Physicochemical Studies on Resistant StarchIn VitroandIn Vivo

Resistant starch (RS), producedin vitroby hydrolysis of retrograded pea starch gels and amylose gels by porcine pancreaticalpha-amylase, was characterised by X-ray diffraction, size exclusion chromatography and methylation analysis. These techniques showed that RSin vitroconsisted of semi-crystalline, mostly linear material that was present in two main molecular size subfractions (DP_n>100 andDP_n20–30) with a third, minor subfraction (DP_n≤5). The extent of retrogradation of amylose was found to be of primary importance in determining the RS content of starch. Analysis ofin vivoRS, recovered during an ileostomy study, produced results that were similar to those obtained from RSin vitro. Anin vitromodel for the structure of resistant starch is proposed.     

Gluten free rice cookies with resistant starch ingredients from modified waxy rice starches: Nutritional aspects and textural characteristics

Experimental gluten-free (GF) rice cookies were formulated with 100% rice flour (CTR) or by substituting 50% of rice flour with native waxy rice starch (WRS) or with three different resistant starch (RS) ingredients obtained from debranched, annealed or acid and heat-moisture treated WRS (RS_a, RS_b and RS_c, respectively). Chemical composition, in vitro starch digestibility and physical and textural characteristics were carried out. Among cookies, RS_a-cookies had the highest total dietary fibre content, the lowest rapidly digestible starch and the highest RS contents. All the three RS preparations have proved effective in increasing the proportion that tested as RS with respect to native WRS. However, the estimated RS loss for each applied RS ingredients caused by the baking process followed the order of RS_a < RS_c < RS_b. Last, the lowest vitro glycaemic index value was measured for RS_a-cookies. Among cookies, differences in colour and hardness were reported. The partial replacement of commercial rice flour with RS_a could contribute to formulate GF cookies with higher dietary fibre content and likely slowly digestible starch properties more than equivalent amounts of RS_b and RS_c.     

Effects of Hydrothermal Processing of Buckwheat (Fagopyrum esculentumMoench) Groats on Starch Enzymatic AvailabilityIn VitroandIn Vivoin Rats

Content of total starch (TS), rapidly digested starch (RDS), slowly digested starch (SDS), resistant starch (RS) and retrograded starch (RS₃), apparent amylose and total amylose were studied in raw (uncooked) and in hydrothermally treated buckwheat groats. Hydrothermally treated buckwheat samples contained 4·0–4·3% of retrograded starch (dmb). This means that about 5·5% of the TS present in the samples appeared as RS₃. There was a good correlation between the retrograded starch by thein vitromethod and the undigested starchin vivoin rats (r=0·91,P<0·01). In untreated groats and in groats dry-heated to 110 °C there was significantly less RDS than in hydrothermally treated samples. Approximately one half of the raw groat starch was not digested within 120 minin vitro. Buckwheat groats prepared by using the traditional procedure of cooking before dehusking followed by warm-air drying, have less than 48% (dmb) of rapidly available starch, in comparison to white wheat bread, where the corresponding value is almost 59%. Buckwheat groats starch with a reduced rate of digestion could be a possible complement to or a substitute for common carbohydrate sources.     

Physico-chemical Characteristics as Indicators of Starch Availability from Milled Rice

The hypothesis was tested that certain physico-chemical characteristics might be used as indicators of total starch availability and rate of starch availability of milled rice. Milled unparboiled (uPB) and parboiled (PB) rice samples (n=93) were characterized using standardized methods of physical tests and chemical analyses and anin vitromethod was used for measuring the rate of starch digestion on a subsample of rice (n=26). The rice varieties were dominated by medium long, bold rice grain with high amylose rice and intermediate gelatinization temperature (GT), but a wide range in all characteristics was measured. Small amounts of resistant starch (RS) were measured in the cooked rice, indicating virtually complete starch availability. The RS of PB rice (0·4 g/100 g rice as eaten) was significantly (P<0·004) higher than the RS of uPB rice (0·1 g/100 g) however. The rate of starch digestion was significantly affected by both variety and parboiling. The starch digestion index (SDI) values of the PB samples (mean value 73·7) were significantly (P<0·001) lower than those of the uPB samples (mean value 79·0). The apparent amylose content (AC) was the strongest determinant for SDI in both uPB and PB rice. The widths and shapes of the raw grains and the elongation after cooking were correlated significantly with SDI values for the uPB rice, while the relatively mild parboiling procedure followed in this study eliminated this correlation. The minimum cooking times were correlated significantly with the SDI values in the uPB samples.     

Comparative Enzyme Kinetics of Two Allelic Forms of Barley (Hordeum vulgare L.) Beta -amylase

The barley (Hordeum vulgare L.) varieties, Franklin and Schooner, contain two different allelic forms of beta -amylase (EC 3.2.1.2) encoded on chromosome 4H by the Bmy 1-Sd1 and Bmy 1-Sd2L alleles, respectively. The corresponding enzymes, referred to as Sd1 and Sd2L, were purified from both mature barley grain and germinated barley (green malt), and their physical and kinetic properties studied. Approximately 4 kDa were cleaved from both Sd1 and Sd2Lbeta -amylases after germination. The K_mvalue for green malt beta -amylase was less than that of mature grain beta -amylase for both varieties when potato starch was used as a substrate, although V_maxwas similar. This indicated that proteolysis after germination increased the affinity of beta -amylase for potato starch. No significant kinetic differences were observed between beta -amylase from mature grain and green malt of the two barley varieties when amylose (degree of polymerisation 100 and 18) and maltopentaose were used as substrates. Kinetic differences were also observed between the two allelic forms of beta -amylase. Sd1 beta -amylase from green malt exhibited a lower K_mvalue for potato starch than Sd2L beta -amylase, demonstrating that at non-saturating starch concentrations Sd1 beta -amylase is better able to hydrolyse starch than Sd2L beta -amylase. As the degree of polymerisation of the substrates decreased from approximately 740 (potato starch) to 5 (maltopentaose), the K_mvalues for beta -amylase increased, whereas V_maxvalues decreased. Maltose, the hydrolytic product of beta -amylase, was found to be a weak competitive inhibitor of both Sd1 and Sd2L green malt beta -amylases with respect to potato starch and amylose. Taken together the kinetic observations for bet a-amylase suggest that the allelic differences and C-terminal proteolysis might be exploited to improve the efficiency of starch hydrolysis during the mashing stage of the brewing process.     

Physicochemical properties and amylopectin fine structures of A- and B-type granules of waxy and normal soft wheat starch

This work fractionated waxy and normal wheat starches into highly purified A- and B-type granule fractions, which were representative of native granule populations within parent native wheat starches, to accurately assess starch characteristics and properties of the two granule types. Wheat starch A- and B-type granules possessed different morphologies, granule specific surface area measurements, compositions, relative crystallinities, amylopectin branch chain distributions, and physical properties (swelling, gelatinization, and pasting behaviors). Within a genotype, total and apparent amylose contents were greater for A-type granules, while lipid-complexed amylose and phospholipid contents were greater for B-type granules. B-type (relative to A-type) granules within a given genotype possessed a greater abundance of short amylopectin branch chains (DP_n < 13) and a lesser proportion of intermediate (DP_n 13–33) and long (DP_n > 33) branch chains, contributing to their lower relative crystallinities. Variation in amylose and phospholipid characteristics appeared to account for observed differences in swelling, gelatinization, and pasting properties between waxy and normal wheat starch fractions of a common granule type. However, starch granule swelling and gelatinization property differences between A- and B-type granules within a given genotype were most consistently explained by their differential amylopectin chain-length distributions.     

Partial-degradation and heat-moisture dual modification on the enzymatic resistance and boiling-stable resistant starch content of corn starches

Normal corn, Hylon V and Hylon VII starches were partially degraded by acid-ethanol treatment and applied to heat-moisture treatment (HMT) for improving the enzymatic resistance of starch. The weight-average degree of polymerization (DP_w) of acid-ethanol-treated (AET) corn starches ranged from 6.75 × 10⁵ to 181, 4.48 × 10⁵ to 121, and 1.94 × 10⁵ to 111 anhydrous glucose units for normal corn, Hylon V and Hylon VII starches, respectively. Starch retained its granular structure after AET and HMT, recovery of starch granules after modifications were higher than 92%. Resistant starch (RS) content and boiling-stable RS content of corn starch increased after dual modification, and the increment increased with increasing duration of AET. The boiling-stable RS content of dual-modified starch increased from 1.5 to 9.2, 12.2 to 24.1, and 18.0 to 36.2% for normal corn, Hylon V and Hylon VII starches, respectively. Increments of RS content and boiling-stable RS content of dual-modified starches were significantly correlated (r² > 0.700) with DP_w of starch, revealing that the enzymatic resistance of dual-modified corn starch granules increased with decreasing molecular size of starch. Result also suggested that starch granules partially degraded with AET could improve the molecular mobility and ordering during the consequent HMT.     

The Role of Dextrins in the Stickiness of Bread Crumb made from Pre-Harvest Sprouted Wheat or Flour Containing ExogenousAlpha-Amylase

Dextrins were extracted in water from bread made from pre-harvest sprouted wheat or standard flour supplemented with exogenousalpha-amylases. The dextrins were separated by gel permeation chromatography and the dextrin content (% of crumb weight) determined for different degree of polymerisation (DP) size classes; DP 1–2, DP 3–10, DP 11–50, DP 51–200 and DP >200. There were significant correlations between the dextrin content in each size class and crumb stickiness (r=0·84–0·91, 22 df ). The most significant correlation (r=0·96) was between total dextrin content and crumb stickiness. Addition of dextrins of various DP ranges from various sources to standard flour produced bread with sticky crumb. Again, the degree of stickiness was generally related to the amount of total dextrin in the crumb and not to size distribution of dextrins. In this instance, extensive enzymic hydrolysis of starch was not necessary to produce sticky crumb; the dextrins caused crumb stickiness directly. Addition of dextrins to reconstituted gluten–starch flour produced bread with unexpectedly low dextrin levels and correspondingly low stickiness scores. It is concluded that, to produce sticky crumb, high levels of dextrin of any size are necessary in the crumb; a sticky mass is produced when dextrins dissolve in the excess «free» water that is normally «bound» to starch, gluten and other insoluble components of bread crumb.     

高直链淀粉小麦西农836淀粉理化性质及消化特性分析

淀粉是人体摄入碳水化合物的主要来源,经消化后以葡萄糖的形式被人体吸收,其消化特性与人体健康密切相关。为探究小麦品种西农836淀粉理化性质与消化特性的关系,以商品粉金沙河、香雪、金龙鱼作为对照,测定其与西农836中直链淀粉含量、淀粉粒度和结晶度、糊化特性以及体外消化率的差异,并在小鼠体内模拟消化。结果表明,与金龙鱼、金沙河、香雪相比,西农836淀粉中直链淀粉含量和B型淀粉粒含量最高,与前3者差异显著（P<0.05）;西农836淀粉的峰值温度最高,峰值黏度和最终黏度最低;淀粉体外消化试验结果显示,西农836的快消化淀粉（RDS）、总消化淀粉（RDS+SDS）含量最低,抗性淀粉（RS）含量最高。小鼠体内消化试验结果表明,与金沙河相比,灌食西农836淀粉的小鼠血糖峰值较低,说明高直链淀粉小麦西农836有利于延缓消化和控制血糖升高。相关性分析结果显示,直链淀粉含量与抗性淀粉含量呈显著正相关（P<0.05）。     

Ae显性突变体对玉米农艺性状及直链淀粉含量的影响分析

玉米直链淀粉是重要的食品和工业原料,高直链淀粉性状的产生受多种酶和基因-环境等因素的共同影响。玉米ae基因（amylose extender）突变导致子粒中直链淀粉含量增高、子粒表面皱缩、淀粉颗粒呈不规则形状、尺寸不均匀且表面基质蛋白增多,用于玉米育种后获得的品种直链淀粉含量升高,产量显著降低。通过将显性Ae突变体与16份优质玉米自交系杂交,对F₁代植株进行开花期、株型、产量性状调查,分析F₁代子粒总淀粉、直链淀粉的含量。结果表明,Ae突变体与不同的自交系杂交,F₁代直链淀粉含量及产量的变化存在明显差异,与基因型有密切关系,以Ae突变体和W16F41、CA240为亲本杂交,可显著提高直链淀粉含量同时产量变化最小。根据F₁代表现筛选直链淀粉含量提高、产量变化较小的双亲配制杂交种,可加速高直链淀粉玉米新品种培育进程。     

Starch swelling power and amylose content of triticale and Triticum timopheevii germplasm

Triticale (× Triticosecale Whittmack) and Triticum timopheevii have undergone little selection relative to other grains for quality characters, including starch amylose content. Using starch swelling power (SSP) in water and spectrophotometric analysis of the iodine binding ratio, 247 lines of triticale and 20 lines of T. timopheevii were screened for amylose content. Following this, the expression of the starch-forming protein granule-bound starch synthase (GBSS) in triticale was investigated by SDS-PAGE in the eight highest and eight lowest SSP lines. A strong correlation (R² = 0.8174) was found between iodine binding and SSP. The SSP of T. timopheevii lines ranged from 13.7 to 16.7, indicating an approximate range of amylose content from 28.1 to 33.8%: a small range within typical results from commercial wheat cultivars. The SSP of triticale ranged from 12.5 to 23.6 suggesting amylose content ranged from 12.8 to 35.1%: a much wider range reflecting the contribution of both the wheat and rye genomes. It appeared that expression of GBSS-4A was down-regulated in low amylose lines. Therefore there is significant potential to select for amylose content in triticale to increase quality in both the animal and human feed markets.     

Starch digestibility and the estimated glycemic score of different types of rice differing in amylose contents

Three types of rice cultivars (indica, japonica and hybrid rice) with four levels of amylose were selected for assessing variability in starch digestibility. A vitro enzymatic starch digestion method was applied to estimate the glycemic index in vivo based on the kinetics of starch hydrolysis in vitro. The results indicated that significant differences in term of glycemic response were observed in three types of rice. Amylose content had an obviously impact on the estimated glycemic score (EGS) value and resistant starch (RS) content. The contents of RS were increased with the increasing amylose in the same type of rice. Japonica rice was significantly lower in RS content compared to indica rice and hybrid rice with similar amylose. The high amylose rice cultivar ZF201, which was characterized by low major RVA parameters, i.e. peak viscosity (PKV), hot paste viscosity (HPV) and cool paste viscosity (CPV), were obviously higher in RS content and lower in EGS. The retrogradation of cooked rice led to a reduction of HI and EGS of all varieties. Starch hydrolysis tends to be more quick and complete for the waxy and low amylose rice than for the intermediate and high amylose rice.     

Survey of amylose content in Secale cereale, triticum monococcum, T. turgidum and T. tauschii

A standard method for determining apparent amylose content was modified for use with samples of 2–3 cereal seeds. Starch was extracted by soaking the seeds overnight in dilute ammonia solution, grinding in NaCl solution in a microfuge tube with an appropriate pestle and decanting the starch slurry. The starch was then washed successively in acetic acid, ethanol and acetone. The amylose content was determined by dispersing 5·0 mg of the starch in ethanol, adding NaOH solution, heating until a clear gel was formed, diluting, neutralising with citric acid, staining with iodine and reading in a spectrophotometer at 620 nm. The method provided a very strong correlation with a standard method for much larger samples. The apparent amylose content was determined for 1083 accessions of Triticum monococcum (einkorn), T. turgidum (emmer), T. tauschii and Secale cereale (rye). The 10 extreme accessions of each species were re-analysed a further three times and the two most extreme individual lines were selected for genetic studies. Apparent amylose content of T. monococcum ranged from 15 to 28%; that of T. turgidum, 19–31%; T. tauschii, 21–34%; and rye 12–28%. These ranges are considered sufficiently broad to allow amylose content to be further diversified through breeding.     

Formulating low glycaemic index rice flour to be used as a functional ingredient

Amylose and resistant starch (RS) content in rice flour were manipulated. The experiment was conducted using a full factorial design. Rice flour with average amylose content of 20 and RS content of 0.5 g/100 g dry sample was fortified with pure amylose from potato and high RS modified starch to reach the final amylose content of 30, 40 and 50 and RS content of 2, 4 and 6 g/100 g dry sample. The fortified rice flours were examined for their gelatinisation properties, in-vitro enzymatic starch digestion and gel textural properties. It was found that amylose and RS significantly affect all the fortified rice flour properties (p < 0.05). High amylose and RS improved starch digestion properties, reducing the rate of starch digestion and lowering the glycaemic index (GI) values. Amylose had a more pronounced effect on the fortified rice starch properties than RS. In this study, the fortified rice flour which contained amylose and RS of approximately 74 and 9 g/100 g dry sample respectively was used to produce rice noodles. The noodles exhibited low GI values (GI < 55). However, amylose and RS affected the textures of rice noodles providing low tensile strength and break distance (extensibility).     

Effect of jet-cooked wheat gluten/lecithin blends on maize and rice starch retrogradation

Vital wheat gluten and lecithin (GL) (50:50, w/w) were dry blended in a coffee grinder and a 9.5% (w/v) aqueous slurry was jet-cooked (steam pressures of 65 psi/g inlet and 40 psi/g outlet) to disaggregate wheat gluten and facilitate better dispersion of the two components. The jet-cooked material was freeze-dried and stored at 0 °C for future use. The GL blend was added to pure food grade common maize and rice starch at concentrations of 0 (control), 6, 11, 16, and 21%. Starch gelatinization and retrogradation temperature transitions were determined using Differential Scanning Calorimetry (DSC). From the DSC profiles, the change in the ΔH value was used as an indication of starch retrogradation, where a higher ΔH value indicated higher retrogradation. The ΔH values of the blends at 4 °C had higher values than the −20 °C and the ambient (25 °C) storage temperatures. Overall, the 21% GL/starch blends reduced retrogradation by 50%. The lower amylose content of rice starch relative to maize starch was reflected in Rapid Visco Amylograph (RVA) measurements of peak viscosity, and similarly, Texture Analyzer (TA) measurements indicated that maize starch gel is firmer than rice starch gel. Retrogradation was also evaluated by observing G′, the shear storage modulus, as a function of time after running a standard pasting curve. Using this method, it appears that GL has a significant effect on maize starch retrogradation, since low concentrations (<0.4%, w/w) reduced G′ up to 40%. The opposite behavior was seen in rice starch, where G′ increased directly with added GL. It appears that the amylose level in the rice starch is too low to be affected by the GL, and the increase seen in G′ is most likely due to added solids.     

Effect of particle size on kinetics of starch digestion in milled barley and sorghum grains by porcine alpha-amylase

The influence of milled grain particle size on the kinetics of enzymatic starch digestion was examined. Two types of cereals (barley and sorghum) were ground, and the resulting grounds separated by size using sieving, with sizes ranging from 0.1 to 3 mm. In vitro enzymatic digestion was performed, using pancreatic alpha-amylase, amyloglucosidase and protease, to determine fractional-digestion rates over 24 h. The resulting glucose production rate data were well fitted by simple first-order kinetics. For each sieve screen size, the digestion rate of barley was always higher than that of sorghum. The rate coefficients for digestion showed a decrease with increasing size, and could be well fitted by an inverse square relationship. This is consistent with the supposition that starch digestion in these systems is controlled by diffusion of enzyme through the grain fragment. Apparent diffusion coefficients of alpha-amylase obtained by fitting the size dependence were 0.76 (sorghum) and 1.7 (barley) × 10⁻⁷ cm² s⁻¹, 9 (sorghum) and 4 (barley) times slower than predicted for a molecule of the size of alpha-amylase in water.     

Differences in conformational stability of barley alpha-amylase isozymes 1 and 2. Role of charged groups and isozyme 2 specific salt-bridges

Barley alpha-amylase isozymes 1 (AMY1) and 2 (AMY2) have 80% sequence identity but possess different physico-chemical properties. By incubation in the range 37–85 °C T₅₀ is 75.2 °C of AMY1 and 79.2 °C of AMY2. While AMY2 is also most stable in urea at pH 6.7, [urea]₅₀ being 8.2 M compared to 7.9 M for AMY1, AMY1 has highest stability in urea below pH 6 or in the presence of NaCl. Moreover AMY1 is most stable in guanidinium chloride. Charge screening thus destabilises AMY2 but stabilises AMY1. Isozyme sequence comparison suggests that AMY1 lacks four of the 20 salt-bridges identified in the crystal structure of AMY2. The four residues that differ comprise Lys67_AMY2 and Asp267_AMY2, forming salt-bridges on the surface of the catalytic (β/α)₈-barrel (domain A), and Glu96_AMY2 and His344_AMY2 that participate in charged networks between domain A and the small domain B and the C-terminal domain, respectively. Four corresponding AMY2 mimics A68K; D97E; Q269D; N346H were made in AMY1 by site-directed mutagenesis. While D97E and Q269D have slightly improved stability compared to AMY1 wild-type, N346H and, under certain conditions, A68K are destabilised. The four mutants show 22–176% activity (k_cat/K_m) toward 2-chloro-4-nitrophenol β- -maltoheptaoside and amylose DP17 and 43–117% activity for insoluble starch.     

Water mobility,rheological and textural properties of rice starch gel

Three rice starches from indica (TNuS19), japonica (TNu67) and waxy (TCW70) were used as samples to investigate the water mobility, viscoelasticity and textural properties of starch gels using pulsed nuclear magnetic resonance (PNMR), dynamic rheometer and texture analyzer. The spin–spin relaxation time (T₂), showed water mobility of starch gels was detected with starch concentrations 10–30%. Generally, the TNuS19 and TNu67 at ≥20% showed two components (T_2a and T_2b) in water mobility, where T_2a and T_2b related to solid-like and liquid-like water molecules in starch gels, respectively. However, the TCW70 over the concentrations examined had only T_2b component, higher than those of corresponding TNuS19 and TNu67. The storage (G′) and loss (G″) moduli of starch gels were in the order of TNuS19 > TNu67 > TCW70. Texture analyzer analysis indicated that TNuS19 had higher hardness, stickiness and adhesiveness than did the TNu67 and TCW70, and changed significantly with the starch concentration increase. The value of T_2b was highly correlated with physical properties of starch gels, especially with dynamic rheological parameters. It is suggested that amylose content may play a major role to influence the water mobility of starch gels which affects the specific viscoelasticity and textural properties of starch gels.     

Storage retrogradation behavior of sorghum, maize and rice starch pastes related to amylopectin fine structure

Storage retrogradation behavior and properties of sorghum, maize, and rice starches were compared to better understand the relationship of amylopectin fine structure to quality issues. Long-term changes in texture of starch gels were attributed to amylopectin retrogradation. In starch pastes aged 7 days at 4 °C, change in the storage modulus (ΔG^′) during heating (representing intermolecular associations) was highly and positively correlated (r = 0.93, p < 0.01) with the proportion of fraction I (FrI) long chains from debranched amylopectin. One sorghum cultivar, Mota Maradi, showed a dramatic increase in the storage modulus (G′) over the 7 day storage period that was related to its high proportion of FrI. Pastes/gels made from starches with normal (20–30%) amylose content and higher proportions of FrI long chains from debranched amylopectin tended to become firmer with more syneresis during extended storage. Both degree of polymerization measurements and previous models for amylopectin structure indicate that FrI represents long B chains of amylopectin. Cereal cultivars having amylopectin structures with lower proportion of long B chains were speculated to give improved quality products with lower rates of retrogradation and staling. This is particularly an issue in sorghum foods where products generally lack storage stability and tend to stale relatively quickly.     

Effects of Amylose/Amylopectin Ratio and Baking Conditions on Resistant Starch Formation and Glycaemic Indices

The possible improvement of the nutritional properties of starch in barley flour-based bread by using barley genotypes varying in amylose content (3–44%) was evaluated. Breads were made from 70% whole-meal barley flour and 30% white wheat flour. Test breads were baked from waxy barley (WB), ordinary barley (OB), ordinary Glacier barley (OGB) and high-amylose barley (HAB). Each bread was baked either at conventional baking conditions (45 min, 200 °C) or at pumpernickel conditions (20 h, 120 °C). A white wheat bread (WWB) was used as reference. The resistant starch (RS) content and rate of starch hydrolysis were measuredin vitro. The glycaemic index (GI) and the insulinaemic index (II) of the high-amylose breads were determined in healthy subjects. The amount of RS (total starch basis) varied from <1% (WB) to approximately 4% (HAB) in conventionally baked bread, and from about 2% to 10% in the corresponding long-time/low-temperature baked products. The long-time/low-temperature baked HAB displayed a significantly lower rate of starch hydrolysisin vitrocompared with WWB and reduced the incremental blood-glucose response in healthy subjects (GI=71). In contrast, the GI of the conventionally baked HAB was similar to that for WWB. It is concluded that a barley flour-based bread of low GI and high RS content can be obtained by choosing high-amylose barley and appropriate baking conditions.