Effects of glutelin and globulin on the physicochemical properties of rice starch and flour

The effect of two rice endosperm proteins, glutelin and globulin, on the physicochemical properties of rice starch and flour was investigated. Albumin, globulin, prolamin and glutelin were sequentially extracted from defatted rice flour with de-ionised water, 1.5 M NaCl, propan-2-ol and 0.1 M NaOH, respectively, followed by dialysis and lyophilisation. Globulin and glutelin were then added to pure rice starch at various concentrations, separately and together, and the pasting and textural properties of mixtures were analysed by the Rapid Visco Analyser (RVA) and TA-XT2 textural analyser, respectively. The presence of glutelin in rice starch caused an increase in pasting temperature but a decrease in the viscosity parameters of the starch paste. The concentration of glutelin was also positively correlated with the hardness and adhesive properties of the starch gel. The presence of globulin, on the other hand, resulted in a decrease in all the pasting and textural parameters except gel hardness and the changes were linearly correlated with the concentration of the protein for most of the physical parameters. When the two proteins were added to rice starch together, the outcomes in pasting and textural properties were generally dependent upon the relative concentrations of the two proteins, but were also influenced by the presence of the other two protein fractions, albumin and prolamin. The presence of globulin initially accelerated the rate of water absorption by starch during cooking while the presence of glutelin slowed it down, but in both cases, the ultimate amount of water absorbed was significantly lower than that by pure starch. The contrasting effects of the different protein fractions mean that it might be possible to manipulate the textural properties of rice starch and flour to achieve desirable sensory outcomes by varying the proportions of the protein fractions in product formulations.     

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.     

Comparison of functional and structural properties of native and industrial process-modified proteins from long-grain indica rice

Rice proteins, as a cheap plant protein source from the by-products of rice dreg processing, could potentially replace commonly used proteins such as soy and whey proteins in selected food products. In this study, the functional properties, surface hydrophobicity (H₀), sulfhydryl and disulfide bond contents, thermal properties, as well as secondary structures of native rice endosperm protein (REP) and processed rice dreg protein (RDP) extracted from long-grain indica rice, were compared. RDP was found to have a higher solubility associated with its relatively higher emulsifying and foaming properties than REP, as well as its water/oil holding capacity, although it was a denatured protein. The emulsifying properties were dependent on the solubility and H₀, while solubility was also related to the disulfide bond contents. Distinct differences in H₀, thermal properties, and disulfide bond contents between REP and RDP could be due to the conformational changes, as the industrial processing steps in the production of rice syrups caused an increase in β-turns at the expense of β-sheets and random coils of REP, leading to the unfolding of β-sheets into higher-ordered supramolecular structures for RDP, which could be responsible for its better functional properties.     

Effects of protein oxidation on gelatinization characteristics during rice storage

Gliadin and glutelin are major rice storage proteins. In this study, we evaluated changes in these proteins to determine the influence of pasting properties on rice storage. Notably, the physical and chemical properties of these proteins changed steadily. We analyzed protein oxidation indexes and determined correlations between the protein oxidation index and gelatinization property index. The results showed that significant oxidation of gliadin and glutelin occurred during the process of rice storage (P < 0.05). Protein oxidation had a significant impact on pasting properties. For glutelin, changes in the structure and function of the protein during rice storage had a significant impact on the five rice pasting property indexes, including peak viscosity (PV), holding strength (HS), breakdown, final viscosity (FV), and setback (SB; P < 0.05). In particular, the levels of carbonyl compounds and active sulfur and the surface hydrophobicity of glutelin were significantly correlated with rice pasting property indexes (P < 0.05). However, gliadin only significantly affected three indexes, i.e., PV, HS, and FV (P < 0.05). Thus, these findings suggested that the carbonyl compounds, active sulfur, and surface hydrophobicity of glutelin could be used as sensitive indexes for changes in rice quality evaluation.     

Antioxidative properties of partially purified barley hordein, rice bran protein fractions and their hydrolysates

Antioxidative properties of proteins from barley and rice bran and their hydrolysates were examined. Three major hordein fractions of barley, B, C and D hordeins, were partially purified by gel filtration. Albumin, globulin, prolamin and glutelin fractions of rice bran were fractioned by the Osborne method. Hydrolysates of these protein fractions were prepared by digesting with pepsin followed by trypsin. Antioxidant properties in terms of antioxidative activity against linoleic acid peroxidation and reducing activity without the lipid adjuvant were investigated. The globulin fraction from rice bran protein revealed the strongest antioxidative activity throughout the incubation time of 7 days (p ≤ 0.05). The albumin fraction of rice bran protein showed the highest reducing activity (6964 μmol of Fe²⁺) followed by globulin, prolamin, glutelin and hordein fractions with activities of 2904, 2017, 1809 and 1333 μmol of Fe²⁺, respectively (p ≤ 0.05). Partially purified C hordein exhibited the highest reducing activity compared with B and D hordeins. Protein hydrolysates obtained after digestion with pepsin and trypsin exhibited much greater antioxidative, as well as reducing, activities than those from before digestion.     

Stabilization of Tarom and Domesiah cultivars rice bran: Physicochemical,functional and nutritional properties

Extrusion is a multi-step thermal process which has been extensively utilized in food preparations. Effects of temperature, moisture content and speed screw on the stabilization of rice bran were optimized using response surface methodology. Furthermore, the effect of extrusion processing on the physicochemical, nutritional and functional properties of Tarom and Domesiah cultivars stabilized rice bran (SRB) were studied. The colour of rice bran was improved by extrusion processing, but the protein content was reduced, which can be related to the denaturation of protein. Extrusion had also a reduction significant effect on the phyitic acid and vitamin E in stabilized rice bran. However, the content of vitamins B₂, B₃, B₅ and folic acid were remained unchanged, but the dietary fibre was enhanced which has beneficial health effect. In comparison with raw rice bran, water holding capacity was enhanced, but the oil absorption capacity was reduced. Foaming capacity and foaming stability of SRB was more than that of untreated rice bran. Although, they were less than that of rice bran protein concentrate/isolate. As a result, extrusion process improves some functional and nutritional properties of rice bran which are valuable for industrial applications and have potential as food ingredient to improve consumer health.     

Microstructure and rheological properties of mixtures of acid-deamidated rice protein and dextran

Microstructure and rheological properties of mixtures of acid-deamidated rice protein (ADRP) and dextran were studied. The microstructures of the ADRP/dextran mixtures were described using confocal laser scanning microscopy (CLSM), which revealed the effective association among ADRP and formation of a protein network-like structure in the mixture with higher protein concentration. Mechanical properties of the mixtures were observed by rheometer. The steady shear measurements showed a correlation with the CLSM results via a marked increase in the viscosity of the mixtures with protein association. Frequency sweeps further evidenced the build-up of the gelled network-like structure. The differences in fracture forces observed by textural measurements between mixture and single ADRP gel also suggested the difference in microstructures. The formation of network-like structure appeared to have occurred through a phase separation of ADRP and dextran.     

Characterization of rice storage proteins by SE-HPLC and micro z-arm mixer

While the effect of protein content and composition on the functional properties of wheat flour is well studied, our knowledge on the same properties of rice flour is limited. This work was conducted to study the relationship between the dough mixing properties of flour from different rice cultivars and protein content and composition. An efficient sonication-based two-step extraction procedure was applied to isolate rice flour proteins. The size-exclusion HPLC (SE-HPLC) method, originally developed for separating wheat proteins, was applied with some minor modifications in order to study the size distribution of rice flour proteins. Four fractions were distinguished on the SE-HPLC profile and were further characterized by SDS-PAGE. Fractions I–III consisted of glutelins, while fraction IV contained albumin, globulin and prolamin proteins. When rice dough was characterized on the basis of mixing parameters in a micro z-arm mixer, significant differences were observed depending on the protein composition of the flour. Statistical analysis results indicated that the functional properties of the flour from different rice cultivars were associated with the amount of polymeric proteins and their size distribution.     

Development and evaluation of rheological and bioactive properties of rice protein-based gels

The rice industry produces a large amount of by-products daily. In fact, it is estimated that approximately 100 million tons of rice residues and by-products are generated each year. However, new protein sources are demanded for human food because of the continuous increase in the global population coupled with the almost total inability to increase global food production.A rice protein concentrate (RPC), which is a by-product of the rice industry, and two different hydrolysates (RPH₂₅ and RPH₁₂₀) obtained from RPC, have been used in order to evaluate the potential of RPC to form a gel-like food product at three different pH values (2.0, 6.5 and 8.0). The gelation process was monitored and subsequently, mechanical spectra were obtained. In addition, protein interactions (ionic interactions, hydrophobic interactions, hydrogen bonds and disulphide bonds) were also determined in order to understand the gel structure. Finally, an antioxidant characterisation was carried out using three different reagents: DDPH, ABTS and Folin-Ciocalteu.A proper degree of hydrolysis and an optimal pH value seem to be key factors in the manufacturing of gels, showing a remarkable influence on both rheological properties and antioxidant activities.     

Bacillolysin,papain, and subtilisin improve the quality of gluten-free rice bread

Protease has been shown to be an effective food additive for improving the quality of gluten-free rice bread. In this study, we found that bacillolysin (Protin SD-NY10, metallo protease), papain (cysteine protease), and subtilisin (Protin SD-AY10, serine protease) increased the specific volume of gluten-free rice breads by 30–60% compared with untreated breads. These proteases also decreased crumb hardness by 10–30% compared with untreated breads. Many fine bubble cells were observed in the crumb of the protease-treated rice breads using scanning electron microscopy. Optical microscopic observation revealed fine networks of small protein aggregates stained by Coomassie Brilliant Blue (CBB) in the rice batter of the improved gluten-free rice breads. Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of protein in the rice batter suggested that the amount of low molecular weight proteins (less than 10 kDa) increased with the use of Protin SD-NY10, Protin SD-AY10 and papain treatments compared with untreated rice batter. Thus, we considered that the small proteins aggregates were formed through disulfide bonds. This fine network was effective for retaining CO₂ gas during the fermentation process, resulting in an increase in the specific volume and a decrease in the crumb hardness of gluten-free rice bread.     

植物拉丝蛋白的功能特性及其应用

叙述了植物拉丝蛋白的定义和功能特性,并介绍了植物拉丝蛋白的主要功能性及其在食品加工中的应用。     

Optimization of microwave-assisted extraction of rice bran protein and its hydrolysates properties

Microwave-assisted extraction (MAE) was applied for extracting rice bran protein with a response surface methodology (RSM). The optimal condition was 1000 W of microwave power, 90 s of extraction time, and a solid to liquid ratio of 0.89 g rice bran/10 mL of distilled water. The protein yield of MAE was higher than that of alkaline extraction (ALK) by about 1.54-fold (P < 0.05), while the protein digestibility was similar. The protein hydrolysates (PHs) with at different degrees of hydrolysis (DH) (5.04, 10.37 and 15.04%) were produced by alcalase. The molecular weight (MW) of the rice bran protein concentrates (RBPC) and the PHs ranged between <11 kDa and 100 kDa. The excessive enzymatic hydrolysis resulted in a negative effect on water and oil absorption capacities. The PHs with DH15.04% acted as the strongest DPPH radical scavenger, ferric reducing agent, and also metal ion chelator (P < 0.05). However, a DH of 5.04% was sufficient for improving the functional properties of RBPC, especially foam ability and the emulsion activity index. This study suggests that the desirable properties of rice bran protein can be controlled with enzymatic modification.     

Composition and functional properties of protein isolates obtained from commercial legumes grown in northern Spain

Pea (Pisum sativum), faba bean (Vicia faba) and soybean (Glycine max) seeds were characterized, and protein isolates were prepared following an isoelectric point precipitation procedure. Soybean seeds showed the highest protein content (36.7%) and carbohydrate was the major constituent in the pea (59.4%) and the faba bean seeds (52.1%). Protein contents were higher than 80% in all the protein isolates. The amino acid contents in the protein isolates were, in general, higher than those in their own starting seeds. The antinutritional factor contents were reduced after the protein isolate preparation. The highest reductions achieved for tannins were 95% in the faba bean protein isolate, and for phytates (45%) and trypsin inhibitor activity (46%) in the pea protein isolate. Haemagglutinating activity was not detected in any of the protein isolates. Minimum solubility values were observed at a pH range between 4.0 and 6.0, and maximal solubilities were obtained at basic pH values. The faba bean protein isolate showed the highest water and oil absorption capacities, and the best gelling properties. The soybean protein isolate had the best foam expansion capacity. Thus, the protein isolates had an improvement in some of the characteristics compared to their original seeds with lower contents in tannins, phytates and haemagglutinating activity, but had weak functional properties.     

Application of resequencing to rice genomics,functional genomics and evolutionary analysis

Rice is a model system used for crop genomics studies. The completion of the rice genome draft sequences in 2002 not only accelerated functional genome studies, but also initiated a new era of resequencing rice genomes. Based on the reference genome in rice, next-generation sequencing (NGS) using the high-throughput sequencing system can efficiently accomplish whole genome resequencing of various genetic populations and diverse germplasm resources. Resequencing technology has been effectively utilized in evolutionary analysis, rice genomics and functional genomics studies. This technique is beneficial for both bridging the knowledge gap between genotype and phenotype and facilitating molecular breeding via gene design in rice. Here, we also discuss the limitation, application and future prospects of rice resequencing.     

QTL mapping for crude protein and protein fraction contents in rice (Oryza sativa L.)

Improvement of rice storage proteins is important in rice breeding for high nutritional quality. Seventy-one recombinant inbred lines (RIL) derived from a cross between japonica variety Asominori and indica variety IR24 were used to study the inheritance of crude protein and protein fraction contents in rice. A total of 16 QTL were identified and mapped on eight chromosomes. Several QTL affecting contents of different protein fractions were mapped in the same chromosomal region. In particular, two QTL with a significant contribution were identified to simultaneously affect prolamin and glutelin contents. One QTL denoted as qCP-12 affecting crude protein content (CP) was located in the same region as QTL qGLT-12 affecting glutelin content, in agreement with the positive correlation between glutelin level and protein content. QTL with larger genetic effects were further confirmed using two sets of chromosome segment substitution lines (CSSL), where Asominori and IR24 were used as the recurrent parents. By QTL comparative analysis, two QTL for CP, three for globulin content and one for prolamin content were located in the vicinity of CP QTL previously identified in polished rice. Application of these results in rice breeding is discussed.     

Temperature during grain ripening affects the ratio of type-II/type-I protein body and starch pasting properties of rice (Oryza sativa L.)

The starch and protein properties of rice grain are important factors for sake brewing and these properties are reported to be influenced by temperatures during grain ripening. Amylose content, nitrogen content, protein composition, pasting properties measured by a Rapid Visco Analyser (RVA), and their relationship to temperatures during ripening were investigated in a rice cultivar, Yamadanishiki, which was grown under various conditions in the same experimental field. The average temperature after heading was significantly correlated with amylose content and RVA properties, but not with nitrogen content. Under high temperatures during ripening, a decrease in prolamin, which accumulated in type I protein body (PB-I), and an increase in glutelin, which deposits in type II PB (PB-II), were recognized. The ratio of PB-II/PB-I and RVA pasting temperatures were distinctly increased as the temperature became higher. High temperatures during grain ripening would lead to difficulties in digesting steamed rice grains by Aspergillus oryzae, together with ease in digesting rice protein. The average temperature of 11–20 days after heading showed a higher correlation coefficient than that of 1–10 or 21–30 days, implying that temperatures during the middle stage of grain development would be important in determining the rice component that relates to brewing properties.     

Effect of different carbohydrates on the functional properties of black rice glutelin (BRG) modified by the maillard reaction

The objective of this study was to investigate the effects of the glycosylation of BRG on its structures and functional properties. The glycosylation of BRG was achieved via Maillard reactions with four carbohydrates, including arabinose (AN), sodium alginate (SA), maltodextrin (MD), and lactose (LT), and the corresponding conjugates were named BRG-AN, BRG-SA, BRG-MD, and BRG-LT, respectively. The formation of the BRG conjugates was confirmed by changes in the BRG amino groups, conjugation degree, as well as molecular weight. BRG-AN and BRG-MD presented a significantly higher conjugation degree and lower amino group levels compared to the other two conjugates. Circular dichroism (CD) analysis indicated that all the conjugated BRG displayed markedly decreased levels of β-sheets and increased levels of α-helixes. However, only BRG-AN increased significantly in irregular loops. Results from the Fourier Transform Infrared Spectroscopy (FTIR) analysis indicated that the most apparent changes in the structures of BRG conjugates were evident as absorption peaks at 3389 cm⁻¹, 1528 cm⁻¹, 1230 cm⁻¹, and 953–1180 cm⁻¹. After glycosylation, the solubility, emulsion activity index (EAI), and emulsion stability index (ESI) of BRG were significantly improved. After glycosylation of the BRG, induced by Maillard reactions with four carbohydrates, the denaturation temperature (T_d) and enthalpy (ΔH) change values increased substantially from 90.16 °C to 124.28 °C and 11.01 J/g to 18.43 J/g, respectively. The results indicated that BRG-AN exhibited better solubility, EAI, and ESI than the other BRG conjugates.     

Effects of prolamin on the textural and pasting properties of rice flour and starch

Prolamin is a major class of rice proteins but its influence on the physicochemical properties of rice is not clear. Rapid Visco Analyser (RVA) and TA-XT2 TPA textural analyses were performed on rice starch with the addition of prolamin extracted from three rice cultivars (Hitomebore, M103 and Amaroo), and on rice flour with the prolamin removed by propan-2-ol extraction. Addition of prolamin to rice starch was found to cause a significant (P<0.05) increase in RVA breakdown viscosity but significant (P<0.05) decreases in hardness, adhesiveness and gumminess of the starch gel. Similarly, when prolamin was removed from rice flour, exactly the opposite effect was observed. Addition of prolamin to rice starch also caused it to absorb water faster during cooking but the gelatinised starch absorbed less water compared with control samples without prolamin.     

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.     

Kinetics of starch digestion and functional properties of twin-screw extruded sorghum

The time-course of starch digestion in twin-screw extruded milled sorghum grain was investigated using an in-vitro procedure based on glucometry. The sorghum grains were hammer-milled, and extruded at three levels each of moisture and screw speed. Irrespective of the extrusion conditions, extruded and non-extruded milled sorghum grain exhibited monophasic digestograms, and the modified first-order kinetic and Peleg models adequately described the digestograms. Extrusion increased the rate of digestion by about ten times compared with non-extrudates. Starch gelatinisation varied in the extrudates, and microscopy revealed a mixture of raw, gelatinised and destructured starch and protein components in the extrudates. Starch digestion parameters significantly (p < 0.05) correlated with extruder response and various functional properties of the extrudates. Extrusion conditions for maximum starch gelatinisation in milled sorghum grain for fastest digestion as an efficient animal feed were interpolated, as well as the conditions for directly-expanded extrudates with potential for human food, where minimum starch digestion is desired.