Karen A. K. Moldenhauer

Correlation Between Cooked Rice Texture and Rapid Visco Analyser Measurements

ABSTRACT Although amylose content is considered the most important determinant of cooked rice texture, this constituent falls short as a predictor, because cultivars with similar amylose contents may differ in textural properties. Thus, amylography is used as one of a battery of tests, in addition to measuring amylose content, to improve differentiation of cultivars. The purpose of our study was to determine how well amylography conducted with a Rapid Visco Analyser (RVA) serves as a predictor of cooked rice texture, alone and in combination, with amylose content. Textural properties of 87 samples representing short-, medium-, and long-grain rice cultivars were assessed by descriptive sensory and instrumental texture profile (TPA) analyses and related to RVA measurements. None of the cooked rice textural attributes, whether measured by descriptive analysis or TPA, were modeled by RVA with high accuracy (i.e., high r2). Sensory texture attributes cohesiveness of mass, stickiness, and initial starchy coatin...

Prediction of cooked rice texture quality using near-infrared reflectance analysis of whole-grain milled samples

ABSTRACT Rice quality is based on chemical and physical properties affecting its appearance, flavor, and texture characteristics. Sensory quality can be assessed by a combination of descriptive sensory and physicochemical property evaluations. The purpose of the present study was to assess the potential of near-infrared reflectance spectroscopy (NIRS) and NIRS in combination with other physicochemical measurements for the determination of sensory texture attributes in whole-grain milled rice samples. Six rice samples representing combinations of variety and growing locations received treatments of two degrees of milling and five drying conditions to achieve final moisture levels of 12 or 15% (n = 120). Quality measurements of the cooked rice included sensory and instrumental texture analyses. Quality measurements of the uncooked rice included amylose and protein (chemical reference), whiteness, transparency, and degree of milling (appearance units of milled rice), and NIRS analyses. Partial least squares ...

Effects of Postharvest Processing on Texture Profile Analysis of Cooked Rice

ABSTRACT The effects of drying conditions, final moisture content, and degree of milling on the texture of cooked rice varieties, as measured by texture profile analysis, were investigated. Instrumentally measured textural properties were not significantly (α = 0.05) affected by drying conditions, with the exception of cohesiveness. Cohesiveness was lower in rice dried at lower temperatures (18°C or ambient) than in that dried at the higher commercial temperatures. Final moisture content and degree of milling significantly (α = 0.05) affected textural property values for adhesiveness, cohesiveness, hardness, and springiness; their effects were interdependent. The effects of deep milling were more pronounced in the rice dried to 15% moisture than that dried to 12%. In general, textural property values for hardness were higher and those for cohesiveness, adhesiveness, and springiness were lower in regular-milled rice dried to 15% moisture than in that dried to 12%. In contrast, hardness values were lower an...

Effects of Degree of Milling, Drying Condition, and Final Moisture Content on Sensory Texture of Cooked Rice

ABSTRACT Different cultures have different preferences for cooked rice flavor and texture characteristics. These differences provide opportunities for U.S. rice varieties to fit into global markets to meet consumer demands worldwide. It is important to assess the properties of U.S. rice varieties and determine the factors that influence their eating quality. Cooked rice texture attributes can be affected by postharvest handling practices, such as degree of milling, drying condition, and final moisture. This article reports the effects of postharvest handling parameters on the texture of cooked medium- and short-grain rice varieties grown in Arkansas (AR) and California (CA), as measured by descriptive sensory analysis. The rice samples were Bengal (AR), Koshihikari (AR), Koshihikari (CA), M-401 (AR), M-401 (CA), and M-202 (CA). The six rice varieties were regular- or deepmilled and dried under one of five drying conditions to achieve final moisture levels of 12 or 15% (n = 120). A trained sensory panel de...

Genotypic and phenotypic characterization of genetic differentiation and diversity in the USDA rice mini-core collection

A rice mini-core collection consisting of 217 accessions has been developed to represent the USDA core and whole collections that include 1,794 and 18,709 accessions, respectively. To improve the efficiency of mining valuable genes and broadening the genetic diversity in breeding, genetic structure and diversity were analyzed using both genotypic (128 molecular markers) and phenotypic (14 numerical traits) data. This mini-core had 13.5 alleles per locus, which is the most among the reported germplasm collections of rice. Similarly, polymorphic information content (PIC) value was 0.71 in the mini-core which is the highest with one exception. The high genetic diversity in the mini-core suggests there is a good possibility of mining genes of interest and selecting parents which will improve food production and quality. A model-based clustering analysis resulted in lowland rice including three groups, aus (39 accessions), indica (71) and their admixtures (5), upland rice including temperate japonica (32), tropical japonica (40), aromatic (6) and their admixtures (12) and wild rice (12) including glaberrima and four other species of Oryza. Group differentiation was analyzed using both genotypic distance Fst from 128 molecular markers and phenotypic (Mahalanobis) distance D2 from 14 traits. Both dendrograms built by Fst and D2 reached similar-differentiative relationship among these genetic groups, and the correlation coefficient showed high value 0.85 between Fst matrix and D2 matrix. The information of genetic and phenotypic differentiation could be helpful for the association mapping of genes of interest. Analysis of genotypic and phenotypic diversity based on genetic structure would facilitate parent selection for broadening genetic base of modern rice cultivars via breeding effort.

Unraveling the complex trait of harvest index with association mapping in rice (Oryza sativa L.).

Harvest index is a measure of success in partitioning assimilated photosynthate. An improvement of harvest index means an increase in the economic portion of the plant. Our objective was to identify genetic markers associated with harvest index traits using 203 O. sativa accessions. The phenotyping for 14 traits was conducted in both temperate (Arkansas) and subtropical (Texas) climates and the genotyping used 154 SSRs and an indel marker. Heading, plant height and weight, and panicle length had negative correlations, while seed set and grain weight/panicle had positive correlations with harvest index across both locations. Subsequent genetic diversity and population structure analyses identified five groups in this collection, which corresponded to their geographic origins. Model comparisons revealed that different dimensions of principal components analysis (PCA) affected harvest index traits for mapping accuracy, and kinship did not help. In total, 36 markers in Arkansas and 28 markers in Texas were identified to be significantly associated with harvest index traits. Seven and two markers were consistently associated with two or more harvest index correlated traits in Arkansas and Texas, respectively. Additionally, four markers were constitutively identified at both locations, while 32 and 24 markers were identified specifically in Arkansas and Texas, respectively. Allelic analysis of four constitutive markers demonstrated that allele 253 bp of RM431 had significantly greater effect on decreasing plant height, and 390 bp of RM24011 had the greatest effect on decreasing panicle length across both locations. Many of these identified markers are located either nearby or flanking the regions where the QTLs for harvest index have been reported. Thus, the results from this association mapping study complement and enrich the information from linkage-based QTL studies and will be the basis for improving harvest index directly and indirectly in rice.

Effects of Drying Conditions, Final Moisture Content, and Degree of Milling on Rice Flavor

ABSTRACT The extent that postharvest processing parameters influence the sensory quality of cooked rice is not well known. In this investigation, the effects of drying conditions, final moisture content, and degree of milling on the flavor of rice varieties Bengal, M-401, and Koshihikari were determined by descriptive sensory analysis. No trends were observed indicating an increase or decrease in flavor attributes with increased drying temperatures (18–60°C). Intensities of desirable and undesirable flavor attributes were higher in rice dried to 15% moisture compared to 12% moisture. The effects of deep-milling on flavor attribute intensities were dependent on moisture content and variety or location.

Maximum Outcrossing Rate and Genetic Compatibility between Red Rice (Oryza sativa) Biotypes and Clearfield™ Rice

Abstract The transfer of the imazethapyr-resistant gene from Clearfield™ (CL) rice to red rice is an ecological risk. Flowering synchronization and genetic compatibility between cultivated rice and red rice could influence gene transfer. We examined the (1) variability in maximum outcrossing rate between 12 red rice biotypes and ‘CL161’ rice during their peak flowering overlap in the field and (2) genetic compatibility of red rice biotypes with CL161 rice. Experiments were conducted at Stuttgart, AR, and Fayetteville, AR, from 2005 to 2007. To evaluate the flowering synchrony of red rice and CL161 rice as well as its impact on outcrossing rate, field experiments were conducted at four planting times from early April to late May. The red rice biotypes were planted in the middle row of nine-row CL161 plots and flowering was monitored. Outcrosses were evaluated in subsequent years by herbicide response and simple-sequence-repeat marker assays. To determine compatibility, manual crosses were performed between 12 red rice biotypes and CL161 rice in the greenhouse. The flowering duration of all red rice types ranged from 5 to 16 d after the onset of flowering in contrast to 6 d in CL161 rice. Ten of the twelve types of red rice had ≥ 70% overlap in flowering time with CL161 rice in at least one planting date. The maximum field outcrossing rate between red rice biotypes and CL161 ranged from 0.03 to 0.25%. The field outcrossing rate between red rice biotypes differed (P < 0.01), but flowering synchronization was not directly related to outcrossing rate. Manual crosses resulted in seed sets of 49 to 94%. The majority of red rice biotypes had similar compatibility with CL161 rice. Thus, other factors must contribute to hybridization rates in the field. Follow-up experiments should investigate other plant factors and environmental influence on hybridization rate. Nomenclature: Imazethapyr; red rice, Oryza sativa L. ORYSA; rice Oryza sativa ‘CL161’.

Categorizing Rice Cultivars Based on Cluster Analysis of Amylose Content, Protein Content and Sensory Attributes

ABSTRACT Presently, rice cultivars are categorized according to grain dimensions, amylose content, and alkali spreading value (gelatinization temperature type). Categorization of rice cultivars based on total sensory impact is needed. This work endeavors to divide world rices into groups based on amylose, protein, flavor, and texture properties. Ninety-one rice samples representing 79 different cultivars and seven growing locations were separated into seven groups with Wards Cluster Analysis. Cluster 1 included a third of the rice samples and had cultivars with a large diversity of grain shapes and amylose contents. Mean attribute scores for this cluster were near the grand mean for the collective rice samples for nearly every sensory attribute. Cluster 2 included conventional U.S. short- and medium-grain cultivars. Cluster 3 included conventional U.S. medium cultivars that were produced in Louisiana. Mean sensory scores for this cluster characterized these cultivars as having relatively undesirable flav...

Near-Infrared Reflectance Analysis for Prediction of Cooked Rice Texture

ABSTRACT The ability of near-infrared (NIR) spectroscopy to predict sensory texture attributes of diverse rice cultivars was examined. The sensory texture of 87 samples representing 77 different short-, medium-, and long-grain cultivars was evaluated by trained panelists using descriptive analysis. Correlations between sensory texture attributes and NIR reflectance data were examined using the multivariate method of partial least squares (PLS) regression. Texture attributes (hardness, initial starchy coating, cohesiveness of mass, slickness, and stickiness) measured by panelists in the early evaluation phases were successfully predicted (R2calibration 0.71–0.96). Cohesiveness of mass, the maximum degree to which the sample holds together in a mass while chewing, was best modeled with R2calibration = 0.96 and R2validation = 0.90. Key wavelengths contributing to the models describing the texture attributes were wavelengths also contributing to models for amylose, protein, and lipid contents.