Analysis of Genotypic Diversity in the Starch Physicochemical Properties of Nonwaxy Rice: Apparent Amylose Content, Pasting Viscosity and Gel Texture

The effects of chain-length distributions on starch-related properties in waxy rices

Normal rice starch consists of amylopectin and amylose, whose relative amounts and chain-length distributions (CLDs) are major determinants of the digestibility and rheology of cooked rice, and are related to metabolic health and consumer preference. Here, the mechanism of how molecular structural features of pure amylopectin (waxy) starches affect starch properties was explored. Following debranching, chain-length distributions of seven waxy varieties were measured using size-exclusion chromatography, and parameterized using biosynthesis-based models, which involve breaking up the chain-length distribution into contributions from five enzyme sets covering overlapping ranges of chain length; structure-property correlations involving the fifth set were found to be statistically significant. Digestibility was measured in vitro, and parameters for the slower and longer digestion phase quantified using non-linear least-squares fitting. The coefficient for the significant correlation involving amylopectin fine structure for the fifth set was -0.903, while the amounts of amylopectin short and long chains were found to dominate breakdown viscosity (correlation coefficients 0.801 and - 0.911, respectively). This provides a methodology for finding or developing healthier starch in terms of lower digestion rate, while also having acceptable palatability. As rice breeders can to some extent control CLDs, this can help the development of waxy rices with improved properties.

Structures, gelatinization properties and enzyme hydrolyses of starches from transparent and floury grains of rices subjected to field natural extreme high temperature

Three rice varieties underwent the field natural extreme high temperature (EHT) with daily average temperature over 30 °C from 21 to 89 days after sowing, and had transparent, chalky and floury grains. The structures, gelatinization properties and enzyme hydrolyses of starches from transparent and floury grains were investigated. Compared with control transparent grains, floury grains subjected to EHT markedly decreased the contents of amylose molecules, amylopectin A chains and amylopectin B1 chains and increased the contents of amylopectin B2 and B3+ chains and the average branch-chain length of amylopectin. Both transparent and floury grains had A-type starches, but floury grain starches exhibited higher relative crystallinity, gelatinization temperature, retrogradation and pasting viscosities than transparent grain starches. Floury grain starches had lower hydrolysis rates than transparent grain starches. Native starches were more resistant to digestion but gelatinized and retrograded starches were more prone to digestion in floury grains than in transparent grains.

Transcription factor OsbZIP10 modulates rice grain quality by regulating OsGIF1

Understanding and optimizing the process of grain filling helps the quest to maximize rice (Oryza sativa L.) seed yield and quality, yet the intricate mechanisms at play remain fragmented. Transcription factors (TFs) are major players in the gene networks underlying the grain filling process. Here, we employed grain incomplete filling (OsGIF1)/cell wall invertase 2, a key gene involved in grain filling, to explore its upstream TFs and identified a bZIP family TF, OsbZIP10, to be a transcriptional activator of OsGIF1. Rice grains of the knockouts of OsbZIP10 showed increased white-core rates but lower amylose content (AC), leading to better eating and cooking qualities in all genetic backgrounds investigated, though the impact of mutations in OsbZIP10 on grain weight depended on genetic background. Multi-omics analyses suggested that, in addition to OsGIF1, multiple genes involved in different biological processes contributing to grain filling were targeted by OsbZIP10, including OsAGPS1, a gene encoding the ADP-Glc pyrophosphorylase (AGPase) small subunit, and genes contributing to homeostasis of reactive oxygen species. Distinct genetic make-up was observed in OsbZIP10 between japonica and indica rice varieties, with the majority varieties of each subspecies belonging to two different haplotypes that were closely associated with AC. Overexpressing the haplotype linked to high-AC in the low-AC genetic background increased AC. Overall, this study sheds crucial light on the significance of the OsbZIP10-OsGIF1 module in the determination of rice grain quality, offering a potential avenue for genetic engineering of rice to produce seeds with tailored attributes.

OsCRLK2, a Receptor-Like Kinase Identified by QTL Analysis, is Involved in the Regulation of Rice Quality

The quality of rice (Oryza sativa L) is determined by a combination of appearance, flavor, aroma, texture, storage characteristics, and nutritional composition. Rice quality directly influences acceptance by consumers and commercial value. The genetic mechanism underlying rice quality is highly complex, and is influenced by genotype, environment, and chemical factors such as starch type, protein content, and amino acid composition. Minor variations in these chemical components may lead to substantial differences in rice quality. Among these components, starch is the most crucial and influential factor in determining rice quality. In this study, quantitative trait loci (QTLs) associated with eight physicochemical properties related to the rapid viscosity analysis (RVA) profile were identified using a high-density sequence map constructed using recombinant inbred lines (RILs). Fifty-nine QTLs were identified across three environments, among which qGT6.4 was a novel locus co-located across all three environments. By integrating RNA-seq data, we identified the differentially expressed candidate gene OsCRLK2 within the qGT6.4 interval. osclrk2 mutants exhibited decreased gelatinization temperature (GT), apparent amylose content (AAC) and viscosity, and increased chalkiness. Furthermore, osclrk2 mutants exhibited downregulated expression of the majority of starch biosynthesis-related genes compared to wild type (WT) plants. In summary, OsCRLK2, which encodes a receptor-like protein kinase, appears to consistently influence rice quality across different environments. This discovery provides a new genetic resource for use in the molecular breeding of rice cultivars with improved quality.

Correlation between in vitro starch digestibility and starch structure/physicochemical properties in rice

Natural resistant starch (RS) in rice provides human health benefits, and its concentration in rice is influenced by the structure and physicochemical properties of starch. The native starch structures and physicochemical properties of three rice varieties, QR, BR58, and BR50, and their relationships to in vitro digestibility were studied. The starch granules in all three varieties were irregular or polyhedral in shape. There were a few oval granules and a few pinhole structures in QR, no oval granules but a higher number of pinholes in BR58, and no oval granules and pinholes in BR50. QR is a low-amylose (13.8 %), low-RS (0.2 %) variety. BR58 is a low-amylose (15.3 %), high-RS (6.5 %) variety. BR50 is a high-amylose (26.7 %), high-RS (8.3 %) variety. All three starches exhibited typical A-type diffraction patterns. Starch molecular weight, chain length distribution, starch branching degree, pasting capabilities, and thermal properties differed considerably between the rice starches. The RS contents of the rice starch varieties were positively correlated with AAC, Mw/Mn, Mz/Mn, peak 3, B, PTime, and Tp and negatively correlated with Mn, peak 2, DB, PV, and BD, according to Pearson's correlation analysis. These findings may be helpful for the breeding and development of high-RS rice varieties.

CRISPR/Cas9-mediated enhancement of semi-dwarf glutinous traits in elite Xiangdaowan rice (Oryza sativa L.): targeting SD1 and Wx genes for yield and quality improvement

In rice cultivation, the traits of semi-dwarfism and glutinous texture are pivotal for optimizing yield potential and grain quality, respectively. Xiangdaowan (XDW) rice, renowned for its exceptional aromatic properties, has faced challenges due to its tall stature and high amylose content, resulting in poor lodging resistance and suboptimal culinary attributes. To address these issues, we employed CRISPR/Cas9 technology to precisely edit the SD1 and Wx genes in XDW rice, leading to the development of stable genetically homozygous lines with desired semi-dwarf and glutinous characteristics. The sd1-wx mutant lines exhibited reduced gibberellin content, plant height, and amylose content, while maintaining hardly changed germination rate and other key agronomic traits. Importantly, our study demonstrated that exogenous GA3 application effectively promoted growth by compensating for the deficiency of endogenous gibberellin. Based on this, a semi-dwarf glutinous elite rice (Oryza sativa L.) Lines was developed without too much effect on most agronomic traits. Furthermore, a comparative transcriptome analysis unveiled that differentially expressed genes (DEGs) were primarily associated with the anchored component of the membrane, hydrogen peroxide catabolic process, peroxidase activity, terpene synthase activity, and apoplast. Additionally, terpene synthase genes involved in catalyzing the biosynthesis of diterpenoids to gibberellins were enriched and significantly down-regulated. This comprehensive study provides an efficient method for simultaneously enhancing rice plant height and quality, paving the way for the development of lodging-resistant and high-quality rice varieties.

Understanding the Relationship between the Molecular Structure and Physicochemical Properties of Soft Rice Starch

The relationship between the molecular structure and physicochemical properties of soft rice starch (SRS) has been investigated in this research. The amylose content of SRS ranged from 10.76% to 11.85%, classified as the very low amylose type. Compared to waxy and japonica rice starch, the largest amount of small starch granules and the highest viscosity were shown in the SRS. The results of X-ray diffraction and Fourier transform infrared proved that the SRS depicted a typical A-type pattern with a low short-range ordered structure. Additionally, SRS had a great deal of A and B1 chains. Molecular weights and density of starch from soft rice were lower than those from waxy rice but higher than those from japonica rice. Furthermore, SRS possessed a higher amount of resistant starch. Correlation analysis indicated that the amylose content and the chain-length distributions of amylopectin play a major role in influencing the molecular structure and physicochemical properties of rice starch. In conclusion, the low amylose content, highest viscosity, and other excellent properties of soft rice starch make it have bright application prospects in instant rice and rice cakes.

In vitro fecal fermentation characteristics of mutant rice starch depend more on amylose content than crystalline structure

To obtain the relation between rice starch features and fermentation characteristics, rice starches with various polymorphic types and apparent amylose contents were subjected to in vitro fecal fermentation. Gas and short-chain fatty acid production was evaluated as a function of fermentation time, and the microbial responses were monitored by 16S rRNA sequencing technique at the end of fermentation. Regardless of polymorphic type, three high-amylose mutant rice starches (i.e., GM03, A-type; BP577, B-type; Wx21TT, C-type) displayed significantly slower fermentation rate during the first 12 h and higher final butyrate yield (17.6-17.9 mM) compared to the A-type normal starches (9311 and Wx22TT), and promoted the proliferation of Roseburia. However, A-type normal rice starches presented higher propionate production, and increased the growth of Bacteroides and Megamonas. The principal component and redundancy analyses indicated that three high-amylose mutant rice starches showed similar abundance and migration of microbial communities, and the apparent amylose content was closely correlated with the abundance of their five key amplicon sequence variants. Our results demonstrated that amylose content might be a controlling factor in determining the fermentation properties of rice starches than crystalline structure.

High-amylose maize starch: Structure, properties, modifications and industrial applications

High-amylose maize refers to a special type of maize cultivar with a 50 %-90 % amylose content of the total starch. High-amylose maize starch (HAMS) is of interest because it possesses unique functionalities and provides many health benefits for humans. Therefore, many high-amylose maize varieties have been developed via mutation or transgenic breeding approaches. From the literature reviewed, the fine structure of HAMS is different from the waxy and normal corn starches, influencing its gelatinization, retrogradation, solubility, swelling power, freeze-thaw stability, transparency, pasting and rheological properties, and even in vitro digestion. HAMS has undergone physical, chemical, and enzymatical modifications to enhance its characteristics and thereby broaden its possible uses. HAMS has also been used for the benefit of increasing resistant starch levels in food products. This review summarizes the recent developments in our understanding of the extraction and chemical composition, structure, physicochemical properties, digestibility, modifications, and industrial applications of HAMS.

Combined Effects of BEIIb and SSIIa Alleles on Amylose Contents, Starch Fine Structures and Physicochemical Properties of Indica Rice

Starch branching enzyme IIb (BEIIb) and soluble starch synthase IIa (SSIIa) play important roles in starch biosynthesis in cereals. Deficiency in the BEIIb gene produces the amylose extender (ae) mutant rice strain with increased amylose content (AC) and changes in the amylopectin structure. The SSIIa gene is responsible for the genetic control of gelatinization temperature (GT). The combined effects of BEIIb and SSIIa alleles on the AC, fine structures, and physicochemical properties of starches from 12 rice accessions including 10 recombinant inbred lines (RIL) and their two parents were examined in this study. Under the active BEIIb background, starches with the SSIIa-GC allele showed a higher GT than those with the SSIIa-TT allele, resulting from a lower proportion of A chain and a larger proportion of B1 chains in the amylopectin of SSIIa-GC. However, starch with the BEIIb mutant allele (be2b) in combination with any SSIIa genotype displayed more amylose long chains, higher amylose content, B2 and B3 chains, and molecular order, but smaller relative crystallinity and proportion of amylopectin A and B1 chains than those with BEIIb, leading to a higher GT and lower paste viscosities. These results suggest that BEIIb is more important in determining the structural and physicochemical properties than SSIIa. These results provide additional insights into the structure-function relationship in indica rice rather than that in japonica rice and are useful for breeding rice with high amylose content and high resistant starch.

Understanding the texture and digestibility attributes of rice noodles supplemented with common vetch starch

The effects of common vetch starch (CVS) substitution on rice noodle quality were investigated, aiming to improve their texture and reduce starch digestibility. The CVS had larger granule sizes, higher amylose content and more long branch chains compared with rice starch (RS). When the CVS substitution level was 20 %, the rice noodles had the best texture quality, as the mixtures with more total starch and amylose could form denser gel structures. Moreover, the starch chains were easier to rearrange to form double helix ordered structures, resulting in a slower digestion rate. With the further increase of CVS, the noodle structure weakened and the starch digestion rate increased. This was due to the formation of looser gel structures and less ordered structures as RS granules could be easily separated into different parts by large amount of CVS with larger granule sizes, and RS with more short chains tended to be cross-linked with RS during retrogradation. With increasing CVS substitution level, the estimated glycemic index (eGI) of rice noodles decreased and then tended to be stable. Therefore, appropriate CVS substitution could improve the texture quality of rice noodles and reduce the eGI value, and the best substitution level was 20 %.

qFC6, a major gene for crude fat content and quality in rice

qFC6, a major quantitative trait locus for rice crude fat content, was fine mapped to be identical with Wx. FC6 negatively regulates crude fat content and rice quality. Starch, protein and lipids are the three major components in rice endosperm. The lipids content in rice influences both storage and quality. In this study, we identified a quantitative trait locus (QTL), qFC6, for crude fat (free lipids) content through association analysis and linkage analysis. Gene-based association analysis revealed that LOC_Os06g04200, also known as Wx, was the candidate gene for qFC6. Complementation and knockout transgenic lines revealed that Wx negatively regulates crude fat content. Lipid composition and content analysis by gas chromatography and taste evaluation analysis showed that FC6 positively influenced bound lipids content and negatively affected both free lipids content and taste. Besides, higher free lipids content rice varieties exhibit more lustrous appearance after cooking and by adding extra oil during cooking could improve rice luster and taste score, indicating that higher free lipids content may make rice more lustrous and delicious. Together, we cloned a QTL coordinating rice crude fat content and eating quality and assisted in uncovering the genetic basis of rice lipid content and in the improvement of rice eating quality.

Effects of Wx Genotype, Nitrogen Fertilization, and Temperature on Rice Grain Quality

Quality is a complex trait that is not only the key determinant of the market value of the rice grain, but is also a major constraint in rice breeding. It is influenced by both genetic and environmental factors. However, the combined effects of genotypes and environmental factors on rice grain quality remain unclear. In this study, we used a three-factor experimental design to examine the grain quality of different Wx genotypes grown under different nitrogen fertilization and temperature conditions during grain development. We found that the three factors contributed differently to taste, appearance, and nutritional quality. Increased Wx function and nitrogen fertilization significantly reduced eating quality, whereas high temperature (HT) had almost no effect. The main effects of temperature on appearance quality and moderate Wx function at low temperatures (LTs) contributed to better appearance, and higher nitrogen fertilization promoted appearance at HTs. With regard to nutritional quality, Wx alleles promoted amylose content (AC) as well as starch-lipids content (SLC); nitrogen fertilization increased storage protein content (PC); and higher temperature increased lipid content but decreased the PC. This study helps to broaden the understanding of the major factors that affect the quality of rice and provides constructive messages for rice quality improvement and the cultivation of high-quality rice varieties.

Development of Certified Reference Materials for the Determination of Apparent Amylose Content in Rice

Apparent amylose content (AAC) is one of the most important parameters in rice quality evaluation. In this study, four rice reference materials used to test rice AAC were developed. The AAC of rice reference materials were measured by a spectrophotometric method with a defatting procedure, calibrated from potato amylose and waxy rice amylopectin at the absorption wavelengths of 620 and 720 nm. Homogeneity test (n = 20) was judged by F-test based on the mean squares of among and within bottles, and short- and long-term stability monitoring was performed by T-test to check if there was significant degradation at the delivery temperature of under 40 °C (14 days) and at 0–4 °C storage condition (18 months), respectively. After joint evaluation by ten laboratories, Dixion and Cochran statistical analyses were presented. The expanded uncertainties were calculated based on the uncertainty of homogeneity, short- and long-term stability, and inter-laboratory validation containing factor k = 2. It found that the four reference materials were homogenous and stable, and had the AAC (g/100 g, k = 2) of 2.96 ± 1.01, 10.68 ± 0.66, 17.18 ± 1.04, and 16.09 ± 1.29, respectively, at 620 nm, and 1.46 ± 0.49, 10.44 ± 0.56, 16.82 ± 0.75, and 24.33 ± 0.52, respectively, at 720 nm. It was indicated that 720 nm was more suitable for the determination of rice AAC with lower uncertainties. The determinations of the AAC of 11 rice varieties were carried out by two methods, the method without defatting and with calibration from the four rice reference materials and the method with a defatting procedure and calibrating from potato amylose and waxy rice amylopectin. It confirmed that the undefatted rice reference materials could achieve satisfactory results to test the rice samples with the AAC ranging from 1 to 25 g/100 g. It would greatly reduce the time cost and improve testing efficiency and applicability, and provide technical support for the high-quality development of the rice industry.

Physicochemical, Nutritional, and Antioxidant Properties in Seven Sweet Potato Flours

Sweet potato flour is a key ingredient for the production of new food products worldwide, which imparts desired properties, nutritional value, antioxidants, and natural color to processed foods. However, little information regarding the functional properties of the sweet potato flour is available. In this study, the genetic diversity in the physiochemical, nutritional, and antioxidant properties of wholemeal flour from seven sweet potato varieties was investigated. The total phenolic content (TPC) of the free and bound fractions ranged from 13.85 to 90.74 mg gallic acid equivalent (GAE)/100 g and from 5.07 to 24.29 mg GAE/100 g, respectively. The average protein content of sweet potato was 5.41 g/100 g ranging from 3.40 to 8.60 g/100 g DW. The total amino acid content averaged 45.13 mg/g DW. The average contents of 12 mineral elements were in the order of K > P > Ca > Mg > Mn > Fe > Zn > Cu > Ni > Se > Cr > Cd. K and P contents were the highest among all accessions, which were positively correlated with most of the other minerals. The average starch content of sweet potato was 53.90 g/100 g DW, ranging from 31.68 to 64.90%. The peak viscosity (PV), hot paste viscosity (HPV), and cold paste viscosity (CPV) were in the range of 90.7-318.8 Rapid Visco Unit (RVU), 77.3-208.3 RVU, and 102.6-272.7 RVU, respectively. The hardness values and cohesiveness (Coh) varied among different sweet potatoes, with a range of 8.20-18.48 g and 0.22-0.68, respectively. The gelatinization onset, peak, conclusion temperatures, and enthalpy were in the ranges of 59.39-71.91°C, 70.19-88.40°C, 78.98-95.79°C, 1.85-5.65 J/g, respectively.

Natural variation in WHITE-CORE RATE 1 regulates redox homeostasis in rice endosperm to affect grain quality

Grain chalkiness reduces the quality of rice (Oryza sativa) and is a highly undesirable trait for breeding and marketing. However, the underlying molecular cause of chalkiness remains largely unknown. Here, we cloned the F-box gene WHITE-CORE RATE 1 (WCR1), which negatively regulates grain chalkiness and improves grain quality in rice. A functional A/G variation in the promoter region of WCR1 generates the alleles WCR1A and WCR1G, which originated from tropical japonica and wild rice Oryza rufipogon, respectively. OsDOF17 is a transcriptional activator that binds to the AAAAG cis-element in the WCR1A promoter. WCR1 positively affects the transcription of the metallothionein gene MT2b and interacts with MT2b to inhibit its 26S proteasome-mediated degradation, leading to decreased reactive oxygen species production and delayed programmed cell death in rice endosperm. This, in turn, leads to reduced chalkiness. Our findings uncover a molecular mechanism underlying rice chalkiness and identify the promising natural variant WCR1A, with application potential for rice breeding.

The role of different Wx and BEIIb allele combinations on fine structures and functional properties of indica rice starches

This study examined the effects of the combinations of Waxy (Wx) and starch branching enzyme IIb (BEIIb) alleles on starch fine structure and functional properties in indica rice cultivars. The results showed that be2b mutant starches with BEIIb deficiency had higher amylose content, shorter amylose long chains, a higher proportion of amylopectin long chains and molecular order, but a lower proportion of amylopectin short chains and relative crystallinity, resulting in higher gelatinization temperature but lower enthalpy and paste viscosity. Compared with the rice lines carrying Wx^b allele, Wx^a allele contributed to relatively higher amylose content, longer amylopectin chains, less short-range ordered structure and lower relative crystallinity, leading to a little lower gelatinization enthalpy. This study provides new insight into structure-function relations among rice lines with different allele combinations of starch synthesis related genes, which is a useful strategy for rice quality breeding.

Fine mapping of qWCR7, a grain chalkiness QTL in rice

Chalkiness is one of the key determinants of rice quality and is a highly undesirable trait for breeding and marketing. In this study, qWCR7, a major quantitative trait locus (QTL) of white-core rate (WCR), was genetically validated using a BC3F2 segregation population and further fine mapped using a near isogenic line (NIL) population, of which both were derived from a cross between the donor parent DL208 and the recurrent parent ZS97. qWCR7 was finally narrowed to a genomic interval of ~ 68 kb, containing seven annotated genes. Among those, two genes displayed markedly different expression levels in endosperm of NILs. Transcriptome analysis showed that the synthesis and accumulation of metabolites played a key role in chalkiness formation. The contents of storage components and expression levels of related genes were detected, suggesting that starch and storage protein were closely related to white-core trait. Our findings have laid the foundation of map-based cloning of qWCR7, which may have potential value in quality improvement during rice breeding.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-021-01260-x.

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.

Physicochemical characterizations of starches isolated from Tetrastigma hemsleyanum Diels et Gilg

Physicochemical characteristics of starch isolated from Tetrastigma hemsleyanum Diels et Gilg (T. hemsleyanum) tuber root of 4 different origins were firstly analyzed in this study. The starch granules of T. hemsleyanum tuber root were oval or globular, showed unimodal distribution with average size of 21.66-28.79 μm. T. hemsleyanum starch had typical B-type diffraction pattern. T. hemsleyanum root was rich in starch, and apparent amylose content ranged from 39.82% to 47.67%. The amylopectin chain profiles showed that over 50% of the total detectable chains had degree of polymerization (DP) with 13-24. T. hemsleyanum tuber root had high RS content, which reached up to 61.44% in flour and 68.81% in isolated starch. After cooking, the RS content decreased, but was still high up to 7.52% in flour and 9.93% in isolated starch. The peak gelatinization temperature of T. hemsleyanum starch ranged from 68.12 to 74.42 °C. The peak viscosity of T. hemsleyanum flour and starch ranged from 778 to 1258 cP and 1577 to 2009 cP respectively. The results indicate that T. hemsleyanum is a potential source for novel starch with high resistant starch and provide some guides for comprehensive utilization of T. hemsleyanum starch in food and pharmaceuticals industry.

The origin of Wxla provides new insights into the improvement of grain quality in rice

Appearance and taste are important factors in rice (Oryza sativa) grain quality. Here, we investigated the taste scores and related eating-quality traits of 533 diverse cultivars to assess the relationships between-and genetic basis of-rice taste and eating-quality. A genome-wide association study highlighted the Wx gene as the major factor underlying variation in taste and eating quality. Notably, a novel waxy (Wx) allele, Wx^la , which combined two mutations from Wx^b and Wxⁱⁿ , exhibited a unique phenotype. Reduced GBSSI activity conferred Wx^la rice with both a transparent appearance and good eating quality. Haplotype analysis revealed that Wx^la was derived from intragenic recombination. In fact, the recombination rate at the Wx locus was estimated to be 3.34 kb/cM, which was about 75-fold higher than the genome-wide mean, indicating that intragenic recombination is a major force driving diversity at the Wx locus. Based on our results, we propose a new network for Wx evolution, noting that new Wx alleles could easily be generated by crossing genotypes with different Wx alleles. This study thus provides insights into the evolution of the Wx locus and facilitates molecular breeding for quality in rice.

Breeding of High Cooking and Eating Quality in Rice by Marker-Assisted Backcrossing (MABc) Using KASP Markers

The primary goals of rice breeding programs are grain quality and yield potential improvement. With the high demand for rice varieties of premium cooking and eating quality, we developed low-amylose content breeding lines crossed with Samgwang and Milkyqueen through the marker-assisted backcross (MABc) breeding program. Trait markers of the SSIIIa gene referring to low-amylose content were identified through an SNP mapping activity, and the markers were applied to select favorable lines for a foreground selection. To rapidly recover the genetic background of Samgwang (recurrent parent genome, RPG), 386 genome-wide markers were used to select BC₁F₁ and BC₂F₁ individuals. Seven BC₂F₁ lines with targeted traits were selected, and the genetic background recovery range varied within 97.4–99.1% of RPG. The amylose content of the selected BC₂F₂ grains ranged from 12.4–16.8%. We demonstrated the MABc using a trait and genome-wide markers, allowing us to efficiently select lines of a target trait and reduce the breeding cycle effectively. In addition, the BC₂F₂ lines confirmed by molecular markers in this study can be utilized as parental lines for subsequent breeding programs of high-quality rice for cooking and eating.

Starch-lipid interaction alters the molecular structure and ultimate starch bioavailability: A comprehensive review

Starch bioavailability which results in eliciting postprandial glycaemic response, is a trait of great significance and is majorly influenced by the physical interaction among the matrix components governed by their molecular structure as well as dynamics. Among physical interactions limiting starch bioavailability, starch and any guest molecules like lipid interact together to alter the molecular structure into a compact V-type arrangement endorsing the processed crystallinity, thus limiting carbolytic enzymatic digestion and further bioavailability. Considering the importance of starch-lipid dynamics affecting bioavailability, intensive research based on endogenous (internal lipids which are embedded into the food matrix) as well as exogenous (those are added from outside into the food matrix during processing like cooking) lipids have been carried out, endorsing physical interactions at colloidal and microstructural levels. The shared insights on such binary (starch-lipid) interactions revealed the evolution of characterization techniques as well as their role on altering the functional and nutritional value. It is very much vital to have a thorough understanding about the mechanisms on the molecular level to make use of these matrix interactions in the most efficient way, while certain basic questions are still remaining unaddressed. Do starch - lipid complexation affects the ultimate starch bioavailability? If so, then whether such complexation ability depends on amylose - fatty acid/lipid content? Whether the complexation is influenced further by fatty acid type/concentration/chain length or saturation? Further comprehending this, whether the altered bioavailability by binary (starch-lipid) could further be affected by ternary (starch-lipid-protein) and quaternary (starch-lipid-protein-phenolics) interactions are also discussed in this comprehensive review.

Correlation of taste values with chemical compositions and Rapid Visco Analyser profiles of 36 indica rice (Oryza sativa L.) varieties

Yield, taste quality, and cultivar utilisation improvements are important research topics in indica rice breeding. Herein, we compared the relative effectiveness and relationship of three taste evaluation methods, namely, chemical composition, Rapid Visco Analyser (RVA), and taste analyser. We assessed associations among these methods using 36 indica varieties commonly grown in Yunnan, Sichuan, and Guizhou, China. Temperature and sunlight duration during grain filling influenced rice cooking quality. Varieties with high taste quality had low amylose and protein contents; high peak viscosities and breakdowns; and low hold viscosities, setbacks, and final viscosities. Protein and combined protein and amylose explained 38.6% and 62.1% of the variation in taste value, respectively. The RVA profile was affected by protein, amylose, and amylopectin contents and explained 60.5% of the taste-value variation. This study lays the foundation for taste evaluation of high-quality rice varieties early in the breeding process, which can improve cultivation and marketing potential.

High-energy alkaline milling as a potential physical and chemical cornstarch ecofriendly treatment to produce nixtamalized flours

In this study, hard corn grains were nixtamalized (alkali-heat treatment) by a high-energy ball mill to investigate the effects on its physicochemical, textural, and microstructural properties. Ball milling modifies the structure and properties of cornstarch. The gelatinization peak of starch was evidenced and thermal and pasting properties were significantly affected. With regard to rheological properties, the viscosity peak increased from 2454 cP in traditional nixtamalized flour to 4294 cP in high-energy milling treatments with 1.4% of Ca(OH)₂ and 20% moisture content, C1.4, while enthalpy ranged from 3.5 to 0.34 J/g, respectively. High-energy milling influenced the Fourier-Transform InfraRed Spectroscopic (FT-IR) patterns. All of the samples of the corn-grain starches presented the typical A-type X-ray diffraction pattern. The crystallinity of starch from CG showed a lower intensity in peaks 2θ ~ 15 and 23° compared with starch from WG and YG. The textural properties of the masas were influenced, adhesiveness was reduced, but cohesiveness was increased by the addition of Ca(OH)₂. In the structural characterization by E-SEM, the control presented a greater amount of agglomerated starch granules, followed by the high-energy milling treatments. The results suggest that high-energy alkaline milling could be a potential physical and chemical method to modify corn-starch properties and obtain nixtamalized products.

Starch properties of high and low amylose proso millet (Panicum miliaceum L.) genotypes are differentially affected by varying salt and pH

Variation in salt content and in pH are common in starch-based foods and can affect starch properties and final product texture. Fifteen accessions of proso millet starch with diverse amylose content were selected to investigate single factor and interaction effects of pH and NaCl on thermal, pasting, and textural properties. Pasting properties and gelatinization temperatures were markedly altered by salt addition. Changes in pH only had substantial effects on ΔH, but other properties were generally stable under different pH conditions. From two-way ANOVA, interactive effects of salt and pH were found to affect ΔH. The response of starch of different genotypes in terms of thermal and pasting properties differed under the same pH and salinity conditions. The reason is likely that ions in the starch-water system performed the roles of both reducing water activity and building of hydrogen bonds, which will have opposite effects on starch gelatinization.

Marker Assisted Gene Pyramiding (MAGP) for bacterial blight and blast resistance into mega rice variety "Tellahamsa"

Bacterial blight (BB) and fungal blast diseases are the major biotic constraints that limit rice productivity. To sustain yield improvement in rice, it is necessary to developed yield potential of the rice varieties by incorporation of biotic stress resistance genes. Tellahamsa is a well-adapted popular high yielding rice variety in Telangana state, India. However, the variety is highly susceptible to BB and blast. In this study, simultaneous stepwise transfer of genes through marker-assisted backcross breeding (MABB) strategy was used to introgress two major BB (Xa21 and xa13) and two major blast resistance genes (Pi54 and Pi1) into Tellahamsa. In each generation (from F₁ to ICF₃) foreground selection was done using gene-specific markers viz., pTA248 (Xa21), xa13prom (xa13), Pi54MAS (Pi54) and RM224 (Pi1). Two independent BC₂F₁ lines of Tellahamsa/ISM (Cross-I) and Tellahamsa/NLR145 (Cross-II) possessing 92% and 94% recurrent parent genome (RPG) respectively were intercrossed to develop ICF1—ICF₃ generations. These gene pyramided lines were evaluated for key agro-morphological traits, quality, and resistance against blast at three different hotspot locations as well as BB at two locations. Two ICF₃ gene pyramided lines viz., TH-625-159 and TH-625-491 possessing four genes exhibited a high level of resistance to BB and blast. In the future, these improved Tellahamsa lines could be developed as mega varieties for different agro-climatic zones and also as potential donors for different pre-breeding rice research.

Diversity analysis of starch physicochemical properties in 95 proso millet (Panicum miliaceum L.) accessions

In this study, 95 accessions of proso millet (Panicum miliaceum L.) were characterized for starch physicochemical properties, including apparent amylose content (AAC), gel textural properties, Rapid Visco Analyzer (RVA) pasting viscosity properties, thermal and retrogradation properties. Based on genotypic data, the genetic diversity and inter-relationship of these starch traits were analyzed. Diverse starch quality was found, for example, AAC ranged from 0 to 32.3%, gelatinization temperature (GT) varied from 71.5 to 79.0 ℃, and RVA profile showed distinct patterns among proso millet of different AAC types. Interestingly, high AAC proso millet usually had GT lower than that of low AAC proso millet, which is different from the findings in rice starch. Many starch traits were significantly correlated and most of the 18 tested traits could be classified as either AAC-related traits or GT-related traits. In summary, the information presented here will be useful for further development of proso millet products.

Evaluation of Whole-Genome Sequence, Genetic Diversity, and Agronomic Traits of Basmati Rice (Oryza sativa L.)

Basmati is considered a unique varietal group of rice (Oryza sativa L.) because of its aroma and superior grain quality. Previous genetic analyses of rice showed that most of the Basmati varieties are classified into the aromatic group. Despite various efforts, genomic relationship of Basmati rice with other varietal groups and genomic variation in Basmati rice are yet to be understood. In the present study, we resequenced the whole genome of three traditional Basmati varieties at a coverage of more than 25X using Illumina HiSeq2500 and mapped the obtained sequences to the reference genome sequences of Nipponbare (japonica rice), Kasalath (aus rice), and Zhenshan 97 (indica rice). Comparison of these sequences revealed common single nucleotide polymorphisms (SNPs) in the genic regions of three Basmati varieties. Analysis of these SNPs revealed that Basmati varieties showed fewer sequence variations compared with the aus group than with the japonica and indica groups. Gene ontology (GO) enrichment analysis indicated that SNPs were present in genes with various biological, molecular, and cellular functions. Additionally, functional annotation of the Basmati mutated gene cluster shared by Nipponbare, Kasalath, and Zhenshan 97 was found to be associated with the metabolic process involved in the cellular aromatic compound, suggesting that aroma is an important specific genomic feature of Basmati varieties. Furthermore, 30 traditional Basmati varieties were classified into three different groups, aromatic (22 varieties), aus (four varieties), and indica (four varieties), based on genome-wide SNPs. All 22 aromatic Basmati varieties harbored the fragrant-inducing Badh2 allele. We also performed comparative analysis of 13 key agronomic and grain quality traits of Basmati rice and other rice varieties. Three traits including length-to-width ratio of grain (L/W ratio), panicle length (PL), and amylose content (AC) showed significant (P < 0.05 and P < 0.01) differences between the aromatic and indica/aus groups. Comparative analysis of genome structure, based on genome sequence variation and GO analysis, revealed that the Basmati genome was derived mostly from the aus and japonica groups. Overall, whole-genome sequence data and genetic diversity information obtained in this study will serve as an important resource for molecular breeding and genetic analysis of Basmati varieties.

Gelatinization, pasting and retrogradation properties and molecular fine structure of starches from seven cassava cultivars

Genetic diversity in the physicochemical properties and fine structures of seven cassava starches samples was studied. The apparent amylose content ranged from 24.8 to 27.6%. The whole branched starches showed significant differences in average hydrodynamic radius, ranging from 53.35 to 58.45 nm, while debranched starch exhibited differences in degrees of polymerization and height of both amylose and amylopectin peaks. The molecular size of amylose and amylopectin was positively correlated. The amount of short chains fa (6 ≤ X ≤ 12) and fb1 (13 ≤ X ≤ 24) had significant differences among the cultivars. Structure-function relation analysis indicated that the CPV and SB were mainly determined by amylopectin fine structures, BD, PTi and Tp and retrogradation properties were mainly determined by the amylose fine structure, while PTe and To were mainly affected by both amylose and amylopectin fine structures. The current findings will be helpful to improve the understanding cassava starch quality for use in industrial starch applications.

A novel starch: Characterizations of starches separated from tea (Camellia sinensis (L.) O. Ktze) seed

The physicochemical, thermal and crystal properties of starches isolated from 3 different tea (Camellia sinensis (L.) O. Ktze) seeds were analyzed in this study. The shape of tea starch granules were flat spherical or oval shape, showed unimodal or bimodal distribution with average size of around 9 μm. Tea starch was typical A-type starch. Apparent amylose contents of three tea seed starches ranged from 27.06% to 33.17%. The chains having degree of polymerization (DP) 13-24 were over 50% of the total detectable chains for tea amylopectin. Peak gelatinization temperature of tea starch ranged from 65 to 77 °C and the water solubility reached up to 9.70%. The peak viscosity of tea starches were as high as 5300 cP and final viscosity ranged from 4000 to 6700 cP. The results indicated that tea seed starch had potential as gel reagents and provide some guides for comprehensive utilization of tea starch in food and non-food applications.

Genetic diversity and stability in starch physicochemical property traits of potato breeding lines

Cross breeding may create wider genetic variation than two parents used in hybridization, but breeding efforts towards starch quality improvement are less reported in potato. A cross was made between Zhongshu-3 and Favorita to select desired starch properties in progenies. Among 206 F₁ clones with potential high yield, starch qualities such as apparent amylose content (AAC), pasting viscosity, and thermal properties were further evaluated. A wide variation was observed in different starch physicochemical indices for 206 potato accessions. Twenty clones with high/low AAC, peak viscosity and peak gelatinization temperature were selected and then grown at another location to evaluate the stability of the traits. Similar wide range of variation in the starch properties was observed. Cluster analysis based on starch properties of the 20 selected clones indicating relative stability of the starch property traits across different locations. New breeding lines identified have potential for application in food and other industries.