Modelling starch phase transitions and water uptake of rice kernels during cooking

To model the cooking processes of rice, starch gelatinization, the level of fusion of the amylose-lipid complex, and equilibrium water uptake have to be known for any given condition. Starch phase transitions were measured by DSC in two milled Korean round rice kernels whose water contents ranged from 0.18 to 4.7 g g⁻¹ db. Two to three partially overlapping transitions were assessed. Starch thermal transitions were modelled using a double step approach. First, a mechanistic double sigmoid model was fitted with DSC data for any water content value. Each parameter of the mechanistic model was then modelled with conservative empirical water content functions. In this way we obtained an explicit form of phase transition levels as a function of both temperature and water content. In parallel, the water uptake kinetics of rice kernels was determined in the temperature range of 50 °C–100 °C. Equilibrium water uptake was found to be linked to starch phase transitions and a model was built to calculate equilibrium water uptake as a function of modelled starch gelatinization and amylose-lipid complex fusion levels.     

Starch gelatinization distribution and peripheral cell disruption in cooking rice grains monitored by microscopy

Starch gelatinization kinetics governs rice cooking behaviour (cooking time and texture). Starch gelatinization however occurs unevenly in the cooking grain. The aim of this study was to investigate the dynamics of starch gelatinization topography in rice kernels cooked in excess water at two temperatures: 75 °C and 95 °C, for times ranging from 5 to 30 min. Gelatinization front position was assessed over time on 40 μm cross sections using four different tracking methods: directly or after iodine staining using a microscope or a stereomicroscope under normal or polarized light. The four methods gave similar results and the obtained kinetics can be used to model starch gelatinization during grain cooking.     

Impact of proteins on pasting and cooking properties of waxy and non-waxy rice

Changes of RVA viscosity and texture properties of waxy rice (n=9) and non-waxy rice (n=10) were analyzed through protein removal or disulfide bond disruption. Protease or DTT had similar effects on the pasting behavior of the waxy rice, but affected differently that of non-waxy rice. For all waxy rice flour treated with DTT or protease, the peak, breakdown and consistency viscosity values all significantly decreased, and the viscosity curves barely rose from the baseline. Pre-incubation of flours with a protease increased RVA pasting temperatures, decreased viscosities along all the points of the curves and the slopes of the linear parts of the curves for all non-waxy cultivars. DTT decreased RVA pasting temperatures and peak viscosities of all non-waxy flour, but increased breakdown viscosities in six non-waxy rice cultivars. With DTT-added cooking water, the hardness of cooked waxy and non-waxy rice, as determined by Instron, generally decreased. With DTT-added cooking water, the adhesiveness of all cooked waxy rice significantly decreased, while it increased significantly or remained the same in all cooked non-waxy rice. The above results indicated that the protein agent of a network linked by disulfide bonds increased the RVA gelatinized paste rigidity, the hardness and adhesiveness of cooked rice of all waxy cultivars, while in non-waxy cultivars, both the network and the increase of the gelatinized paste concentrations resulting from protein hydration contributed to the enhancements of the RVA paste rigidity and the cooked rice hardness.     

Modelling water uptake,growth and sucrose accumulation of sugarcane subjected to water stress

Water stress affects the rate of water uptake, biomass accumulation and structural growth of sugarcane differently and, consequently, alters the partitioning of assimilate to sucrose storage. The CANEGRO sugarcane model is unable to accurately simulate the subtle rate changes in the source and sink processes during the progression of water stress during dry spells, with subsequent poor prediction of sucrose yields. The aim of this study was to test eight different water balance models by comparing simulated and experimentally determined rates of water uptake (WU), carbon assimilation (CAR), plant extension (PER) and sucrose accumulation (SA).     

Changes in gelatinization and rheological characteristics of japonica rice starch induced by pressure/heat combinations

Rice starch suspensions of 10% dry matter (DM) were treated by heat (0.1 MPa at 20–85 °C) or pressure/heat combinations (100–600 MPa at 20, 40 and 50 °C) for 15 min to investigate their gelatinization and rheological characteristics. The maximum swelling index of about 12 g water per gram of DM was obtained by thermal treatment at 85 °C, meanwhile, that of 7.0 g was observed by 600-MPa pressurization at 50 °C. The higher temperatures or pressures resulted in the higher degrees of gelatinization. Furthermore, treatments of 0.1 MPa at 85 °C, 500 MPa at 50 °C and 600 MPa at various temperatures caused complete gelatinization of rice starch. The consistency index (K) and storage modulus (G′) dramatically increased from 70 °C or 400 MPa. The G′ values were higher in pressure-treated samples than those in thermal-treated samples. Therefore, an application of pressure/heat combinations as a processing method to improve the quality of rice starch products would be possible.     

Physical properties of cryomilled rice starch

Cryomilling of rice starch was evaluated as a non-chemical way to modify starch structure and properties. Cryomilling in a liquid nitrogen bath (63–77.2 K) was done to Quest (10.80% amylose) and Pelde (20.75% amylose) rice starch at five different time frames (0, 15, 30, 45, and 60 min). The viscosity of the cryomilled rice starch decreased significantly (p < 0.05) with increasing milling duration, including peak viscosity, hot-paste viscosity, cold-paste viscosity, breakdown, and consistency. Increasing milling time significantly increased (p < 0.05) water solubility index and water absorption index. Infra-red spectroscopy and X-ray diffraction crystallography both showed that the crystallinity of the cryomilled starch decreased with increasing milling time. Differential scanning calorimetry (DSC) analyses showed that after 60 min cryomilling there was partial loss of crystallinity (86% for Quest and 91% for Pelde) of both cryomilled starches. The cryomilling process modified the rice starch by causing a loss of crystallinity, that reduced its pasting temperature and increased water absorption, and by fragmentation of starch (probably the amylopectin fraction) that reduced the viscosity and increased solubility.     

Determination of thermal and retrogradation properties of rice starch using near-infrared spectroscopy

Starch is a major component of rice grain and thus plays an important role in grain quality. For breeding rice with improved quality, the thermal and retrogradation properties of starch may be routinely measured. Since direct measurement is time-consuming and expensive, rapid predictive methods based on near-infrared spectroscopy (NIRS) can be applied to measure these quality parameters. In this study, calibration models for measurement of thermal and retrogradation properties were built from the spectra of grain and flour samples. The results indicated that both grain and flour spectra could give similar accuracy (r²=∼0.78) in determining the peak temperature (T_p) and conclusion temperature (T_c) of gelatinization. However, flour spectra (r²=0.80) were superior to the grain spectra (r²=0.73) in measuring onset temperature (T_o). Furthermore, the thermal properties of width at half peak height (ΔT_1/2) and enthalpy of gelatinization (ΔH_g), and retrogradation properties of enthalpy of retrogradation (ΔH_r) and retrogradation percentage (R%) could only be successfully modeled with the flour spectra. The models reported in the present study are usable for routine screening of a large number of samples in early generation of selection in breeding programs. For accurate assay of the thermal and retrogradation properties, however, direct instrumental measurement should be employed in later generations.     

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.     

Effects of inhibition of starch branching enzymes on starch ordered structure and component accumulation in developing kernels of rice

Three rice varieties, Te-qing (TQ), Wu-xiang 9915 (WX) and Guang-ling-xiang-nuo (GLXN) with different amylose contents, and their derived lines with inhibition of starch branching enzyme I and IIb (SBEI/IIb) (GLXN-, WX- and TQ-SBEI/IIb^–) were used to investigate and compare the starch ordered structure and component accumulation in developing kernels. The starches in developing kernels of TQ, WX and GLXN all showed a typical A-type crystallinity and had similar short-range ordered structure, but their relative crystallinities gradually decreased in TQ and WX and had no significant change in GLXN with kernel development. For wild-type rices, starch components gradually increased in developing kernels. With inhibition of SBEI/IIb, the accumulation of amylose and amylopectin long branch-chains in kernels was slightly affected, but amylopectin short branch-chains seriously decreased, resulting in a significantly lower dry weight and starch content in kernel. The B-type crystallinity in developing starch gradually accumulated with kernel development of TQ-, Wx- and GLXN-SBEI/IIb^– lines. The inhibition of SBEI/IIb decreased the relative crystallinity but increased the short-range ordered structure of starches. The effects of inhibition of SBEI/IIb on starch ordered structure and component accumulation mainly appeared after 10 days after flowering, and were the most conspicuous for indica rice TQ. Though the inhibition of SBEI/IIb influenced the ordered structure and component accumulation of starch, the starch content and components in developing kernels all showed significantly positive correlations with kernel dry weight.     

Effect of high water temperature during vegetative growth on rice growth and yield under a cool climate

Global warming is likely to increase spring temperatures in regions with a cool climate. To examine the effects of this change on rice productivity, we exposed rice plants to a higher (by +2.7 to +2.8 °C) water temperature (T_w) during the vegetative growth period (for 35-50 days) under three levels of N fertilization. High T_w during vegetative growth made the heading stage occur 4-7 days earlier for all levels of N fertilization in both years. The crop growth rate during the treatment period was greatly enhanced by high T_w: by 51-82% in 2008 and by 49-62% in 2009. There was no T_w × N fertilizer interaction. This increased growth was associated with increased leaf expansion and increased canopy radiation capture rather than with increased radiation-use efficiency. However, the positive effect decreased during subsequent growth stages under all levels of N fertilization, leading to no significant differences in total biomass at maturity. High T_w during vegetative growth greatly reduced SPAD values during the grain-filling stage compared with SPAD values in the control T_w treatment, for all levels of N fertilization, and decreased leaf photosynthesis during the mid-grain filling stage. Grain yield was not significantly affected by high T_w at any N fertilizer level or in either year.     

Modeling of water and nitrogen balance in the ponded water of rice fields

A water and nitrogen balance model for the surface ponded water compartment of rice fields was developed. The model estimates the daily ponded water depth and the daily losses and the uses of NH₄–N and NO₃–N in their transformation processes. The model was applied with data obtained from two rice fields during 2005 at Thessaloniki plain in northern Greece. Significant amounts of applied irrigation water were lost with the surface runoff and deep percolation to groundwater. The gaseous losses of nitrogen (volatilization and denitrification) and nitrogen uptake by algae were the main processes of nitrogen reduction in the ponded water of rice fields. The study showed that the system of a rice field is a natural system where an important amount of influent nitrogen applied by irrigation water can be reduced. These processes decrease the possibilities of water resources contamination.     

Water uptake during cooking of dry beans (Phaseolus vulgaris L.)

Water uptake during cooking of ten dry bean (Phaseolus vulgaris L.) varieties was investigated. Water uptake during early stages of cooking was characteristic of the variety. Although the optimal cooking times varied widely (52–85 min), all the beans absorbed similar amounts of water when cooked for their optimal times. Cooking times were significantly correlated with W_{20 min} (r=–0.92) and hardness index (r=0.76) of beans. Most other physical characteristics excepting the surface area of beans were generally unrelated to theW _{20 min},W _opt, and cooking times. No significant correlation was observed between phytate content and cooking times of beans. On cooking for their respective optimal times, all varieties absorbed nearly 1.5 times their weight of water and attained a moisture content of about 65% (wet basis).     

Influence of environmental temperature during grain filling period on granule size distribution of rice starch and its relation to gelatinization properties

High temperature (HT) is the major environmental factor affecting grain starch properties of cooking rice cultivars. However, little information has been available on the effect of environmental temperature on the starch granule size distribution of rice grains. In this paper, five indica rice genotypes, including the wild type (9311) and its four mutants differing in amylose content (AC), were used to investigate the effect of environmental temperature on the starch granule size distribution, as well as its relation to AC and gelatinization properties of rice starch. Two temperature treatments (HT and NT) at filling stage were imposed to rice plants under the controlled temperature chambers. The result showed that HT increased the average diameter of starch granules and enhanced the proportion of large starch granules (LSG, D > 2.6 μm) by number, volume and surface area, respectively. However, influence of HT on GT and starch granule size distribution was relatively independent of their alteration in AC level for different rice genotypes. Therefore, HT-induced increase in the average diameter of starch granules and LSG percentage was strongly responsible for the higher starch gelatinization temperature and inferior cooked palatability of HT-ripening rice grains, which be not inherently associated with their varying AC level.     

Development of new markers to genotype the functional SNPs of SSIIa, a gene responsible for gelatinization temperature of rice starch

Gelatinization temperature (GT) is an important quality predictor that determines the cooking quality of rice. GT is genetically controlled by the starch synthase IIa (SSIIa) gene. Two functional single nucleotide polymorphisms (SNPs) inside the SSIIa have already been found to be responsible for the variation of GT. One of these, GC/TT SNP at 4329/4330 bp, could be genotyped by four primers in a single PCR ( Bao et al., 2006a), but another one, G/A SNP at 4198 bp, has not been detected by a PCR-based marker. Here, we developed cleaved amplified polymorphic sequence (CAPS) and derived cleaved amplified polymorphic sequence (dCAPS) markers to detect these SNPs. A dCAPS marker that the PCR products were cleaved by the BseR I restriction endonuclease was designed to detect GC/TT SNP. Both CAPS and dCAPS markers were designed to detect G/A SNP using the restriction endonuclease Nla III and Tsp45 I, respectively. All the markers developed were co-dominant. It was known that the A allele of G/A SNP was rare among rice germplasm, but it was still in use by rice breeders. 11 rice accessions including landrace and breeding lines with A allele of G/A SNP were detected. The F₂ individuals from two crosses were used to analyze the co-segregation between the SNP alleles and the GT. The segregation ratio of two SNPs did not conform to the expected Mendelian ratio of 1:2:1, but the SNPs were co-segregated with GT. The markers developed in the present study would be useful in molecular breeding for the improvement of the quality of rice grain.     

Effects of ultrasonic treatment on the cooking and fermentation properties of Shanlan rice

Shanlan rice is an endemic upland rice in Hainan province, China. In this study, we investigated the effects of ultrasonic treatment (UT) on the cooking and fermentation properties of Shanlan rice. These effects were evaluated by multiple physical and chemical indicators via scanning electron microscopy (SEM), low-field nuclear magnetic resonance (LF-NMR), and high-performance liquid chromatography (HPLC). According to the minimal cooking time and the content of total leached solids, the optimal ultrasonic power and time were determined to be 240 W and 30 min, respectively. The results indicated that the ultrasonic treatment broke the rice surface, loosened the inner structure of rice, and extended the relaxation time. These changes increased water absorption during the cooking process by 8.2% and promoted saccharification and alcohol production at the initial fermentation stage, with a 54.1% higher alcohol content on the first day. The rice wine brewed from the treated rice showed differences in the non-volatile acid contents; malic acid and tartaric acid contents increased, while the acetic acid content decreased significantly. Moreover, the red colour and brightness of the rice wine were significantly improved after the ultrasonic treatment, with a 16.6% increase in the rice wine yield.     

Analysis of quantitative trait loci for some starch properties of rice (Oryza sativa L.): thermal properties, gel texture and swelling volume

To understand the genetic basis of gelatinization temperature (GT), gel textural traits and flour swelling volume, quantitative trait loci (QTL) were mapped for these traits using a doubled haploid (DH) population derived from a cross between indica variety Zai-Ye-Qing 8 (ZYQ8) and japonica variety Jing-Xi 17 (JX17). The results indicated that the starch property parameters were continuously distributed among the DH lines, and some DH lines showed transgressive segregation for all the parameters. A total of 16 QTLs were identified for seven traits. A major QTL, the alk gene on chromosome 6 was significant for the three GT traits, onset temperature (T_o), peak temperature (T_p), and completion temperature (T_c). This locus could explain 49.4, 38.9, and 28.3% of the total variance, respectively, indicating that GT parameters were substantially controlled by the alk gene which has previously been identified for alkali spreading value (ASV). The additive effects of alk on T_o,T_p and T_c were from ZYQ8. Another two QTLs on chromosomes 1 and 7 were also identified for the three GT parameters, whose positive effects were contributed from JX17. Another QTL on chromosome 10 with the positive effects coming from ZYQ8 was significant only for T_c. However, the enthalpy (ΔH) of gelatinization was controlled by two minor QTLs on chromosomes 1 and 7. A major QTL, the Wx gene on chromosome 6 was identified for gel hardness and flour swelling volume which explained 58.8 and 36.6% of the total variances, respectively. Another two QTLs were also detected for flour swelling volume, one of which (qSV-7) could explain 21.4% of the total variance. However, gel cohesiveness was controlled by a major QTL located between alk and Wx on chromosome 6.     

Effect of irrigation method and N-fertilizer management on rice yield, water productivity and nutrient-use efficiencies in typical lowland rice conditions in China

Alternate wetting and drying irrigation (AWD) has been reported to save water compared with continuous flooding (CF) in rice cultivation. However, the reported effects on yield varied greatly and detailed agro-hydrological characterization is often lacking so that generalizations are difficult to make. Furthermore, it is not known how AWD modifies nutrient use efficiencies and if it requires different N-fertilizer management compared with CF. This study quantified the agro-hydrological conditions of the commonly practiced AWD and compared the impact of AWD and CF irrigations at different N-fertilizer management regimes on rice growth and yield, water productivity, and fertilizer-use efficiencies in five crop seasons in 1999 and 2000 at two typical lowland rice sites in China (Jinhua, Zheijang Province and Tuanlin, Hubei Province), with shallow groundwater tables.Grain yields varied from 3.2 to 4.5 t ha^–1 with 0 kg N ha^–1 to 5.3–8.9 t ha^–1 with farmers N-rates (150 kg N ha^–1 in Jinhua and 180 in Tuanlin). In both sites, no significant water by nitrogen interaction on grain yields, biomass, water productivity, nutrient uptakes and N-use efficiency were observed. Yield and biomass did not significantly differ (P >0.05) between AWD and CF and among N timings. The productivity of irrigation water in AWD was about 5–35% higher than in CF, but differences were significant (P <0.05) only when the rainfall was low and evaporation was high. Increasing the number of splits to 4–6 times increase the total N uptake, but not total P-uptake, and total K-uptake compared with farmers practices of two splits. Apparent Nitrogen recovery (ANR) increased as the number of splits increased, but there was no significant difference in ANR between AWD and CF. During the drying cycles of AWD irrigation, the perched water table depths seldom went deeper than – 20 cm and the soil in the root zone remained moist most of the time. The results suggest that in typical irrigated lowlands in China, AWD can reduce water input without affecting rice yields and does not require N-fertilizer management differently from continuous flooding. The results can be applied to many other irrigated lowland rice areas in Asia which have a shallow groundwater table.     

The large-effect drought-resistance QTL qtl12.1 increases water uptake in upland rice

Drought stress is the most important abiotic factor limiting upland rice yields. Identification of quantitative trait loci (QTL) conferring improved drought resistance may facilitate breeding progress. We previously mapped a QTL with a large effect on grain yield under severe drought stress (qtl12.1) in the Vandana/Way Rarem population. In the current paper, we present results from a series of experiments investigating the physiological mechanism(s) by which qtl12.1 affects grain yield under drought conditions. We performed detailed plant water status measurements on a subset of lines having similar crop growth duration but contrasting genotypes at qtl12.1 under field (24 genotypes) and greenhouse (14 genotypes) conditions. The Way Rarem-derived allele of qtl12.1 was confirmed to improve grain yield under drought mainly through a slight improvement (7%) in plant water uptake under water-limited conditions. Such an apparently small increase in water uptake associated with this allele could explain the large effect on yield observed under field conditions. Our results suggest that this improvement of plant water uptake is likely associated with improved root architecture.     

Effects of added water and retrogradation on starch digestibility of cooked rice flours with different amylose content

Flours derived from rice varieties with different amylose content possess distinct physicochemical and molecular properties. The aim of this study was to determine optimal processing conditions for preparing rice flour-based foods with reduced starch digestibility. To do so, we evaluated the in vitro starch digestibility of rice flours with five varieties. Reducing the amount of water (from 10-fold to 4-fold of rice flour) used for cooking rice flour lowered its starch digestibility, and the magnitude of the decrease was positively correlated with amylose content. When retrogradation of cooked rice flour proceeded for 7 days, the digestibility of high-amylose rice flours declined rapidly in the first 3 days, whereas the digestibility of low-amylose rice flours declined continuously. Our analysis also demonstrated that the chain length distribution of starch molecules and the final and setback viscosity pasting properties were the most important parameters affecting the digestibility of rice flours. Based on our results, it appears possible to reduce rice starch digestibility by establishing optimum processing conditions for different varieties. We suggest a 7-fold addition of water and retrogradation for 1 day for high-amylose rice varieties and a 4-fold addition of water with 3 days of retrogradation for low-amylose rice.     

Effects of gamma irradiation on starch granule structure and physicochemical properties of brown rice starch

In the present research effects of gamma irradiation (5–20 kGy) on the physicochemical, antioxidant and thermal properties of brown rice starch were studied. Scanning electron microscopy displayed mostly polyhedral shapes with no surface fractures. XRD displayed characteristic A type pattern and decrease in per cent crystallinity (22.53–20.41%) was observed as the dose increased from 5 to 20 kGy. DPPH % inhibition and FRAP values were increased in a dose dependent manner. Pasting properties (peak, final and setback viscosity) decreased with irradiation. Pasting temperature also significantly decreased with irradiation for all the irradiated starches. The transition temperatures, enthalpy of gelatinization, pH and apparent amylose content of starch decreased significantly with increase in irradiation dose.