Relationships between transparency, amylose content, starch cavity, and moisture of brown rice kernels

Deciphering the Role of Waxy Gene Mutations in Enhancing Rice Grain Quality

Amylose content (AC) stands as a pivotal determinant of rice grain quality, primarily governed by the Waxy gene (Wx). The allelic variation within this gene, particularly the presence of the Wxmp allele derived from the ancestral Wxmq allele, significantly influences AC and is prevalent among soft japonica rice varieties in southern China. Although both alleles are associated with lower AC, there remains a paucity of detailed understanding regarding the interplay between specific functional single nucleotide polymorphisms (SNPs) within these alleles and the overarching rice grain quality. To investigate this, we engineered three distinct transgenic rice lines, each harboring the Wxmp, Wxmq, or Wxb-5c alleles in the background of the glutinous rice cultivar Nip(wx). This suite of transgenic rice lines showcased varying degrees of grain transparency inversely correlated to AC, which in turn influenced other physicochemical properties of the rice grains, such as taste value of cooked rice, gel consistency, and starch pasting properties. Additionally, analyses of gene expression and enzyme activity revealed that the functional SNPs, Ex4-53G to A and Ex5-53T to C, lead to a decline in the activity of granule-bound starch synthase I (GBSSI) without altering expression levels.

A new source of starchy flour: Physicochemical and nutritional properties of starchy kiwifruit flour

The physicochemical and nutritional properties of three starchy kiwifruit flour (SKF) were systematically studied. The results revealed that the total starch content of SKF was 66.63-80.42%. SKF showed a B-type crystal structure with a grain size between 7.08 and 9.02 μm. In comparison to corn starch and potato starch, SKF possessed a lower pH (3.43-4.28), transparency (0.68-1.11%) and setback value (0.20-1.73 Pa·s) and a higher swelling power (9.42-15.02 g/g) and hot paste viscosity (1.73-2.10 Pa·s). Moreover, SFK was rich in protein and various mineral elements. It also contained high levels of total phenolics and exhibited a strong antioxidant capacity. The resistant starch content in SKF was as high as 67.19-73.22%, and the rapidly digestible starch content was remarkably lower than that of corn and potato starch. Overall, these unique physicochemical properties of SKF, coupled with its nutritional benefits, give it a good development potential in the food industry.

A comparative study of grain quality and physicochemical properties of premium japonica rice from three typical production regions

Grain quality indicates rice commodity value. This research compared grain quality and physicochemical properties of premium japonica rice from three production regions, Yangtze River downstream of China (YRDCN), Northeast region of China (NECN) and Japan. Results showed that there were distinct quality and physicochemical characteristics variance among the three groups of japonica rice, while CVs of most quality parameters from low to high was Japan, YRDCN and NECN. YRDCN rice presented obvious lower apparent amylose content (AAC) and ratio of each chain-length sections of amylopectin, and showed higher protein contents especially glutelin and ratio in short and intermediate amylopectin molecules. Among three rice groups, YRDCN rice presented weaker appearance, whereas did not show inferior cooking and eating properties, which was primarily linked to lower AAC. Rice AAC and starch fine structure significantly correlated with pasting parameters, swelling power and solubility, while protein content had close relation with taste analyzer parameters. Results of this study indicated improvement direction for japonica rice of YRDCN, and also provided reference for consumers' rice purchasing selection in accordance with individual taste preference.

Nitrogen fertilizer affects the cooking quality and starch properties of proso millet (Panicum miliaceum L.)

Nitrogen has a critical influence on the yield and quality of proso millet. However, the exact impact of nitrogen on the cooking quality of proso millet is not clear. In this study, the cooking quality and starch properties of two proso millet varieties (waxy-Shaanxi millet [wSM] variety and non-waxy-Shaanxi millet [nSM] variety) were compared and analyzed under nitrogen fertilizer treatment (N150, 150 kg/hm2) and a control group without nitrogen application (N0, 0 kg/hm2). Compared with the N0 group, the N150 treatment significantly increased protein content, amylose levels, and total yield. Employing rapid visco analyser and differential scanning calorimetry analyses, we observed that under the N150 treatment, the peak viscosity and breakdown viscosity of proso millet powder were diminished, while the setback viscosity and enthalpy values (ΔH) increased. In addition, nitrogen treatment increased the solids content in the obtained rice soup and significantly hardened the texture of the rice. At the same time, we noticed that the absorption capacity of starch in water and oil was enhanced. These results showed that nitrogen fertilizer had significant effects on the cooking quality and starch properties of proso millet.

Combined effects of SSII-2RNAi and different Wx alleles on rice grain transparency and physicochemical properties

Near-isogenic lines Nip(Wx^b/SSII-2), Nip(Wx^b/ss2-2), Nip(Wx^mw/SSII-2), Nip(Wx^mw/ss2-2), Nip(Wx^mp/SSII-2) and Nip(Wx^mp/ss2-2) in the Nipponbare (Nip) background containing the SSII-2RNAi cassette combined with different Waxy (Wx) alleles were investigated in terms of rice grain transparency and quality profiles. Rice lines carrying the SSII-2RNAi cassette displayed downregulation of SSII-2, SSII-3 and Wx genes. Introduction of the SSII-2RNAi cassette decreased apparent amylose content (AAC) in all transgenic lines, but grain transparency differed between low AAC rice lines. Grains from Nip(Wx^b/SSII-2) and Nip(Wx^b/ss2-2) were transparent, while those of rice were increasingly translucent with decreasing moisture due to cavities within starch granules. Rice grain transparency was positively correlated with grain moisture and AAC, but negatively correlated with cavity area within starch granules. Starch fine structure analysis revealed a marked increase in short amylopectin chains with DP 6-12, but a decrease in intermediate chains with DP 13-24, resulting in decreased gelatinisation temperature. Starch crystalline structure analysis showed that the transgenic rice starches have lower crystallinity and lamellar repeat distance than controls due to differences in starch fine structure. The results highlight the molecular basis underpinning rice grain transparency, and provide strategies for improving rice grain transparency.

Phenotypic differences in the appearance of soft rice and its endosperm structural basis

In view of the significant differences among genotypes in the appearance of soft rice, it is necessary to conduct research on the differences in the appearance quality of soft rice and their mechanisms. It can provide a theoretical basis for the selection and breeding of superior appearance varieties at a later stage. In order to clarify the differences in appearance phenotypes between different soft rice genotypes and structural basis of endosperm structures behind the differences, four soft rice varieties were selected in this study, including two varieties with good-appearance and two varieties with cloudy appearance. The differences in appearance phenotypes and endosperm structure in mature grains of soft rice with different appearance phenotypes were scientifically analyzed. The development process of their endosperm differences at the filling stage was investigated. The results show that the difference in the rice appearance of soft rice varieties mainly lay in the chalk-free seed transparency and chalkiness. These differences were caused by two completely different types of endosperm structure. Fewer and smaller starch grain cavities were responsible for higher chalk-free transparency of soft rice grains, denser starch granules arrangement caused lower chalkiness of soft rice grains. Ten days after flowering, the starch granules in the back and heart of good-appearance soft rice were already significantly fuller and more closely packed than those of cloudy soft rice. At the same time, the number and area of starch granule holes were significantly smaller than those of cloudy soft rice. This difference gradually increased until maturity. Therefore, based on appearance evaluation, soft rice with good-appearance should have higher transparency and lower chalkiness. The endosperm starch granules should be full and tightly arranged. The number of starch grain cavities and the area should be smaller. These differences develop in the early stages of grouting and gradually increase.

Loss-of-function mutations of OsbHLH044 transcription factor lead to salinity sensitivity and a greater chalkiness in rice (Oryza sativa L.)

The most hazardous abiotic stress, salinity, restricted the world crop production, and grain chalkiness affected the grain quality to limit consumers' acceptance. The basic helix-loop-helix (bHLH) proteins modulate massive biological processes in plants. Here the CRISPR/Cas9 gene editing mutants were obtained to detect the function of OsbHLH044. The loss-of-function of OsbHLH044 mutants showed numerous altered plant phenotypes. Notably, the osbhlh044 mutants resulted in prominently reduced morphological and physiological parameters under salt stress. Lower antioxidant activities and higher lipid peroxidation and hydrogen peroxide (H₂O₂) accumulation in the osbhlh044 mutants caused salinity sensitivity due to elevated reactive oxygen species (ROS). Under salt stress, both shoots and roots of the osbhlh044 mutants acquired higher Na⁺. Moreover, the expression of ion homeostasis-related genes (OsHKTs, OsHAK, OsSOSs, and OsNHX) and ABA-responsive gene (OsLEA3) was significantly altered in the osbhlh044 mutants after salt stress. The expression levels of genes coding for starch (OsAGPL1, OsSSIIa, OsWx, and OsFLO2) and seed storage proteins (GluA1 and Globulin 1) were significantly decreased, indicating that they synthesize less store starch and proteins, resulting in grain chalkiness in the osbhlh044 mutants. Yeast one Hybrid (Y1H) showed that OsbHLH044 could activate salt- (OsHKT1;3, OsHAK7, OsSOS1, OsSOS2, OsNHX2, and OsLEA3 but not OsHKT2;1), and starch-related genes (OsSSIIa, OsWx, and OsFLO2) by binding to the G-boxes of their promoters. Therefore, the OsbHLH044 gene editing mutants revealed multiple functions, specifically a positive regulator of salt stress and grain quality, which might bring new insights into the breeding of rice varieties.

Nitrogenous Fertilizer Levels Affect the Physicochemical Properties of Sorghum Starch

Nitrogen is a key factor affecting sorghum growth and grain quality. This experiment was designed to investigate the physicochemical properties of sorghum starch in four sorghum varieties (Liaoza 10, Liaoza 19, Jinza 31, and Jinza 34) under four nitrogen levels: 0 kg/ha urea (N1), 300 kg/ha urea as base fertilizer (N2), 300 kg/ha urea as topdressing at the jointing stage (N3), and 450 kg/ha urea as topdressing at the jointing stage (N4). The results showed that grain size and amylose content increased with increasing nitrogen fertilizer level, peaking at N3. The peak viscosity, final viscosity, gelatinization temperature, initial temperature, final temperature, and enthalpy value increased with the nitrogenous fertilizer level, peaking at N3. The application of nitrogen fertilizer at the jointing period significantly increased the above indicators. However, excess nitrogen at the jointing period (N4) can significantly reduce the above indicators, thus changing the physicochemical properties and structure of sorghum starch. Overall, nitrogen significantly affects the structure and physicochemical properties of sorghum starch.

Genetic control of grain appearance quality in rice

Grain appearance, one of the key determinants of rice quality, reflects the ability to attract consumers, and is characterized by four major properties: grain shape, chalkiness, transparency, and color. Mining of valuable genes, genetic mechanisms, and breeding cultivars with improved grain appearance are essential research areas in rice biology. However, grain appearance is a complex and comprehensive trait, making it challenging to understand the molecular details, and therefore, achieve precise improvement. This review highlights the current findings of grain appearance control, including a detailed description of the key genes involved in the formation of grain appearance, and the major environmental factors affecting chalkiness. We also discuss the integration of current knowledge on valuable genes to enable accurate breeding strategies for generation of rice grains with superior appearance quality.

Starch molecular structural differences between chalky and translucent parts of chalky rice grains

Chalky rice has an undesirable appearance and reduced commercial value. To understand the relationship between starch structural characteristics and chalkiness, a comprehensive investigation was conducted of molecular structural differences between starch in chalky and translucent parts of the same chalky grains (three Japonica and two Indica rices), this strategy being such as to minimize genetic and environmental effects. Compared to translucent parts, chalky parts had a larger ratio of large to small branched molecules and more short amylopectin chains (degree of polymerization < 35), but fewer longer chains, which affect higher-level starch structures, such as crystallinity. No significant differences in amylose structure were observed. White-belly and white-core chalky grains showed distinguishable starch characteristics, suggesting studying different chalkiness types separately. These findings extend understanding of chalkiness from the perspective of starch structure, and control of this structure can in the future help breeders to develop strategies against the formation of chalkiness.

The Underlying Physicochemical Properties and Starch Structures of indica Rice Grains with Translucent Endosperms under Low-Moisture Conditions

Rice grain quality is a complex trait that includes processing, appearance, eating, cooking, and nutrition components. The amylose content (AC) in the rice endosperm affects the eating and cooking quality along with the appearance of milled rice. In this study, four indica rice varieties with different ACs were used to study the factors affecting endosperm transparency along with the physical and chemical characteristics and eating quality of translucent endosperm varieties. Endosperm transparency was positively correlated with water content and negatively correlated with the cumulative area of cavities within starch granules. The indica landrace 28Zhan had a translucent endosperm and exhibited good taste. Based on starch fine structure analysis, long-chain amylopectin and the B2 chain of amylopectin might be major contributors to the good taste and relatively slow digestion of this landrace.

Optimization of ultrasonic-assisted enzymatic extraction of kiwi starch and evaluation of its structural, physicochemical, and functional characteristics

A new ultrasound-assisted enzymatic extraction (UAEE) method of starch from kiwifruit was established and optimized using response surface methodology (RSM). Under optimal conditions (the pectinase-to-cellulase-to-papain ratio = 1:2:1 g/kg, solid/liquid ratio = 1:6.68, extraction pH = 5.23, ultrasound power = 300 W, and extraction temperature = 52 °C), the kiwi starch (KS) yield was about 4.25%, and the starch content of KS was 873.23 mg/g. Compared to other extraction methods, UAEE can obtain KS with high yield and purity with a shorter extraction time and less solvent and enzyme. The extracted KS has a low gelatinization enthalpy (8.02 J/g) and a high peak viscosity (7933 cP), with obvious particle properties and low adhesion. In addition, KS is rich in polyphenols, has strong antioxidant activity, and has higher contents of amylose starch (30.74%) and resistant starch (60.18%). This study established a novel and highly efficient method for KS extraction and suggest several possible applications for KS in the food industry.

Agro-morphological and genetic diversity studies in Rice (Oryza sativa L.) germplasm using microsatellite markers

BACKGROUND

Knowledge of the genetic diversity and population structure of germplasm collections is an important foundation for crop improvement. Rice production across a broad range of rice-growing environments results in a diverse array of local rice varieties. Many rice varieties have been lost as a result of biodiversity loss and are now grown in Pakistan.

METHODS AND RESULTS

To protect the biodiversity of rice varieties, an experiment was carried out to check the genetic and morphological variations between 8 exotic and 7 local rice genotypes, using 5 different SSR markers, i.e., RM3, RM259, RM341, RM520, and RM11943. The analysis of morphological and quality traits of rice observed significant variation across genotypes. The results revealed that genotype Irri-Pak attained the highest plant height and primary branch plant-1, while genotype Mushkan produced a higher number of productive tillers and obtained a higher fertility factor (%). Similarly, the highest value for panicle length was observed for genotype Faker-e-Malakand, 1000-grains weight in genotype Calmochi, and maximum days to maturity was noticed in genotype Swati-2014. Moreover, the genotype Brio attained the highest value of stem diameter, while maximum seed length was noted in the genotype Sug Dasi. The highest number of primary branches plant^-1 in genotype Ibge-I and secondary branches plant^-1 in genotype Calmochi were noticed. A higher concentration of sodium and potassium was observed for the genotype Marte, while the genotype Muskan attained the maximum content of copper. Moreover, the highest concentration of iron in genotype Originario, zinc in genotype JP-5, and cadmium content were noticed in genotype Ibge. Similarly, the dendrogram analysis for quantitative parameters showed three clusters at 74.13% similarities. Whereas all the genotypes of European origin formed a separate cluster. A set of 5 simple sequence repeat primers, covering four chromosomes, amplified a total of 14 alleles and showed 100% polymorphism with an average PIC value ranging from 0.39 to 0.91. The UPGMA cluster analysis separated the 15 rice genotypes into 3 main groups based on 32.5% similarities and the highest genetic distance (45.1%) was observed between two genotypes (Fakher-e-malakand and Musa), having different geographical origins. There was no genetic distance between the genotypes Marte and Brio, irrespective of having the same origin.

CONCLUSIONS

The maximum genetic distances were noted for genotype, Fakhre-e-Malakand and Musa having a different origin, while the minimum genetic distance was shown by genotypes, Marte and Onice, from the same origin.

Comparative Study of Physicochemical Properties and Starch Granule Structure in Seven Ginkgo Kernel Flours

Ginkgo biloba L. is an important economic tree species in China, and its kernels have been used as a popular food in Asian countries. Herein, the morphology, basic chemical components, starch granule structures, and physicochemical properties of kernel flours from seven ginkgo cultivars were investigated, and their relationships were analyzed. The kernels were oval or spherical in shape, with variable sizes. The starch granules exhibited both regular and irregular Maltese cross patterns. Amylose was mainly distributed in amorphous growth rings. A spatial variation in the 865/942 cm-1 ratio was observed within individual starch granules. Variations in total starch content, apparent amylose content (AAC), crude protein content (CPC), total amino acid content (TAAC), starch fine structure, and thermal and pasting properties were observed among the seven kernel flours. Pearson correlation coefficients and principle component analyses showed that the thermal properties were affected by kernel CPC, TAAC, AAC, and starch fine structure, while the pasting properties were affected by AAC and starch fine structure. Furthermore, experiments showed that the seed protein structure and α-amylase activity affected the pasting properties of ginkgo kernel flours.

Influence of starch fine structure and storage proteins on the eating quality of rice varieties with similar amylose contents

BACKGROUND

Rice eating quality largely dictates consumer preference, and the demand for new rice varieties with excellent eating quality from farmers is increasing. Identification of factors contributing to eating quality is helpful for developing high-quality rice varieties.

RESULTS

Two groups of rice with different apparent amylose content (AACs) were used in this study. One group contained four varieties with low AACs (8.8-9.4%), whereas the other contained four traditional varieties with medium AACs (17.2-17.5%). The physicochemical properties, starch fine structure and crystallinity and storage protein composition of the two groups were analyzed. We found that, in both groups, the rice varieties with high eating quality had more short-chain amylopectin, lower glutelin and prolamin content, and a higher albumin content. In addition, the low-AAC varieties produced opaque endosperms, which may result from an increased number of pores in the center of starch granules.

CONCLUSIONS

Both the fine structure of starch and the storage protein composition were closely related to rice eating quality. In both groups, short branch-chain amylopectin, short-chain amylopectin [degree of polymerization (DP) 6-12], and albumin had positive effects on eating quality. By contrast, long branch-chain amylopectin, long-chain amylopectin (DP 35-60), glutelin and prolamin had adverse effects on eating quality of rice. © 2020 Society of Chemical Industry.

A rare Waxy allele coordinately improves rice eating and cooking quality and grain transparency

In rice (Oryza sativa), amylose content (AC) is the major factor that determines eating and cooking quality (ECQ). The diversity in AC is largely attributed to natural allelic variation at the Waxy (Wx) locus. Here we identified a rare Wx allele, Wx^mw , which combines a favorable AC, improved ECQ and grain transparency. Based on a phylogenetic analysis of Wx genomic sequences from 370 rice accessions, we speculated that Wx^mw may have derived from recombination between two important natural Wx alleles, Wxⁱⁿ and Wx^b . We validated the effects of Wx^mw on rice grain quality using both transgenic lines and near-isogenic lines (NILs). When introgressed into the japonica Nipponbare (NIP) background, Wx^mw resulted in a moderate AC that was intermediate between that of NILs carrying the Wx^b allele and NILs with the Wx^mp allele. Notably, mature grains of NILs fixed for Wx^mw had an improved transparent endosperm relative to soft rice. Further, we introduced Wx^mw into a high-yielding japonica cultivar via molecular marker-assisted selection: the introgressed lines exhibited clear improvements in ECQ and endosperm transparency. Our results suggest that Wx^mw is a promising allele to improve grain quality, especially ECQ and grain transparency of high-yielding japonica cultivars, in rice breeding programs.

Starch Components, Starch Properties and Appearance Quality of Opaque Kernels from Rice Mutants

Rice mutants with altered starch components and properties are important genetic resources in rice breeding programmes. In this study, 44 mutants with altered starch components were screened from 135 rice mutants with opaque kernels using a starch–iodine absorption spectrum method, and nine mutants from them were further selected for investigating their starch properties and kernel appearance quality. The results showed that the iodine absorption spectrum parameters, OD620, OD620/550, and λmax, could reflect the changes of starch components in rice mutants, and had significantly positive relationships with amylose content and negative relationships with the proportion of short branch-chains of amylopectin. The endosperm starches from nine mutants all showed A-type crystalline structure and similar short-range ordered structure, but had different relative crystallinities. The changes of starch components in mutants not only resulted in the different gelatinization properties of starch but also changed the appearance quality of brown rice kernels. This study provided abundant genetic plants for studying the molecular mechanism of starch synthesis and the quality regulation of rice kernels.

Genetic Variation of Physicochemical Properties and Digestibility of Foxtail Millet (Setaria italica) Landraces of Taiwan

Foxtail millet is considered a 'smart food' because of nutrient richness and resilience to environments. A diversity panel of 92 foxtail millet landraces preserved by Taiwan indigenous peoples containing amylose content (AC) in the range of 0.7% to 16.9% exhibited diverse physiochemical properties revealed by a rapid viscosity analyzer (RVA). AC was significantly correlated with 5 RVA parameters, and some RVA parameters were also highly correlated with one another. In comparison to rice, foxtail millet contained less starch (65.9-73.1%) and no significant difference in totals of resistant starch (RS), slowly digestible starch (SDS), hydrolysis index (HI), and expected glycemic index (eGI) according to in vitro digestibility assays of raw flour with similar AC. RS was significantly positively correlated with AC and four RVA parameters, cold paste viscosity (CPV), setback viscosity (SBV), peak time (PeT), and pasting temperature (PaT), implying that suitable food processing to alter physicochemical properties of foxtail millet might mitigate hyperglycemia. This investigation of pasting properties and digestibility of diverse foxtail millet germplasm revealed much variation and showed potential for multi-dimensional utilizations in daily staple food and food industries.