Milled Rice Flour Research Articles

Causes of Variation in the Water Content Measurements of Milled Rice Flour Estimated from Proficiency Testing

Causes of Variation in the Water Content Measurements of Milled Rice Flour Estimated from Proficiency Testing

Quality attributes of paddy rice as affected by frozen storage

ABSTRACT After harvest, paddy rice may encounter frozen conditions during the storage and transportation periods. However, the effect of frozen storage on quality of paddy rice remains unclear. In this research, two moisture contents of paddy rice (13.5% and 15.1%) were stored at two frozen temperatures (−18°C and −30°C) for two months and then evaluated for quality attributes, including germination rate, peroxidase and polyphenol oxidase activities, fat acidity, milling quality, pasting property, cooking property, and texture of the cooked rice. The results showed that the frozen storage generally decreased the germination rate, activities of peroxidase and polyphenol oxidase, husked rice yield, head rice yield of paddy rice, reduced the water uptake ratio and volume expansion rate of milled rice during cooking, and lowered the hardness of cooked rice. At frozen condition, the decrease of temperature and the increase of moisture content led to a more pronounced reduction in germination rate and peroxidase activity. Frozen treatment of paddy rice did not significantly affect the pasting temperature of milled rice flour, but decreased the peak viscosity. Fat acidity of paddy rice slightly increased after frozen storage.

Delayed sowing does not improve palatability-related traits in high-quality rice

The demand for and consumption of soft-textured, high-quality rice with low amylose content have substantially increased in China with improved economic and living standards. Shifting sowing date is a common strategy to optimize temperature conditions and improve rice quality. In this study, a high-quality rice cultivar with low amylose content (Jingliangyou 1468) was grown under four sowing dates (May 15th and 25th, and June 4th and 14th) in 2019 and 2020 to determine the effects of sowing date on palatability-related traits and evaluate relationships between palatability-related traits and daily mean temperature during the grain-filling period. Results showed that delaying sowing date decreased daily mean temperature during the grain-filling period and consequently increased amylose content and setback viscosity of milled rice flour, which in turn increased hardness and chewiness of cooked rice. The finding of this study suggests that the strategy of delayed sowing does not improve the palatability of high-quality rice in the context of consumers’ preference for soft-textured rice.

Texture and digestion properties of hybrid rice: A comparison between two cultivars released 18 years apart

Field experiments were conducted to compare two hybrid rice cultivars—a recently released high-quality cultivar (Jingliangyou 1468, JLY1468) and a relatively older cultivar (Liangyoupeijiu, LYPJ). Results showed that hardness, springiness, cohesiveness, resilience, and chewiness of cooked milled rice were all lower in JLY1468 than in LYPJ, due to its lower amylose content and altered paste properties of milled rice flour. Active digestion duration of cooked milled rice was 26% shorter and the glucose production rate from starch digestion was 33% faster in JLY1468 compared with LYPJ. Texture and starch digestion properties of cooked milled rice as a factor of temperature during the grain-filling period were different between LYPJ and JLY1468 due to differing amylose contents and gel consistencies of milled rice flour in response to temperature. This study highlights that attention should be paid to potential health risks associated with the development of high-quality hybrid rice cultivars with soft texture.

Low‐temperature stress during the flowering period alters the source–sink relationship and grain quality in field‐grown late‐season rice

AbstractLate‐season rice, a major contributor to the production of high‐quality rice in China, often experiences low temperatures during the flowering period. The objective of this study was to determine the effect of low temperature stress on grain quality and to identify related physiological factors in late‐season rice. Sink and source characteristics and grain quality traits of two high‐quality late‐season rice cultivars were compared between a year in which low temperatures occurred during the flowering period (2020) and a normal year (2019) under field conditions. Low temperatures during the flowering period in 2020 resulted in a reduction in spikelet filling and consequent increases in source–sink ratios and grain weight and N content compared to 2019. The head rice rate and protein content of the milled rice were increased in 2020 compared to 2019. Starch gel consistency and peak, trough, breakdown, final, and consistency viscosities were reduced while setback viscosity, paste temperature, and texture properties (hardness, springiness, cohesiveness, resilience, and chewiness) were increased for milled rice (or milled rice flour or cooked milled rice) in 2020 compared to 2019. The glucose production rate and total glucose production from in vitro digestion of cooked milled rice was reduced in 2020 compared to 2019. The results of this study suggest that low temperature stress during the flowering period can improve milling, nutritional, and health qualities but reduce the cooking and eating quality in late‐season rice by altering the source–sink relationship.

Assessment of starch branching and lamellar structure in rice flours

Apparent amylose content is used to describe milled rice flour composition. This spectrophotometric method is often the only direct measurement of starch structure in routine quality analysis. However, starch exhibits 6 levels of structure. The (supra)molecular starch structure in rice flours was measured: average degree of branching by 1H NMR spectroscopy and semi-crystalline lamellar structure by small angle X-ray scattering (SAXS). The suitability of these methods in routine quality analysis for breeding programs or the food industry was assessed in terms of precision and accuracy. Determination of apparent amylose content exhibits high precision (ca 5 % error) but low accuracy. Determination of average degree of branching exhibits a similar precision but good accuracy. Sample preparation (dissolution) is the first source of error in 1H NMR spectroscopy and presumably also in spectrophotometry. Within narrow ranges of apparent amylose content (less than 2.5 % absolute difference) differences in average degree of branching and lamellar structure could be observed. The difference between chemical structures of different amyloses/amylopectins within a given sample is not negligible. This opens a way to explore how finer details of molecular and supramolecular starch structure can play a role in understanding rice quality.

Quality improvement effects of electrolyzed water on rice noodles prepared with semidry-milled rice flours.

To investigate the effects of electrolyzed water treatment on the qualities of rice noodles prepared with semidry- milled rice flour, pasting properties and thermal properties of rice flour, and the cooking and textural properties of rice noodles were determined. Higher peak viscosity and lower melting enthalpy were observed in electrolyzed water (EW) treated rice flour. The hardness, gumminess and chewiness of rice noodle in slightly acidic electrolyzed water treated rice noodles with available chlorine concentration (ACC) 20.32mg/L were increased significantly (p < 0.05). The cooking loss decreased significantly in strong acidic electrolyzed water treated noodles with ACC 10.09mg/L treatment (p < 0.05). The results indicated that EW could promote the gelatinization of rice flour, and improve the textural qualities of rice noodles. Therefore EW was appropriate to be used in rice noodle production.

Assisted selection of eating quality progeny of indica (O. sativa L. ssp. indica) and japonica (O. sativa L. ssp. japonica) hybrids using rice starch properties

Eating quality (EQ) of rice is mainly determined by sensory evaluation using tasting, which is affected by the taster’s geographic residential area, gender, and age. The sensory evaluation protocol also requires rice samples (usually > 500 g) larger than the amount harvested from the early generations of breeding in many cases, thereby hindering the sensory tasting practices. The characteristics of rice starch have a significant impact on EQ; however, information on starch assisted-selection of EQ is insufficient. In this study, the recombinant inbred lines and backcross recombinant inbred lines constructed by the hybridization of japonica (O. sativa L. ssp. japonica) rice (cv. Toyonishiki) and indica (O. sativa L. ssp. indica) rice (cv. Qishanzhan) were used as test materials to analyze and explore the relationships between the amylose content (AC), rapid visco analyzer (RVA) profile characteristics, and the EQ score obtained from sensory tasting assessment. We provided a feasible solution to use rice starch properties to assist in selection of EQ. The results indicated that AC and RVA profile characteristics including trough viscosity (TV), final viscosity (FV), breakdown (BD), and setback (SB) were closely related to the EQ values. Furthermore, an integrated indicator—i.e., starch properties quality (SPQ)—that represented a more comprehensive characterization of rice starch, was derived based on the EQ evaluation hierarchy and weighted AC, TV, FV, BD, and SB values. The correlation between SPQ and EQ was significant (p < 0.001), and was significantly higher compared with using individual indicators. Moreover, the SPQ method requires less rice samples (i.e., 3 g of milled rice flour) and can be applied to assisted-selection for EQ in early generations of breeding. This study provid esessential technical support for the rapid and accurate identification of the EQ of progeny of indica–japonica hybrids.

Development of a novel formula for estimating the amylose content of starch using japonica milled rice flours based on the iodine absorption curve.

The apparent amylose content (AAC) is usually measured by an iodine colorimetric method using the starch as a sample. Nevertheless, it is time-consuming and labor-intensive to prepare rice starch. Therefore, we compared two methods, starch method and milled rice flour method. The former AACs were higher than the latter and correlated with pasting properties, physical properties and sensory scores better than the latter. Therefore, we developed a novel formula for estimating the AACs of starches from japonica rice cultivars using milled rice flours instead of using rice starch. The correlation coefficients of the new formula were 0.89 for calibration and 0.94 for validation, which showed that this equation can be applied to unknown japonica rice samples, and will lead to easy, rapid, and accurate iodine method to determine rice AACs using milled rice flours instead of starch. Abbreviations: AAC: apparent amylose content; RS: resistant starch; SLC: super-long chain; CD: chain length distribution; RVA: Rapid Visco Analyzer; SB: setback; BD: breakdown; Max.vis: maximum viscosity; Min.vis: minimum viscosity; Pt: pasting temperature; Cons: consistency; Final.vis: Final viscosity; SB/Cons: setback/consistency; Max/Min: maximum viscosity/minimum viscosity; Max/Fin: maximum viscosity/final viscosity.

Endogenous alpha-amylase explains the different pasting and rheological properties of wet and dry milled glutinous rice flour

Wet-milled glutinous rice flour (WMF) and dry milled glutinous rice flour (DMF) have different pasting and rheological properties but the underlying mechanism has not been defined. Dry milling methods can result in glutinous rice flour (GRF) with higher residual alpha-amylase activity and damaged starch content compared to flours prepared by wet milling methods. The addition of alpha-amylase significantly increased starch hydrolysis and reduced the peak, trough, and final viscosity of GRF gels. The pasting viscosity and dynamic modules of WMF-Water gels were significantly higher than those of DMF-Water gels. Inhibiting amylase activity significantly reduced the differences in paste viscosity and dynamic modules between WMF and DMF. Scanning electron microscopy (SEM) showed that alpha-amylase affected the microstructure of the DMF. FT-IR spectra results indicated no new formation of covalent bonds in GRF-Water or GRF-Ag gels. These results suggested that endogenous alpha-amylase influenced starch hydrolysis and subsequently the viscoelastic property of GRF gels, indicating that residual endogenous alpha-amylase explains the differences in pasting and rheological properties between WMF and DMF.

Application of pulverization and thermal treatment to pigmented broken rice: insight into flour physical, functional and product forming properties.

The utilization of rice for food purposes involves pulverization and thermal processing which may affect its quality characteristics. Hence pigmented broken rice was processed in plate mill and hammer mill followed by thermal treatment by toasting to study the physical, and functional characteristics and their effect on rice noodle quality. Results showed that plate milled rice flour showed high concentration of particles with size below 148µm particle (44%), increased redness (21%), bulk density (17%), sedimentation value (75%), damaged starch (72%), peak viscosity (17%), and caused microstructural changes compared to the hammer mill. The toasting of plate milled red and black rice flour caused an insignificant influence on particle size, color, and bulk density. However, it increased the sedimentation value to 134% and 94% and damaged starch by 44% and 19% in red and black rice flour respectively. Further, a reduction in peak viscosity (22%) in red, and increase (16%) in black, along with microstructural changes were also observed. The rice noodle prepared using plate milled, and toasted red rice flour was sensorily acceptable and exhibited excellent textural properties. The study showed that plate milling and thermal treatment significantly affect the quality characteristics of pigmented rice flour and end-product quality.

세포외 다당류를 생성하는 유산균 Weissella cibaria JNU29의 분리 및 특성과 이를 이용한 한국전통 설기떡 제조

Due to the nutritional value of rice cakes, there is renewed interest in this traditional Korean food, and thus various efforts have been made to improve its storage stability. In this study, lactic acid bacteria that produce exopolysaccharides (EPS) were isolated and their physiochemical properties were analyzed. The bacteria were used to produce ‘Sulgidduk’ (a Korean rice cake) with improved storage stability. Among the 107 strains isolated from traditional fermented foods, only five strains were confirmed to produce EPS in MRS media with 10% sucrose. Two of these strains were identified as members of the genus Weissella and three were identified as the Bacillus genus via sequence analysis of 16S rDNA. Among the five strains, the strain Weissella cibaria JNU29 was selected for application to ‘Sulgidduk’, since it is food applicable, viable in artificial gastric and bile juices, and produces the highest content of EPS (16.72 g/L). TLC and HPLC analysis showed that the EPS produced by W. cibaria JNU29 strain was a homopolysaccharide composed of only glucose. A culture solution of the W. cibaria JNU29 strain was mixed with milled rice flour to prepare ‘Sulgidduk’. After incubation for 48 h, the ‘Sulgidduk’ showed lower hardness values than that of the control without the culture solution, and the lactic acid bacteria survived to a level of 7 log CFU/g. Thus, the W. cibaria JNU29 strain, which produces EPS, can be applied for the production of ‘Sulgidduk’, as it delays retrogradation and prevents mold-induced decay to improve shelf life.

Evaluation on quality indices and retained tocopherol contents in the production of the rice-based cereal by extrusion

Rice bran is rich in vitamin E, dietary fiber, mineral and fat. In this study, puffed rice ball was made from brown or milled rice flour by using twin-screw extruder. Two feed moisture (15 and 20%) and two screw speed (200 and 250 rpm) were set, and the physicochemical properties and content of α-,β-, γ-, and δ-tocopherols were determined. The data showed that extrudates made from brown rice had a high a and b value in color, expansion ratio, water solubility index, but low in L value, bulk density and water absorption index than that made from milled rice flour. Extrudates made from brown rice flour had the higher content of α- and γ- tocopherols (4.8 and 5.7 μg/g). Regarding the effects of feed moisture and screw speed of extruder, the data showed that 15% feed moisture in flour and 250 rpm screw speed yielded to a high expansion ratio, high water solubility index, and low bulk density in the final products.

Milling affects rheological and gel textural properties of rice flour

AbstractBackground and objectiveGenerally, most milled rice is consumed as cooked grain. Nevertheless, a steady increase in new processes and products involving rice flour as a fundamental ingredient can be observed, which imposes a need for deeper knowledge of the properties of milled rice flours. The objective of this study is to investigate the effects of combinations of milling speed (750, 950, and 1,050 r/min) and milling time (20, 40, and 60 s) on the rheological and gel textural properties of waxy, low‐, and high‐amylose rice of flour.FindingsSteady shear rheological measurements revealed that a positive relationship exists between milling revolution (speed × time) and the consistency coefficient values or hysteresis area of rice flour pastes; that is, the more the total milling revolutions, the higher the viscosity and stronger the thixotropic properties. During rheological measurement, waxy and low‐amylose rice flour pastes from milled rice with higher storage moduli and lower the ratio of storage moduli and loss moduli δ exhibited more elastic properties and higher gel strength than those from unmilled rice, indicating that a more rigid structure was formed. As milling speeds and durations increased, the hardness of waxy and low‐amylose rice flour gels increased, but the adhesiveness decreased.ConclusionsThis study showed that milling speed had more pronounced effects on the extent of change than did milling time regarding steady flow and textural properties. Meanwhile, both milling speed and duration could change the properties of rice flour to different extents.Significance and noveltyThese findings provided fundamentals for the effects of combinations of milling speed and milling time on the rheological and gel textural properties of the flours produced from waxy, low‐, and high‐amylose rice grains. Moreover, this research may help enable rice millers to produce improved functional rice products with minimal processing by precise control of suitable milling conditions.

The impacts of particle size on starch structural characteristics and oil-binding ability of rice flour subjected to dry heating treatment

As a main starch source in human diet, milled rice flour has been widely used in various foods, and its particle size may impact the quality of final products. This study investigated the effects of particle size on starch structure and oil-binding ability of rice flour subjected to dry heating treatment. The results showed that fine fraction of rice flour had lower starch content. All samples showed A-type crystalline structure of starch, and this crystalline type was not changed by dry heating treatment, although the crystallinity was reduced. Rice flour with smaller size exhibited lower starch gelatinization temperatures and enthalpy change, and displayed higher hydrophobicity and oil-binding ability. The hydrophobicity of rice flour was improved by dry heating as observed from the increased three-phase contact angle, attributing to elevated surface hydrophobicity of rice protein. These results will provide guidance for developing functional ingredients with improved oil-binding ability for non-gluten foods.

Combined speed and duration of milling affect the physicochemical properties of rice flour

The properties of flour from polished rice that had been subjected to various milling conditions were investigated. Waxy, low- and high-amylose rice were milled at different speeds (1050, 950, and 750 r/min) for different durations (20, 40 and 60 s). The swelling power was increased with milling duration and speed compared to brown rice flour. The solubility of milled waxy rice flour was substantially lower than for brown rice flour, but for milled low- and high-amylose rice flour, it was unchanged or slightly reduced. The peak viscosity of low- and high-amylose rice flour was more affected by milling duration, whereas the final viscosity was more affected by milling speed. Total milling revolutions led to greater effect on pasting properties of WRF than LARF and HARF. Milling duration was a greater determinant of thermal properties than was milling speed. Milling conditions had different effects on the digestibility of different rice flours. Milling speed had less effect on digestibility than did milling duration for waxy rice flour, but speed had a greater effect on the digestibility of low- and high-amylose rice flour. This study showed that both milling duration and speed impacted the physicochemical and digestibility properties of different rice flours, but to different extents.

Pasting behaviour of high impact ball milled rice flours and its correlation with the starch structure.

The effects of rotational speed and milling time on pasting profile, particle size and morphology, damaged starch and gelatinization enthalpy of modified rice flours were analysed by response surface methodology to investigate the relationships among functional attributes and starch structure. Morphological changes were corroborated by scanning electron microscopy. Peak time (Pt), pasting temperature (PT), peak and final viscosities from rapid visco-analysis showed a significant decrease with increasing of milling severity. The reduction in final viscosity (FV up to 4770mPas), particularly for the refined flour fraction (volume median diameter, D50 < 140µm), evidenced the poor capacity of damaged starch to bind water during heating step. In comparison with native flour, the modified flours presented higher values of damaged starch (DS 5.94-16.46%), and viscosities as well as lower values of gelatinization enthalpy (ΔH 4.67-0.71J/g), Pt and PT denoting a lower resistance to shear stress and cooking. Such behavior is desirable in mixture design to enhance flour particles dispersion and to facilitate the interaction among food ingredients. Structural changes of starch were strongly associated to pasting behavior as it can be appreciated from the significant correlations founded: FV-DS, setback viscosity (SB)-DS, SB-D50, SB-ΔH. Planetary ball milling is a novel green method to obtain physically modified rice flours with distinctive characteristics regarding native flours, which could be well controlled by selecting suitable milling conditions. More studies should be required to expand the applications of the modified rice flours, in food and non-food products, with specific functional requirements.

Quality evaluation of gluten free protein rich broken rice pasta

Due to the evolving socioeconomics, government rules and changing eating habits of consumers, protein fortification is one of the important concerns regarding research and processing of foods. With the objective of development of gluten-free pasta, underestimated broken milled rice flour was used as the main raw material. For the improvement in protein content of gluten-free broken rice pasta, defatted soy flour was utilised for the partial replacement of broken rice flour by 5, 10, 15, 20 and 25%. L* value decreased whereas a* and b* increased with the increasing replacement by defatted soy flour. Textural properties like hardness and chewiness were significantly affected whereas springiness and cohesiveness were not significantly affected by the increasing replacement by defatted soy flour. Up to 15% replacement by defatted soy flour in gluten free broken rice pasta was accepted on the basis of sensory evaluation. Protein content was improved from 6.36 to 12.43% at optimised 15% level replacement of defatted soy flour.

The Effect of Variety and Processing Methods on the Functional and Chemical Properties of Rice Flour

The effect of varieties, local (Abakalike) and foreign (Mama Gold) and two processing methods, semi-dry and wet grinding methods on the characteristics of rice flour were investigated. Functional and chemical properties of the rice flour were analyzed using standard methods. The functional parameters analyzed were dispersibility, relative bulk density, swelling power and water absorption capacity while chemical parameter were moisture content, protein, ash, sugar, starch, amylase and amylopectin. The parameters were influenced by variety and processing methods. Highest dispersibility, relative bulk density and swelling power values were associated with sample A which is the foreign variety, while solubility and water absorption capacity were associated with sample B, which is the local variety, all processed by the semi-dry grinding method. The semi-dry ground rice flour produced highest protein and ash as seen in sample B, while wet milled rice flour were associated with highest moisture and starch contents. The flour produced from the local rice (Abakalike) had highest protein, ash sugar and amylose over the foreign variety with all the parameters showing significant differences.

Optimization of Near‐Infrared Reflectance Model in Measuring Gelatinization Characteristics of Rice Flour with a Rapid Viscosity Analyzer (RVA) and Differential Scanning Calorimeter (DSC)

This study compared the calibration models generated by combinations of different mathematical and preprocessing treatments as well as regression algorithms to optimize the analysis of gelatinization properties of rice flour by using near‐infrared spectroscopy, in comparison with conventional techniques of differential scanning calorimetry (DSC) and rapid viscosity analysis (RVA). A total of 220 milled rice flours were used for model construction. A model generated by the modified partial least squares regression (MPLS) with mathematical treatment “2, 8, 8, 2” (second‐order derivative computed based on eight data points, and eight and two data points in the second smoothing, respectively) and detrend preprocessing was identified as the best for simultaneously measuring onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) of DSC. MPLS/“2, 8, 8, 2”/weighted multiplicative scattering correction preprocessing was identified as the best for RVA properties. The results indicated that near‐infrared reflectance spectroscopy could be used to rapidly predict gelatinization properties of rice flour for the purposes of quality evaluation of germplasm and selection of intermediate lines in breeding programs.