Viscoelastic properties of waxy and nonwaxy rice flours, their fat and protein-free starch, and the microstructure of their cooked kernels

Effects of distribution, structure and interactions of starch, protein and cell walls on textural formation of cooked rice: A review

The constitution and forms of rice determine its processing and cooking properties and further control the cooked rice quality. As the two main components, starch and protein content correlations and their characteristics have been extensively explored. However, rice is mainly consumed as polished kernels, components distribution, cytoplasmic matrix, and cell walls work together, and the properties of extracted components or flour are difficult to reflect the quality of cooked rice accurately. Thus, this review summarizes the multi-scale structure changes of main components during real rice cooking conditions. The dynamic thermal changes and leaching behaviors in rice kernels are compared with pure starch or rice flour. The in situ changes and interactions of starch granules, protein bodies, and cell walls during cooking are reviewed. Based on this, different textural evaluation methods are compared, and the advantages and disadvantages are pointed out. The oral chewing perception and bionic chewing simulation for textual evaluation have gradually become hot. Both rice quality controllers and eating quality evaluators attempt to establish an accurate quality evaluation system with the increased demand for high-quality rice.

Effects of composition, thermal, and theological properties of rice raw material on rice noodle quality

The study aims to evaluate the relationships between characteristics of regional rice raw material and resulting quality of rice noodles. Four of most commonly used rice cultivars in Guangxi for noodles production were investigated. The results showed that compositions of rice flour primarily affected gelatinization and retrogradation, which then influenced the textural and sensory properties of rice noodles. Amylose content had strong positive correlation with peak viscosity (PV) and trough viscosity (TV) of rice flour (P < 0.01). PV and TV had strong negative correlations with adhesive strength (P < 0.01) and positive correlations with chewiness (P < 0.05), hardness, peak load and deformation at peak of rice noodles (P < 0.01). Protein content had positive correlation with the Setback of rice flour (P < 0.05), which is known to have influences on retrogradation. In addition, solubility had positive correlations with cooking loss (P < 0.01) and broken rate (P < 0.05) of rice noodles and strong negative correlation with its springiness (P < 0.01). Swelling power had negative correlation with broken rate (P < 0.05). As sensory score of rice noodles was negatively correlated with broken rate (P < 0.05) and cooking loss (P < 0.01) and positively correlated with springiness (P < 0.01), solubility and swelling power of rice flours were presumed to be useful for predicting consumer acceptability of rice noodles.

A Degradable-Renewable Ionic Skin Based on Edible Glutinous Rice Gel

Traditional wearable devices are commonly nonrecyclable and nondegradable, resulting in energy waste and environmental pollution. Here, a household degradable and renewable ionic skin based on edible glutinous rice gel is developed for a strain, temperature and salivary enzyme activity sensor. This gel depends on intermolecular and intramolecular H-bonds among amylopectin and amylose, and this presents excellent skin-like properties, including stretchability, self-healing property, and adhesion to various substrates. The glutinous rice gel-based skin sensor can be used to monitor vital signs and physiological parameters such as body temperature and heart rate. The sensor also achieves specific speech recognition and detects temperature and body micromovements, which provides the potential to reconstruct language or sensory/motor functions. More importantly, because of the excellent biocompatibility and degradability, the sensor can directly detect the activity of human salivary amylase, which is useful for diagnosing pancreas-, kidney-, and spleen-related diseases in the elderly. Finally, the raw material of ionic skin that originates from traditional grains is degradable and renewable as well as it can be used to prepare household wearable devices. Hence, this work not only extends the application of wearable electronics in daily life but also facilitates health monitoring in the elderly and improves their quality of life.

Posttranslational Modification of Waxy to Genetically Improve Starch Quality in Rice Grain

The waxy (Wx) gene, encoding the granule-bound starch synthase (GBSS), is responsible for amylose biosynthesis and plays a crucial role in defining eating and cooking quality. The waxy locus controls both the non-waxy and waxy rice phenotypes. Rice starch can be altered into various forms by either reducing or increasing the amylose content, depending on consumer preference and region. Low-amylose rice is preferred by consumers because of its softness and sticky appearance. A better way of improving crops other than downregulation and overexpression of a gene or genes may be achieved through the posttranslational modification of sites or regulatory enzymes that regulate them because of their significance. The impact of posttranslational GBSSI modifications on extra-long unit chains (ELCs) remains largely unknown. Numerous studies have been reported on different crops, such as wheat, maize, and barley, but the rice starch granule proteome remains largely unknown. There is a need to improve the yield of low-amylose rice by employing posttranslational modification of Wx, since the market demand is increasing every day in order to meet the market demand for low-amylose rice in the regional area that prefers low-amylose rice, particularly in China. In this review, we have conducted an in-depth review of waxy rice, starch properties, starch biosynthesis, and posttranslational modification of waxy protein to genetically improve starch quality in rice grains.

Investigating the structural properties and in vitro digestion of rice flours

The physicochemical properties, swelling power, solubility, and digestibility of flour from four rice varieties (black, brown, white, and waxy rice flour) were analyzed. The results showed that the black and brown rice had high-amylose percentage (21.8% and 20.5%), a relatively low percentage of starch content (68.1% and 79.1%), and lower swelling power (6.6% and 7.6%) and solubility (13.5% and 15.7%), respectively. Waxy rice flour attributed to lower gelatinization temperatures and higher enthalpy values. Meanwhile, the brown, black, and white rice showed higher gelatinization temperature and lower enthalpy value. The black and brown rice flour exhibited lower pasting and viscosity values as compared to waxy rice flour. The results showed that all rice flour had an A-type X-ray diffraction pattern, and after cooking all rice flour showed V-type polymorphs except waxy rice flour. Brown and black rice flour after cooking have lower digestion rate than white rice and waxy rice flour, probably due to its lower expansion and solubility rates, and higher gelatinization temperature.

Sonication increases the porosity of uncooked rice kernels affording softer textural properties, loss of intrinsic nutrients and increased uptake capacity during fortification

This work investigates the effect of sonication on brown and milled rice grains of both waxy and non-waxy varieties. We report herein the microstructural analysis of uncooked rice kernels under sonication and its effect on the textural properties. X-ray computed tomography results showed the formation of microporous surfaces and the creation of cracks and fissures. Sonication increased the % porosity of the rice samples allowing for easy penetration of water during the cooking process and promotes softer texture. Moreover, the effect of sonication in brown rice resulted to the decrease in endogenous iron and phosphorus contents but increased its capacity for iron uptake through fortification when sonicated rice is soaked in the mineral solution.

Efficient fortification of folic acid in rice through ultrasonic treatment and absorption

Folate deficiencies are prevalent in countries with insufficient food diversity. Rice fortification is seen as a viable way to improve the daily intake of folates. This work reports an efficient process of rice fortification involving ultrasonic treatment and absorption of the folic acid fortificant. Increased porosity due to sonication allowed the efficient absorption of folic acid into the brown rice kernel up to 5.195 × 10⁴ μg/100 g, a 1,982-fold increase from its inherent content. The absorbed folic acid in brown rice has 93.53% retention after washing and cooking. Fortification of ultrasound-treated milled rice with folic acid was also efficient affording 6.559 × 10⁴ μg/100 g, a 4,054-fold increase from its basal content. The effect of fortification caused a decrease in the thermal and pasting temperatures. The fortification also caused yellow coloration, decrease in hardness, and increase in the adhesiveness of the rice. The resulting fortified brown rice showed improved textural properties favorable for consumers.

Characteristics of pasting properties and morphology changes of rice starch and flour under different heating modes

The pasting behavior of rice starch and its relationship with cooking properties of rice have been extensively studied. However, the viscosity changes of rice starch and flour under conventional cooking mode and high temperature and high pressure (HTHP) mode remain unknown. In this study, three typical rice starches and seven rice flours of different types and varieties were used to evaluate the effect of cooking modes on their pasting behaviors. A detailed discussion about the relationships among chemical composition, thermal properties, and crystallinity were conducted to explain the different pasting behaviors of the rice samples. The pasting behavior of rice starch was found to be similar with rice flour under standard and conventional heating modes, while remarkably different when treated at different HTHP levels, especially for sticky rice flour. The morphological changes of rice samples at 95 °C and 120 °C confirmed that high temperature long time heating caused extending of molecules, which exhibited layered structure at 120 °C. The rice flour samples showed different morphologies after heating at different modes due to varied amylose content and crystallinity, which contributed to different pasting behavior. These results provide useful information for developing strategies to control rice cooking and improve eating quality.

Pasting, rheological, and retrogradation properties of low-amylose rice starch with date syrup

Effects of date syrup on pasting, rheological, and retrogradation properties of low-amylose rice starch were investigated using three levels of date syrup (starch:syrup 1:1, 1:2, or 1:3). Measurements were carried out using HR-2 Discovery Rheometer equipped with a pasting cell and parallel plate geometry. The pasting measurements showed that the peak viscosity of the control is significantly higher than the samples with date syrup (p < 0.05), while the final viscosity increases with increased date syrup levels. Addition of date syrup increases the solid-like behavior of the gel in reverse order with increased date syrup levels. Low-amylose starch gel used in this study showed minor changes in elastic modulus (G') during one week cold storage indicting that low-amylose rice starch is resistant to retrogradation. Addition of date syrup slightly resulted in increased retrogradation compared to the control.

Identification of the main retrogradation-related properties of rice starch

The retrogradation of rice in shelf life is the biggest barrier to the industrial production of traditional foods using rice as material. Many rice breeders have tried their best to screen low-retrogradation rice cultivars without a specific indicator. To identify the main retrogradation-related properties of rice, the starch, amylose, and amylopectin from 16 rice cultivars were extracted from rice powder and their physicochemical properties, such as visible absorbance, infrared, average molecule weight (amylopectin), chain-length distribution (amylopectin), X-ray diffraction, and differential scanning calorimetry, were determined. The correlation between starch retrogradation rates and those physicochemical properties was investigated. The results show that a significant positive correlation (R(2) = 0.85; r = 0.926; p < 0.01) exists only between proportions of the chains [degree of polymerization (DP) > 10] in amylopectin and the retrogradation rates of different rice starches. The findings in the paper offer a shortcut for rice breeders to screen cultivars with a low retrogradation rate. Because the genes related to the branching enzyme control the DP of amylopectin, they can be exploited as molecular markers to screen low-retrogradation rice cultivars.

Effect of wide variation of the Waxy gene on starch properties in hull-less barley from Qinghai-Tibet plateau in China

Granule-bound starch synthase I (GBSS I) plays an important role in the synthesis of amylose and in the determination of starch properties in barley grains. Genomic DNAs for the Waxy gene encoding GBSS I protein were sequenced from 34 barley accessions or lines from Qinghai-Tibet plateau in China, to identify Waxy gene nucleotide variations and study the roles of polymorphic sites of the Waxy gene on expression levels of Waxy transcripts and GBSS I proteins and on resulting starch properties. A total of 116 DNA polymorphic sites were identified within the barley Waxy gene, which divided the studied accessions into 11 haplotypes. Among 33 nucleotide polymorphic sites in coding regions, 5 SNPs in three exons were found to play different roles on the expression level of the Waxy transcript and the GBSS I protein and on the amylose content and starch properties. One SNP G(3935)-to-T substitution in the 10th exon in the accession Z999 (HP II-2) caused a high expression level of the Waxy transcript and the GBSS I protein and the amylose free phenotype. The other SNP alteration was a C(2453)-to-T in the fifth exon in the accession Z1191 (HP I-5), which drastically reduced the expression level of the Waxy transcript and the GBSS I protein and, finally, produced the amylose free phenotype. Three SNPs in the seventh exon in the accession Z1337 (HP I-6) did not significantly change the level of Waxy transcript, the GBSS I protein, and starch properties, except obviously reducing the breakdown value of starch viscosity and extending the peak time. A total of 84 DNA polymorphic sites were found in the noncoding regions. A 403 bp deletion at 5'UTR in the accession Z1979 (HP I-3) had low transcript level, low GBSS I protein level, and low amylose content due to the deletion of cis-acting DNA regulatory elements. A 191 bp insertion and a 15 bp insertion in the first intron and second exons, respectively, may be closely related to a higher transcript level of the Waxy gene and significant differences in some starch properties of the Waxy I DNA group as compared to the Waxy II DNA group. This study indicates the specific variations of the Waxy gene have a great effect on amylose synthesis and starch properties of hull-less barley, which could be very useful to produce new barley with variable starch properties.

Differences between easy- and difficult-to-mill chickpea (Cicer arietinum L.) genotypes. Part II: protein, lipid and mineral composition

BACKGROUND

Part I introduced the concept of easy- and difficult-to-mill chickpea genotypes, the broad chemical composition of their seed fractions and proposed mechanistic explanations for physical differences consistent with observed variation in milling ease. Part II continues this research by delving deeper into the amino acid, fatty acid and mineral components.

RESULTS

No association between fatty acid composition and ease of milling was observed. However, particular amino acids and mineral elements were identified that further support roles of lectins, pectins and mineral-facilitated binding in the adhesion of chickpea seed coat and cotyledons.

CONCLUSION

These differences suggest underlying mechanisms that could be exploited by breeding programmes to improve milling performance. This study shows that the content and composition of amino acids, fatty acids and minerals within different chickpea tissues vary with seed type (desi and kabuli) and within desi genotypes in ways that are consistent with physical explanations of how seed structure and properties relate to milling behaviour.

Differences between easy- and difficult-to-mill chickpea (Cicer arietinum L.) genotypes. Part I: broad chemical composition

BACKGROUND

Ease of milling is an important quality trait for chickpeas (Cicer arietinum L.) and involves two separate processes: removal of the seed coat and splitting of cotyledons. Four chickpea genotypes (two desi types, one kabuli type and one interspecific hybrid with 'wild' C. echinospermum parentage) of differing ease of milling were examined to identify associated seed composition differences in the seed coat, cotyledons and their junctions (abaxial and adaxial).

RESULTS

Several components in different fractions were associated with ease of milling chickpea seeds: primarily soluble and insoluble non-starch polysaccharides (including pectins) and protein at the seed coat and cotyledon junctions, and the lignin content of the seed coat.

CONCLUSION

This study shows that the chemical composition of chickpea does vary with seed type (desi and kabuli) and within desi genotypes in ways that are consistent with physical explanations of how seed structure and properties relate to milling behaviour.