Effect of wheat bran dietary fiber on structural properties of wheat starch after synergistic fermentation of Lactobacillus plantarum and Saccharomyces cerevisiae

This study investigated the changes in the structure of wheat starch after synergistic fermentation of Lactobacillus plantarum and Saccharomyces cerevisiae at different wheat bran dietary fiber (WBDF) levels. The results showed that WBDF was slightly resistant to the decrease in acidity within the fermentation system. The amylose content decreased from 32.12% to 19.92% (P < 0.05), amylose/amylopectin ratio decreased from 0.47 to 0.25 (P < 0.05), and relative crystallinity decreased from 12.17% to 9.40% (P < 0.05) in the samples containing WBDF compared with the control. Scanning electron microscopy showed more eroded starch as the WBDF level increased. Fourier-transform infrared spectroscopy revealed a decrease in the starch-hydrogen binding absorbance in the 3600-3000 cm^-1 wavemumber; and the 1047/1022 and 995/1022 cm^-1 data indicated an increase in the degree of order and degree of double helix of the samples containing WBDF. The results of the study might help understand the interaction between dietary fibers and starch during fermentation and guide the production of fermented high-fiber flour products.

Natural Polymorphisms in Arabidopsis Result in Wide Variation or Loss of the Amylose Component of Starch

Starch granules contain two Glc polymers, amylopectin and amylose. Amylose makes up approximately 10% to 30% (w/w) of all natural starches thus far examined, but mutants of crop and model plants that produce amylose-free starch are generally indistinguishable from their wild-type counterparts with respect to growth, starch content, and granule morphology. Since the function and adaptive significance of amylose are unknown, we asked whether there is natural genetic variation in amylose synthesis within a wild, uncultivated species. We examined polymorphisms among the 1,135 sequenced accessions of Arabidopsis (Arabidopsis thaliana) in GRANULE-BOUND STARCH SYNTHASE (GBSS), encoding the enzyme responsible for amylose synthesis. We identified 18 accessions that are predicted to have polymorphisms in GBSS that affect protein function, and five of these accessions produced starch with no or extremely low amylose (< 0.5% [w/w]). Eight further accessions had amylose contents that were significantly lower or higher than that of Col-0 (9% [w/w]), ranging from 5% to 12% (w/w). We examined the effect of the polymorphisms on GBSS function and uncovered three mechanisms by which GBSS sequence variation led to different amylose contents: (1) altered GBSS abundance, (2) altered GBSS activity, and (3) altered affinity of GBSS for binding PROTEIN TARGETING TO STARCH1-a protein that targets GBSS to starch granules. These findings demonstrate that amylose in leaves is not essential for the viability of some naturally occurring Arabidopsis genotypes, at least over short timescales and under some environmental conditions and open an opportunity to explore the adaptive significance of amylose.

Flour functional properties of purple maize (Zea mays L.) from Argentina. Influence of environmental growing conditions

The objective was to characterize thermal and viscosity properties of flour of purple maize from Argentina, and to evaluate the environmental effects on composition and flour properties. Half-sib families were selected from original germplasm and reproduced during 2014 and 2015. Chemical composition, thermal and pasting properties of whole grain flour were determined. Non-purple genotypes were used as controls. Composition of purple maize did not show significant differences with controls, but amylose content was significantly lower. High variability in pasting and thermal properties of flour was observed between genotypes. Anthocyanin content positively correlated with breakdown (r = 0.37, P < 0.05), indicating that anthocyanins increased starch granules fragility during cooking. The higher gelatinization enthalpy of purple genotypes was coincident with the lower amylose content in relation to non-purple. The amylopectin retrogradation enthalpy negatively correlated with polyphenols (r = -0.35, P < 0.05) and anthocyanins (r = -0.40, P < 0.05), probably due to interactions formed after starch gelatinization. Flour functionality parameters showed higher effect of genotype and lower effects of environment and genotype × environment interaction. The variability found among genotypes indicates different flour behavior that would facilitate the identification of progenies with particular properties for production of functional maize based-foods.

Characteristics of pea, lentil and faba bean starches isolated from air-classified flours in comparison with commercial starches

This study aimed to isolate starches of a high purity from starch-rich pea, lentil and faba bean flours and to characterize and compare the isolated starches with important commercial starches. Isolated pulse starches had a purity of 94.8-97.9% and contained only 0.9-1.1% damaged starch. The isolated pulse starches showed amylose contents and amylopectin branch-chain-length distributions similar to those of commercial pea starch. Therefore, the granular morphologies, crystalline structure, thermal properties, pasting properties, gelling ability and in vitro digestibility of the isolated pulse starches were comparable to those of commercial pea starch but different from those of commercial maize and tapioca starches. The desirable functionality of the pulse starches (e.g., strong gelling ability) renders them suitable for some specific industrial applications, and further modifications can be utilized to enhance their functionality for broader use. This research provided the fundamental knowledge required for future efforts to promote value-added utilization of pulse starches.

Unambiguous Ex Situ and in Cell 2D 13C Solid-State NMR Characterization of Starch and Its Constituents

Starch is the most abundant energy storage molecule in plants and is an essential part of the human diet. This glucose polymer is composed of amorphous and crystalline domains in different forms (A and B types) with specific physicochemical properties that determine its bioavailability for an organism, as well as its value in the food industry. Using two-dimensional (2D) high resolution solid-state nuclear magnetic resonance (SS-NMR) on 13C-labelled starches that were obtained from Chlamydomonas reinhardtii microalgae, we established a complete and unambiguous assignment for starch and its constituents (amylopectin and amylose) in the two crystalline forms and in the amorphous state. We also assigned so far unreported non-reducing end groups and assessed starch chain length, crystallinity and amylose content. Starch was then characterized in situ, i.e., by 13C solid-state NMR of intact microalgal cells. Our in-cell methodology also enabled the identification of the effect of nitrogen starvation on starch metabolism. This work shows how solid-state NMR can enable the identification of starch structure, chemical modifications and biosynthesis in situ in intact microorganisms, eliminating time consuming and potentially altering purification steps.

WB1, a Regulator of Endosperm Development in Rice, Is Identified by a Modified MutMap Method

Abnormally developed endosperm strongly affects rice (Oryza sativa) appearance quality and grain weight. Endosperm formation is a complex process, and although many enzymes and related regulators have been identified, many other related factors remain largely unknown. Here, we report the isolation and characterization of a recessive mutation of White Belly 1 (WB1), which regulates rice endosperm development, using a modified MutMap method in the rice mutant wb1. The wb1 mutant develops a white-belly endosperm and abnormal starch granules in the inner portion of white grains. Representative of the white-belly phenotype, grains of wb1 showed a higher grain chalkiness rate and degree and a lower 1000-grain weight (decreased by ~34%), in comparison with that of Wild Type (WT). The contents of amylose and amylopectin in wb1 significantly decreased, and its physical properties were also altered. We adopted the modified MutMap method to identify 2.52 Mb candidate regions with a high specificity, where we detected 275 SNPs in chromosome 4. Finally, we identified 19 SNPs at 12 candidate genes. Transcript levels analysis of all candidate genes showed that WB1 (Os04t0413500), encoding a cell-wall invertase, was the most probable cause of white-belly endosperm phenotype. Switching off WB1 with the CRISPR/cas9 system in Japonica cv. Nipponbare demonstrates that WB1 regulates endosperm development and that different mutations of WB1 disrupt its biological function. All of these results taken together suggest that the wb1 mutant is controlled by the mutation of WB1, and that the modified MutMap method is feasible to identify mutant genes, and could promote genetic improvement in rice.

The impact of extrusion on the nutritional composition, dietary fiber and in vitro digestibility of gluten-free snacks based on rice, pea and carob flour blends

Consumers and the food industry are demanding healthier products. Expanded snacks with a high nutritional value were developed from different rice, pea and carob flour blends. The proximate composition, starch (total and resistant), amylose and amylopectin, dietary fiber (soluble and insoluble) contents, and the in vitro protein digestibility of different rice-legume formulations, were evaluated before and after the extrusion process. Compared with the corresponding non-extruded blends (control), the extrusion treatment did not change the total protein content, however, it reduced the soluble protein (61-86%), the fat (69-92%) and the resistant starch contents (100%). The total starch content of all studied blends increased (2-19%) after extrusion. The processing increased the in vitro protein digestibility, reaching values around 88-95% after extrusion. Total dietary fiber was reduced around 30%, and the insoluble fraction was affected to a larger extent than the soluble fraction by the extrusion process. Because of its balanced nutritional composition, high dietary fiber content, as well as low energy density, these novel gluten-free snack-like foods could be considered as functional foods and a healthier alternative to commercially available gluten-containing or gluten-free and low nutritional value snacks.

Dietary starch types affect liver nutrient metabolism of finishing pigs

This study aimed to evaluate the effect of different starch types on liver nutrient metabolism of finishing pigs. In all ninety barrows were randomly allocated to three diets with five replicates of six pigs, containing purified waxy maize starch (WMS), non-waxy maize starch (NMS) and pea starch (PS) (the amylose to amylopectin ratios were 0·07, 0·19 and 0·28, respectively). After 28 d of treatments, two per pen (close to the average body weight of the pen) were weighed individually, slaughtered and liver samples were collected. Compared with the WMS diet, the PS diet decreased the activities of glycogen phosphorylase, phosphoenolpyruvate carboxykinase and the expression of phosphoenolpyruvate carboxykinase 1 in liver (P0·05). Compared with the WMS diet, the PS diet reduced the expressions of glutamate dehydrogenase and carbamoyl phosphate synthetase 1 in liver (P<0·05). PS diet decreased the expression of the insulin receptor, and increased the expressions of mammalian target of rapamycin complex 1 and ribosomal protein S6 kinase β-1 in liver compared with the WMS diet (P<0·05). These findings indicated that the diet with higher amylose content could down-regulate gluconeogenesis, and cause less fat deposition and more protein deposition by affecting the insulin/PI3K/protein kinase B signalling pathway in liver of finishing pigs.

Characterization of the endosperm starch and the pleiotropic effects of biosynthetic enzymes on their properties in novel mutant rice lines with high resistant starch and amylose content

Resistant starch (RS) is beneficial to human health. In order to reduce the current prevalence of diabetes and obesity, several transgenic and mutant crops containing high RS content are being developed. RS content of steamed rice with starch-branching enzyme (BE)IIb-deficient mutant endosperms is considerably high. To understand the mechanisms of RS synthesis and to increase RS content, we developed novel mutant rice lines by introducing the gene encoding starch synthase (SS)IIa and/or granule-bound starch synthase (GBSS)I from an indica rice cultivar into a japonica rice-based BEIIb-deficient mutant line, be2b. Introduction of SSIIa from an indica rice cultivar produced higher levels of amylopectin chains with degree of polymerization (DP) 11-18 than those in be2b; the extent of the change was slight due to the shortage of donor chains for SSIIa (DP 6-12) owing to BEIIb deficiency. The introduction of GBSSI from an indica rice cultivar significantly increased amylose content (by approximately 10%) in the endosperm starch. RS content of the new mutant lines was the same as or slightly higher than that of the be2b parent line. The relationship linking starch structure, RS content, and starch biosynthetic enzymes in the new mutant lines has also been discussed.

Effect of starch type on the physico-chemical properties of edible films

Food preservation is mostly related to packaging in oil-based plastics, inducing environmental problems, but this drawback could be limited by using edible/biodegradable films and coatings. Physical and chemical properties were assessed and reflect the role of the starch type (wheat, corn or potato) and thus that of the amylose/amylopectin ratio, which influences thickness, colour, moisture, wettability, thermal, surface and mechanical properties. Higher amylose content in films induces higher moisture sensitivity, and thus affects the mechanical and barrier properties. Films made from potato starch constitute a greater barrier for oxygen and water vapour though they have weaker mechanical properties than wheat and corn starch films. Starch species with higher amylose content have lower wettability properties, and better mechanical resistance, which strongly depends on the water content due to the hydrophilic nature of starch films, so they could be used for products with higher water activity, such as cheese, fruits and vegetables. It especially concerns wheat starch systems, and the contact angle indicates less hydrophilic surfaces (above 90°) than those of corn and potato starch films (below 90°). The starch origin influences optical properties and thickness: with more amylose, films are opalescent and thicker; with less, they are transparent and thinner.

Amylose content decreases during tuber development in potato

BACKGROUND

Potato starch is composed primarily of amylopectin and amylose in an approximately 3:1 ratio. Amylose is considered to be nutritionally desirable in North American and European markets, so there is interest in finding strategies to increase the amylose content of potato starch. There is also interest in marketing 'baby' potatoes, which are harvested when they are physiologically immature. This study was carried out to determine weekly changes in amylose content in potato tubers of 11 North American cultivars during the growing season. The trial was repeated across 3 years.

RESULTS

We determined that amylose content is highest early and it decreases in a linear fashion as the growing season progresses. Mean amylose content across cultivars and years declined from 30.0% in late June to 26.8% in late August. The rate of decrease varied across years, with slopes of linear regression plots ranging from -0.17 in 2012 to -0.74 in 2011. Amylose content in tuber starch varied among cultivars, with the highest levels observed in Ranger Russet (30.7%) and White Pearl (31.6%); it was lowest in Kennebec (25.7%) and Langlade (25.6%).

CONCLUSIONS

This study adds to a growing body of literature on the nutritional value of immature potato tubers. In addition to having higher levels of some phytonutrients, as reported in other studies, immature tubers have a higher proportion of amylose in the starch. This is nutritionally desirable in affluent regions where high fiber content is more important than calories from carbohydrates. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

A systematic review of the influence of rice characteristics and processing methods on postprandial glycaemic and insulinaemic responses

Rice is an important staple food for more than half of the world's population. Especially in Asian countries, rice is a major contributor to dietary glycaemic load (GL). Sustained consumption of higher-GL diets has been implicated in the development of chronic diseases such as type 2 diabetes mellitus. Given that a reduction in postprandial glycaemic and insulinaemic responses is generally seen as a beneficial dietary change, it is useful to determine the variation in the range of postprandial glucose (PPG) and insulin (PPI) responses to rice and the primary intrinsic and processing factors known to affect such responses. Therefore, we identified relevant original research articles on glycaemic response to rice through a systematic search of the literature in Scopus, Medline and SciFinder databases up to July 2014. Based on a glucose reference value of 100, the observed glycaemic index values for rice varieties ranged from 48 to 93, while the insulinaemic index ranged from 39 to 95. There are three main factors that appear to explain most of the variation in glycaemic and insulinaemic responses to rice: (1) inherent starch characteristics (amylose:amylopectin ratio and rice cultivar); (2) post-harvest processing (particularly parboiling); (3) consumer processing (cooking, storage and reheating). The milling process shows a clear effect when compared at identical cooking times, with brown rice always producing a lower PPG and PPI response than white rice. However, at longer cooking times normally used for the preparation of brown rice, smaller and inconsistent differences are observed between brown and white rice.

Effect of multiple freezing/thawing cycles on the structural and functional properties of waxy rice starch

The structural and functional properties of non-gelatinized waxy rice starch were investigated after 1, 3, 7, and 10 freezing/thawing cycles. Freezing caused an increasing damaged starch from 1.36% in native waxy rice starch to 5.77% in 10 freezing/thawing-treated starch (FTS), as evidenced by the cracking surface on starch granules. More dry matter concentration was leached, which was characterized by high amylopectin concentration (4.34 mg/mL). The leaching was accompanied by a decrease in relative crystallinity from 35.19% in native starch to 31.34% in 10 FTS. Freezing treatment also led to significant deviations in the functional characteristics, for instance decreased gelatinization temperature range, enthalpy, and pasting viscosities. The resistant starch content of 10FTS significantly decreased from 58.9% to 19%, whereas the slowly digested starch content greatly increased from 23.8% in native starch to 50.3%. The increase in susceptibility to enzyme hydrolysis may be attributed to porous granular surface, amylopectin leaching, and the decrease in the relative crystallinity caused by freezing water.

Transcriptomic identification and expression of starch and sucrose metabolism genes in the seeds of Chinese chestnut (Castanea mollissima)

The Chinese chestnut (Castanea mollissima) seed provides a rich source of carbohydrates as food and feed. However, little is known about starch biosynthesis in the seeds. The objectives of this study were to determine seed composition profiles and identify genes involved in starch and sucrose metabolism. Metabolite analysis showed that starch was the major component and rapidly accumulated during seed endosperm development. Amylopectin was approximately 3-fold of amylose content in chestnut starch. Illumina platform-based transcriptome sequencing generated 56671 unigenes in two cDNA libraries from seed endosperms collected at 45 and 75 days after flowering (DAF). A total of 1537 unigenes showed expression differences ≥2-fold in the two stages of seeds including 570 up-regulated and 967 down-regulated unigenes. One hundred and fifty-two unigenes were identified as involved in starch and sucrose metabolism, including 1 for glycogenin glucosyltransferase, 4 for adenylate transporter (brittle1-type), 3 for ADP-glucose pyrophosphorylase (AGP, not brittle2- or shrunken2-type), 3 for starch synthase (SS), 2 for starch branching enzyme, 5 for starch debranching enzyme, 11 for sucrose synthase, and 3 for sucrose-phosphate synthase. Among them, 58 unigenes showed a ≥2-fold expression difference between the 45 and 75 DAF seeds including 11 up- and 47 down-regulated unigenes. The expression of 21 unigenes putatively coding for major enzymes in starch and sucrose metabolism was validated by qPCR using RNA from five seed stages. Expression profiles and correlation analysis indicated that the mRNA levels of AGP (large and small subunits), granule-bound SS2, and soluble SS1 and SS4 were well-correlated with starch accumulation in the seeds. This study suggests that the starch biosynthesis pathway in Chinese chestnut is similar to that of potato tuber/Arabidopsis leaf and differs from that of maize endosperm. The information provides valuable metabolite and genetic resources for future research in starch and sucrose metabolism in Chinese chestnut tree.

Differences of starch granule distribution in grains from different spikelet positions in winter wheat

Wheat starch development is a complex process and is markedly difference by changes in spikelet spatial position. The present study deals with endosperm starch granule distribution and spatial position during filling development. The study was conducted with pure starch isolated from wheat (Triticum aestivum L.), Jimai20 and Shannong1391, at 7-35 days after anthesis (DAA). The results showed that grain number, spikelet weight and grain weight per spikelet in different spatial position showed parabolic changes. Upper spikelets had highest starch and amylose content followed by basal spikelets, then middle spikelets. The paper also suggested the volume percents of B-type and A-type granule in grain of middle spikelets were remarkably higher and lower than those of basal and upper spikelets, respectively. However, no significant difference occurred in the number percents of the two type granule. The ratio of amylase to amylopectin was positively correlated with the volume proportion of 22.8-42.8 µm, but was negatively related to the volume proportion of <9.9 µm. The results indicated that the formation and distribution of starch granules were affected significantly by spikelet position, and grains at upper and basal spikelet had the potential of increasing grain weight through increasing the volume of B-type granules.

Increasing lysine content of waxy maize through introgression of opaque-2 and opaque-16 genes using molecular assisted and biochemical development

The low lysine content of waxy maize cannot meet the nutritional requirements of humans, livestock, or poultry. In the present study, the high-lysine genes o2 and o16 were backcrossed into wx lines using the maize high-lysine inbreds TAIXI19 (o2o2) and QCL3021 (o16o16) as donors and the waxy maize inbred line QCL5019 (wxwx) as a receptor. In the triple-cross F1, backcross, and inbred generations, the SSR markers phi027 and phi112 within the wx and o2 genes and the SSR marker umc1121 linked to the o16 gene were used for foreground selection. Background selection of the whole-genome SSR markers was performed for the selected individuals. The grain lysine content was determined using the dye-binding lysine method. The waxiness of the grain was determined with the I2-KI staining and dual-wavelength spectrophotometric analysis. The BC2F2 generation included 7 plants of genotype wxwxo2o2O16_, 19 plants of genotype wxwxo16o16O2_, and 3 plants of genotype wxwxo2o2o16o16. In these seeds, the average amylopectin content was 96.67%, 96.87%, and 96.62%, respectively, which is similar to that of QCL5019. The average lysine content was 0.555%, 0.380%, and 0.616%, respectively, representing increases of 75.1%, 19.9%, 94.3%, respectively, over QCL5019. The average genetic background recovery rate of the BC2F3 families was 95.3%, 94.3%, 94.2%, respectively. Among these 3 wxwxo2o2O16O16 families, 4 wxwxo2o2O16o16 families, and 3 wxwxo2o2o16o16 families, the longest imported parent donor fragment was 113.35 cM and the shortest fragment was 11.75 cM. No significant differences in lysine content were found between the BC2F4 seeds and the BC2F3 seeds in these 10 families. This allowed us to increase the lysine content of waxy corn and produce seeds with excellent nutritional characteristics suitable for human consumption, animal feed, and food processing. This may be of significance in the breeding of high-quality corn and in improvement of the nutrition of humans, livestock, and poultry.

Characterization of normal and waxy corn starch for bioethanol production

Objectives of this study were to compare ethanol production between normal and waxy corn using a cold fermentation process and to understand effects of starch structures and properties on ethanol production. Ethanol yields positively correlated (p < 0.01) with starch contents of kernels of the normal and waxy corn. The average starch-ethanol conversion efficiency of waxy corn (93.0%) was substantially greater than that of normal corn (88.2%). Waxy corn starch consisted of very little amylose and mostly amylopectin that had a shorter average branch chain length than normal corn amylopectin. Regression analyses showed that average amylopectin branch chain lengths and percentage of long branch chains (DP > 37) of waxy corn starch negatively correlated with the starch hydrolysis rate and the ethanol yield. These results indicated that starch structures and properties of the normal and waxy corn had significant effects on the ethanol yield using a cold fermentation process.

Structural changes of starch during baking and staling of rye bread

Rye sourdough breads go stale more slowly than wheat breads. To understand the peculiarities of bread staling, rye sourdough bread, wheat bread, and a number of starches were studied using wide-angle X-ray diffraction, nuclear magnetic resonance ((13)C CP MAS NMR, (1)H NMR, (31)P NMR), polarized light microscopy, rheological methods, microcalorimetry, and measurement of water activity. The degree of crystallinity of starch in breads decreased with hydration and baking to 3% and increased during 11 days of storage to 21% in rye sourdough bread and to 26% in wheat bread. (13)C NMR spectra show that the chemical structures of rye and wheat amylopectin and amylose contents are very similar; differences were found in the starch phospholipid fraction characterized by (31)P NMR. The (13)C CP MAS NMR spectra demonstrate that starch in rye sourdough breads crystallize in different forms than in wheat bread. It is proposed that different proportions of water incorporation into the crystalline structure of starch during staling and changes in starch fine structure cause the different rates of staling of rye and wheat bread.

The dent stage of maize kernels is the most conducive for fumonisin biosynthesis under field conditions

The fungal pathogen Fusarium verticillioides infects maize ears and produces fumonisins, known for their adverse effects on human and animal health. Basic questions remain unanswered regarding the kernel stage(s) associated with fumonisin biosynthesis and the kernel components involved in fumonisin regulation during F. verticillioides-maize interaction under field conditions. In this 2-year field study, the time course of F. verticillioides growth and fumonisin accumulation in developing maize kernels, along with the variations in kernel pH and amylopectin content, were monitored using relevant and accurate analytical tools. In all experiments, the most significant increase in fumonisin accumulation or in fumonisin productivity (i.e., fumonisin production per unit of fungus) was shown to occur within a very short period of time, between 22/32 and 42 days after inoculation and corresponding to the dent stage. This stage was also characterized by acidification in the kernel pH and a maximum level of amylopectin content. Our data clearly support published results based on in vitro experiments suggesting that the physiological stages of the maize kernel play a major role in regulating fumonisin production. Here we have validated this result for in planta and field conditions, and we demonstrate that under such conditions the dent stage is the most conducive for fumonisin accumulation.

Chemical profile, rumen degradation kinetics, and energy value of four hull-less barley cultivars: comparison of the zero-amylose waxy, waxy, high-amylose, and normal starch cultivars

The objective of this study was to compare three new Canadian hull-less barley cultivars with altered starch characteristics (zero-amylose waxy, CDC Fibar; waxy, CDC Rattan; and high-amylose, HB08302) with conventional normal starch hull-less barley (HB) cultivar (CDC McGwire) in terms of ruminant feed value. The study revealed that altered starch HB cultivars possessed several desirable feed characteristics, distinct from conventional normal starch HB, although they were similar in some respects: (1) basic chemical and carbohydrate subfraction profiles varied; (2) starch degradation kinetics showed altered starch HB containing higher soluble starch, rumen undegraded starch, lower degradable starch, and slower degradation rate; (3) all altered starch HB cultivars had similar soluble and degradable starch, different from that of conventional normal starch HB; (4) two waxy HB cultivars were lower, whereas the high-amylose cultivar was similar in effective degradability of the starch as compared to conventional normal starch HB; (5) zero-amylose waxy HB had the greater effective degradability of protein among HB cultivars; and (6) amylopectin in HB had a positive relationship with protein supply (increasing amylopectin was correlated with increased effective degradability of protein). Overall, these results demonstrate that the alteration of starch structure in granule affects not only starch fermentation and utilization but also protein value in hull-less barley. In summary, the HB cultivars with modified starch might be a better feed grain for ruminants than the normal starch HB.

A novel factor FLOURY ENDOSPERM2 is involved in regulation of rice grain size and starch quality

Rice (Oryza sativa) endosperm accumulates a massive amount of storage starch and storage proteins during seed development. However, little is known about the regulatory system involved in the production of storage substances. The rice flo2 mutation resulted in reduced grain size and starch quality. Map-based cloning identified FLOURY ENDOSPERM2 (FLO2), a member of a novel gene family conserved in plants, as the gene responsible for the rice flo2 mutation. FLO2 harbors a tetratricopeptide repeat motif, considered to mediate a protein-protein interactions. FLO2 was abundantly expressed in developing seeds coincident with production of storage starch and protein, as well as in leaves, while abundant expression of its homologs was observed only in leaves. The flo2 mutation decreased expression of genes involved in production of storage starch and storage proteins in the endosperm. Differences between cultivars in their responsiveness of FLO2 expression during high-temperature stress indicated that FLO2 may be involved in heat tolerance during seed development. Overexpression of FLO2 enlarged the size of grains significantly. These results suggest that FLO2 plays a pivotal regulatory role in rice grain size and starch quality by affecting storage substance accumulation in the endosperm.

Starch digestion mechanistic information from the time evolution of molecular size distributions

Size-exclusion chromatography [SEC, also termed gel permeation chromatography (GPC)] is used to measure the time evolution of the distributions of molecular size and of branch length as starch is subjected to in vitro digestion, including studying the development of enzyme-resistant starch. The method is applied to maize starches with varying amylose contents; the starches were extruded so as to provide an analogue for processed food. The initial rates of digestion of amylose and amylopectin components were found to be the same for high-amylose starches. A small starch species, not present in the original starting material, was formed during the digestion process; this new species has a slower digestion rate and is probably formed by retrogradation of longer branches of amylose and amylopectin as they are partially or wholly liberated from their parent starch molecule during the digestion process. The data suggest that the well-known connection between high amylose content and resistant starch arises from the greater number of longer branches, which can form the small retrograded species. The method is useful for the purpose of comparisons between different starches undergoing the process of digestion, by observing the changes in their molecular structures, as an adjunct to detailed studies of the enzyme-resistant fraction.

A rapid, direct observation method to isolate mutants with defects in starch grain morphology in rice

Starch forms transparent grains, referred to as starch grains (SGs), in amyloplasts. Despite the simple glucose polymer composition of starch, SGs exhibit different morphologies depending on plant species, especially in the endosperm of the Poaceae family. This study reports a novel method for preparing thin sections of endosperm without chemical fixation or resin embedding that allowed us to visualize subcellular SGs clearly. Using this method, we observed the SG morphologies of >5,000 mutagenized rice seeds and were able to isolate mutants in which SGs were morphologically altered. In five mutants, named ssg (substandard starch grain), increased numbers of small SGs (ssg1-ssg3), enlarged SGs (ssg4) and abnormal interior structures of SGs (ssg5) were observed. Amylopectin chain length distribution analysis and identification of the mutated gene suggested a possible allelic relationship between ssg1, ssg2, ssg3 and the previously isolated amylose-extender (ae) mutants, while ssg4 and ssg5 seemed to be novel mutants. Compared with conventional observation methods, the methods developed here are more effective for obtaining fine images of subcellular SGs and are suitable for the observation of a large number of samples.

Pressure-temperature phase diagrams of maize starches with different amylose contents

The amylose/amylopectin ratio in starch granules has a distinct impact on the physicochemical properties of starches. In this study the effects of high pressure and temperature combinations on the gelatinization of four maize starches with different amylose contents were investigated in an excess of water (90% w/w). Microscopy was used to determine the loss of birefringence in starch granules. Experiments were undertaken in the pressure range of 0.1-750 MPa and temperature range of 30-110 degrees C, holding the conditions constant for 5 min. Temperature and pressure stabilities of high amylose starches were found to be significantly higher than those of waxy and normal maize starch. Thermodynamic models are proposed to describe the loss in birefringence as a function of pressure and temperature. From the pressure-temperature phase diagrams constructed it was evident that maize starch gelatinization is not accelerated at pressures below 300-400 MPa. However, at higher pressures the threshold temperature to initiate starch granule hydration and gelatinization is significantly reduced for all starches investigated. This study extends the knowledge of the impact of high pressure on food components and will possibly make the technology more attractive to use as a substitute for or in combination with conventional food-processing methods.

Effect of fermentation with Rhizopus oligosporus on some physico-chemical properties of starch extracts from soybean flour

Studies were carried out on the changes that occurred on some selected physico-chemical properties of starch extracts from soybean flour when fermented with Rhizopus oligosporus. This was done in order to increase the utilization potentials of the flour. Starch extracts were obtained from flour obtained from fermented soybean using R. oligosporus with a fermentation period of between 0 and 72h. Some physico-chemical properties, as well as the amylose, amylopectin, and the pasting characteristics of the starch extracts were determined using standard methods. Increasing trends with increasing fermentation period were observed with respect to most of the physico-chemical characteristics investigated, except for the reconstitution index that showed decreasing trends. While the peak, breakdown and final viscosities also decreased, the swelling power and solubility slightly increased with increase in fermentation period. The proportion of amylopectin which was constantly high showed further slight increases with fermentation, apparently because of the decreasing proportion of amylose probably due to utilization by the mould R. oligosporus used for fermentation.