and digestibility of twenty-two samples of lotus seed starch (LS) by comparing with those of potato and maize starches. LS granules had more elongated shape and longer repeat distance of lamellae than potato and maize starch granules. The enzymatic susceptibility of LS granules was more affected by AAM than granular architecture. Using these LSs as a model system, the relationships between lamellar structure of starch granules and properties of their gelatinized counterparts were investigated. In LSs, thinner amorphous lamella and thicker crystalline lamella were associated with higher swelling power and yield stress. The relationships were found to be connected via certain structural characteristics of amylopectin.

Exploring the functional attributes and in vitro starch and protein digestibility of pea flours having a wide range of amylose content

In this study, ten pea flours covering a broad range of amylose content (37.2-77.6 %, dsb) were characterized for functional and nutritional properties. As the amylose contents increased, the starch contents of the pea flours showed a downward trend (r = -0.990, p < 0.001 in Pearson correlation) but their protein and total dietary fiber contents exhibited an upward trend (r = 0.915, p < 0.001 and r = 0.885, p < 0.001, respectively). A greater amylose content tended to increase starch gelatinization temperatures of the pea flours, which thus required a higher cooking temperature for pasting viscosity development and subsequent gel formation. An increased amylose level reduced in vitro starch digestibility of the cooked pea flours (r = -0.944, p < 0.001) but did not influence in vitro protein digestibility. The insightful findings will be valuable for utilizing the diverse pea lines to create new flour, starch, and protein ingredients.

Unlocking the Potential of High-Amylose Starch for Gut Health: Not All Function the Same

High-amylose starch has unique functional properties and nutritional values in food applications. This type of starch is generally resistant to enzymatic digestion in the gastrointestinal tract, and contains an increased fraction of resistant starch (RS), which is a type of dietary fiber. The digestion and fermentation of high-amylose starch in the gut are of current research interest, as the processes are related to its nutritional functionality. This review summarizes recent in vitro and in vivo studies on the digestion and fermentation of high-amylose starches from different botanical sources and those that have been obtained by modifications. The RS content and fermentation properties are compared among high-amylose starches. This review aims to provide a current understanding of the relationship between high-amylose starch structures and fermentation-related nutritional properties. The results of these studies suggest that both modifications and food processing of high-amylose starch result in distinct fermentation products and nutritional properties. The review provides insight into the potential future applications of diverse high-amylose starches as bioactive compounds to modulate colonic fermentation.

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.

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 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.

Contributions of Dexter French (1918-1981) to cycloamylose/cyclodextrin and starch science

Professor Dexter French (1918-1981) was an American chemist and biochemist at Iowa State College (University in 1959). He devoted his career to advance knowledge of polysaccharides and oligosaccharides, in particular starch, cyclodextrins, and enzymes. Cyclodextrins are oligosaccharides obtained from starch and are typically cage molecules with a hydrophobic cavity that can encapsulate other compounds nowadays the basis for many industrial applications. Since the 1960s, he has been recognized as an outstanding authority in the field of starches and cyclodextrins and has inspired researchers in laboratories around the world. This review, on the fortieth anniversary of his death, commemorates his remarkable contribution to starch and cyclodextrin chemistry. Firstly, we give an overview of his personal life and career. Secondly, we highlight some of the results on starch and cyclodextrins from Professor French and his group. A third part discusses his impact on the modern chemistry of cyclodextrins and starch.

Morphology, structure, properties and applications of starch ghost: A review

Starch ghost, an insoluble structure of gelatinized starch, plays an important role in the applications of starch. In this review, we summarized the preparation, morphology, structure, properties and applications of starch ghost. The preparation steps of starch ghost include gelatinization, purification and preservation, and many factors influence the yield of starch ghost. The morphology and content of starch ghost can be influenced by many factors like starch resource and amylose content. Ghosts from non-waxy starches are composed of amylopectin with long branch-chains and amylose. These molecules cross-link to each other to reinforce the structure, and tend to form B-type double helix in ghosts from high-amylose starches. Some surface proteins that bind tightly to starch granules are also present in starch ghost. Protein and lipid are thought to have limited effects on the structural stability, but they make a big difference in the morphology of starch ghost. Starch ghost shows a different resistance to amylase among various starches, but it can be further digested under the high shear force. The mechanical, enzymatic hydrolysis and electrochemical properties of starch ghost make it widely used as emulsifier, stabilizer, thickener and starch-based films or gels in food and non-food processing industries.

Characterization of Starch in Cucurbita moschata Germplasms throughout Fruit Development

Pumpkins (Cucurbita moschata; Cucurbitaceae) are the rich source of nutrients and valued for their biologically active substances to be used for the treatment of several diseases. The contents, composition, and conformation of starch are the significant quality traits of C. moschata. Two germplasms were targeted for analysis regarding the taste difference. Results indicated that the total starch contents and amylose/amylopectin ratio were high in CMO-X as compared to CMO-E during each fruit development stage. Scanning electron microscopy and transmission electron microscopy observations revealed that smooth surface starch granules fused together to enhance the starch accumulation. For a comparison of fruit development in CMO-E and CMO-X, the putative pathway for starch metabolism was developed and homologs were identified for each key gene involved in the pathway. GBSS and SBE were correlated with the difference in the amylose/amylopectin ratio of CMO-E and CMO-X. Conclusively, the developmental regulation of genes associated with starch accumulation can be considered as an important factor for the determination of fruit quality.

Nanotechnology in agriculture: Current status, challenges and future opportunities

Nanotechnology has shown promising potential to promote sustainable agriculture. This article reviews the recent developments on applications of nanotechnology in agriculture including crop production and protection with emphasis on nanofertilizers, nanopesticides, nanobiosensors and nano-enabled remediation strategies for contaminated soils. Nanomaterials play an important role regarding the fate, mobility and toxicity of soil pollutants and are essential part of different biotic and abiotic remediation strategies. Efficiency and fate of nanomaterials is strongly dictated by their properties and interactions with soil constituents which is also critically discussed in this review. Investigations into the remediation applications and fate of nanoparticles in soil remain scarce and are mostly limited to laboratory studies. Once entered in the soil system, nanomaterials may affect the soil quality and plant growth which is discussed in context of their effects on nutrient release in target soils, soil biota, soil organic matter and plant morphological and physiological responses. The mechanisms involved in uptake and translocation of nanomaterials within plants and associated defense mechanisms have also been discussed. Future research directions have been identified to promote the research into sustainable development of nano-enabled agriculture.

The defective effect of starch branching enzyme IIb from weak to strong induces the formation of biphasic starch granules in amylose-extender maize endosperm

Biphasic starch granules in maize ae mutant underwent the weak to strong SBEIIb-defective effect during endosperm development, leading to no birefringence in their exterior due to extended long branch-chains of amylopectin. Biphasic starch granules are usually detected regionally in cereal endosperm lacking starch branching enzyme (SBE). However, their molecular structure, formation mechanism, and regional distribution are unclear. In this research, biphasic starch granules were observed in the inner region of crown endosperm of maize ae mutant, and had poorly oriented structure with comb-like profiles in their exterior. The inner endosperm (IE) rich in biphasic starch granules and outer endosperm (OE) without biphasic starch granules were investigated. The starch had lower amylose content and higher proportion of long branch-chains of amylopectin in IE than in OE, and the exterior of biphasic starch granules had less amylose and more long branch-chains of amylopectin than the interior. Compared with OE, the expression pattern of starch synthesis related enzymes changed significantly in IE. The granule-bound starch synthase I activity within biphasic starch granules decreased slightly. The IE experienced more severe hypoxic stress than OE, and the up-regulated anaerobic respiration pathway indicated an increase in carbon consumption. The starch in IE underwent the SBEIIb-defective effect from weak to strong due to the lack of sufficient carbon inflow, leading to the formation of biphasic starch granules and their regional distribution in endosperm. The results provided information for understanding the biphasic starch granules.

A rapid and universal method for isolating starch granules in plant tissues

Starch is the major form of carbohydrate storage in plants and exists as discrete starch granules (SGs). Isolation of high-quality SGs in different plant tissues is a prerequisite for studying the roles of SGs during plant growth, development, and responses to abiotic stress. However, it is difficult to isolate transitory SGs from leaves and storage SGs from pollen grains due to their small sizes and low quantities. Herein, we develop a novel method for isolating SGs by using the aqueous two-phase system (ATS) of ethanol/NaH₂ PO₄ . The ATS method efficiently separated SGs from contaminants based on their differences in density, solubility, and polarity. Using this method, we first isolated and purified three kinds of SGs from maize seeds, pollen, and leaves. The biochemical, microscopic, and proteomic analyses demonstrated the high purity of the isolated SGs. Proteomic analysis revealed distinct differences in SG-bound proteins between seed SGs and pollen SGs. As a simple, rapid, and low-cost method, the ATS-based method exhibits highly universal and reproducible results for starch-containing tissues in various plant species.

Morphological, molecular evolution an in vitro digestibility of filamentous granules of banana starch during fruit development

The development of starch granules of a banana cultivar (morado variety - Musa AAA subgroup Red dacca) from filamentous shape to semi-spherical and finally to oval shape, was studied. The purity of the extracted starch changed from 83.5% (6 weeks) to 95.4% (16 weeks). Impurities were ascribed to cellulosic and latex fractions responsible for the integrity of the pristine fruit. The amylose content was stabilized at about 29.6% after the 12th week. The thermal analysis showed that the gelatinization enthalpy increased from 5.0 to 11.2 J/g from the 6th to the 12th week, indicating an increased degree of internal molecular organization. The analysis of chain-length distribution and gel permeation chromatography, showing that the content of long chains (B1, B2, and B3+) increased with the development of the starch granule. Also, XRD analysis indicated that C- type X-ray diffraction pattern from early to later phases of development, although the relative crystallinity content increased from 19.3 to 23.5% after 16 weeks of development. FTIR revealed the formation of more ordered structures with the development time. In vitro digestion tests showed that the resistant starch fraction increased from 37.5% for week 6 to 55.5% for week 16.

Inhibition of starch branching enzymes in waxy rice increases the proportion of long branch-chains of amylopectin resulting in the comb-like profiles of starch granules

Starches with comb-like profiles have been detected in some cereal endosperms with inhibiting expression of starch branching enzyme (SBE). Although amylose is considered to be an important factor in the formation of the comb-like profile, the details remain unclear. In this study, a transgenic rice line (GLXN-SBEI/IIb^-) was derived from japonica waxy rice cultivar Guang-ling-xiang-nuo (GLXN) through antisense RNA inhibition of both SBEI and SBEIIb. The expression and activity of SBEI, SBEIIb and SBEIIa were declined. The GLXN-SBEI/IIb^- endosperm contained large and small starch granules, and these starch granules had the comb-like profiles. The comb-like profiles of starches were detected in GLXN-SBEI/IIb^- endosperm after 10 days after flowering with gradually increasing proportion of long branch-chains of amylopectin. The long branch-chains of amylopectin were responsible for forming the comb-like profiles at the outer region of starch granules. The gradually decreasing expression of SBEs influenced the synthesis of amylopectin during endosperm development, resulting in different structure between the inner and outer regions of starch granules from GLXN-SBEI/IIb^- endosperm. The above results indicated that the long branch-chains of amylopectin, not amylose, led to the formation of comb-like profiles of starch granules in cereal crops with inhibiting expression of SBEs.

A simple and rapid method for preparing the whole section of starchy seed to investigate the morphology and distribution of starch in different regions of seed

BACKGROUND

Storage starch in starchy seed influences the seed weight and texture, and determines its applications in food and nonfood industries. Starch granules from different plant sources have significantly different shapes and sizes, and even more the difference exists in the different regions of the same tissue. Therefore, it is very important to in situ investigate the morphology and distribution of starch in the whole seed. However, a simple and rapid method is deficient to prepare the whole section of starchy seed for investigating the morphology and distribution of starch in the whole seeds for a large number of samples.

RESULTS

A simple and rapid method was established to prepare the whole section of starchy seed, especially for floury seed, in this study. The whole seeds of translucent and chalky rice, vitreous and floury maize, and normal barley and wheat were sectioned successfully using the newly established method. The iodine-stained section clearly exhibited the shapes and size of starch granules in different regions of seed. The starch granules with different morphologies and iodine-staining colors existed regionally in the seeds of high-amylose rice and maize. The sections of lotus and kidney bean seeds also showed the feasibility of this method for starchy non-cereal seeds.

CONCLUSION

The simple and rapid method was proven effective for preparing the whole sections of starchy seeds. The whole section of seed could be used to investigate the morphology and distribution of starch granules in different regions of the whole seed. The method was especially suitable for large sample numbers to investigate the starch morphology in short time.

Progress in High-Amylose Cereal Crops through Inactivation of Starch Branching Enzymes

High-amylose cereal starches provide many health benefits for humans. The inhibition or mutation of starch branching enzyme (SBE) genes is an effective method to develop high-amylose cereal crops. This review summarizes the development of high-amylose cereal crops through the inactivation of one or more SBE isoforms or combination with other genes. This review also reveals the causes of increase in amylose content in high-amylose crops. A series of changes, including amylopectin structure, crystalline structure, thermal properties, and hydrolysis properties, occurs as amylose content increases. The different morphological starch granules nominated as heterogeneous starch granules or differently stained starch granules are detected in high-amylose cereal crops. Detailed studies on four heterogeneous starch granules in high-amylose rice, which is developed by antisense RNA inhibition of SBEI/IIb, indicate that granules with different morphologies possess various molecular structures and physicochemical and functional properties. This variation diversifies their applications in food and non-food industries. However, current knowledge regarding how these heterogeneous starch granules form and why they exhibit regional distribution in endosperm remain largely unknown.

Different structures of heterogeneous starch granules from high-amylose rice

High-amylose cereal starches usually have heterogeneous starch granules in morphological structure. In the present study, the polygonal, aggregate, elongated, and hollow starch granules were separated from different regions of the kernels of high-amylose rice, and their structures were investigated. The results showed that the polygonal starch granules had low amylose content and high short branch-chain and branching degree of amylopectin, and exhibited A-type crystallinity. The aggregate starch granules had high long branch-chain of amylopectin, relative crystallinity, and double helix content, and exhibited C-type crystallinity. The elongated starch granules had high amylose content and low branching degree of amylopectin and relative crystallinity, and exhibited C-type crystallinity. The hollow starch granules had very high amylose content, proportion of amorphous conformation, and amylose-lipid complex, and very low branch-chain of amylopectin, branching degree of amylopectin, and double helix content, and exhibited no crystallinity. The different structures of heterogeneous starch granules from high-amylose rice resulted in significantly different thermal properties.

Heterogeneous structure and spatial distribution in endosperm of high-amylose rice starch granules with different morphologies

Starch granules from high-amylose cereal mutants or transgenic lines usually have different morphologies. It is not clear whether the structure and spatial distribution of starch granules with different morphologies in endosperm is homogeneous or heterogeneous. In the present study, the structure and spatial distribution in endosperm of morphologically different starch granules from high-amylose transgenic rice line (TRS) were investigated. The TRS endosperm had individual, aggregate, elongated, and interior hollow starch granules. The individual and interior hollow granules had the lowest and the highest amylose content and gelatinization resistance, respectively, among the four types of granules. The individual granules were mainly distributed in the middle of the endosperm; the aggregate granules in the starchy endosperm cells between the subaleurone layer and the middle of the endosperm; the elongated granules in the peripheral starchy endosperm cells adjacent to the subaleurone layer; and the interior hollow granules in the subaleurone layer cells.

Effects of grain development on formation of resistant starch in rice

Three rice mutants with different contents of resistant starch (RS) were selected to investigate the effects of grain filling process on the formation of resistant starch. During grain development, the content of RS was increased with grain maturation and showed negative correlations with the grain weight and the starch molecular weight (Mn, Mw) and a positive correlation with the distribution of molecular mass (polydispersity, Pd). The morphologies of starch granules in high-RS rice were almost uniform in single starch granules and exhibited different proliferation modes from common rice. The lower activities of ADP-glucose pyrophosphorylase and starch branching enzyme and the higher activity of starch synthase and starch de-branching enzyme observed in high-RS rice might be responsible for the formation of small irregular starch granules with large spaces between them. In addition, the lower molecular weight and the broad distribution of molecular weights lead to differences in the physiochemical properties of starch.