Comparison of eating quality and physicochemical properties between Japanese and Chinese rice cultivars

Effects of foliar selenium, biochar, and pig manure on cadmium accumulation in rice grains and assessment of health risk

Addressing cadmium (Cd) contamination in agricultural lands is crucial, given its health implications and accumulation in crops. This study used pot experiments to evaluate the impact of foliar selenium spray (Se) (0.40 mM), corn straw biochar (1%), and pig manure (1%) on the growth of rice plants, the accumulation of Cd in rice grain, and to examine their influence on health risk indices associated with Cd exposure. The treatments were designated as follows: a control group without any amendment (CK), biochar (T1), pig manure (T2), Se (T3), Se and biochar (T4), Se and pig manure (T5), and Se along with biochar and pig manure (T6). Our results indicated that the treatments affected soil pH and redox potential and improved growth and the nitrogen and phosphorus content in rice plants. The soil-plant analysis development (SPAD) meter readings of leaves during the tillering stage indicated a 5.27%-15.86% increase in treatments T2 to T6 compared to CK. The flag leaves of T2 exhibited increases of 12.06%-38.94% for electrolyte leakage and an 82.61%-91.60% decline in SOD compared to treatments T3 to T6. Treatments T1 to T6 increased protein content; however, amylose content was significantly reduced in T6. Treatment T6 recorded the lowest Cd concentration in rice grains (0.018 mg/kg), while T2 recorded the highest (0.051 mg/kg). The CK treatment group showed a grain Cd content reduction of 29.30% compared to T2. The assessment of acceptable daily intake, hazard quotient, and carcinogenic risk revealed an ascending order as follows: T6 < T3 < T5 < T4 < T1 < CK < T2. In conclusion, the application of treatment T6 demonstrates the potential to lower oxidative stress, enhance production, reduce cancer risk, and ensure the safe cultivation of rice in environments affected by Cd contamination.

Analysis of Erect-Panicle Japonica Rice in Northern China: Yield, Quality Status, and Quality Improvement Directions

China is the only country that extensively cultivates the indica and japonica rice varieties, with the largest japonica rice production area being in northeast China. A study of the relationship between the yield and quality of japonica rice and the effect of nitrogen fertilizer application on this relationship is important. In this paper, we aimed to assess the current yield and quality of japonica rice in northeast China. We selected erect-panicle varieties as the test materials. Field experiments were conducted using different nitrogen fertilizer levels for two consecutive years to analyze the rice varieties' yield, quality, interrelationship, and nitrogen fertilizer response. The average yield following high- and low-nitrogen treatments exceeded 10,000.00 kg/hm2, with a maximum of 12,285.63 kg/hm2. The high-yield-high-nitrogen treatment group had more panicles, a higher seed-setting rate, and a higher 1000-grain weight than the other groups. The high-yield-low-nitrogen group had a higher number of panicles and seed-setting rate than the other groups. The low-yield-high-nitrogen group had a lower number of whole grains, grain length-to-width ratio, and taste value than the other groups. The low-yield-low-nitrogen group had fewer primary branches than the other groups; excluding the primary branch-setting rate and 1000-grain weight, the values of the other panicle traits of the group were significantly higher than those of the other groups. The high-nitrogen-high-flavor group had lower panicle and spikelet numbers and higher spikelet fertility rates than the other groups. The low-nitrogen-high-flavor group had higher spikelet fertility rates and 1000-grain weight than the other groups. Compared to the other groups, the low-nitrogen-high-flavor group had a higher head rice yield, and the high-nitrogen-high-flavor group had a lower chalkiness rate. The main goal of the breeding and cultivation of high-yield and high-quality erect-panicle japonica rice in northern China is to achieve "dual high, dual low, and one high and one low" conditions, signifying a high yield with high or low nitrogen levels, low protein and amylose contents, high head rice rates, and low chalkiness. This study provides a new technique for enhancing the taste of northern erect-panicle japonica rice to promote the sustainable, high-yield, and high-quality development of japonica rice in northern China.

Effect of starch and protein on eating quality of japonica rice in Yangtze River Delta

This study examined four types of japonica rice from Yangtze River Delta, categorized based on amylose content (AC) and protein content (PC): high AC with high PC, high AC with low PC, low AC with high PC, and low AC with low PC. It systematically explored the effect of starch, protein and their interactions on eating quality of japonica rice. Rheological analysis revealed that increased amylose, long chains amylopectin or protein levels during cooking strengthen starch-protein interactions (hydrogen bonding), forming a firm gel network. Scanning electron microscopy showed that increased amylose, long chains amylopectin or protein levels made protein and starch more stable in combination during cooking, limiting starch structure cleavage. Therefore, the eating quality of high AC in similar PC japonica rice and high PC in similar AC japonica rice were poor. Further, correlation and random-forest analysis (RFA) identified amylose as the most influential factor in starch-protein interactions affecting rice eating quality, followed by amylopectin and protein. RFA also revealed that in high AC japonica rice, the interactions of Fb3 and albumin with amylose were more conducive to forming good eating quality. In low AC japonica rice, the interactions of Fb2 and prolamin with amylose were more beneficial.

Differences in rice component distribution across layers and their relationship with taste

BACKGROUND

Rice taste is closely associated with endosperm composition, which varies among different rice layers. Although clarifying the relationship between this difference and nutritional taste can guide rice breeding and cultivation practices, research on this topic is limited.

RESULTS

Here, typical rice varieties having excellent and poor taste characteristics were selected to analyze the distribution characteristics and differences of their components. The varieties with excellent taste exhibited lower apparent amylose content (AAC) and protein content (PC), lesser short-chain (Fa) and long-chain (Fb3 ) amylopectin (AP) and more medium-chain (Fb1+2 ) AP, higher long-to-short chain ratio (Fa:Fb3 ), and higher nitrogen (N), magnesium (Mg) and calcium (Ca) content in layer 1 (L1) than the varieties with poor taste. Layer 2 (L2) played a key role in AAC and PC regulation in the varieties with excellent taste by reducing AAC and appropriately increasing PC, consequently improving rice taste. AP structure in layer 3 (L3) substantially affected the taste of the two types of varieties. The mineral content was the highest in L1, and increased potassium (K), Ca, and Mg content improved taste in all varieties.

CONCLUSION

AAC in each layer contributes to rice taste. PC and minerals primarily act on L1 and L2, whereas AP acts on L2 and L3. Therefore, the endosperm formation process should be exploited for improving rice taste. Furthermore, key resources and cultivation should be identified and regulated, respectively, to improve rice taste. © 2023 Society of Chemical 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.

The differences in metabolites, starch structure, and physicochemical properties of rice were related to the decrease in taste quality under high nitrogen fertilizer application

Nitrogen fertilizer application is one of the key cultivation practices to improve rice yields. However, the application of high nitrogen fertilizers often leads to a reduction in the stickiness of the rice after cooking, thus reducing the taste quality of rice. Moreover, there are differences in taste quality among rice varieties, and the mechanism has not been studied in depth. In this study, two rice varieties (Meixiangzhan2hao and Exiang2hao) were planted under two nitrogen fertilizer levels. The physicochemical properties and taste quality of the rice were determined after maturity. Our results showed that high nitrogen fertilizer level alters tryptophan metabolism in rice, increasing most amino acid content and protein content in rice. The high content of protein and the higher short-range ordered structure of starch inhibited the gelatinization characteristics of starch and reduced the taste quality of rice. Under high nitrogen fertilizer application, Exiang2hao showed smaller increases in protein content, lower level of amylose and relative crystallinity, and higher content of lipid metabolites. These differences in chemical substances resulted in a less pronounced reduction in the taste quality of Exiang2hao. In this study, the taste quality of different rice varieties under different levels of nitrogen fertilizer application was analyzed, providing new ideas for future improvement of rice taste quality.

Exploration of unique starch physicochemical properties of novel buckwheat lines created by crossing Golden buckwheat and Tatary buckwheat

Buckwheat is considered as a healthy cereal food, and it is essential to cultivate new buckwheat lines with good starch physicochemical properties for both consumers and food producers. Six novel buckwheat (Duoku, Dk) were generated by crossing of Golden buckwheat and Tatary buckwheat, and their kernel appearance properties and starch physicochemical properties were analyzed together with one domestic line (Cimiqiao) and one wild line (Yeku). The results showed that Dk samples had better appearance properties than two control samples. The Dk samples showed lower amylose content, similar amylopectin molecular structure and chain length distributions, and larger starch granules compared with Cimiqiao. The digestion results showed that two Dk samples: Dk6 & Dk9 had high resistant starch content; while the other two Dk samples: Dk37 & Dk38 had a steady glucose releasing rate. The Dk samples also showed high gelatinization temperature, indicating they were good raw materials for producing glass noodle. This study proved that Dk buckwheat had unique starch physicochemical properties, and could be used as new food materials in the future.

Improving rice eating and cooking quality by enhancing endogenous expression of a nitrogen-dependent floral regulator

Improving rice eating and cooking quality (ECQ) is one of the primary tasks in rice production to meet the rising demands of consumers. However, improving grain ECQ without compromising yield faces a great challenge under varied nitrogen (N) supplies. Here, we report the approach to upgrade rice ECQ by native promoter-controlled high expression of a key N-dependent floral and circadian clock regulator Nhd1. The amplification of endogenous Nhd1 abundance alters rice heading date but does not affect the entire length of growth duration, N use efficiency and grain yield under both low and sufficient N conditions. Enhanced expression of Nhd1 reduces amylose content, pasting temperature and protein content while increasing gel consistence in grains. Metabolome and transcriptome analyses revealed that increased expression of Nhd1 mainly regulates the metabolism of carbohydrates and amino acids in the grain filling stage. Moreover, expression level of Nhd1 shows a positive relationship with grain ECQ in some local main cultivars. Thus, intensifying endogenous abundance of Nhd1 is a promising strategy to upgrade grain ECQ in rice production.

Nitrogen fertilization modulates rice seed endophytic microbiomes and grain quality

The intensive use of chemical fertilizer, particularly nitrogen (N) has resulted in not only markedly increased crop yields but also detrimental effects on ecosystems. Plant microbiomes represent an eco-friendly alternative for plant nutrition and productivity, and the effect of N fertilization on plant and soil microbes has been well studied. However, if and how N fertilization modulates seed endophytic microbiomes and grain quality remains largely unknown. Here, we investigated the effect of different N fertilization rates on rice seed endophytic bacterial and fungal communities as well as on grain quality. Higher bacterial and fungal community diversity and richness, but lower grain protein and amino acid contents were found in seeds of rice treated moderate N fertilization than those treated insufficient or excessive N input. There were also more complex co-occurrence networks, and an enrichment of putative beneficial bacterial taxa in seeds under moderate N application, while there was an opposite trend under the excessive N treatment. In addition, the grain amylose and amylopectin contents were positively correlated with the relative abundance of bacterial and fungal dominant genera, while the grain amino acid contents were negatively correlated with the bacterial dominant genera but positively associated with fungal dominant genera. Together, we demonstrate that moderate N fertilization can enhance bacterial and fungal community colonization in seeds and improve grain eating and cooking qualities. This study extends our knowledge regarding the significant role of rational fertilization on seed-microbe interactions in sustainable agriculture.

Research on the Relationship between the Amylopectin Structure and the Physicochemical Properties of Starch Extracted from Glutinous Rice

Glutinous rice has very low amylose content and is a good material for determining the structure and physicochemical properties of amylopectin. We selected 29 glutinous rice varieties and determined the amylopectin structure by high-performance anion exchange chromatography with the pulsed amperometric detection method. We also determined the correlation between amylopectin structure and the physicochemical properties of starch extracted from these varieties. The results showed that the amylopectin chain ratio Σdegree of polymerization (DP) ≤ 11/ΣDP ≤ 24 of 29 glutinous rice varieties was greater than 0.26, signifying that these varieties contained type II amylopectin. The results of the correlation analysis with gelatinization temperature showed that ΣDP 6-11 was significantly negatively correlated with the onset gelatinization temperature (GT) (T_O), peak GT (T_P), and conclusion GT (T_C). Among the thermodynamic properties, ΣDP 12-24 was significantly positively correlated with To, Tp, and Tc, ΣDP 25-36 was significantly negatively correlated with To, Tp, and Tc, and ΣDP ≥ 37 had no correlation with the thermodynamic properties. The results of correlation analysis with RVA spectrum characteristic values showed that ΣDP 6-11 was significantly negatively correlated with hot paste viscosity (HPV), cool paste viscosity (CPV), consistency viscosity (CSV), peak time (PeT), and pasting temperature (PaT) among the Rapid Visco Analyzer (RVA) profile characteristics, ΣDP 12-24 was significantly positively correlated with HPV, CPV, CSV, PeT, and PaT, and ΣDP ≥ 25 had no correlation with the viscosity characteristics. Therefore, we concluded that the amylopectin structure had a greater effect on the T_O, T_P, T_C, ΔH and peak viscosity, HPV, CPV, CSV, PeT, and PaT. The glutinous rice varieties with a higher distribution of short chains and a lower distribution of medium and long chains in the amylopectin structure resulted in lower GT and RVA spectrum characteristic values.

Different nitrogen fertilizer application in the field affects the morphology and structure of protein and starch in rice during cooking

Nitrogen fertilization is one of the most important cultivation practices that affects the eating quality of rice. During the cooking process, nitrogen fertilizer application in the field changed the structure of protein and starch during cooking, which eventually reduced the rice eating quality. However, the morphology and structure of rice during cooking under high nitrogen fertilizer application in the field have not been explored. The relationship between the morphological and structural changes of rice protein and starch during cooking and the rice eating quality has not been studied. In this study, we conducted field trials at two nitrogen fertilizer levels (0 N and 350 N), and the rice was cooked after harvest. Our results showed that the peak viscosity of rice flour was 3326 cp and 2453 cp at 0 N and 350 N, respectively, and the peak viscosity of rice starch was 3424 cp and 3378 cp, respectively. Rice proteins played an important role in the starch gelatinization properties and thermodynamic properties. High nitrogen fertilizer application increased the protein content of rice from 5.97 % to 11.32 %, and more protein bodies adhered to the surface of amyloplasts eventually inhibiting starch gelatinization. The rice proteins could bind to amylose-lipid complexes during cooking, promoting the formation of V-type diffraction peaks. What is more, under high nitrogen fertilizer, rice protein had more β-sheets, which slowed the entry of water into the interior of starch molecules and prevented the destruction of the short-range ordered structure of starch. Our study provides the possibility to further improve the eating quality of rice under nitrogen fertilizer treatment.

A comparative HS-SPME/GC-MS-based metabolomics approach for discriminating selected japonica rice varieties from different regions of China in raw and cooked form

Japonica rice is widely planted in different regions of China. Rice of different geographical origins may have substantially different economic values. In this study, An untargeted metabolomics based approach using headspace solid-phase microextraction coupled to gas chromatography-mass spectrometry (HS-SPME/GC-MS) was applied to distinguish 27 japonica rice varieties originated from South, Northern and Northeastern China in raw and cooked form, respectively. Orthogonal partial least-squares discriminant analysis (OPLS-DA) models exhibited good geographic discrimination. Sixteen and twenty-two volatiles were selected as the discriminant markers in raw and cooked rice, respectively. However, only hexanal, 3,5-octadien-2-one and 2-butyl-2-octenal were selected both in raw and cooked rice. Markers in raw rice mainly involved in terpenes, lipoxygenases, indole, and shikimate and benzoic acid pathways. Markers in cooked rice were mainly derived from lipid oxidation. The results provided a deeper understanding of volatiles variation of rice in China from different geographic origins.

Salt tolerance at vegetative stage is partially associated with changes in grain quality and starch physicochemical properties of rice exposed to salinity stress at reproductive stage

BACKGROUND

Rice yield and grain quality are highly sensitive to soil salinity. Distinct rice genotypes respond to salinity stress differently. To explore the variation in grain yield and grain trait adaptation to moderate, reproductive-stage salinity stress (4 dS/m electrical conductivity), four rice cultivars differing in degrees of vegetative salt tolerance, including Pokkali (salt-tolerant), RD15 (moderately salt-tolerant), KDML105 (moderately salt-susceptible) and IR29 (salt-susceptible), were examined.

RESULTS

Grain fertility and 100-grain weight of RD15, KDML105 and IR29, as well as grain morphology of KDML105 and IR29, were significantly disturbed. Interestingly, grain starch accumulation in RD15 and KDML105 was enhanced under stress. However, only RD15 showed changes in starch physicochemical properties, including increased granule diameter, decreased gelatinization peak temperature (T_p ) and decreased retrogradation onset temperature (T_o ). Notably, Pokkali maintained productivity, grain quality, and starch properties, while the grain quality of IR29 remained unchanged under salinity stress. Multivariate analysis displayed clear separation of productivity, grain morphology, and starch variables of RD15 in the salt-treated group relative to the control group, suggesting that it was the cultivar most impacted by salt stress despite its moderate salt-tolerance at vegetative stage.

CONCLUSION

Our results demonstrate specific salinity responses among the rice genotypes, and suggest discrepancies between degrees of salt tolerance at vegetative stage versus the ability to maintain both grain quality and starch properties in response to salinity stress imposed at reproductive stage. © 2021 Society of Chemical Industry.

Effects of Thickness Fraction Process on Physicochemical Properties, Cooking Qualities, and Sensory Characteristics of Long-Grain Rice Samples

A process of removing thinner kernels of rough rice, i.e., thickness fraction process, has been suggested as a method for increasing milling yields in the rice industry. This study aimed at determining whether physicochemical properties, cooking qualities, and sensory characteristics of rice samples could be changed by the addition of a thickness fraction into the rice process stream. Each of four long-grain rice cultivar lots was assigned into two groups: unfractionated and thickness-fractionated. For the thickness-fractionated group, thin rice kernels (<1.9 mm) of rough rice were discarded from unfractionated rice samples. Unfractionated and thickness-fractionated rice samples were compared with respect to physicochemical properties, cooking qualities, and sensory characteristics. The results showed that the removal of such thin kernels decreased the breakage and chalkiness rates and increased head rice yields. Fractionated rice samples exhibited lower amylose contents and crude protein contents but higher gelatinization temperatures than unfractionated rice samples. While the optimum cooking duration and width–expansion ratios of thickness-fractionated rice samples were higher than those of unfractionated ones, there was a negligible impact of the thickness fraction process on sensory characteristics of long-grain rice samples. In conclusion, the thickness fraction process affects physicochemical properties and cooking qualities more than the sensory characteristics of rice samples.

Characteristics of Physicochemical Properties of Chalky Grains of Japonica Rice Generated by High Temperature during Ripening

Global warming has caused devastating damage to starch biosynthesis, which has led to the increase in chalky grains of rice. This study was conducted to characterize the qualities of chalky rice grains and to develop the estimation formulae for their quality damage degree. We evaluated the chalkiness of 40 Japonica rice samples harvested in 2019, in Japan. Seven samples with a high ratio of chalky rice grains were selected and divided into two groups (whole grain and chalky grain). As a results of the various physicochemical measurements, it was shown that the surface layer hardness (H1) of cooked rice grains from chalky grains was significantly lower, and their overall hardness was significantly lower than those from the whole grains. In addition, α- and β-amylase activities, and sugar contents of the chalky rice grains were significantly higher than those of the whole rice grains. The developed estimation formula for the degree of retrogradation of H1 based on the α-amylase activities and pasting properties, showed correlation coefficients of 0.84 and 0.81 in the calibration and validation tests, respectively. This result presents the formula that could be used to estimate and to characterize the cooking properties of the rice samples ripened under high temperature.

Differences in Eating Quality Attributes between Japonica Rice from the Northeast Region and Semiglutinous Japonica Rice from the Yangtze River Delta of China

Differences in cooked rice and starch and protein physicochemical properties of three japonica rice were compared systematically. Cultivars of japonica rice, Daohuaxiang2, from Northeast China (NR) and two semiglutinous japonica rice (SGJR), Nangeng46 and Nangeng2728, from the Yangtze River Delta (YRD) were investigated. Both Daohuaxiang2 and Nangeng46 achieved high taste values, but there were great differences in starch and protein physicochemical properties. Daohuaxiang2 showed higher apparent amylose content (AAC), lower protein content (PC), and longer amylopectin (especially fb2 and fb3) and amylose chain lengths, resulting in thicker starch lamellae and larger starch granule size. Its cooked rice absorbed more water and expanded to larger sizes. All of these differences created a more compact gel network and harder but more elastic cooked rice for Daohuaxiang2. Nangeng46 produced a lower AAC, a higher PC, shorter amylopectin and amylose chain lengths, thinner starch lamellae, and smaller starch granule sizes, creating a looser gel network and softer cooked rice. The two SGJR, Nangeng46 and Nangeng2728, had similar low AACs but great differences in taste values. The better-tasting Nangeng46 had a lower PC (especially glutelin content) and higher proportion of amylopectin fa chains, which likely reduced the hardness, improved the appearance, and increased the adhesiveness of its cooked rice. Overall, both types of japonica rice from the NR and YRD could potentially have good eating qualities where Nangeng46's cooked rice was comparable to that of Daohuaxiang2 because of its lower AC. Moreover, its lower PC and higher proportion of amylopectin fa chains likely improved its eating quality over the inferior-tasting SGJR, Nangeng2728. This research lays a foundation for the improvement of the taste of japonica rice in rice breeding.

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.

Evaluation of Hardness and Retrogradation of Cooked Rice Based on Its Pasting Properties Using a Novel RVA Testing

With rice being one of the most important crops worldwide, rapid and objective quality evaluation methods based on physicochemical measurements of rice are necessary. We compared the pasting properties of various rice samples using three different heating and cooling programs (maximum temperatures were 93, 120, and 140 °C, respectively) in a newly developed high-temperature-type Rapid Visco Analyzer (RVA , RVA 4800). Furthermore, we investigated the relationship between the different pasting properties measured by the three programs, with starch microstructure measured by iodine scanning analysis, the physical properties of the cooked rice measured by a Tensipresser after 2 h at 25 °C or after 24 h at 6 °C, and prolamin ratio measured by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The consistency value (final viscosity-minimum viscosity) yielded by a new program of maintenance for 2 min at 120 °C using RVA 4800 had a higher positive correlation with retrograded surface hardness H1(R) (r = 0.92), retrograded overall hardness H2(R) (r = 0.90), and the absorbance at λmax (Aλmax) of cooked rice (r = 0.88) and resistant starch (r = 0.80) than those by the conventional program at 93 °C. We developed estimation formulae for H1(R) for various kinds of rice, of which the determination coefficient was 0.86. It led to an easy and rapid assay method for the cooking properties of the various rice samples.

Raman spectroscopic analysis of polysaccharides in popular Japanese rice cultivars

Analytical algorithms based on Raman spectroscopy are proposed for the determination of amylopectin and amylose concentrations in polished white rice, and applied to characterize and compare linear and branched polysaccharide structures in nine different types of Japanese rice. A selected algorithm used symmetric bending vibrations of the COC glycosidic linkage from a relatively narrow spectral zone between 830 and 895 cm^-1. It specifically compared the intensity of Raman signals from two types of bending common to both starch components (C1-O-C5 and C1-O-C4 at 868 and 855 cm^-1, respectively) and that at the branch point peculiar to amylopectin (C1-O-C6 at 844 cm^-1). Raman data were confronted with data collected by conventional amylose-iodine colorimetry method. Consistency was found between Raman and colorimetric methods over the entire series of tested rice cultivars, thus validating the newly proposed spectroscopic algorithm. The amylose content of the tested rice species broadly varied between 1.2 and 20.4%. The proposed Raman algorithm allows fast and nondestructive determination of amylose content in rice with minimal sample preparation. These characteristics might be key in the development of portable Raman devices capable to promptly screen polysaccharides in different rice cultivars with respect to their interannual and plantation-related fluctuations.

Effect of biochar on rice starch properties and starch-related gene expression and enzyme activities

We determined the effects of biochar on starch properties and the activities of enzymes and expression levels of genes related to starch in two Japonica rice cultivars. The two rice varieties were subjected to five biochar treatments (0, control; and 5, 10, 20, and 40 t/hm²). In both rice varieties, the content of apparent amylose and resistant starch were lower in biochar treatments than in the control. The proportion of fa chains was higher and that of fb3 chain was lower in the biochar treatments than in the control. Starch viscosity and cooking taste quality were improved by the biochar treatments. In both rice varieties, the activity of granule-bound starch synthase was significantly decreased by biochar treatments, and the activities of soluble starch synthase, starch branching enzyme, and starch debranching enzyme were significantly increased. The transcript levels of genes encoding starch synthases and starch branching enzymes were significantly increased by biochar treatments. We conclude that biochar at a dose of 5-10 t/hm² can regulate the activity of starch-related enzymes, and this affects the type, content, and fine structure of starch. Therefore, the addition of biochar to soil can improve the viscosity and taste quality of rice starch.

Effects of different heat–moisture treatments on the physicochemical properties of brown rice flour

We evaluated the effect of heat–moisture treatment (HMT) on the main chemical components, physical properties, and enzyme activities of two types of brown rice flour: high-amylose Koshinokaori and normal-quality Koshiibuki. Five different HMTs using brown rice (moisture content was 12.0%) were assessed: 0.1 MPa/120 °C for 5 or 10 min, 0.2 MPa/134 °C for 5 or 10 min and 0.3 MPa/144 °C for 10 min. HMT, decreased the α-amylase and lipase activities, and fat acidity, and slightly increased the dietary fiber and resistant starch levels. After 2 months’ storage at 35 °C, rice samples that were treated with 0.2 MPa/134 °C or 0.3 MPa/144 °C for 10 min had a lower fat acidity than untreated samples, which would be useful for long-term storage and export of rice flour. And HMT exhibited inhibition of retrogradation in the pasting and physical properties, which is profitable to promote the qualities of the rice products.