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Effect of Nitrogen Management on Structure and Physicochemical Properties of Rice Starch Dawei Zhu, Hongcheng Zhang, Baowei Guo, Ke Xu, Qigen Dai, Cunxu Wei, Haiyan Wei, Hui Gao, Zhongyang Huo, yajie hu, and peiyuan cui J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.6b03173 • Publication Date (Web): 07 Oct 2016 Downloaded from http://pubs.acs.org on October 17, 2016

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Title: Effect of Nitrogen Management on the Structure and Physicochemical

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Properties of Rice Starch

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Dawei Zhu, Hongcheng Zhang*, Baowei Guo, Ke Xu, Qigen Dai, Cunxu Wei, Haiyan

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Wei, Hui Gao, Yajie Hu, Peiyuan Cui, Zhongyang Huo*

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Innovation Center of Rice Cultivation Technology in Yangtze River Valley, Ministry

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of Agriculture/ Key Laboratory of Crop Genetics and Physiology of Jiangsu Province,

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Yangzhou University, Yangzhou 225001, Jiangsu Province, China.

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* Corresponding Author

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Hongcheng Zhang

Email: [email protected]

Zhongyang Huo

Email: [email protected]

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Abstract

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Nitrogen management (nitrogen application ratio at transplanting, tillering, and panicle

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initiation growth stages) is an important parameter in crop cultivation and is closely associated

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with rice yield and grain quality. The physicochemical and structural properties of starches

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separated from two rice varieties grown under three different nitrogen management ratios (9:1; 7:3;

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6:4) were investigated. As the percentage of nitrogen used in the panicle initiation stage increased,

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the content of small starch granules improved, whereas the content of large granules decreased.

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Amylose content decreased with increasing nitrogen ratio at the panicle initiation stage, thereby

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resulting in high swelling power, water solubility, gelatinization enthalpy, and low retrogradation.

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The X-ray diffraction patterns of the starches were found to be A type. The present study indicated

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that the best nitrogen management ratio for the cultivation of rice with the highest yield, desirable

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starch physicochemical properties for high quality cooked rice, and a moderate protein level is 7:3.

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Keywords: Rice starch; Structural properties; Thermal properties; Pasting properties.

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Introduction

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Rice (Oryza sativa L.) is the most important grain crop in Asia, with more than half of the

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world's population dependent on rice and its associated products to obtain most of their caloric and

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nutrition requirements.1-3 Major improvements in living standards has resulted in a greater need to

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improve the quality of cultivated rice.4 Rice quality depends not only on the genotype of the plant

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but also on fertilization conditions, soil type, and the climatic conditions during rice growth.5,6

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Starch comprises more than 80% of the total weight of rice grains and constitutes the main caloric

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source in rice. Among various indices in starch, amylose content is considered as the main factor

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that determines the overall quality of cooked rice. In addition, other factors such as granule size

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distribution, crystallinity, thermal properties, and pasting temperature of starch also affect the

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quality of cooked rice.7-9

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Nitrogen (N) is the most important element in rice fertilizers that significantly affects rice

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growth and development.10,11 N management [N application ratio at transplanting, tillering, and

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panicle initiation (PI) stages] is an important parameter in rice cultivation and is closely associated

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with rice yield and grain quality.12−14 The N management ratio of most Chinese farmers has

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traditionally been 90%: 10% (the sum of ratios of transplanting and tillering stages: PI stage).

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However, plant physiologists have found that this ratio leads to suboptimal efficiency in N

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utilization and have speculated that improved rice yield and quality could be obtained by

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increasing the amount of fertilizers used at the PI stage, which in turn can significantly increase N

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fertilizer utilization efficiency.15 Lin et al.16 suggested that higher rice yield could be obtained with

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a N ratio of 70%: 30% (sum of ratios of transplanting and tillering stages: PI stage) or 60%: 40%.

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Zhang et al.17 obtained similar results and reported that rice yield could be optimized using a ratio

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of 70%: 30%, and better grain quality could be achieved using a ratio of 60%:40%. However,

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most of research studies thus far have concentrated on the effect of N management on grain yield,

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whereas only a few have investigated its effect on starch physicochemical properties. To the best

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of our knowledge, research studies on the physicochemical properties of starch obtained from rice

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grown under different N management conditions are limited.18,19 Further research in this field is of

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critical importance in order to establish fertilizing conditions that would improve grain starch

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quality. Therefore, we report our findings on the structure and physicochemical properties of rice

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starch obtained from cultivars exposed to different N management conditions.

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Material and Methods

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Plant Materials and Experimental Design

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Experiments were conducted at the Yangzhou University Farm (119°42' E, 32°39' N) during

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the 2015 rice cultivating season. The soil type was sandy loam, and the preceding crop was wheat.

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Total availability of N, phosphorous (P), and potassium (K) was determined to be 1.4 g·kg−1, 35.1

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mg·kg−1, and 88.3 mg·kg−1, respectively. The two varieties of rice used in the present study were

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Nanjing 46 (NJ 46) and Nanjing 5055 (NJ 5055), which are widely applied along the lower

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elevations of the Yangtze River and were kindly provided by the Jiangsu Academy of Agricultural

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Sciences.

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The experiment was arranged in a split plot design, with the three main plots divided into

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different N management ratios, having sum of ratios of transplanting and tillering stages: PI stage

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ratios of 90%: 10%, 70%: 30%, and 60%: 40%, respectively, and a total N application of 150

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kg/ha (Table 1). The subplots were divided into the two different rice varieties. In addition, we had

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a separate plot with no added N that was used as control. Seeds were sown on May 25, 2015 and

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the seedlings were transplanted on June 14, 2015. The transplanting density was 255,000 hills per

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hectare, and one hill had three seedlings. The plot area was 16 m2 (4 m × 4 m). Other practices

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were in conformity with local recommendations. Protein content was determined according to the

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AACC (1984) procedures.20 Assays of total starch ratio were performed using commercial kits

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Sigma (HK, China).

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Starch Isolation

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Starch was isolated according to the method of Wei et al.21 with minor modifications. Rice

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flour (20 g) was steeped in a 0.45% sodium metabisulfite aqueous solution with 10 mg·g−1

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alkaline protease at room temperature for 24 h to remove the protein. The homogenate was sieved

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(200-mesh), and the residue remaining on the mesh sieve was collected. The residues were mixed

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with 30 mL of deionized water and stirred for 2 min and then sieved (200-mesh) again. The

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filtered starch slurry was centrifuged at 3,000 g for 10 min. The supernatant was discarded and the

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faintly colored upper residual layer was removed; the remaining white layer was resuspended with

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20 mL of deionized water and again centrifuged at 3,000 g for 10 min. The supernatant was then

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again scooped. The above-mentioned centrifugal steps were repeated five times to ensure that the

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impurities were totally removed. Finally, the starch was then dried at 30°C at ambient pressure and

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collected with a 200-mesh sieve.

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Granule Size Analysis

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The granule size distribution of starch was studied using a laser diffraction particle size

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analyzer (Mastersizer 2000, Malvern, England). The starch samples were immersed in absolute

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ethyl alcohol and stirred at 2,000 rpm. The instrument was adjusted to measure starch granule size,

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which ranged from 0.1 to 2,000 µm.

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Measurements of Iodine Absorption Spectrum and Apparent Amylose Content 5

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(AAC)

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Starch was defatted in methanol/water (85:15, v/v) and then dissolved in dimethyl sulfoxide

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containing urea (UDMSO) solution. The starch-UDMSO solution was treated with an I2-KI

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solution according to the method of Man et al. 22 The iodine absorption spectrum was scanned

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from wavelength of 400 nm to 900 nm using a spectrophotometer (Ultrospec 6300pro, Amersham

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Biosciences). Iodine blue values were measured at a wavelength of 680 nm, and the AAC was

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calculated from the absorbance that was measure at a wavelength of 620 nm, with reference to a

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standard curve that was prepared using amylopectin from corn and amylose from potato.

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X-ray Diffraction Analysis

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X-ray diffractograms were generated using an X-ray powder diffractometer (XRD) (D8

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Advance, Bruker-AXS, Germany) that was operated at 200 mA and 40 kV, over a diffraction angle

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(2θ) range of 3° to 40°, with a step size of 0.02°, and a sampling interval of 0.6 s. Relative

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crystallinity (%) was calculated using MDI Jade 6 software.

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Analysis of Structural Order of the Starch External Region

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Attenuated reflectance Fourier Transform IR (ATR-FTIR) analysis was conducted using a

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DTGS detector equipped with an ATR single-reflectance cell that contained a germanium crystal

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(45° incidence angle) (Varian 7000, PIKE Technologies, USA) as previously described by Man et

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al.19

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Determination of Swelling Power and Water Solubility

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Determination of swelling power and water solubility was conducted according to the method

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of Konik-Rose et al.23 Starch samples (m0) were mixed with water (2%, w/v), placed in a 2-mL

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centrifuge tube (m1), and heated in a water bath at 95°C for 30 min. The tubes were subjected to

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gentle shaking for 1 min. The samples were then cooled down to room temperature, centrifuged at

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8,000g for 10 min, and the supernatant were discarded. The colloid in the centrifuge tube was

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weighed (m2), and the sediments were dried to constant weight (m3) at 60°C. The swelling power

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and solubility were calculated as follows: Swelling power = (m2 − m1)/(m3 − m1) (g/g), and

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Solubility (%) = 100 × (m0 + m1 − m3)/m0 × 100%.

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Determination of Thermal Properties

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Thermal properties were examined by using differential scanning calorimetry (DSC) (Model

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200 F3 Maia, Netzsch, Germany) following the procedure described by Lu and Lu.24 Starch

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samples (5 mg, dry weight) were mixed with 10 µL of water and sealed in an aluminum pan at 4°C

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for 12 h. After equilibrating for 1 h at room temperature, the samples were scanned against a blank

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(empty pan) at a heating rate of 10°C/min from 25°C to 100 °C. Retrogradation percentage (%R)

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was calculated as %R = 100 × ∆Hret/∆Hgel.

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Determination of Pasting Properties

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Starch pasting properties were determined by using a rapid viscosity analyzer (Model 3D,

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Newport Scientific, Australia) according to the method of Lu and Lu. 24 The starch sample (2.5 g,

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dry weight) was mixed with 25 mL of deionized H2O, and the pasting programmed cycle was set

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at 13 min. Starch samples were first heated at 50°C for 1 min and then heated from 50°C to 95°C

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at a heating rate of 12°C/min. The temperature was held at 95°C for 2.5 min, and the starch was

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then cooled down to 50°C at a cooling rate of 12°C/min, and held at that temperature for 2 min.

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Statistical Analysis

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The data shown in all of the tables were expressed as the mean of triplicate experiments.

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One-way ANOVA and Tukey's test (P < 0.05) were performed using the SPSS 16.0 Statistical

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Software Program.

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Results and Discussion

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Grain Yield and the Contents of Protein and Starch

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The grain yield of NJ 9108 and NJ 5055 under different N management conditions showed

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significant variation (Table 1). As the percentage of N fertilizer used at the PI stage increased,

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grain yield initially increased and then subsequently decreased. Protein content significantly

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increased with higher N ratios at the PI stage, whereas starch content decreased with increasing N

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ratio at the PI stage. In rice grains, carbon metabolism and N metabolism utilize similar reducing

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power ATP and carbon skeleton. Competition for ATP and carbon skeleton generally occurs during

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higher rates of protein synthesis. Therefore, when more protein is synthesized, a lower starch

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content is observed.25,26

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Starch Granule Size Distribution

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The starch granules obtained from rice grown under different N management conditions

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showed significant variations in size distribution (Table 2, Fig 1A, B). In the present study, starch

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granules were classified into small (< 1 µm), medium (1–5 µm), large (5–20 µm) granules

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according to the figure of granule size distribution. When the ratio (sum of ratios of transplanting

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and tillering stages: PI stage) of N management was 6:4, both rice varieties exhibited the highest

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content of small- and medium-sized starch granules. With increasing N ratio utilized at the PI

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stage, the amount of small- and medium-sized starch granules increased, whereas that of large

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starch granules decreased. Higher N ratios (i.e., greater percentage used in the PI stage) have been

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reported to extent the whole growth period, in particular the late grain filling stages.

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reports have shown that large wheat starch granules appear during the early filling stage, whereas

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small starch granules develop approximately 20 days after flowering.29 Therefore, prolonging the

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late grain filling stage allows the formation of small- and medium-sized starch granules, which

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possibly explains our observation that the amount of large granules decreased with high N ratios at

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the PI stage.

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Iodine Absorbance Properties of Starch

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Maximum absorption wavelength (λmax), blue value, and apparent amylose content (AAC)

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decreased in both rice varieties as the ratio of fertilizer used at the PI stage increased (Table 3).

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Amylose content as determined on the basis of iodine and starch affinity is described as apparent

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amylose content (AAC), which may overestimate the amylose content because long branch-chains

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of amylopectin can also bind to iodine.

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greater proportion of long-chain highly branched amylopectin.

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may be mainly attributable to a decrease in the number of large granules under higher N ratios at

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the PI stage. Ma et al.32 investigated starch synthesis using different supply dates for N and found

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that a high N ratio at early growth stages improved the activity of starch synthase (GBSS),

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whereas that at later growth stages enhanced starch branching enzyme (SBE) enzyme. Therefore,

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with decreasing N ratios in transplanting and tillering stages, GBSS activity decreased, thereby

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resulting in a decrease in amylose content.

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XRD Patterns of Starch Samples

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Lindeboom et al. reported that large granules had a 31

Therefore, a decrease in AAC

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Based on their XRD spectra, native starches can be classified into types A-, B-, and C.33 The

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X-ray diffraction patterns of starch samples obtained under different fertilizer ratios are presented

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in Fig. 1C, D In all starch samples, strong peaks were observed at about 15° and 23° 2θ, and an

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unresolved doublet was detected at 17° and 18° 2θ. This XRD peak pattern resembled that of

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typical A-type cereal starches,34 indicating that N management does not alter crystallinity type.

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However, variations in relative crystallinity (Table 3) were observed with different N

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managements, with higher crystallinity occurring as the ratio of N that was added at the PI stage

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increased from 10% to 40%. Therefore, starch samples with high amylose content have lower

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relative crystallinity, which is in agreement with the findings of previous reports that relative

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crystallinity is negatively correlated to amylose content.35

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ATR-FTIR Spectra of Starch Samples

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The infrared spectrum of starch is influenced by the composition of its surface and can be

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used to investigate short-range degree of order. The bands at 1,045 cm−1 and 1,022 cm−1 can

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provide a measurement tool for the crystalline and amorphous characteristics of starch,

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respectively. The ratio of the intensity of the peaks at 1,045 cm−1 and 1,022 cm−1 was used to

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measure the degree of crystallinity, whereas the ratio 1,022 cm−1/955 cm−1 can be used to quantify

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the proportion of amorphous to ordered structure in starch.36-37

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Starch obtained from rice grown in the no-N condition showed the highest 1,045 cm−1 /1022

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cm−1 ratio (Table 3), indicating that the degree of order near the starch granule surface was higher

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than in other conditions, whereas the ratio of 1,022 cm−1 /955 cm−1 was the lowest compared to

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other N ratios. These results indicate that starch samples with high proportions of large starch

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granules have a high degree of order, which is in agreement with the findings of previous reports,

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which show that the short-range degree is significantly positively correlated with granule size.33

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Swelling Power and Water Solubility of Starch

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Swelling power and water solubility varied among different N management ratios; swelling

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power ranged from 14.9–28.6 and 15.1–22.7 g·g−1 for NJ 5055 and NJ 46 respectively, water

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solubility varied from 15.3–21.5% and 14.0–18.6% for NJ 5055 and NJ 46, respectively (Table 3).

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Swelling power and water solubility both exhibited steady increases with higher N percentage at

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the PI stage, reaching a maximum with an N management ratio of 6:4.

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Swelling power and water solubility were used to measure the extent of interactions between

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starch chains within the amorphous and crystalline domains.38,39 Higher swelling power and water

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solubility were primarily attributed to lower AAC in the starch obtained with a N management

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ratio of 6:4, as amylose can restrain further swelling and help maintain the structure of swollen

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starch granules.40 In addition, starch samples contained with high D(3,2) and D(4,2) values have

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higher water affinity because these have more surface bind with water, and greater swelling

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compared to larger granules obtained from other N management treatments.41

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Thermal Properties of Starch

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The gelatinization properties of rice starch are strongly associated with the quality and flavor

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characteristics of cooked rice. In the present study, significant changes in the gelatinization

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properties were observed with different N management ratios (Table 4). Gelatinization enthalpy

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(∆Hgel), which reflects the quantity and quality of starch crystallinity, is used to measure the loss

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of double helical and crystalline structures during starch gelatinization.

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∆Hgel was observed with increasing amounts of N that was applied at the PI stage. The high ∆Hgel

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at N management ratios of 7:3 and 6:4 can be attributed to the high relative crystallinity in starch

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granules and low amylose contents.44 Furthermore, Sasaki and Matsuki investigated 12 wheat

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starches and found that high gelatinization enthalpy (△Hgel) is usually coupled with high swelling

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power.45

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42-43

A gradual increase in

A decrease in gelatinization temperature was observed with higher N percentage at the PI

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stage, with the highest temperature observed in the control experiment (N management ratio: 0).

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Higher gelatinization temperature means higher cooking temperature and longer cooking time.

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Higher gelatinization temperatures are generally attributable to high amylose content, which

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results from the use of high nitrogen ratios at transplanting and tillering stages because higher

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amounts of amylose restrict the hydration of amorphous regions.46 In addition, Wang et al. studied

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starches from Chinese rice cultivars and concluded that the variation in gelatinization temperature

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might be due to differences in the amount of long chains in amylopectin because rice varieties

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with a high proportion of long chains in amylopectin require higher temperatures to completely

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dissociate.47,48

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The enthalpy of retrogradation (∆Hret) and retrogradation (%R) were used to measure the

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tendency toward retrogradation as the starch sample was cooled. ∆Hret and %R decreased with

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higher N percentage at the PI stage, peaking at the control experiment, which may be caused by

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high amounts of longer chains in amylopectin.49 Sang et al. studied sorghum starch and found that

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the high level of long chains in amylopectin results in high retrogradation.50 In addition, the ratio

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of amylose to amylopectin, phosphate esters, and granular structure also influences ∆Hret and %R,

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and amylopectin plays an important role in starch retrogradation.

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Pasting Properties of Starch

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Peak viscosity is defined as the highest viscosity that is reached during gelatinization of

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starch and reflects the extent of swelling and their water-binding capacity of starch granules,

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whereas pasting temperature is defined as the temperature when starch pastes started pasting.

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Significant variations in pasting properties of rice starch were observed under different N

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management (Table 5, Fig 1E, F). The highest peak viscosity in both rice varieties was found with

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a ratio of 6:4; however, a slight decrease in pasting temperature was observed with this ratio and

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other fertilizing conditions compared to starch samples from no-nitrogen conditions. As previously

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indicated, amylose can inhibit starch granules from swelling, as well as help in maintaining the

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structure of swollen granules40, 55. Therefore, starch samples with lower amylose contents have

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higher peak viscosity and lower pasting temperature, which have been confirmed by our

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experimental results. The highest trough and final viscosity values, which are related to the

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amount of amylose leached from starch granules,56,57 were also highest with a nitrogen

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management ratio of 6:4. Li et al. reported a significant positive correlation between both trough

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and final viscosities and swelling power.

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the degree of disintegration of starch granules under heating, with a high breakdown value,

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indicating that starch has lower tolerance for prolonged heating times during cooking. Setback

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viscosity describes the viscosity of starch paste at the beginning of retrogradation during cooling,59

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a process caused by leached amylose rearrangement during cooling. Breakdown viscosity and

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setback viscosity values are useful for the determination of potential cooking characteristics of a

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certain type of starch. For example, in East Asia, people prefer rice with a more elastic and sticky

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texture, and thus rice varieties with high breakdown and low setback values are popular, whereas

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consumers in North America enjoy rice with a hard and fluffy texture, and these are rice varieties

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with low breakdown value and high setback values.

58

Breakdown viscosity reflects starch paste stability and

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The optimal N ratios for the production of rice with thermal and pasting properties

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appropriate for cooking are thus 7:3 and 6:4. However, rice grown under a 6:4 nitrogen

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management have significantly higher protein levels than under other treatments (Table 1), and

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high protein levels have been proven to have an undesirable effect on the texture of cooked rice.

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These considerations, in addition to desirable high grain yields, indicate that the best N

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management ratio is 7:3.

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AUTHOR INFORMATION

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*Corresponding Author

274

Hongcheng Zhang

Email: [email protected]

275

Zhongyang Huo

Email: [email protected]

276

Funding

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The Wheat and Rice Balanced High Yield Technical Scheme CX (15)1002, Special Scientific

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Research of Agriculture Public Welfare Profession, and Priority Academic Program Development

279

of Jiangsu Higher Education Institutions supported this study.

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Notes

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The authors have no competing financial interests to declare.

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Reference

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Tables and figures Table 1. Total nitrogen, ratio of nitrogen application of experiment, grain yield, and protein and starch contenta Variety

NJ 5055

NJ 46

443 444

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a b

Total nitrogen (kg/ha)

Treatment

0 150 150 150 0

Ratio of nitrogen application (%) b

Grain yield (t/ha)

Protein (%)

Starch (%)

Transplanting

Tillering

PI

0 9: 1 7: 3 6: 4 0

0 90 40 30 0

0 0 30 30 0

0 10 30 40 0

6.5 ± 0.05c 10.2 ± 0.03b 11.3 ± 0.02a 10.4 ± 0.02a,b 6.0 ± 0.04d

9.3 ± 0.02d 10.1 ± 0.15c 11.1 ± 0.02b 12.0 ± 0.06a 8.0 ± 0.07d

87.2 ± 0.1a 86.6 ± 0.2b 85.8 ± 0.2c 85.4 ± 0.2c 88.5 ± 0.1a

150

9: 1

90

0

10

8.8 ± 0.03c

8.3 ± 0.05c

87.8 ± 0.3b

150

7: 3

40

30

30

10.0 ± 0.03a

9.3 ± 0.13b

86.9 ± 0.1c

150

6: 4

30

30

40

9.5 ± 0.02b

10.1 ± 0.04a

86.2 ± 0.1c

Data are expressed as the mean ± standard deviation, n = 3. Values in the same column with different letters are significantly different (P < 0.05). 0 stands for the blank experiment; 9:1, 7:3, and 6:4 stand for the ratio of nitrogen at the transplanting and tillering stages to the PI stage.

445

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Table 2. Volume distribution percentage of starch granules under different nitrogen management a Variety

NJ 5055

NJ 46

447 448

a b

Treatmentb

Small starch granules (< 1 µm)(%)

Medium starch granules (1–5 µm)(%)

Large starch granules (5–20 µm) (%)

D (3,2) (µm)

D (4,3) (µm)

0 9: 1 7: 3 6: 4 0

6.9 ± 0.03c 7.2 ± 0.12b 7.6 ± 0.06a 7.7 ± 0.08a 6.4 ± 0.05c

30.7 ± 0.5d 35.0 ± 0.4c 43.8 ± 0.2b 47.2 ± 0.2a 32.7 ± 0.3d

62.1 ± 0.6a 57.3 ± 0.3b 47.4 ± 0.3c 44.1 ± 0.4d 61.0 ± 0.6a

6.032 ± 0.005c 6.847 ± 0.004b 7.605 ± 0.003a 8.041 ± 0.003a 6.940 ± 0.001c

6.042 ± 0.004c 6.402 ± 0.009b 6.877 ± 0.005a 7.031 ± 0.002a 6.104 ± 0.008c

9: 1

6.8 ± 0.09b

41.9 ± 0.3c

51.3 ± 0.7b

7.556 ± 0.002b

6.551 ± 0.007b

7: 3

7.4 ± 0.06a

44.8 ± 0.2b

47.8 ± 0.3c

8.013 ± 0.002a

6.941 ± 0.006a

6: 4

7.6 ± 0.04a

48.9 ± 0.1a

43.5 ± 0.4d

8.214 ± 0.002a

7.046 ± 0.002a

Data are expressed as the mean ± standard deviation, n = 3. Values in the same column with different letters are significantly different (P < 0.05). 0 stands for the blank experiment; 9:1, 7:3, and 6:4 stand for the ratio of nitrogen at the transplanting and tillering stages to the PI stage.

449

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Table 3. Iodine absorbance, relative crystallinity, and IR ratio under different nitrogen management a Variety

NJ 5055

NJ 46

451 452 453

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a b

Treatmentb

Blue value

λ max (nm)

Apparent amylose content (%)

Relative crystallinity (%)

0

0.149 ± 0.006a

564 ± 0.3a

15.5 ± 0.2a

9: 1

0.141 ± 0.004b

558 ± 0.4b

7: 3

0.129 ± 0.008c

6: 4

IR 1,045/1,022 cm−1

1,022/995 cm−1

Swelling power (g/g)

Water solubility (%)

19.2 ± 0.2c

0.88 ± 0.002a

0.73 ± 0.007c

14.9 ± 0.2d

15.4 ± 0.3d

13.2 ± 0.4b

21.2 ± 0.3b

0.72 ± 0.006b

0.88 ± 0.006c

17.8 ± 0.3c

17.9 ± 0.3c

557 ± 0.2c

11.3 ± 0.4c

24.4 ± 0.6a

0.64 ± 0.004c

1.06 ± 0.004b

25.3 ± 0.5b

18.2 ± 0.2b

0.122 ± 0.012c

557 ± 0.2c

10.4 ± 0.1c

25.3 ± 0.5a

0.61 ± 0.003c

1.08 ± 0.003a

28.6 ± 0.2a

21.2 ± 0.4a

0

0.167 ± 0.013a

571 ± 0.3a

16.2 ± 0.3a

18.7 ± 0.3c

0.92 ± 0.002a

0.70 ± 0.002c

15.2 ± 0.2d

14.0 ± 0.2d

9: 1

0.148 ± 0.006b

561 ± 0.4b

14.6 ± 0.2b

20.0 ± 0.2b

0.83 ± 0.003b

0.92 ± 0.002b

16.0 ± 0.6c

15.7 ± 0.4c

7: 3

0.139 ± 0.004c

558 ± 0.2c

12.2 ± 0.2c

22.1 ± 0.2a

0.68 ± 0.004c

1.01 ± 0.006a

18.4 ± 0.4b

17.6 ± 0.6b

6: 4

0.133 ± 0.002c

558 ± 0.1c

11.5 ± 0.2c

24.7 ± 0.3a

0.67 ± 0.005c

1.04 ± 0.008a

22.7 ± 0.4a

18.7 ± 0.7a

Data are means±standard deviations, n = 3.Values in the same column with different letters are significantly different (P < 0.05). 0 stands for blank experiment; 9: 1, 7: 3, and 6: 4 stand for the ratio of nitrogen at transplanting and tillering stages to PI stage.

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Table 4. Thermal properties of starch samples under different nitrogen management a Variety

NJ 5055

NJ 46

Treatmentb

∆Hgel (J/g) c

To (°C)

Tp (°C)

Tc (°C )

∆Hret (J/g)

a

a

a

a

%R

0 9: 1 7: 3 6: 4 0

8.95 ± 0.2 9.45 ± 0.2b 10.97 ± 0.3a 11.39 ± 0.1a 8.28 ± 0.3c

61.2 ± 0.2 60.3 ± 0.2b 59.7 ± 0.3b,c 59.1 ± 0.2c 59.8 ± 0.2a

66.9 ± 0.1 66.1 ± 0.1b 65.1 ± 0.1c 64.8 ± 0.2c 65.1 ± 0.3a

76.7 ± 0.2 75.3 ± 0.2b 75.1 ± 0.1b 74.5 ± 0.4b 73.4 ± 0.2a

2.65 ± 0.1 2.24 ± 0.1b 1.51 ± 0.2c 1.44 ± 0.1c 2.24 ± 0.1a

29.6 ± 0.6a 23.7 ± 0.4b 13.7 ± 0.2c 12.6 ± 0.3c 27.1 ± 0.2a

9: 1

9.04 ± 0.4b

59.7 ± 0.4a

64.9 ± 0.3a

71.6 ± 0.3b

2.07 ± 0.1b

22.8 ± 0.4b

7: 3

10.28 ± 0.3a

59.3 ± 0.3b

63.2 ± 0.2b

71.4 ± 0.3b

1.59 ± 0.3c

15.4 ± 0.4c

6: 4

10.68 ± 0.5a

59.1 ± 0.3b

62.9 ± 0.1b

71.2 ± 0.1b

1.47 ± 0.2c

13.7 ± 0.2c

455

a

Data are expressed as the mean±standard deviation, n = 3. Values in the same column with different letters are significantly different (P < 0.05).

456

b

0 stands for the blank experiment; 9:1, 7:3, and 6:4 stand for the ratio of nitrogen at the transplanting and tillering stages to the PI stage.

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Table 5. Pasting properties of starch samples under different nitrogen levelsa Variety

NJ 5055

NJ 46

458 459

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a b

Treatmentb

Ptemp (°C)

PV (cP)

TV (cP)

FV (cP)

BD (cP)

SB (cP)

0 9: 1 7: 3 6: 4 0

a

70.5 ± 0.3 69.7 ± 0.2b 69.3 ± 0.3b 69.8 ± 0.4b 68.6 ± 0.2a

c

2,332 ± 30 2,553 ± 34b 2,756 ± 32a 2,983 ± 28a 2,692 ± 36c

c

1,016 ± 12 1,189 ± 10b 1,394 ± 13a 1,473 ± 11a 1,226 ± 10c

c

1,608 ± 13 1,878 ± 16b 1,983 ± 17a 2,192 ± 17a 1,875 ± 16c

c

1,164 ± 10 1,276 ± 12c 1,416 ± 13b 1,610 ± 12a 1,466 ± 11c

1,011 ± 5a 965 ± 7a 750 ± 9b 570 ± 8c 1,035 ± 8a

9: 1

67.3 ± 0.5b

2,942 ± 35b

1,564 ± 14b

2,173 ± 18b

1,478 ± 10c

947 ± 11a

7: 3

67.3 ± 0.2b

3,316 ± 32a

1,648 ± 12a

2,469 ± 22a

1,668 ± 13b

747 ± 10b

6: 4

67.3 ± 0.4b

3,572 ± 30a

1,795 ± 11a

2,537 ± 20a

1,777 ± 14a

469 ± 12c

Data are expressed as the mean ± standard deviation, n = 3. Values in the same column with different letters are significantly different (P < 0.05). 0 stands for the blank experiment; 9:1, 7:3, and 6:4 stand for the ratio of nitrogen at the transplanting and tillering stages to the PI stage.

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Figure captions Fig. 1 Granule size distribution of starches (A, B) and X-ray diffraction patterns of starches (C, D) and RVA patterns of starches (E, F) under different nitrogen management.

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