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Differences in Viscosity of Superior and Inferior Spikelets of Japonica Rice with Varying Percentage Apparent Amylose Content Zhao-hui Ma, Hai-tao Cheng, Y Nitta, Naohiro Aoki, Yun Chen, Heng-xue Chen, Ryu Ohsugi, and Wen-yan Lyu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b00048 • Publication Date (Web): 30 Mar 2017 Downloaded from http://pubs.acs.org on April 3, 2017
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Title
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Differences in Viscosity of Superior and Inferior Spikelets of Japonica Rice with
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Varying Percentage Apparent Amylose Content
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Authors
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Zhao-hui Ma, Hai-tao Cheng, Y Nitta, Naohiro Aoki, Yun Chen, Heng-xue Chen,
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Ryu Ohsugi, Wen-yan Lyu*
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Z.H. Maa, H.T. Cheng, Y. Chen, H.X. Chen and W.Y. Lyu*, Rice Research Institute,
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Key Laboratory of Crop Physiology, Ecology, Genetics and Breeding, Ministry of
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Agriculture, Shenyang Agricultural University, Shenyang Liaoning China, 110161,
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CN; Y Nitta, The College of Agriculture Ibaraki University Ami, Ibaraki 300-0393,
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Japan, Ibaraki, 062-8555, JP; N. Aoki, The University of Tokyo, Graduate School of
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Agricultural and Life Sciences1-1-1 Yayoi, Bunkyo-ku Tokyo, 113-8657, JP; R.
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Ohsugi, The University of Tokyo, Graduate School of Agricultural and Life Sciences
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1-1-1 Yayoi Bunkyo-ku Tokyo, JP.
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*Corresponding author—Wen-yan Lyu
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Differences in Viscosity of Superior and Inferior Spikelets of Japonica Rice with
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Varying Percentage Apparent Amylose Content
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ABSTRACT: Viscosity, a crucial characteristic for rice palatability, is affected by
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endosperm characters. We compared correlations between differences in viscosity of
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japonica rice with varying palatability and endosperm characters. Changes in apparent
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amylose and protein content (AAC and PC%, respectively), and amylopectin
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side-chain distribution, and the relationship of these traits with palatability were
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investigated in superior and inferior spikelets of good cultivars with low amylose
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content from Hokkaido and common cultivars from northeastern Japan, using rapid
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visco analyser characteristics and rice-grain microstructures. Significant differences
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occurred in PC%, AAC%, breakdown, setback, peak time, and pasting temperature of
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different cultivars and grain positions. Amylopectin components showed remarkable
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differences in grain surfaces, surface layers, and section structure between the grain
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varieties. Hokkaido cultivars showed better viscosity than northeastern cultivars,
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particularly initial stage grains. Correlation analysis indicated viscosity was mainly
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AAC%-dependent, whereas differences in endosperm characteristics between spikelet
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positions were mainly due to grain-filling temperature.
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Keywords: viscosity, japonica rice, low AAC%, grain position, filling grain
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INTRODUCTION
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Rice (Oryza sativa L.) is a basic cereal crop and the primary staple food of over
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half the world population, particularly in Asia. Therefore, its palatability is of great
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importance. Rice is divided into the japonica and indica subspecies, which have 2
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different palatability traits. Viscoelasticity is considered the determinant of rice
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palatability. Japonica rice is known to have good viscosity and elasticity as well as
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moderate hardness, which are characteristics related to endosperm composition1,2.
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Starch, the basis of rice endosperm, has two main components: amylose and
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amylopectin. The amylose content includes real amylose and extra-long unit chains of
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amylopectin, which are measured using the iodine-blue colorimetric method and,
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therefore, denoted as percentage apparent amylose content (AAC%)2,3. For japonica
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cultivars, lower AAC%, water absorbance, and swelling correspond to greater rice
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viscosity and palatability4.
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In recent years, researchers have discovered that amylopectin structure affects rice
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palatability. Rice texture is softer when short to intermediate chains are increased in
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amylopectin5,6. Conversely, rice is hard and difficult to cook when the midchain
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proportion is higher than chains of other lengths7,8.
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In addition to starch, protein has great influence on rice palatability, as determined
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by starch pasting9. High protein content increases rice hardness and decreases the
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viscosity10 and glossiness of rice11. The most direct way to evaluate rice palatability is
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a sensory test, but these are difficult to carry out. Toyoshima et al.12 reported that a
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rapid visco analyzer (RVA) could evaluate the viscosity of polished rice flour, widely
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used in flour viscosity trait measurements, and their results were closely correlated to
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palatability traits. Rice with high palatability has a higher breakdown and a lower
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final viscosity and setback than low palatable varieties13. The morphological
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characteristics of grain are closely related to palatability. Previous studies have 3
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explored liquid-nitrogen quick-freezing, a vacuum freeze-drying method that can
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maintain rice grain reset conditions after cooking14. Rice grain surfaces and sectional
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structures were observed using scanning electron microscopy (SEM). Highly
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palatable rice with high viscosity exhibited more bright cracking features with fewer
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dark film structures and moderate pasting on the grain surface, which showed
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reticulate structures mixed with clintheriform sheet structures that are closely related
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to viscosity and spongy inner features. Rice with low palatability did not have these
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characteristics15-17.
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Koshikikari is a world-famous rice cultivar with good palatability and the largest
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cultivated area in Japan since 1979. Nevertheless, most breeders grow other cultivars
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in addition to Koshikikari. Through the market-oriented rice breeding program
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(1989-1996), breeders obtained materials with lower AAC% than that of common rice
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varieties (“low-AAC% cultivars,” AAC% < 16.5%), including Oborozuki,
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Yukigasumi, and Yukisayaka from Hokkaido. These cultivars are known as the most
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palatable local cultivars because of their AAC% and good palatability evaluations18.
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However, few studies have investigated the microstructures of these low AAC% rice
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cultivars.
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Environmental conditions influenced palatability by regulating grouting. Rice is a
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compound botrys glumous flower and its growth conditions vary according to
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position, and therefore result in varying grain composition and character. Superior
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grains grow on top and have earlier flowering and higher grain plumpness than
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inferior grains, which grow near the bottom. However, good grain plumpness is 4
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observed in bottom spikelets as well. Various practices for producing polished rice
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from caryopsis have been used for enrichment. Hence, it would be useful to compare
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correlations between palatability and grain position in superior and inferior grains.
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Therefore, we investigated the differences between low-AAC% rice with good
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palatability from Hokkaido and common cultivars to compare superior and inferior
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grains in the Tokyo region. This study was designed to determine the intergranular
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differences that affect viscosity in low-AAC% rice cultivars.
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MATERIALS AND METHODS
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Materials
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Three low-AAC% cultivars and three common cultivars were obtained from
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Hokkaido and Northeast Japan, respectively. The low AAC% characteristics of
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Oborozuki and Yukigasumi are controlled by the Wx1-1 in chromosome 6, and those
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of Yukisayaka are controlled by qAC9.3 in chromosome 919. Yukisayaka has low
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protein content but does not possess the endosperm opacifying traits of Oborozuki and
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Yukigasumi. Common cultivars include Akitakomachi and Hitomebore, which are
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descendants of Koshihikari with similar palatability to the parent cultivar, and
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Tohoku194, which is a descendant of Sasanisiki and has a lower viscosity than that of
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Koshihikari.
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Cultivation and management
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Field experiments were carried out at the Institute for Sustainable Agro-ecosystem
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Services at the University of Tokyo（N35°44′, S139°32′）in 2015. All cultivars were 5
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sown on May 20, 2015, and the common and Hokkaido varieties were transplanted on
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June 16 and June 29 2015, respectively. Each cultivar was transplanted in seven rows.
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The planting space was 30.0 × 15.0 cm and each experiment was replicated twice. As
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a base, 500 kg·ha-1 (N:P2O5:K2O = 12:16:18%) of compound fertilizer was used. The
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temperature data of the crop growth stage was logged using as automatic temperature
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recorder that was set in the field.
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Grains obtained and filling stage division
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Samples were obtained at the initial and end stages of the heading period (superior 20-22
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spikelet, UP; inferior spikelet, LP)
. The middle flag leaf of each plant was
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designated as a standard, starting from the neck of the panicle drawn out of the sheath
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below 1 cm. The sample panicle was harvested 45 to 52 days after designation (Table
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1). The total grain from the primary branches was collected (top three and bottom four)
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from UP and LP after natural withering. The marking date, the day before, and the
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day after the marking date were designated as 0, -1, and +1 according to related
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research22, so that the filling data was marked. In this study, the filling stage was
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divided as follow: from the marking date, the -5 to -1, 0–5, and 6–14 of the UP, and
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the -2–5, 6–16, and 17–32 of LP were the early, middle, and late stage of the filling
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period, respectively. Therefore, the duration of the three phases in the UP and LP
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were up to day 5, 6, and 9, and day 7, 11, and 16, respectively. After polishing, the
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inadequate grain was eliminated using a 1.9-mm sieve.
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Production of polished rice and flour
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The brown rice was polished using an experimental friction-type rice milling
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machine (Grani Polisher Pearlest, Kett Electric Laboratory, Japan) to obtain a milling
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yield of 90–91%. White rice flour was prepared using a somatic cell crusher
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(Yasuikikai Company, Multi-Beads Shocker series, MB901U[S]) with a 100-mesh
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screen.
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Measurement of water content of white rice flour
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The water content was measured using a 130℃ drying method, and the results of
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AAC% and PC% were converted to a
