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).     

Acetylation of intact white rice grains to alter the physicochemical properties

The effect of acetylation of milled rice grains of selected varieties (TDK 8, YRW 4, Reiziq, Amber 33, and SHZ 2) with varying apparent amylose contents (3.8–26.6%) on their physicochemical properties was investigated. Milled rice samples were treated with different acetic anhydride concentrations (0.004–0.04 g per 100 g of milled rice samples in 225 mL of water). Results showed that glutinous (TDK 8), very low amylose (YRW 4) and low amylose containing varieties (Reiziq) were prone to acetylation even with 0.004 g of acetic anhydride. X-ray diffraction patterns showed an increase in the crystallinity in acetylated samples and formation of V-type crystals, suggesting the possible interaction of acetic anhydride with starch. Acetylation of rice grains resulted in reduced peak and final viscosities and gel strength, particularly in glutinous (TDK 8) and very low amylose (YRW 4) rice. Differential calorimetric study showed that acetic anhydride treatment resulted in reduced thermal transition temperatures and enthalpy of all varieties. Although increase in the retrogradation thermal temperatures was observed, the enthalpy of retrogradation was reduced with increasing acetylation, suggesting that the extent of starch retrogradation was lower in all varieties with more prominent reduction in the glutinous type. Furthermore, the texture of cooked acetic anhydride treated rice grains was less hard and showed more adhesiveness. This study demonstrated that the acetylation of rice grains (instead of flour) was successfully achieved, showing the potential of applying acetylation to alter the textural, pasting, thermal and retrogradation properties of rice.     

Hydrothermal modification of wheat starch. Part 2. Thermal characteristics of pasting and rheological properties of pastes

Water suspensions of starch (with the concentration of 8 g/100 g) were prepared in a measuring vessel of a Brabender viscograph and heated to temperatures of 74, 76.5, 79, 81.5, 84, 86.5, 89, 91.5 or 94 °C under continuous stirring. The resultant solution was cooled and frozen, and then defrosted. Thermal characteristics of re-pasting, rheological properties of produced pastes, starch solubility in water and swelling power were determined.The heating and freezing of the wheat starch suspension induced changes in its properties, with tendency and extent of these changes depending on temperature of pre-heating. The thermal characteristics of the analyzed starches revealed three peaks that corresponded to transitions proceeding during solubilization of retrograded amylopectin and retrograded amylose and solubilization of amylose–lipid complexes. Retrogradation of amylose induced by starch pre-heating followed by its freezing affected also the consistency coefficient and yield stress of the pastes formed by the analyzed starches. Values of these rheological parameters were higher at higher temperatures of pre-heating, compared to the pastes prepared from native starch, and were changing accordingly to the determined second order polynomial function. Amylose retrogradation occurring during the production of starch preparations diminished their solubility in water and increased their swelling power compared to native starch.     

Effect of germination time and temperature on the functionality and protein solubility of sorghum flour

Sorghum was germinated for different time (12, 24, 36 and 48 h) at different temperatures (25, 30 and 35 °C) and the changes in their nutritional and functional properties of germinated sorghum flour were assessed and compared with native sorghum flour. Germination inversely affects the crude protein, fat, fibre and ash content. A decrease in water absorption and swelling power and increase in oil absorption capacity was observed due to enzymatic starch modification as the germination duration progressed. Germination of sorghum increased the gel consistency while paste clarity was decreased as compared to native flour. Proteins were modified by action of enzymes during higher germination time and temperature conditions, which results in significantly higher protein solubility of germinated sorghum flour, which also result in enhancing the foaming and emulsifying properties of the flour. Lowest % synersis value and least gelation concentrations were observed in native sorghum has, which increased during germination and were highest in sorghum germinated for 48 h at 35 °C. Germination in overall can be used as low cost natural bio-processing technique for the preparation of modified flour with enhanced function properties without chemical modification or genetic engineering.     

Particle size heterogeneity in milled barley and sorghum grains: Effects on physico-chemical properties and starch digestibility

The average particle size of ground grains is known to influence properties related to processing (e.g. water absorption and solubility) and nutritional value (e.g. starch digestion rate) of human foods and animal feeds. The purpose of this study was to identify the contributions made by individual size fractions of hammer-milled barley and sorghum grains to average bulk compositional, hydration, rheological, and enzyme susceptibility properties. Barley and sorghum grains were each hammer-milled through a 4 mm screen and subsequently fractionated on a set of eight sieves ranging from 0.125 mm to 2.8 mm. Individual fractions were characterised for (1) starch, aNDF, and water content, (2) water absorption index (WAI) and water solubility index (WSI), (3) viscosity profile during cooking and cooling in excess water, and (4) in vitro starch digestibility. Weighted average values based on fraction yields and property values for WAI, WSI, and starch digestibility were not significantly different from values obtained for non-fractionated ground grains of both barley and sorghum. Glucose yields from starch digestion varied about ten-fold between the smallest and largest particle fractions, and WAI and WSI had value ranges of 1.9–2.8 g/g (sorghum), 2.1–4.0 g/g (barley) and 1.3–4.5% (sorghum), 0.7–10.3% (barley), respectively. Viscosity profiles for milled sorghum grain fractions were dominated by starch swelling which became increasingly restricted as particle sizes increased. Viscosity profiles for milled barley grain fractions did not exhibit typical starch-based behaviour and were most likely dominated by soluble fibres. Taken together, the results show that there is considerable potential for designing combinations of hydration, rheological and digestibility properties of ground grains through informed selection of appropriate grains and particle size distributions.     

Changes in the properties of rice varieties with different amylose content on dry heat parboiling

Dry heat parboiling is a unique paddy processing technique that has been scarcely exploited. Dry heat parboiling at high temperature for short time and low temperature for long time on physical and physicochemical properties of three rice varieties differing in amylose content were studied. Hardness of the kernels increased from 66.4 N, 68.8 N and 59.8 N in raw samples to 89.1 N, 86.9 N and 59.8 N in parboiled high amylose, low amylose and waxy rice samples respectively. Rapid migration and evaporation of water from severely heated kernels caused cavity formation at the centre. Irreversible damage of amylopectin structures to leachable fractions caused continuous rise of the pasting curve. Crystallinity was thereby reduced. Parboiled high amylose samples gave X-ray diffraction patterns with peaks characteristic of A, B and V-type starch crystallinity. Crystalline starch-lipid complexes were observed in low amylose and waxy rices. The significant increase in the amount of rapidly digestible starch from 56.7%, 61.7% and 66.6% in raw samples to 92.1%, 90.8% and 94.8% respectively in severely processed rice samples and subsequent reduction in resistant starch from 24.5%, 21.2% and 18.4% to 0.4%, 1.9% and 0.1% indicated possibilities for targeted food use of the dry heat parboiled samples.     

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.     

In vitro starch digestibility and predicted glycaemic indexes of buckwheat,oat, quinoa,sorghum, teff and commercial gluten-free bread

The in vitro starch digestibility of five gluten-free breads (from buckwheat, oat, quinoa, sorghum or teff flour) was analysed using a multi-enzyme dialysis system. Hydrolysis indexes (HI) and predicted glycaemic indexes (pGI) were calculated from the area under the curve (AUC; g RSR/100g TAC*min) of reducing sugars released (RSR), and related to that of white wheat bread. Total available carbohydrates (TAC; mg/4 g bread “as eaten”) were highest in sorghum (1634 mg) and oat bread (1384 mg). The AUC was highest for quinoa (3260 g RSR), followed by buckwheat (2377 g RSR) and teff bread (2026 g RSR). Quinoa bread showed highest predicted GI (95). GIs of buckwheat (GI 80), teff (74), sorghum (72) and oat (71) breads were significantly lower. Significantly higher gelatinization temperatures in teff (71 °C) and sorghum flour (69 °C) as determined by differential scanning calorimetry (DSC) correlated with lower pGIs (74 and 72). Larger granule diameters in oat (3–10 μm) and sorghum (6–18 μm) in comparison to quinoa (1.3 μm) and buckwheat flour (3–7 μm) as assessed with scanning electron microscopy resulted in lower specific surface area of starch granules. The data is in agreement with predictions that smaller starch granules result in a higher GI.     

Compositional variation amongst sorghum hybrids: Effect of kafirin concentration on metabolizable energy

Kafirins are stored proteins that negatively affect the nutritional quality of sorghum grain. Kafirin concentration and other chemical characteristics were determined in 12 sorghum hybrids and varied significantly, from 58% (HB1) to 42% (HB12) as percent total protein. Kafirin concentration correlated negatively with crude protein (CP) (−0.49), with acid detergent fiber (−0.40), apparent metabolizable energy (−0.61), and true metabolizable energy corrected for N (−0.63). HB12 was the hybrid with the lowest content of kafirins, amylose and tannins, and the highest content of apparent metabolizable energy. No differences were observed in the concentration of starch, but differences were found in apparent metabolizable energy (3325–2944 kcal kg⁻¹) probably due to a greater availability of starch, related to differences in kafirin concentration.     

In vitro starch digestibility and predicted glycaemic indexes of buckwheat,oat, quinoa,sorghum, teff and commercial gluten-free bread

The in vitro starch digestibility of five gluten-free breads (from buckwheat, oat, quinoa, sorghum or teff flour) was analysed using a multi-enzyme dialysis system. Hydrolysis indexes (HI) and predicted glycaemic indexes (pGI) were calculated from the area under the curve (AUC; g RSR/100g TAC*min) of reducing sugars released (RSR), and related to that of white wheat bread. Total available carbohydrates (TAC; mg/4 g bread “as eaten”) were highest in sorghum (1634 mg) and oat bread (1384 mg). The AUC was highest for quinoa (3260 g RSR), followed by buckwheat (2377 g RSR) and teff bread (2026 g RSR). Quinoa bread showed highest predicted GI (95). GIs of buckwheat (GI 80), teff (74), sorghum (72) and oat (71) breads were significantly lower. Significantly higher gelatinization temperatures in teff (71 °C) and sorghum flour (69 °C) as determined by differential scanning calorimetry (DSC) correlated with lower pGIs (74 and 72). Larger granule diameters in oat (3–10 μm) and sorghum (6–18 μm) in comparison to quinoa (1.3 μm) and buckwheat flour (3–7 μm) as assessed with scanning electron microscopy resulted in lower specific surface area of starch granules. The data is in agreement with predictions that smaller starch granules result in a higher GI.     

Processing and evaluation of heat moisture treated (HMT) amaranth starch noodles; An inclusive comparison with corn starch noodles

AS, HMT-AS and CS starches were studied for amylose content, swelling power, water absorption capacity, color, particle size (PSA), pasting profile (RVA) and thermal (DSC) properties. Based on the laboratory scale experiments, noodles with good expansion, minimum cooking time and firm texture were prepared. Noodles were successfully prepared from AS, HMT-AS and CS starches. Noodles prepared from native amaranth starch (AS) and heat moisture treated (HMT) were tested for different functional properties and compared to cornstarch noodles. Standardized noodles were evaluated for cooking loss, texture profile (TPA), sensory and micro-structural analysis by SEM. HMT-AS noodles had experience less cooking loss of 20.15 g/100 g in comparison to AS noodles (22.20 g/100 g). The HMT-AS based starch noodles shown firmer texture, along with augmented taste and distinct flavor in comparison to AS and CS noodles.     

Small-scale mashing procedure for predicting ethanol yield of sorghum grain

A small-scale mashing (SSM) procedure requiring only 300 mg of samples was investigated as a possible method of predicting ethanol yield of sorghum grain. The initial SSM procedure, which was conducted similarly to the mashing step in a traditional fermentation test, hydrolyzed just 38.5–47.2% of total sorghum starch to glucose. The initial procedure was simplified to contain only one liquefaction step, which did not influence subsequent saccharification. Thereafter, parameters such as temperature, pH, enzyme dosage, and saccharification time were optimized. Results showed that 91.2–97.5% of the total starch in 18 sorghum hybrids had been hydrolyzed to glucose using the following conditions: liquefaction at 86 °C for 90 min, 20 μL of α-amylase per 30 g of sample; pH adjustment by adding 50 μL of 2 M acetate buffer at pH 4.2 to each microtube; saccharification at 68 °C for 90 min, 200 μL of amyloglucosidase per 30 g of sample. There were strong linear correlations between completely hydrolyzed starch (CHS) from SSM and ethanol yields from both traditional (R² = 0.86) and simultaneous saccharification and fermentation (SSF, R² = 0.93) procedures. CHS was a better indicator for predicting ethanol yield in fermentation than total starch.     

Compositional variation amongst sorghum hybrids: Effect of kafirin concentration on metabolizable energy

Kafirins are stored proteins that negatively affect the nutritional quality of sorghum grain. Kafirin concentration and other chemical characteristics were determined in 12 sorghum hybrids and varied significantly, from 58% (HB1) to 42% (HB12) as percent total protein. Kafirin concentration correlated negatively with crude protein (CP) (−0.49), with acid detergent fiber (−0.40), apparent metabolizable energy (−0.61), and true metabolizable energy corrected for N (−0.63). HB12 was the hybrid with the lowest content of kafirins, amylose and tannins, and the highest content of apparent metabolizable energy. No differences were observed in the concentration of starch, but differences were found in apparent metabolizable energy (3325–2944 kcal kg⁻¹) probably due to a greater availability of starch, related to differences in kafirin concentration.     

Genetic and Environmental Variation in Sorghum Starch Properties

Starch was isolated from eight local Zimbabwean landrace varieties, an improved cultivar (SV2) and a hybrid (DC-75) of sorghum grown in four environments. Amylose content, pasting (peak (PV), hot-paste (HPV), cool-paste (CPV) viscosity), textural and thermal (gelatinisation peak temperature (T_p) and gelatinisation energy (ΔH)) properties of the starches were determined. The F -tests from analyses of variance detected significant (p<0·001) differences among genotypes and growing environments for the starch properties measured. The results indicate that a range of genetic and environmental variability exists for these traits in sorghum genotypes although the latter could be greater than varietal effects. Hybrid DC-75 largely differed in starch amylose content, pasting PV, and gel hardness from the local landrace varieties. Environments used for local landrace varieties caused significant differences in starch properties, hence selection and monitoring of growing conditions is essential if a particular genotype is to maintain minimum variation in the desired pasting, textural or thermal properties. Genotype×environment interactions indicate that in breeding programmes, selection for starch properties at a single location would be misleading.     

The composition of floury and vitreous endosperm affects starch digestibility kinetics of the whole maize kernel

Maize grain starch is the major energy source in animal nutrition, and its high digestion and utilization largely depend on endosperm traits and the structure of the starch-lipoprotein matrix. The aim of this work was to determine floury and vitreous endosperm traits and its relation to starch digestibility rate. In total, kernels of 30 hybrids were manually dissected, and amylose, total zein and starch and non-starch lipids were determined in both vitreous and floury endosperm. Starch digestibility of the whole kernel was determined based on glucose released during a two-step in vitro pig model of enzymatic digestion, and starch digestibility rate was calculated according to the first-order kinetics. The vitreous endosperm of tested hybrids had higher contents of amylose (204.6 vs 190.4 g/kg), zein (63.2 vs 40.4 k/kg) and starch lipids (5.6 vs 4.9 g/kg), and lower content of non-starch lipids (7.3 vs 9.6 g/kg) than floury endosperm. Digestibility coefficients varied among hybrids, and starch digestibility rate varied from 0.73 to 1.63 1/h. Lipids in both vitreous and floury endosperm negatively correlated with the most of digestion coefficients, whereas zein correlated in vitreous and amylose in the floury endosperm (P < 0.05). Starch digestibility rate negatively correlated with all traits, except amylose content in vitreous endosperm. As a result, a linear regression model with four variables including contents of zein and starch lipids in vitreous and zein and amylose in floury endosperm can predict more than 65% variability of starch digestibility rate of tested hybrids.     

Effect of process conditions and amylose/amylopectin ratio on the pasting behavior of maize starch: A modeling approach

The effects of different process conditions on the pasting behavior of the 14%, w/w suspensions of high amylose, waxy and normal maize starches at mixing speeds of 50, 160 and 250 rpm with the heating rates of 2.5, 5 and 10 °C/min were investigated. In addition, the impact of the starch mixture with an amylose-amylopectin ratio of 0–70% at 160 rpm and a heating rate of 5 °C/min on the pasting parameters was studied. According to the results, when stirring speed decreased from 250 rpm to 50 rpm, the peak viscosity dramatically increased. Furthermore, both heating and stirring rates significantly affected the pasting properties (p < 0.05). The amylose content of maize starch had a negative correlation with peak viscosity, trough viscosity, breakdown viscosity, final viscosity, and setback viscosity. Besides, syneresis values decreased as amylose content decreased from 70% to 0%. According to the kinetic modelling of pasting curves, starch coefficients were found to be higher than 1 for all starches, indicating that the penetration of water into starch granules increased granule swelling rate. The findings of the present study confirmed that both process conditions and amylose/amylopectin ratio can be optimized without necessity of starch modification to obtain the products with the desired quality.     

Physicochemical characterization and in-vitro digestibility of extruded rice noodles with different amylose contents based on rheological approaches

The physicochemical properties and in-vitro digestibility of extruded rice noodles with different amylose contents were characterized from a rheological point of view. Thermo-mechanical measurements showed that the rice flour with higher amylose contents exhibited greater stability to dual-mixing and higher degrees of starch gelatinization and retrogradation. In addition, greater elastic properties were clearly observed in the high amylose rice samples. The use of high amylose rice flour produced noodles with a harder texture, consequently contributing to reduced cooking loss. Furthermore, the rheological changes of extruded rice noodles were monitored in real time during the in-vitro starch digestion. The rice noodle digesta with higher amylose contents exhibited greater viscosities throughout the simulated oral-gastric-intestinal digestion steps. The flow behaviors of the rice noodle digesta consisted of the Power-law region and infinite shear plateau that were satisfactorily characterized by the Sisko model (R² > 0.99).     

Effect of a gibberellin-biosynthesis inhibitor treatment on the physicochemical properties of sorghum starch

Inhibition of plant growth by Trinexapac-ethyl, TE, a gibberellin-biosynthesis inhibitor, can produce a shorter stemmed plant, requiring less nutrients and water to grow, while maintaining grain yield. Although TE and other plant growth regulators are commonly used in grain crops, their effects on starch biosynthesis in the grains have not been systematically examined. The changes in the structural and functional properties of starch in grains harvested from TE-treated sorghum (Sorghum bicolor (L.) Moench) were examined, and the results compared with those from the untreated controls. TE treatment had little or no effects on the molecular structures of starch, starch granule morphology, and starch and amylose contents, but increased the protein content of the grains significantly. Consistent with the lack of change in the molecular structure, there were no significant effects on the thermal properties of the starch. The pasting properties of TE-treated sorghum flours, however, showed lower peak viscosity, trough, and final viscosity, which were attributed to their higher protein contents. The TE treatment thus does not have an appreciable effect on the biosynthesis of starch during grain development in sorghum.     

藁城8901与豫麦50籽粒淀粉粒的粒度分布特征

为研究小麦籽粒发育过程中胚乳淀粉粒形成与粒度分布特征,以小麦品种藁城8901与豫麦50为材料,研究了籽粒胚乳淀粉粒形成、生长与分布特征。结果表明,花后4d,小麦胚乳出现不同范围大小的淀粉粒,最大粒径8μm。花后7d,籽粒中淀粉粒增多增大,最大粒径20μm左右。花后10~14d,淀粉粒体积继续增大,并产生了一个新的小淀粉粒群体。花后17d,淀粉粒以体积增大为主。花后21d,淀粉粒最大粒径较成熟期变化较小。花后24d,小于0.6μm的淀粉粒数目急剧增加,大于0.6μm的淀粉粒数目占比则明显减少,表明这一时期又产生了一个新淀粉粒群体(后期形成的B型淀粉粒)。花后24~28d,小于0.6μm的淀粉粒数目仍不断增加,而直径较大的淀粉粒数目增加减少,表明籽粒中新淀粉粒的产生仍在继续,但以小粒径淀粉粒为主。花后28d至成熟期,最小粒径淀粉粒进一步生长,其他淀粉粒粒径变化相对较小。