Developments in understanding the basis of cooked-rice texture

Evaluation of Cooked Rice for Eating Quality and Its Components in Geng Rice

At present, ''eating well" is increasingly desired by people instead of merely ''being full". Rice provides the majority of daily caloric needs for half of the global human population. However, eating quality is difficult to objectively evaluate in rice breeding programs. This study was carried out to objectively quantify and predict eating quality in Geng rice. First, eating quality and its components were identified by trained panels. Analysis of variance and broad-sense heritability showed that variation among varieties was significant for all traits except hardness. Among them, viscosity, taste, and appearance were significantly correlated with eating quality. We established an image acquisition and processing system to quantify cooked rice appearance and optimized the process of measuring cooked rice viscosity with a texture analyzer. The results show that yellow areas of the images were significantly correlated with appearance, and adhesiveness was significantly correlated with viscosity. Based on these results, multiple regression analysis was used to predict eating quality: eating quality = 0.37 × adhesiveness - 0.71 × yellow area + 0.89 × taste - 0.34, R2 = 0.85. The correlation coefficient between the predicted and actual values was 0.86. We anticipate that this predictive model will be useful in future breeding programs for high-eating-quality rice.

Accurate prediction of the eating and cooking quality of rice using artificial neural networks and the texture properties of cooked rice

Accurate prediction of the eating and cooking quality (ECQ) of rice is of great importance. Statistical and machine learning models were developed to predict the overall acceptability of cooked rice. The results showed that the models developed using stepwise multiple linear regression, principal component analysis plus multiple linear regression, partial least square regression, k-nearest neighbor, random forest, and gradient boosted decision tree had determination coefficients (R²) of 0.156-0.452, 0.357, 0.160-0.460, 0.192-0.746, 0.453-0.708, and 0.469-0.880, respectively, which were improved to 0.675-0.979 by artificial neural networks (ANN) models. The ANN models also had lower root mean square errors (0.574-1.32). Further, the ANN model using textural properties could accurately predict 92.1 % of overall acceptability, which could be improved to >96 % using the components and/or pasting characteristics. Overall, the accuracy of ECQ prediction was substantially improved by the model developed using ANN with texture properties of rice.

Water migration, texture and oral processing properties of semi-waxy rice during retrogradation

Semi-waxy rice, a low-amylose content (8%-13%) rice variety, can resist retrogradation. It is becoming more and more popular and widely cultivated in East China where consumers prefer cooked rice with soft and tender texture. In this study, water migration, texture and oral processing properties of cooked rice during retrogradation were investigated in order to characterize semi-waxy rice. The results confirmed that the water mobility and migration of semi-waxy rice during retrogradation is weaker than that of waxy rice and stronger than that of nonwaxy rice. Simultaneously, the hardness of semi-waxy rice was higher than that of waxy rice and lower than that of nonwaxy rice. The oral processing properties confirmed that freshly waxy rice was too adhesive and needed more work to breakdown slow breakdown structure (Type Ⅱ structure) compared to freshly semi-waxy rice. Meanwhile, nonwaxy rice was too hard, and more work was needed to break both fast breakdown structure (Type I structure) and slow breakdown structure (Type Ⅱ structure). The oral processing properties confirmed that retrograded semi-waxy rice generated more reducing sugar than retrograded waxy rice and nonwaxy rice. Thus, semi-waxy rice can retard retrogradation, and the texture of cooked semi-waxy rice is neither too adhesive as waxy rice nor too hard as nonwaxy rice. PRACTICAL APPLICATION: Semi-waxy rice cultivars have been widely cultivated in East China and well accepted by the consumers. This study aims to characterize semi-waxy rice and provide theoretical basis for semi-waxy rice study.

Nitrogen fertilizer application rate impacts eating and cooking quality of rice after storage

The effect of nitrogen fertilizer application on the quality of rice post-storage is not well understood. The eating and cooking quality (ECQ) of rice treated with 0 (CK, control), 160 (IN, insufficient nitrogen), 260 (AN, adequate nitrogen), and 420 (EN, excessive nitrogen) kg N/ha was analyzed over 12 months of storage. Results showed that the rate of nitrogen fertilizer application had no significant impact on the changes in taste value during storage. However, EN application significantly increased the hardness (p < 0.05), reduced the gumminess (p < 0.05), and delayed the decline in the viscosity of rice paste by two months after one-year storage, compared with other treatments. In conclusion, although EN application resulted in an inferior texture of rice, it delayed the quality change by two months during storage. It was demonstrated that a rational nitrogen application rate (0-260 kg N/ha) for rice cultivation is particularly important to obtain high ECQ; however, EN may be beneficial for the stability of the ECQ during storage.

The increased stickiness of non-glutinous rice by alkali soaking and its molecular causes

Non-glutinous rice is always less sticky than glutinous rice. By soaking two non-glutinous rice (Jingmi and Xianmi) with different concentrations of NaOH solution, the stickiness of cooked non-glutinous rice is significantly increased, which is closely associated with the removal of surface proteins of these treated rice grains. By investigating starch leaching characteristics and the molecular structure of leached starch, we find: (i) total solids and amylopectin amount in the leached materials increase by raising NaOH concentration; (ii) the molecular size and chain-length distributions (CLDs) of leached starch significantly differ between samples with different soaking treatments; (iii) a strong correlation between stickiness of cooked rice and total amount of leached amylopectin is established. (iv) molecular causes for the increased stickiness of alkali-soaked rice are put forward to explain the above observations. This study could broaden the applications of non-glutinous rice by altering its stickiness attribute with alkali soaking.

Tooth whitening efficacy of pigmented rice gels containing carbamide peroxide

Carbamide peroxide (CP) is commonly used as a tooth whitening agent. However, efficacy of CP can be enhanced if it is in the suitable delivery system. In the present study, CP loaded in pigmented rice gels were developed and investigated for their physicochemical properties and tooth whitening efficacy. The modified pigmented rice of two varieties, Homnil (HN) and Doisket (DS) were prepared and used as a gelling agent. The outer appearance of the obtained rice gels containing 10% CP (CP-HN and CP-DS, respectively) were transparent and homogeneous texture. The pH of both rice gel bases was neutral but became slightly acidic after incorporating with CP. The adhesive property of HN gel was significantly higher than DS gels. In vitro drug release profile exhibited that the release of CP from CP-DS was significantly higher than CP-HN and the commercial gel (CP-CG), respectively. In vitro tooth whitening efficacy in 45 normal teeth revealed that the tooth whitening efficacy of the gels was time dependent. At the end of the treatment, CP-HN showed significantly higher tooth whitening efficacy than CP-DS and CP-CG, respectively. It is concluded that the physicochemical properties, particularly the adhesive and dissolution properties, play an important role in the tooth whitening efficacy of the CP gels.

Deciphering the Genetic Architecture of Cooked Rice Texture

The textural attributes of cooked rice determine palatability and consumer acceptance. Henceforth, understanding the underlying genetic basis is pivotal for the genetic improvement of preferred textural attributes in breeding programs. We characterized diverse set of 236 Indica accessions from 37 countries for textural attributes, which includes adhesiveness (ADH), hardness (HRD), springiness (SPR), and cohesiveness (COH) as well as amylose content (AC). A set of 147,692 high quality SNPs resulting from genotyping data of 700K high Density Rice Array (HDRA) derived from the Indica diversity panels of 218 lines were retained for marker-trait associations of textural attributes using single-locus (SL) genome wide association studies (GWAS) which resulted in identifying hotspot on chromosome 6 for AC and ADH attributes. Four independent multi-locus approaches (ML-GWAS) including FASTmrEMMA, pLARmEB, mrMLM, and ISIS_EM-BLASSO were implemented to dissect additional loci of major/minor effects influencing the rice texture and to overcome limitations of SL-based GWAS approach. In total 224 significant quantitative trait nucleotide (QTNs) were identified using ML-GWAS, of which 97 were validated with at least two out of the four multi-locus methods. The GWAS results were in accordance with the very significant negative correlation (r = -0.83) observed between AC and ADH, and the significant correlation exhibited by AC (r < 0.4) with HRD, SPR, and COH. The novel haplotypes and putative candidate genes influencing textural properties beyond AC will be a useful resource for deployment into the marker assisted program to capture consumer preferences influencing rice texture and palatability.

Influence of gamma radiation on the physical and sensory properties of two Brazilian rice cultivars

BACKGROUND

Little has been reported about the effects of gamma radiation on the physical and sensory characteristics of rice. Samples were irradiated with ⁶⁰ Co in doses 0, 1, 2 and 5 kGy, on a rate of 0.4 kGy h^-1 .

RESULTS

The evaluation of instrumental color showed that increasing doses promoted the yellowing (higher b* value) of the rice grains. Hardness was decreased and stickiness was increased in cooked rice with increasing doses. Sensory evaluation using quantitative descriptive analysis showed that increasing doses promoted higher occurrence of yellowish appearance, emergence of burnt aroma, and an increase of bitter and burnt taste. The sensory acceptance test by 9-point hedonic scale showed alteration of the samples irradiated with 5 kGy in all evaluated attributes (appearance, color, aroma, taste and texture). The lowest dose (1 kGy), however, had good acceptability by the panelists.

CONCLUSION

Rice may be subjected to 1 kGy dose of gamma radiation without changes or with small changes in physical properties and with good overall acceptability. © 2016 Society of Chemical Industry.

Study on Physical-Chemical Characters and Heritability for Yield Components in Rice (<i>Oryza sativa</i> L.)

Present study was performed to analysis both physical and chemical properties of rice germplasm and heritability for yield components in combinations. A total of 44 lines/varieties obtained from Cuu Long Rice Research Institute genebank, and 30 F1 generation combinations were evaluated. The results showed that the rice line IR79008-B-11-B-B-1 showed overall good physical characters (head rice, grain length, grain width, chalkiness). In terms of chemical characteristics, three varieties IR75499-73-1-B, OM6162, and OM4900 were found to have good amylose content, gel consistency, protein content, gelatinization temperature, and aroma. A very notable finding was that the cross between OM6162/SwarnaSub1 that low amylose content (20.2%), high gel consistency (78.2 mm), high protein content (8.1%), appropriate gelatinization temperature (scale 5), low chalkiness (level 0), high heritability (0.9) for grain yield trait/cluster, and (0.84) for the number of panicles/cluster. Moreover these characters consist of plant height, panicles lenght, number of panicles/cluster, number of filled grains/panicle, number of unfilled/panicle, and grain yield/ cluster showed moderate to high heritability of mean for combination OM6162/SwarnaSub1. The results suggest that the grain yield trait/cluster and the number of panicles/cluster are important yield contributing traits to rice breeders for selecting ideal combinations for higher yield and quality of next generations.

Study on Physical-Chemical Characters and Heritability for Yield Components in Rice (<i>Oryza sativa</i> L.)

Present study was performed to analysis both physical and chemical properties of rice germplasm and heritability for yield components in combinations. A total of 44 lines/varieties obtained from Cuu Long Rice Research Institute genebank, and 30 F1 generation combinations were evaluated. The results showed that the rice line IR79008-B-11-B-B-1 showed overall good physical characters (head rice, grain length, grain width, chalkiness). In terms of chemical characteristics, three varieties IR75499-73-1-B, OM6162, and OM4900 were found to have good amylose content, gel consistency, protein content, gelatinization temperature, and aroma. A very notable finding was that the cross between OM6162/SwarnaSub1 that low amylose content (20.2%), high gel consistency (78.2 mm), high protein content (8.1%), appropriate gelatinization temperature (scale 5), low chalkiness (level 0), high heritability (0.9) for grain yield trait/cluster, and (0.84) for the number of panicles/cluster. Moreover these characters consist of plant height, panicles lenght, number of panicles/cluster, number of filled grains/panicle, number of unfilled/panicle, and grain yield/ cluster showed moderate to high heritability of mean for combination OM6162/SwarnaSub1. The results suggest that the grain yield trait/cluster and the number of panicles/cluster are important yield contributing traits to rice breeders for selecting ideal combinations for higher yield and quality of next generations.

Effect of processing method on physico-chemical and functional properties of two fonio (Digitaria exilis) landraces

In West Africa, landraces or local varieties of fonio are processed into many products by women using small processing units and marketed locally as well as exported to Europe and the United States. The objective of this study was to evaluate the effect of processing methods, namely parboiling, precooking and roasting on the physico-chemical and functional properties of two mainly preferred fonio landraces (Iporhouwan and Namba) by consumers. Results showed that the physico-chemical characteristics and most functional properties were significantly (P < 0.0001) affected by the processing methods. The lowest brightness (L*) values were obtained for parboiled fonio for the two landraces. However, parboiled fonio presented the best biochemical composition as compared to the dehusked, milled, precooked and roasted fonio samples. The protein contents of parboiled fonio samples were 6.06 % and 7.24 % for Iporhouwan and Namba landraces respectively. The values of peak viscosity, trough viscosity, breakdown, final viscosity and setback, were significantly higher for dehusked and milled fonio than for precooked, parboiled and roasted fonio with respect to both landraces. The milled fonio showed highest peak viscosity (2,668.5 cP) which was similar for the both tested landraces.

Determination of rice sensory quality with similarity analysis-artificial neural network method in electronic tongue system

A novel similarity analysis-artificial neural network method was developed in electronic tongue system for predicting rice sensory quality.

Evaluation of texture differences among varieties of cooked quinoa

Texture differences of cooked quinoa were studied among 13 different varieties. Correlations between the texture parameters and seed composition, seed characteristics, cooking quality, flour pasting properties, and flour thermal properties were determined. The results showed that texture of cooked quinoa was significantly differed among varieties. 'Black,' 'Cahuil,' and 'Red Commercial' yielded harder texture, while '49ALC,' '1ESP,' and 'Col.#6197' showed softer texture. '49ALC,' '1ESP,' 'Col.#6197,' and 'QQ63' were more adhesive, while other varieties were not sticky. The texture profile correlated to physical--chemical properties in different ways. Protein content was positively correlated with all the texture profile analysis (TPA) parameters. Seed hardness was positively correlated with TPA hardness, gumminess, and chewiness at P ≤ 0.09. Seed density was negatively correlated with TPA hardness, cohesiveness, gumminess, and chewiness, whereas seed coat proportion was positively correlated with these TPA parameters. Increased cooking time of quinoa was correlated with increased hardness, cohesiveness, gumminess, and chewiness. The water uptake ratio was inversely related to TPA hardness, gumminess, and chewiness. Rapid Visco Analyzer peak viscosity was negatively correlated with the hardness, gumminess, and chewiness (P < 0.07); breakdown was also negatively correlated with those TPA parameters (P < 0.09); final viscosity and setback were negatively correlated with the hardness, cohesiveness, gumminess, and chewiness (P < 0.05); setback was correlated with the adhesiveness as well (r = -0.63, P = 0.02). Onset gelatinization temperature (To ) was significantly positively correlated with all the texture profile parameters, and peak temperature (Tp ) was moderately correlated with cohesiveness, whereas neither conclusion temperature (Tc ) nor enthalpy correlated with the texture of cooked quinoa.

Objective evaluation of whiteness of cooked rice and rice cakes using a portable spectrophotometer

The whiteness of cooked rice and rice cakes was evaluated using a portable spectrophotometer with a whiteness index (WI). Also, by using boiled rice for measurement of Mido values by Mido Meter, it was possible to infer the whiteness of cooked rice without rice cooking. In the analysis of varietal differences of cooked rice, 'Tsuyahime', 'Koshihikari' and 'Koshinokaori' showed high whiteness, while 'Satonoyuki' had inferior whiteness. The whiteness of rice cakes made from 'Koyukimochi' and 'Dewanomochi' was higher than the whiteness of those made from 'Himenomochi' and 'Koganemochi'. While there was a significant correlation (r = 0.84) between WI values and whiteness scores of cooked rice by the sensory test, no correlation was detected between the whiteness scores and Mido values, indicating that the values obtained by a spectrophotometer differ from those obtained by a Mido Meter. Thus, a spectrophotometer may be a novel device for measurement of rice eating quality.

Infrared and Raman spectroscopic characterization of structural changes in albumin, globulin, glutelin, and prolamin during rice aging

Structural changes in albumin, globulin, glutelin, and prolamin from fresh and aged rice were characterized in this study. Infrared and Raman spectroscopies revealed changes in interactions between protein and starch, and the occurrence of structural changes involving secondary and tertiary structures of protein induced by rice aging. The α-helical structure was reduced, and aliphatic amino-acid side chains became more buried in albumin after rice aging. Oxidation of the sulfhydryl group in globulin was evident. The unordered coil in glutelin decreased, and a characteristic frequency of the free sulfhydryl group appeared. The antiparallel β-sheet in prolamin increased, the conformation of disulfide bonds changed, and tyrosine residues became exposed to a polar environment. The association between globulin and starch strengthened, whereas that between glutelin and starch diminished. These differences in structure and interactions with starch might be responsible for the dissimilar pasting properties between fresh and aged rice.

Molecular aspect of good eating quality formation in Japonica rice

The composition of amylopectin is the determinant of rice eating quality under certain threshold of protein content and the ratio of amylose and amylopectin. In molecular biology level, the fine structure of amylopectin is determined by relative activities of starch branching enzyme (SBE), granule-bound starch synthase (GBSS), and soluble starch synthase (SSS) in rice grain under the same ADP-Glucose level. But the underlying mechanism of eating quality in molecular biology level remains unclear. This paper reports the differences on major parameters such as SNP and insertion-deletion sites, RNA expressions, and enzyme activities associated with eating quality of japonica varieties. Eight japonica rice varieties with significant differences in various eating quality parameters such as palatability and protein content were used in this experiment. Association analysis between nucleotide polymorphism and eating quality showed that S12 and S13 loci in SBE1, S55 in SSS1, S58 in SSS2A were significantly associated with apparent amylose content, alkali digestion value, setback viscosity, consistency viscosity, pasting temperature, which explained most of the variation in apparent amylose content, setback viscosity, and consistency viscosity; and explained almost all variations in alkali digestion value and pasting temperature. Thirty-five SNPs and insertion-deletions from SBE1, SBE3, GBSS1, SSS1, and SSS2A differentiated high or intermediate palatability rice varieties from low palatability rice varieties. Correlation analysis between enzyme activities and eating quality properties revealed that SBE25 and SSS15/W15 were positively correlated with palatability, whereas GBSS10 and GBSS15 were negatively correlated. Gene expressions showed that SBE1 and SBE3 expressions in high palatability varieties tended to be higher than middle and low palatability varieties. Collectively, SBE1, SBE3, SSS1, and SSS2A, especially SBE1 and SBE3 could improve eating quality, but GBSS1 decreased eating quality. The results indicated the possibility of developing high palatability cultivars through modification of key genes related to japonica rice eating quality formation in starch biosynthesis.

PCR marker-based evaluation of the eating quality of japonica rice ( Oryza sativa L.)

Evaluation of eating quality in early breeding generations of rice is critical to developing varieties with better palatability. This paper reports DNA markers associated with eating quality of temperate japonica rice and an evaluation method aided by multiple regression analysis. A total of 30 markers comprising STSs, SNPs, and SSRs were tested for their association with palatability using 22 temperate japonica varieties with different palatability values. Eating quality-related traits of the 22 varieties were also measured. Of the 30 markers, 18 were found to be significantly associated with palatability and, consequently, a model regression equation with an R(2) value of 0.99 was formulated to estimate the palatability by the marker data set. Validation of the model equation using selected breeding lines indicated that the marker set and the equation are highly applicable to evaluation of the palatability of cooked rice in temperate japonica varieties.

Histological structures of cooked rice grain

Raw and cooked whole grain sections of milled, medium grain California rice were compared for gross histological and morphological features using fluorescence and scanning electron microscopy (SEM). Cooked and raw grains were compared and the differences were assessed by autofluorescence of the cell walls and correlating fluorescence to SEM images. Milled, raw grains contain fine cracks throughout the endosperm. Cooked grains have wider, more defined cracks, suggesting that they serve as channels for water migration into the grain during cooking. Water penetrates unequally into the grain during cooking: low water penetration produces dense regions with minimal starch gelatinization, and high water penetration produces large voided areas. The voids occur in the transverse orientation of the grain and are the main of cause grain expansion during cooking.