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.     

Comparison of color techniques to measure the color of parboiled rice

A combination of digital camera, computer and graphic software can provide a less expensive and more versatile technique to determine the surface color of parboiled rice compared to instrumental color measurement. The instrument was used to measure rice powder and whole rice. Pearson correlation coefficients and sample paired t-test on total color difference (ΔE), L and b values were calculated. The value of ΔE of samples from the instrumental technique was 0.69–4.61 (powder), 4.7–10.2 (whole rice) with a coefficient of variance (CV) ranging from 3.5 to 25.3% and from 15.4 to 46.6%. Meanwhile, the digital image technique gave a ΔE value ranging from 4.2 to 13.77 with a CV from 6.3 to 21.2%, respectively. A highly significant correlation (R² = 0.7451, R² = 0.8074, R² = 0.7518,) was obtained for ΔE between instrumental (powder and whole rice), Vision Builder and instrumental (powder), and instrumental (whole rice) and Vision Builder. The chromatic b value of instrumental for powder had a significant correlation with the Vision Builder data (R² = 0.7741). The results suggest that although the digital image provided the surface color of parboiled rice, it was less accurate than the instrumental for powder. Therefore results from the digital image should be interpreted with caution.     

Effect of preparation conditions on composition and sensory aroma characteristics of acid hydrolyzed rice bran protein concentrate

Hydrolysates were prepared from rice bran protein concentrate (RBPc) in paste form (P-RBPc), or as spray-dried (S-RBPc) or freeze-dried (F-RBPc) powder by acid hydrolysis with aqueous 0.5N HCl at 95 °C for 12 or 36 h. The forms of the protein raw material had only a slight influence over the sensory aroma characteristics of the liquid hydrolysates. The liquid hydrolysate (S-H-RBPc-12) prepared from S-RBPc with hydrolysis time of only 12 h could produce the desirable aromas as to a similar extent as that of 36 h. In order to demonstrate the effect of drying method on the composition and aroma characteristics, a representative S-H-RBPc-12 was converted into a powder by freeze- and spray-drying techniques. Sensory analysis indicated that the spray-dried powder had higher cracker-like and salty aroma intensities and received a higher overall liking score compared to the freeze-dried hydrolysate powder.     

Effect of processing conditions on bioactive compounds and glycemic index of the selected landrace rice variety in pre-diabetes

Paddy processing can affect glycemic index (GI) and bioactive compounds of rice. Therefore, the effects of processing conditions such as germination, parboiling and polishing on total polyphenols, ferulic acid and gamma-aminobutyric acid (GABA) contents of seven landrace varieties from Thailand were investigated. Subsequently, the best rice variety was chosen to evaluate GI in pre-diabetic subjects. Four different rice forms used were brown rice (BR), parboiled brown rice (PBR), germinated parboiled brown rice (GPBR) and polished rice (PR). Results showed that polishing process strongly reduced all bioactive compounds. In contrast, parboiling the grains slightly increased polyphenol, and germination followed by parboiling significantly increased polyphenol content. Ferulic acid content was found to be similar among BR, PBR and GPBR and the highest GABA content was found in GPBR. Furthermore, Leuang Awn variety exhibited the highest polyphenol (126.70 ± 1.08 mg GAE/100 g), ferulic acid (17.77 ± 0.16 mg/100 g) and GABA content (78.57 ± 1.00 mg/100 g) and was selected for GI study. PBR and GPBR had medium GI values (55.10 ± 5.37 and 60.58 ± 6.48) and PR showed high GI value (83.10 ± 5.10). In conclusion, parboiling and germination had less effects on the bioactive compounds of whole grain rice and produced low-medium GI, which could be beneficial for health promotion.     

Distribution of proteins and amino acids in milled and brown rice as affected by nitrogen fertilization and genotype

A field experiment involving six japonica rice cultivars with contrasting agronomic traits and seven nitrogen (N) fertilizer treatments was performed to determine the effects of N and genotype on distribution of four kinds of grain proteins and amino acids in milled and brown rice. For brown and milled rice, albumin and globulin were controlled more by genotype than N treatments, whereas prolamin and glutelin were largely determined by N. Substantial genotypic differences in response of milled/brown (M/B) ratios of proteins to N treatments were detected. In comparison with large panicle cultivars, small panicle cultivars such as Wuyujing3 had the lower ratio and exhibited more stability under contrasting N treatments. N had significant influence on amino acid composition of brown and milled rice, with contents of the 17 amino acids measured increasing with elevated N rate. However, cysteine and methionine in brown rice and lysine and methionine in milled rice were not significantly affected by N. In addition, N had little effect on ratios of M/B for most of the amino acids.     

Impact of pre-germination on amylopectin molecular structures,crystallinity, and thermal properties of pre-germinated brown rice starches

Ungerminated brown rice (UGBR) and pre-germinated brown rice (PGBR) obtained from different pre-germination durations were studied to investigate the changes in total starch contents of flour, amylopectin molecular structures, crystallinity, and thermal properties of starches as affected by pre-germination. Each paddy of three rice cultivars with different amylose contents (RD6, waxy; KDML105, low amylose; and RD31, high amylose) was soaked in water at 30°C for 12 h and incubated over different periods until the three stages of embryonic growth length (EGL) were achieved. The total starch contents of three-stage PGBR flour from all rice cultivars decreased when pre-germination durations were increased. The three-stage PGBR starches from the three rice cultivars had lower weight-average molecular weight (Mw) and number-average molecular weight (Mn) than UGBR starches. All starches from the three rice cultivars displayed an A-type X-ray diffraction pattern (XRD). Isolated UGBR starch from RD6 had the highest (31.33%) relative crystallinity (RC), while RD31 showed the lowest RC (26.79%). The slight increases in the RC of three-stage PGBR starches from three rice cultivars were found after pre-germination. Isolated PGBR starches from the three rice cultivars had higher gelatinization temperatures and enthalpy, but lower retrogradation enthalpy and %retrogradation than UGBR starches.     

不同施氮量对免耕/翻耕移栽稻生长及产量形成的影响

为探讨免耕移栽稻的氮肥管理措施和比较不同耕作方式下移栽稻的生长规律,研究了不同施氮量处理对免耕/翻耕移栽稻生长及产量形成的影响.结果表明,无论翻耕或免耕,增施氮肥可以促进分蘖的发生和叶面积的扩展;在水稻各生育时期,随着氮肥用量的增加,干物质的积累量有增加的趋势,每穗粒数和收获指数逐渐减少;水稻总吸氮量和实际产量逐渐增加,而氮肥吸收利用率、生理利用率和农学利用率及偏生产能力逐渐减小.翻耕移栽稻的分蘖能力、有效穗数和吸氮量显著高于免耕移栽稻,但翻耕和免耕对水稻产量及其构成因素的影响差异不显著,免耕移栽稻的氮肥生理利用率显著高于翻耕移栽稻.     

Prediction of grain weight,brown rice weight and amylose content in single rice grains using near-infrared reflectance spectroscopy

The potential of near-infrared reflectance spectroscopy (NIRS) for simultaneous analysis of grain weight (mg), brown rice weight (mg) and milled rice amylose content (AC, %) in single rice grains was studied. Calibration equations were developed using 474 single grain samples, scanned as both rice grain and brown rice. An independent set containing 90 F₂ generation grains was used to validate the equations. In general, equations developed using the first derivative resulted in superior calibration and validation statistics compared with the second derivative and those developed using brown rice were superior to those developed from the rice grain. Fitting equations were developed and monitored with an external validation set. The standard error of prediction (corrected for bias) SEP(C) for AC, brown rice weight and rice grain weight for equations developed using brown rice were 2.82, 1.09 and 1.30, with corresponding coefficient of determinations (r²) of 0.85, 0.71 and 0.67, and SEP(C)/S.D. of 0.39, 0.57 and 0.59, respectively. It was demonstrated that NIRS provides a convenient way to screen single intact grains. This will be advantageous in early generation selection in rice breeding programs.     

Retrogradation behaviour of milled and brown rice pastes during ageing

Retrogradation of gelatinised starch is the main phenomenon that influences the texture of cooked rice. The rate of retrogradation is affected by several factors including amylose and amylopectin ratio, protein and fibre. The objective of this study was to analyse the pasting properties and the retrogradation behaviour of six traditional and five aromatic Italian rice varieties. The pasted gels, after cooling, were evaluated by dynamic rheological measurements for up to 7 days of storage at 4 °C. The samples were also analysed by a NIR spectrometer. The pasting properties and the retrogradation behaviour of milled rice flours strongly depended on the rice varieties. During gel ageing, a noticeable increase of G′ and G″ was observed only for the milled rice varieties Asia, Gange, Fragrance and Vialone Nano, characterised by a high amylose content. No further hardening was found either for the other milled varieties or for all the brown samples. The methods used in this work (dynamic oscillatory rheometry and FT-NIR spectroscopy) turned out to be very useful in the definition of rice starch gels ageing.     

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.     

免耕对土壤理化性状和直播稻生长及产量形成的影响

为探明免耕直播稻的生长规律和免耕直播的环境效应,研究了稻田免耕直播对土壤理化性状和水稻生长及产量形成的影响.结果表明,稻田免耕后,土壤容重降低和孔隙性得到改善,土壤养分在土壤表层富集.与翻耕直播相比,免耕直播稻分蘖能力较弱,但无效分蘖较少,成穗率高.直播条件下,免耕更有利于叶面积的扩展.除齐穗期外,其它生育时期免耕稻的根系活力强,平均比翻耕提高4.45%.在最高分蘖期,免耕直播稻的根冠比和单蔸根干重高于翻耕直播稻.在翻耕和免耕条件下,干物质积累量及在茎、叶和穗中的分配比例无显著差异.免耕直播稻的实际产量为8.6 t/hm2,比翻耕直播稻增产5.8%.另外,免耕直播稻的收获指数比翻耕直播稻高,增幅为13.3%,但未达到5%的显著差异水平.     

Effect of wheat bran ball-milling on fragmentation and marker extractability of the aleurone layer

Bran (bran_ml) obtained by roller milling of soft (Scipion) and hard (Baroudeur) wheat cultivars was further ball-milled for increasing times and the observed particle size distribution expressed as a dispersion index. Bran (bran_hi) and aleurone layers were also hand-isolated from the same grains and the pattern of size reduction during ball-milling were compared with bran_ml. Bran_ml and bran_hi were found to fracture more rapidly than isolated aleurone layers due to the presence of the highly friable pericarp and the possible mechanical constraints due to tissues surrounding the aleurone layer. Previously identified markers of the aleurone layer cell contents (phytates) and cell walls (p-coumaric acid) were used to determine their water extractabilities from ball-milled samples and the state and degree of dissociation of the aleurone layer, either as an isolated tissue or within bran_ml and bran_hi. The results suggest that ball-milling rapidly induces fractures in walls of cells in the aleurone layer. The partial opening of the cells in the aleurone layer allowed extraction of most (≈70%) of the water-extractable phytates, even though their mean particle size was much larger than the dimensions of the cells. A further increase in extractability of phytates was observed when the particle size was reduced below the aleurone cell dimensions. Although much less soluble, p-coumaric acid followed a similar trend to phytates. The different behaviour of bran_ml and bran_hi was consistent with a weakening effect of the tissues in the former, probably due to the previous milling process. The bran and aleurone layers from both wheat varieties exhibited a similar behaviour.     

Variation in kernel characteristics and protein molecular weight distribution of Langdon durum-wild emmer wheat chromosome substitution lines

Triticum turgidum L. var. dicoccoides (DIC) provides a useful source of genes to improve agronomic and quality characteristics of durum wheat. Research was performed to identify DIC chromosomes that carry useful genes for quality improvement. Langdon-T. dicoccoides substitution lines consisting of 13 lines based on DIC accession PI 481521, 10 lines on PI 478742, and 2 lines on Israel A were evaluated for kernel characteristics and protein molecular weight distribution. DIC chromosomes 3A from PI 481521, and 1A and 7A from PI 478742 increased kernel hardness. Chromosome 2A from PI 481521 increased kernel weight, which resulted in increased semolina yield. Some substituted DIC chromosomes also affected grain protein concentration and protein molecular weight distribution. For example, chromosomes 2A, 5B, and 7B from PI 481521, and 6B from Israel A increased total protein concentration, which was primarily attributed to an increase of SDS soluble gliadins. Chromosome 6B from PI 478742 was unique in that it led to an increase in SDS insoluble high molecular weight polymeric proteins, which contributed to increased dough mixing strength. Results from this research indicated that chromosome 6B from PI 478742 is a potential gene source to improve dough characteristics of durum wheat by increasing insoluble high molecular weight polymeric protein concentration.     

Effects of semidry flour milling on the quality attributes of rice flour and rice noodles in China

To investigate the effects of semidry-milling on the quality attributes of rice flour and rice noodles, the properties of rice flours and cooking properties of rice noodles prepared with wet-, dry- and semidry-milled rice flours were characterized. The level of starch damage of semidry-milled rice flour at 30% moisture was significantly decreased to the level of wet-milled rice flour (P < 0.05); the whiteness of dry-milled rice flour was decreased compared with wet-milled rice flour (P < 0.05), while that of semidry-milled rice flour was not; the wet- and semidry-milled rice flours showed similar morphology and water hydration properties; the dry milling method reduced significantly the hardness, chewiness, and resilience of rice noodles (P < 0.05) compared with wet-milling, but semidry-milling did not; the cooking qualities of rice noodles produced by semidry-milling were comparable to wet-milling. It indicated the semidry-milling at 30% moisture may provide the protective effects on the characteristics of rice flours, which could be used to produce similar qualities of rice noodles to the wet-milling.     

Protein content,distribution and retention during milling of brown rice

Brown rice of IR36 and IR42 check samples from the 1982 dry and wet season yield trials showed good correlation of milled-rice protein and brown-rice protein (r=0.97**,n=40) with 10% bran-polish removal by an emery abrasive mill. Among selected grain samples of both varieties, 80 to 86% of brown-rice protein was retained in the milled rice with both friction and abrasive mills. Stereological morphometry of 1-µm-thick sections showed that endosperm storage protein decreases in amount with increasing distance from the aleurone layer. A similar protein gradient was found in both average-protein and high-protein samples. Milling removed all of the pericarp, seed coat and nucellus, and virtually all of the aleurone layer and embryo, but removed very little of the nonaleurone endosperm, except from the lateral ridges.     

The impact of heating and cooling on the physico-chemical properties of wheat gluten–water suspensions

The rapid visco analysis (RVA) system was used to measure rheological behaviour in 20% (w/v) gluten-in-water suspensions upon applying temperature profiles. The temperature profiles included a linear temperature increase, a holding step, a cooling step with a linear temperature decrease to 50 °C, and a final holding step at 50 °C. Temperature and duration of the holding phase both affected RVA viscosity and protein extractability. Size-exclusion and reversed-phase HPLC showed that increasing the temperature (up to 95 °C) mainly decreased glutenin extractability. Holding at 95 °C resulted in polymerisation of both gliadin and glutenin. Above 80 °C, the RVA viscosity steadily increased with longer holding times while the gliadin and glutenin extractabilities decreased. Their reduced extractability in 60% ethanol showed that γ-gliadins were more affected after heating than α-gliadins and ω-gliadins. Enrichment of wheat gluten in either gliadin or glutenin showed that both gliadin and glutenin are necessary for the initial viscosity in the RVA profile. The formation of polymers through disulphide bonding caused a viscosity rise in the RVA profile. The amounts of free sulphydryl groups markedly decreased between 70 and 80 °C and when holding the temperature at 95 °C.     

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.     

Nucleotide polymorphisms in OsAGP genes and their possible association with grain weight of rice

ADP-Glucose pyrophosphorylase (AGPase) is a rate-limiting enzyme participating in starch biosynthesis, which may be responsible for the filling rate and starch accumulation in the developing rice kernel. However, it is still unknown whether the naturally occurring variation in the sequence of ADP-Glucose pyrophosphorylase of rice (OsAGP) is related to the grain weight (GW). In this study, we discovered a total of 38 single nucleotide polymorphisms (SNPs) and insertions/deletions (InDels) in the partial sequences of six OsAGP isoform genes from 30 rice accessions with diverse agronomic traits. We then developed ten cleaved amplified polymorphic sequence (CAPS) and derived CAPS (dCAPS) markers for genotyping the SNPs and InDels for an association mapping population consisting of 416 rice accessions. Candidate gene association study indicated that an InDel of OsAGPL4 was associated with GW in two environments and an SNP of OsAGPL2 was associated with GW in one environment. Each gene marker only explained 1% of the variation of GW, thus it could be concluded that both genes contributed little to GW of rice. However, the markers identified in this study could be used for tagging other traits of interests and in molecular breeding.     

Differences in functional properties and biochemical characteristics of congenetic rice proteins

Proteins in brown rice (BR), white rice (WR) and rice bran (RB) were extracted from the same paddy rice and investigated for their components, functional properties and chemical characteristics by SDS-PAGE methodology. BR and WR proteins possessed a poor solubility under weak acid conditions due to a high content of glutenin and richness in higher molecular-weight (MW) protein fractions. Rice bran protein contained significantly lower molecular-weight components (MWs < 50 kDa) than those in WR and BR. Nitrogen solubility, foaming and emulsification properties of their rice protein preparations were affected not only by pH (3–11), but also by the concentrations of NaCl (0.4–2.0%) and sucrose (4.0–20.0%). All of them, particularly rice bran protein, had favorable functional properties in the medium with a high salt or sugar concentration. Therefore, they have a good potential for development in the food industry.     

Impact of continuous or cycle high hydrostatic pressure on the ultrastructure and digestibility of rice starch granules

The effects of continuous or 2-cycle high hydrostatic pressure (HHP) treatments (200 and 600 MPa) on the microstructure and digestibility of rice starches were investigated. The morphological and structural changes were characterized using polarized light microscopy, scanning electron microscopy, atomic force microscopy, X-ray scattering and ¹³C CP/MAS NMR, and the starch digestibility was examined by in vitro hydrolysis. Results showed that HHP at 600 MPa significantly alters the microstructure and lowers the resistant starch (RS) compared with HHP at 200 MPa. Under the same pressure level, the two 15-min cycle treatment induced more structural disruption, gelatinization, disappearance of surface protrusion, and lower RS of rice starches than that of the continuous HHP treatment (30 min). Based on the results on RS, the two 15-min cycle HHP treatment at 200 MPa could be beneficial for improving the functionality of the rice starch.