The effect of ripening temperature on rice (Oryza sativa) grain quality was evaluated by assessing starch structure and gelatinization, pasting, and cooking properties. As the ripening temperature increased, the amylose content and number of short amylopectin chains decreased, whereas intermediate amylopectin chains increased, resulting in higher gelatinization temperatures and enthalpy in the starch. These results suggested that an increase in cooking temperature and time would be required for rice grown at higher temperatures. A high ripening temperature increased the peak, trough, and final viscosities and decreased the setback due to the reduction in amylose and the increase in long amylopectin chains. With regard to starch crystallinity and amylopectin molecular structure, the highest branches and compactness were observed at 28/20 °C. Rice that was grown at temperatures above 28/20 °C showed a deterioration of cooking quality and a tendency toward decreased palatability in sensory tests.

TitleEffects of timing and severity of salinity stress on rice (Oryza sativa L.) yield, grain composition, and starch functionality ABSTRACT: The aim of this work was to examine agronomic, compositional, and functional changes in rice (Oryza sativa L. cv. Nipponbare) grains from plants grown under low-to-moderate salinity stress in the greenhouse. Plants were grown in sodium chloride-containing soil (2 or 4 dS/m 2 electrical conductivity), which was imposed 4-weeks after transplant (called Seedling EC2 and EC4) or after the appearance of the anthers (called Anthesis EC2 and EC4). The former simulates field conditions while the latter permits observation of the isolated effect of salt on grain filling processes. Key findings of this study are the following: (i) Plants showed adaptive responses to prolonged salt treatment with no negative effects on grain weight or fertility. Seedling EC2 plants had more panicles and enhanced caryopsis dimensions, while surprisingly, Seedling EC4 plants did not differ from the control group in the agronomic parameters measured. (ii) Grain starch increased in Seedling EC4 (32.6%) and Anthesis EC2 (39%), respectively, suggesting a stimulatory effect of salt on starch accumulation. (iii) The salinity treatment of 2 dS/m 2 was better tolerated at anthesis than the 4 dS/m 2 treatment as the latter led to reduced grain weight (28.8%) and seed fertility (19.4%) and compensatory increases in protein (20.1%) and nitrogen (19.8%) contents. (iv) Although some salinity treatments led to changes in starch content, these did not alter starch fine structure, morphology, or composition. We observed no differences in reducing sugar and amylose content or starch granule size distribution among any of the treatments. The only alterations in starch were limited to small changes in thermal properties and glucan chain distribution, which were only seen in the Anthesis EC4 treatment. This similarity of compositional and functional features was supported by multivariate analysis of all variables measured, which suggested that differences due to treatments were minimal. Overall, this study documents the specific response of rice under defined conditions, and illustrates that the plasticity of plant response to mild stress is complex and highly context-dependent, even under greenhouse conditions in which other potential environmental stress impacts are minimized. KEYWORDS: rice (Oryza sativa L.), salinity stress, starch, starch functionalityRice (Oryza sativa L.) is one of the most important crops as it is a staple for over 3 billion people globally.1 Starch, and to a lesser extent protein, determine grain yields and quality, two important criteria for rice producers.2 Yield stability is the overriding agronomic consideration in places where rice is critical for food security, while grain sensory attributes are an important driver in other markets.2,3 Rice yield and sensory quality are both affected by environmental stress, and there is increasing concern on the specific effects of both.4−8 Soil salinity i...

Chalk, an opaque area in the rice grain, is an important quality characteristic in rice and occurs most commonly when grains are exposed to high temperatures during development. Chalky rice decreases the value of rice because of its undesirable appearance and eating quality for consumers. We investigated the chemical composition, morphological structure, cooking, texture properties of cooked rice, and pasting and gelatinization properties to evaluate the reason for the deterioration in eating quality of chalky rice.The ultra-structure of chalky kernels differed greatly from that of head rice. Chalky grain had more air spaces, a disordered cellular structure, and rounder amyloplasts than head rice. Chalky rice absorbed water more rapidly during cooking and had a slightly larger expansion volume than head rice, confirming its loose starch granule structure. The lower amylose content of chalky kernels caused a more soluble solid and higher iodine index during cooking indicating their lower eating quality compared to translucent kernels. The lower gelatinization temperature of chalky kernels was suggested to be related to a more short-branch chain amylopectin structure. Chalky kernels resulted in a harder and less adhesive (or sticky) texture of cooked rice, requiring more time for chewing than those of head kernels, caused by its low protein content.The palatability of cooked rice showed a linear decrease with increasing chalky rice proportion in the sensory evaluation. In amylography, the peak and final viscosities greatly decreased when the chalky rice proportion increased from 0 to 5%. It indicated that chalky rice kernels induce quality deterioration even at 5%.

Quantitative trait loci (QTL) related to the grain iron and zinc contents of brown rice were mapped by using a doubled haploid population derived from an intra-japonica cross between 'Hwaseonchal' and 'Goami 2'. QTL-QTL, background-QTL, and backgroundbackground interactions and candidate genes that affect grain iron and zinc contents were preliminarily identified. Twenty-one iron-and zinc-related QTL were found. The major-effect QTL qFe7 and qZn7 provided the highest contribution to phenotypic variance for grain iron and zinc contents. The colocation of zinc-and iron-related QTL on chromosomes 1, 4, 7 and 11 may account for the strong correlation between iron and zinc contents. A region on chromosome 7 and epistatic interaction between loci on chromosomes 2 and 10 affected iron content. qZn7 and qZn11.3 exerted additive effects on zinc content. Eleven iron-and zinc-related candidate genes colocated with qFe7, qZn7 and the region on chromosome 7 with an additive effect on iron content.The major-effect QTL identified here may be useful for breeding biofortified rice. K E Y W O R D Scandidate gene, doubled haploid, iron, japonica rice, quantitative trait loci, zinc | 345 JEONG Et al.

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