Identification and quantitation of the rice aroma compound, 2-acetyl-1-pyrroline,in bread flowers (Vallaris glabra Ktze)

The aroma impact compound, 2-acetyl-1-pyrroline (2AP), has been identified for the first time in headspace of fresh bread flowers (Vallaris glabra Ktze) in which volatile components were extracted by solid-phase microextraction (SPME) at room temperature prior to analysis by gas chromatography-mass spectrometry. A total of 50 volatiles were detected. Among these, 23 volatiles were identified, predominantly in a group of terpenes. More volatiles were found in the extract of fresh bread flowers obtained by continuous steam distillation and solvent extraction (SDS). Of the 40 volatiles identified, the additional components were mainly straight-chain saturated hydrocarbons. 2AP was found in the extracts obtained by both SPME (0.37%) and SDS (2.71% relative proportion). Quantitative analyses of 2AP in bread flowers and other plant materials were performed by solvent extraction employing acidic solutions and capillary GC with flame ionization detection. The highest concentration of 2AP was found in dried flowers of V. glabra at 26.1 mg/kg. By comparison with other plant sources, fresh leaves of Pandanus amaryllifolius Roxb contain 2AP at 10.3 mg/kg and Thai fragrant rice, Khao Dawk Mali 105, at 3.0 mg/kg.     

Evaluation of Thai rice cultivars with low-grain cadmium

To identify rice cultivars with low grain cadmium (Cd) levels, 42 cultivars of Thai rice (Oryza sativa L.) were cultivated in a Cd-contaminated field in the Pha Te village, Mae Sot district, Tak province, Thailand, from 2009 to 2011. Among non-glutinous and late-ripening cultivars, lower levels of Cd accumulated in the grains of RD5, RD15, and Sang Yod than in Khao Dawk Mali 105, a prevailing and popular cultivar in this area. Among glutinous and late-ripening cultivars, Khao’ Niaw Ubon 1 and Khao’ Niaw Ubon 2 accumulated lower Cd levels than a prevailing cultivar RD6. The findings suggest that human cadmium intake can be reduced by selecting low-Cd rice cultivars.     

Precursors of 2-acetyl-1-pyrroline, a potent flavor compound of an aromatic rice variety

The biological formation of a potent flavor compound, 2-acetyl-1-pyrroline, in the aromatic rice variety (Khao Dawk Mali 105) was studied in seedlings and callus of the rice. Concentrations of 2-acetyl-1-pyrroline were determined by GC-MS-SIM using an isotope dilution method. Increases in concentration occurred when proline, ornithine, and glutamate were present in solution, with proline increasing the concentration by more than 3-fold compared to that of the control. Results of tracer experiments using (15)N-proline, (15)N-glycine, and proline-1-(13)C indicated that the nitrogen source of 2-acetyl-1-pyrroline was proline, whereas the carbon source of the acetyl group was not the carboxyl group of proline. 2-acetyl-1-pyrroline was formed in the aromatic rice at temperatures below that of thermal generation in bread baking, and formed in the aerial part of aromatic rice from proline as the nitrogen precursor.     

Physical,Chemical, and Sensory Properties of Antioxidant‐Enriched Raw and Cooked Rice by Vacuum‐Drying Impregnation in a Semidry State

Vacuum drying was employed with a vacuum impregnation technique in a semidry state to enrich rice with antioxidants of beetroot juice. The properties of the vacuum‐dried raw and cooked rice grains were characterized. The various raw rice grains (three varieties and two storage time periods) exhibited a significant absorption of beetroot juice, which was evident from the red‐violet beetroot color of the rice, as distinguished from the white color of the control. The color increase (ΔE= 20−40) was linear with the juice content (R² = 0.96−0.99). Their total phenolic (TP) contents and 2,2‐diphenyl‐2‐picrylhydrazyl radical (DPPH) scavenging activities were enhanced (ΔTP = 21−260 mg of gallic acid equivalents/100 g of rice db and ΔDPPH = 22−64 mg of vitamin C equivalents/100 g of rice db). Their grain integrity was reduced (Δforce = −1 to −63), which was potentially associated with the formation of grain surface cracks (linear relationship of %crack and %juice with R² = 0.94−0.98). After cooking, the enriched rice grains were linearly elongated with added juice (R² = 0.88−0.97, up to 1.6‐, 2.0‐, and 2.0‐fold for Sanpatong 1, Khao Dawk Mali 105, and Chainart 1 rice samples, respectively), and the overall volume of the cooked rice was increased (likely not linear, up to 3.2‐, 4.3‐, and 4.8‐fold for Sanpatong 1, Khao Dawk Mali 105, and Chainart 1 rice samples, respectively). Such improvements in cooking qualities were obtained by this simple vacuum‐drying technique, in comparison to existing rice‐aging processes that are more time consuming. The sensorial scores of the resultant rice products were excellent. Vacuum drying is an effective tool to improve the antioxidant value of rice as well as its cooking quality, and the raw quality remains appreciable. It is a simple and rapid process that could be practical for manufacturing healthy rice products.     

Rapid Variety Identification of Pure Rough Rice by Fourier‐Transform Near‐Infrared Spectroscopy

Rice variety is considered as an important factor influencing cooking and processing quality because of variations in size, shape, and constitution. Difficulty in management of rough rice with lower varietal purity becomes a significant problem in rice production and can result in the reduction of rice quality. Fourier‐transform near‐infrared (FT‐NIR) spectroscopy was used to identify the variety of rough rice through whole‐grain techniques. Moist rough rice samples (n = 259) comprising five varieties (Khao Dawk Mali 105 [KDML105], Pathum Thani 1, Suphan Buri 60, Chainat 1, and Pitsanulok 2) were gathered from different locations around Thailand and scanned in the NIR region of 9088–4000 cm^–1 in reflectance mode. Soft independent modeling of class analogies (SIMCA) and partial least squares discriminant analysis (PLSDA) methods were used for identification by utilizing preprocessed spectra. The highest identification accuracy achieved was 74.42% by the SIMCA model and 99.22% by the PLSDA model. The best PLSDA model demonstrated approximately 97% correct identification for KDML105 samples and 100% for the others. This study raises the possibility of applying FT‐NIR spectroscopy as a nondestructive technique for rapidly identifying moist rough rice varieties in routine quality assurance testing.     

Rapid method for quantitative analysis of the aroma impact compound, 2-acetyl-1-pyrroline, in fragrant rice using automated headspace gas chromatography

A rapid method employing static headspace gas chromatography (HS-GC) has been developed and validated for quantitative analysis of the impact aroma compound, 2-acetyl-1-pyrroline (2AP), in grains of fragrant rice. This developed method excludes wet extraction, and the rice headspace volatiles are brought directly and automatically to GC analysis. The conditions of the static HS autosampler were optimized to achieve high recovery and sensitivity. The most effective amount of rice sample used was 1 g, which provided 51% recovery and a linear multiple headspace extraction (MHE) plot of the peak area of 2AP. The sensitivity of the method was enhanced by utilizing a megabore fused silica capillary column in conjunction with a nitrogen-phosphorus detector (NPD). Method validations performed for both static HS-GC-FID and HS-GC-NPD demonstrated linear calibration ranges of 20-10 000 (r(2) = 0.9997) and 5-8000 (r(2) = 0.9998) ng of 2AP/g of rice sample, respectively. The limits of detection for both systems were 20 and 5 ng of 2AP, and the limits of quantitation were 0.30 and 0.01 g of brown rice sample, respectively. Reproducibility calculated as intraday and interday coefficients of variation were 3.25% RSD (n = 15) and 3.92% RSD (n = 35), respectively, for SHS-GC-FID and 1.87% RSD (n = 15) and 2.85% RSD (n = 35), respectively, for SHS-GC-NPD. The method was found to be effective when applied to the evaluation of aroma quality, based on 2AP concentrations, of some fragrant rice samples.     

Rapid Gas Chromatographic Technique for Quantifying 2‐Acetyl‐1‐Pyrroline and Hexanal in Rice (Oryza sativa,L.)

The aroma of rice plays a role in its consumer acceptability. The popcorn‐like smell of aromatic rice stemming primarily from its 2‐ acetyl‐1‐pyrroline (2‐AP) content is considered desirable by many consumers. Conversely, hexanal has been correlated with off odors in rice that develop from lipid oxidation. A rapid method for 2‐AP and hexanal quantification suitable for use in breeding programs, large‐scale research efforts, and quality assurance programs is needed. While developing such a method, sample preparation (degree of milling, particle size), solvent extraction time and temperature, and gas chromatographic parameters were studied. Particle size had no influence on 2‐AP or hexanal recovered. One extraction solubilized ≈80% of the 2‐AP and 56% of the hexanal present in milled rice. The optimum extraction method was assessed to require 0.3 g of ground brown or milled rice in methylene chloride held at 85°C for 2.5 hr. The complete gas chromatographic run requires ≈25 min, and 50 samples can be analyzed per day. The optimized method's linear response (R² = 0.99) and reproducibility was demonstrated. The stability of 2‐AP and hexanal in frozen milled rice and in refrigerated methylene chloride extracts was excellent for at least six months. Milled and unmilled commercial and breeders' aromatic rice samples contained 10–1,104 ng/g of 2‐AP and 148–2,541 ng/g of hexanal. Genotype had the greatest effect on the 2‐AP and hexanal content of two lines grown over four years and in four states.     

Analysis of phenolic compounds in white rice, brown rice, and germinated brown rice

Two hydroxycinnamate sucrose esters, 6'-O-(E)-feruloylsucrose and 6'-O-(E)-sinapoylsucrose, were isolated from methanol extracts of rice bran. Soluble and insoluble phenolic compounds as well as 6'-O-(E)-feruloylsucrose and 6'-O-(E)-sinapoylsucrose from white rice, brown rice, and germinated brown rice were analyzed using HPLC. The results demonstrated that the content of insoluble phenolic compounds was significantly higher than that of soluble phenolics in rice, whereas almost all compounds identified in germinated brown rice and brown rice were more abundant than those in white rice. 6'-O-(E)-Feruloylsucrose (1.09 mg/100 g of flour) and 6'-O-(E)-sinapoylsucrose (0.41 mg/100 g of flour) were found to be the major soluble phenolic compounds in brown rice. During germination, an approximately 70% decrease was observed in the content of the two hydroxycinnamate sucrose esters, whereas free phenolic acid content increased significantly; the ferulic acid content of brown rice (0.32 mg/100 g of flour) increased to 0.48 mg/100 g of flour and became the most abundant phenolic compound in germinated brown rice. The content of sinapinic acid increased to 0.21 mg/100 g of flour, which is nearly 10 times as much as that in brown rice (0.02 mg/100 g of flour). In addition, the total content of insoluble phenolic compounds increased from 18.47 mg/100 g of flour in brown rice to 24.78 mg/100 g of flour in germinated brown rice. These data suggest that appropriate germination of brown rice may be a method to improve health-related benefits.     

氮锌肥配施对南方香粳稻产量和品质的影响

【目的】研究氮锌肥配施对南方香粳稻产量和外观加工品质、蒸煮食味品质、香气的影响,为南方香粳稻的调优栽培提供科学依据。【方法】田间试验于2020和2021年在扬州大学试验基地进行,供试粳稻品种为宁香粳9号和南粳46。在施锌(+Zn)和不施锌(Zn0)条件下,分别设3个施氮水平：0 (N0)、180 kg/hm²(N180)、270 kg/hm²(N270),共6个处理。于收获期,测定产量和产量构成因素,分析籽粒加工外观、食味和香气品质。【结果】提高氮肥用量可显著增加香粳稻产量,而施用锌肥对香粳稻产量无显著影响,+ZnN270处理宁香粳9号和南粳46产量均最高,分别达10.48 t/hm²和10.40 t/hm²;相同氮肥用量下,增施锌肥对产量没有显著影响。宁香粳9号和南粳46的最佳稻米加工和外观品质均以+ZnN270处理最优。在相同氮肥用量下,施用锌肥改善了香粳稻的加工和外观品质。与N0处理相比,在N180和N270处理下两品种的直链淀粉含量下降了8.44%～13.16%,蛋白质含量增加了9.79%～...     

Simple analytical method for organophosphorus pesticide determination in unpolished rice, using removal of fats by zinc acetate

A rapid and simple method is developed for the determination of organophosphorus pesticides in unpolished rice. The new method incorporated acetonitrile-water (1 + 1) extraction, removal of fats by zinc acetate, and further cleanup on an activated charcoal chromatographic column. The higher fatty acids in the extract react rapidly with zinc acetate to form insoluble zinc carboxylates, which precipitate. Additional interferences were cleaned up on an activated charcoal chromatographic column, and organophosphorus pesticides adsorbed on the activated charcoal were eluted with acetone-hexane. Dimethoate is not retained on the activated charcoal and must be extracted with dichloromethane from the first acetonitrile-water eluate. Pesticides are measured by flame photometric gas chromatography. Recoveries from 50 g unpolished rice samples fortified with 5-50 micrograms diazinon, 6-30 micrograms parathion, 8-40 micrograms fenitrothion and IBP, 10-50 micrograms dimethoate and fenthoate, 20-100 micrograms malathion, or 40-200 micrograms EPN ranged from 75.7 to 95.8%.     

基于小波变换的稻米爆腰检测技术研究

稻谷裂纹(俗称爆腰)是导致大米在加工过程中破碎的重要原因，爆腰的检测对裂纹的研究和控制有重要意义。本文提出了一种新的爆腰检测方法。它利用小波变换在图像边缘提取和去噪中的优越性，通过对二进尺度下图像小波变换局部极大值的检测，提取边缘特征，去除噪声，对糙米爆腰图像中的裂纹进行了有效识别。从而实现爆腰率的自动检测，准确率达到92%以上。与传统的检测算子相比，取得了更为良好的效果。     

Lipidemic Response of Hamsters to Rice Bran,Uncooked or Processed White and Brown Rice,and Processed Corn Starch

This study was undertaken to evaluate the lipidemic response of rice bran and the possible enhancement of its healthful properties by using raw or processed white or brown rice in place of corn starch. All diets contained 10% total dietary fiber, 15% fat, and 0.5% cholesterol. Weanling male golden Syrian hamsters were fed cellulose control (CC), processed corn starch (PCS), cellulose with processed brown rice (CPBR), rice bran (RB), RB with white rice (RBWR), RB with processed white rice (RBPWR), RB with brown rice (RBBR), and RB with processed brown rice (RBPBR) diets. After three weeks, the PCS diet significantly lowered total plasma cholesterol (TC) compared with the CC, CPBR, RBWR, and RBPBR diets. RB and RBBR diets significantly lowered TC and LDL‐C compared with CPBR diet. All the RB‐containing and PCS diets significantly lowered liver cholesterol and liver lipid content. Processing white rice increased TDF content 240% and insoluble dietary fiber (IDF) 360%, whereas soluble dietary fiber (SDF) decreased by 25%. Uncooked brown rice contained 7 times as much TDF as uncooked white rice. Processing brown rice decreased its TDF, IDF and SDF contents by 12, 6, and 42%, respectively. The data suggest that a possible mechanism for cholesterol‐lowering by rice bran, with or without added raw or processed rice (white or brown), is by decreasing lipid digestibility and increasing neutral sterol excretion, whereas cholesterol‐lowering by processed corn starch is mediated through other mechanisms.     

Natural levels of dimethyl sulfide in rough rice and its products

Natural levels of dimethyl sulfide (DMS) in rough rice and its products (polished rice, brown rice, and broken rice) were determined by a gas chromatograph equipped with a flame photometric detector and sulfur mode, after extraction with 25% KBr solution in a sealed system. DMS was found to occur naturally in nine newly harvested and stored Australian varieties of rough rice and its products and decreased during storage after harvesting. Natural levels of DMS in rough rice and its products varied with variety, fraction, and period of storage. The order of levels of DMS was rough rice = brown rice > polished rice = broken rice. The range of values was 0.002-30 mg kg(-1) (ppm, w/w).     

提高发芽糙米得率的复合酶预处理工艺优化

为解决传统工艺生产发芽糙米浸泡时间长、生产效率低等问题,提出以纤维素酶和木聚糖酶的复合溶液代替蒸馏水浸泡发芽前糙米的新工艺。以糙米为原料,探究复合酶预处理工艺中酶解时间、酶解温度、复合酶浓度及配比对发芽糙米得率的影响规律,采用二次正交旋转中心组合设计试验,建立了各因素对发芽糙米得率影响的数学模型。结果表明:酶解时间、酶解温度、复合酶浓度及酶配比对发芽糙米得率影响显著(P0.05),得到优化参数组合为:酶解时间135 min,酶解温度35℃,复合酶浓度0.57 g/L、纤维素酶和木聚糖酶质量比1.86:1,在此条件下,与传统工艺相比浸泡时间缩短62.5%、发芽糙米得率及γ-氨基丁酸含量分别提高约3.90%和3.86 mg/(100 g)。通过对酶解后糙米皮层微观结构的观察分析,糙米皮层在复合酶作用下部分降解,胚乳中淀粉更易与水分子相结合,从而吸水速率提升。研究结果可为发芽糙米生产提供参考。     

Comparison of various extraction methods for policosanol from rice bran wax and establishment of chromatographic fingerprint of policosanol

A capillary gas chromatographic (GC) method has been developed for the separation and determination of policosanol components extracted from rice bran wax. A Varian CP-sil 8 CB column was employed, and an oven temperature was programmed. Gas chromatography-mass spectrometry (GC-MS) was used to identify the composition of policosanol. Quantitative analysis was carried out by means of hydrogen flame ionization detector (FID) with dinonyl phthalate (DNP) as internal standard. The results indicated that the extract obtained by dry saponification has the highest contents of octacosanol and triacontanol among extracts by all used extraction methods including dry saponification, saponification in alcohol, saponification in water (neutralized and non-neutralized), and transesterification. Meanwhile, the GC-MS fingerprint of policosanol extracted by dry saponification has been established. Euclidean distance similarity calculation showed remarkable consistency of compositions and contents among 12 batches of policosanol from a rice bran wax variety. This protocol provided a rapid and feasible method for quality control of policosanol products.     

The uptake,distribution, and accumulation of 15N-labelled ammonium and nitrate nitrogen top-dressed at different growth stages of rice

A pot experiment with soil culture was carried out to trace ¹⁵N-labelled nitrogen top-dressed at different growth stages of rice. The study involves the use of a modified vacuum system for determining total nitrogen by gu volumetric measurement, and the N₂ gas sampled in the discharge tube was analysed for nitrogen-15 by the optical spectrographic technique.

The plants took up more nitrogen from (¹⁵NH₄)₂SO₄ than from Na¹⁵NO₃, irrespective of the stage of dressing, and the uptake of both forms was much higher when the planta were top-dressed at the young panicle formation stage as compared with the later dressings. At full maturity the plants had the highest accumulation of labelled nitrogen from both ammonium and nitrate sources when they are top-dressed at the young panicle formation stage. More than 80% ot the labelled nitrogen taken up by the plants waa distributed in the brown rice and this trend was more remarkable when top-dressing was carried out at the milk stage. The distribution patterns of ammonium and nitrate nitrogen were similar in brown rice but differed in leaves and stem.

Nitrogen transported from other parts to the panicle was utilized for the formation ot the husk until the booting stage, and then for brown rice development. With the completeness of husk formation, at the milk stage, nitrogen transported to the grain might have been utilized for brown rice development more rapidly. In the brown rice, nitrogen from ammonium was translocated maximally to the inner part of the endosperm from dressing at the booting stage, and to the embryo from that at the milk stage, whereas that from nitrate was translocated maximally to the embryo from the dressings at both stages.     

Gas chromatographic determination of fatty acids and sterols in orange juice

A gas chromatographic (GC) method has been developed for the simultaneous quantitation of fatty acids and sterols in orange juice, using a bonded phase fused silica capillary column of intermediate polarity, splitless automatic injection, and flame ionization detection. Sample preparation has been simplified by using 1 g C-18 adsorbent in a disposable minicolumn to extract 2 mL orange juice. Methylation of fatty acids and silylation of the sterols were carried out in the eluted extract (low polarity lipid fraction). The method precision was 7%; recoveries ranged from 83 to 113%. The precision of the injection technique was 2%. Seven major fatty acids and 5 sterols in orange juice were quantitated by the GC method and identified by GC/mass spectrometry. Quantitative data for several orange juice samples indicated that the levels of the compounds of interest were in the 1.3-72.0 mg/L range. The results demonstrate that bonded phase fused silica capillary GC has great versatility and potential for the quantitative determination of fatty acids and sterols.     

Chlorinated compounds and phenols in tissue, fat, and blood from rats fed industrial waste site soil extract: methods and analysis

A method was developed to analyze rat tissue, fat, and blood for some of the chlorinated compounds found in an extract of soil from an industrial waste site. Extraction with hexane and then with ethyl ether-hexane (1 + 1) was followed by concentration over steam, and gas chromatographic analysis with an electron capture detector. Volatile compounds were analyzed in a glass column coated with 6% SP-2100 plus 4% OV-11 on Chromosorb W. Semivolatile compounds, chlorinated compounds, and pesticides were analyzed in a 70 m glass capillary column coated with 5% OV-101. Phenols were analyzed in a glass column packed with 1% SP-1240 DA on Supelcoport. However, the most efficient means of separation was to use the same glass column for volatile compounds, a DB-5 fused silica capillary column for semivolatile compounds, pesticides, and phenols, and the same 1% SP-1240 DA glass column for separation of beta-BHC and pentachlorophenol. Recoveries ranged from 86.3 +/- 9.1% (mean +/- standard deviation) to 105 +/- 10.4%. Sensitivities for semivolatile chlorinated compounds, pesticides, and phenols were about 4 ng/g for fat, 1 ng/g for tissue, and 0.2 ng/mL for blood. Sensitivities for volatile compounds were about 4-fold higher (16, 4, and 0.8, respectively). Sensitivities for dichlorobenzenes and dichlorotoluenes were 8 ng/g for fat, 2 ng/g for tissue, and 0.4 ng/mL for blood.     

冬季作物-双季稻轮作种植模式氮、磷、钾养分循环与产量可持续性特征

研究分析农业生态系统NPK养分循环和产量的可持续性,对实现养分资源优化管理和农业可持续发展具有重要意义。基于长期冬季作物-双季稻轮作种植定位试验,分析了2004—2017年冬闲-双季稻、马铃薯-双季稻、紫云英-双季稻、黑麦草-双季稻、油菜-双季稻等轮作种植模式早、晚稻产量的可持续性与稳定性;采用投入产出法（Input-Output Analysis）分析不同轮作种植模式NPK养分循环与平衡状况。结果表明：1）黑麦草-双季稻模式早稻产量变异系数与可持续性指数分别为0.09和0.81,说明稻田冬种黑麦草有利于促进早稻产量稳定性和可持续性的提高;油菜-双季稻模式晚稻产量变异系数与可持续性指数分别为0.07和0.82,说明稻田冬种油菜有益于晚稻产量稳定性和可持续性的提高;2）长期冬季作物-双季稻轮作种植未影响水稻产量和糙米NPK养分含量（P>0.05）;3）在稻田轮作种植周年内目前的NPK投入水平下,黑麦草-双季稻、紫云英-双季稻、油菜-双季稻、马铃薯-双季稻等模式均存在严重的K亏缺现象,K亏缺量分别为375.70 kg（K）·hm^-2、279.98 kg（K）·hm^-2、363.71 kg（K）·hm^-2、93.74 kg（K）·hm^-2;黑麦草-双季稻、紫云英-双季稻、油菜-双季稻等模式均在冬季作物种植季存在严重的K亏缺现象,K亏缺量分别为240.07 kg（K）·hm^-2、89.57 kg（K）·hm^-2、140.08 kg（K）·hm^-2,但马铃薯-双季稻模式在马铃薯种植季K盈余为255.21 kg（K）·hm^-2;同时黑麦草-双季稻模式和紫云英-双季稻模式均存在冬季作物种植季存在N亏缺,N亏缺量分别为59.47 kg（N）·hm^-2和89.17 kg（N）·hm^-2;油菜-双季稻模式和马铃薯-双季稻模式在晚稻种植季均存在严重的K亏缺现象,K亏缺量分别为45.93 kg（K）·hm^-2、124.33 kg（K）·hm^-2。冬季作物-双季稻轮作种植模式的养分循环是冬季作物和外部投入的NPK肥料共同驱动的养分循环,建议科学管理冬季作物和3季的NPK养分投入。     

Growth responses of cereal crops to organic nitrogen in the field

Eleven rice varieties differing in grain size were grown under controlled environmental conditions during the grain-filling period. The grain weight of upper grains in a panicle was examined at successive stages of growth during the grain-filling period. The effect of temperature on the rate and the duration of the period of grain-filling was determined using Khao Lo, a large-grain variety, and Bom Dia, a small-grain variety. Both the grain-filling rate and duration of the period of grain-filling differed among rice varieties and were positively and significantly correlated with the grain size. The duration of the grain-filling period from flowering to the time when almost maximum grain weight was attained ranged from 12 days at 32/24°C in Bom Dia to 36 days at 20/12°C in Khao Lo. The grain-filling rate was low in small-grain varieties, and generally increased with increasing grain size.

By lowering the temperature, the grain-filling rate decreased, the duration of the grain-filling period increased but the grain weight was almost constant.

Weight per grain was closely correlated with hull size. No relationship was found between weight per grain and nitrogen percentage of brown rice.