基于原位观测的糙米籽粒力学特性研究

采用原位观测结合质构仪手段,研究稻谷加工过程中糙米籽粒受挤压力时的力学-结构特性,分析了压距等因素下糙米籽粒的挤压作用过程。结果表明：糙米所受的挤压力随压距的增大而增大,在外力冲击下,籽粒内部产生抗压应力,随之产生裂纹。粳米籽粒存在脆性,先产生裂纹,在挤压力增大之后,裂纹扩展,最后籽粒断裂;籼米和连糯籽粒脆性更明显,在产生裂纹后,短时间裂纹扩展,籽粒迅速断裂;速率对粳米所受挤压峰值力无明显影响;粳米所受的挤压峰值力随籽粒含水率的上升而减小,随温度的上升而减小,裂纹数量随浸泡时间的上升而增加,籽粒破坏程度随温度的上升而增大;3种米型在相同压距和压缩速度下的受挤压峰值力为：籼米>粳米>连糯。     

Effect of ageing-induced changes in rice physicochemical properties on digestion behaviour following storage

The changes in rice grains structure and digestion behaviours were investigated following storage at 4 °C and 37 °C, respectively. Pasting study indicated that rice samples stored at 37 °C demonstrated a consistent increase in the time to peak viscosity of the Rapid ViscoAnalysis parameters, implying a quick ageing progress. Compared to the rice stored at 4 °C, aged rice (stored at 37 °C) showed a coarser morphology after cooking by SEM, suggesting a limited starch gelatinization. Consistently, ageing process led to a decrease in the leaching of starch molecules in cooking residual water, which further confirmed that starch granules in aged rice grain caused less hydration and swelling. The analysis of the amount of cell wall remnants showed that rice stored at 37 °C caused a significant increase in the amount of cell wall remnants along the storage at 37 °C, which might suggest that the cell wall structure of the rice grains became more lignified because of the ageing. Furthermore, the ageing process significantly reduced rice digestion kinetics both in rate and extent. Thus, it is assumed that ageing process leads to the cell walls becoming more strengthened and lignified, which makes the rice grain more organized in its structure, and subsequently reduces starch granules disruption and molecules leaching during the cooking. Therefore, this study suggests that the changes in digestion behaviours of rice are highly associated with the changes in rice physical and chemical properties occurred during storage and the ageing process might be another option for manipulating rice digestion properties.     

Modeling of mass transfer and initiation of hygroscopically induced cracks in rice grains in a thermally controlled soaking condition: With dependency of diffusion coefficient to moisture content and temperature – A 3D finite element approach

Rice grains develop cracks and eventually break during soaking. Since published simulation studies on hygroscopic swelling induced cracking were scarce, the present study attempts to model the mass transfer of moisture and hygroscopic swelling of rice grains using principles of finite element analysis performed in three dimensions (3D). Ultimately, to understand the crack formation in response to the existence of tensile and compressive stresses caused by moisture gradient in the grain during soaking. An empirical equation was developed to establish dependency of the diffusion coefficient of rice to both moisture content and temperature. Using a 3D replica of short grain japonica rice, the modeling was carried out using existing laws of diffusion and was validated using experimental data. Results showed that the rate of moisture diffusion and hygroscopic swelling were found to increase with increase in soaking temperature. The internal stress, however, was found to decrease with increase in soaking temperature. The simulated moisture content and increase in volume of rice grain were favorably in agreement with experimental results. Highly stressed sites that are prone to breakage have been clearly identified.     

微波加速陈化过程中大米理化性质和组织结构的变化

新收获稻米的食用品质不佳,经过自然陈化(3~6个月)可以改善米饭的口感,而采用物理方法不仅能加速稻米陈化还能节省陈化时间,降低仓储成本。本研究采用微波(540 W处理30~50 s)处理稻米,并分析大米糊化性质、质构特性和组织结构的变化。结果显示,微波处理后大米的最终黏度、回生值显著增加,米饭的硬度增加,黏度下降,表明微波处理加速了大米的陈化。组成分析显示,微波处理后大米蛋白质的二硫键增加,同时发现米粒断裂面上的胞间断裂减少,胞内断裂增加,表明微波处理降低了胚乳细胞壁的机械强度。此外,与自然陈化过程中游离脂肪酸含量逐渐上升的变化不同,微波处理后大米中的游离脂肪酸含量降低,可减少哈败味的产生。这说明适度的微波处理可以加速稻米陈化,抑制稻米的哈败味产生,且微波处理的稻米陈化与胚乳细胞壁和二硫键的变化有关。     

Impact of cultivar variation in grain density of rice panicle on grain weight and quality

BACKGROUND: In the last two decades, newly released rice cultivars in southeastern China have been mainly characterised by more grains per cm panicle (GPCP), i.e. a compact panicle. These compact panicle cultivars show high yield potential but inferior quality. Accordingly, experiments were conducted to study the effect of GPCP on grain weight and quality. RESULTS: Two compact panicle and two loose panicle cultivars of japonica rice were used to investigate the effect of GPCP on the variation in grain weight and quality within a panicle. Significant differences in grain quality, including brown rice length, width and length/width ratio, brown rice and head‐milled rice percentages, chalky grain percentage and amylose and protein contents, were found among grains within a panicle. In general, the compact panicle cultivars showed lower grain weight and larger variation in brown rice length, width and length/width ratio, chalky grain percentage and amylose content among grains within a panicle than the loose panicle cultivars. CONCLUSION: GPCP is negatively associated with quality uniformity, and increasing the grain number on top secondary rachises may reduce the variation in grain weight and quality within a panicle. Copyright © 2008 Society of Chemical Industry     

Effects of Grain and Malt â‐Glucan on Distilling Quality in a Population of Hull‐less Barley

A population of barley lines, derived by mutation in the hull‐less variety, Penthouse, was included in a replicated trial, along with Penthouse and the hulled malting cultivar, Optic. Samples were assessed for a range of grain quality traits, then malted, with germination for either 4 or 5 days, prior to kilning. Most lines had grain β‐glucan contents lower than that of Penthouse, but there was no significant correlation between grain and malt β‐glucan content. Malt β‐glucan levels were indicative of differences in cell wall breakdown between 4 and 5 days germination, but negative associations with distilling parameters Extract and Alcohol Yield, were not statistically significant. It was concluded that the lines differed in the rate and extent of cell wall breakdown and that grain shape may influence modification in distal parts of the grain. However, a malting regime, optimised to suit Optic may be less suited to discriminating between hull‐less lines of reasonable quality.     

Relation on microscopic compression creases and crack of wood under static cyclic bending load

The relationship between microscopic compression failure lines and crack-nucleation is reported. Static and reversed cyclic bending load was applied to the specimens made from wood of Agathis species (Agathis sp.). The maximum subjected load was ±450～650 kgf/cm². The observation of the microscopic compression failure line and cracks nucleated at the root of the specimen was made every half cycle of load. The microscopic compression creases nucleate at the tip of the notch on the one side face of the specimen in the compression cycle. The length of the microscopic compression creases shortened in the tension cycle. This is because the microscopic compression creases are stretched parallel to the cell axis. In the next compression cycle, the microscopic compression, creases appear again. After repeating these processes several times and when the shape of the microscopic compression creases has not yet recovered to its original shape a large part of the microscopic compression creases change into cracks. In other word, the cracks nucleate. Mostly, the tip of the microscopic compression creases preceeds the tip of the cracks. The microscopic compression creases and the cracks propagate by steps, and after repeating these processes several times failure of the specimen occurs. The cracks nucleate in the compression cycle and sometimes in the tension cycle too. The cracks follow microscopic compression creases. The microscopic compression creases and the cracks run at nearly right angles to the cell axis.     

Parboiling of rice. Part I: Effect of hot soaking time on quality of milled rice

This study investigated the effect of soaking time on the quality of parboiled rice. The paddy was soaked in water at 25 and 80 °C for 15, 30, 45, 60 and 120 min. The soaked paddy was steamed, dried, stored and milled. With increasing soaking time a significant increase in water absorption and milling and head rice yield (hence reduction in broken rice) was observed. A significant difference in milling yield, at the 1% level, was obtained between the raw rice control and the hot soaked parboiled samples. A large reduction in fissured grain was observed after soaking. It is suggested that parboiling fills the void spaces and cements the cracks inside the endosperm, making the grain harder and minimizing internal fissuring and thereby breakage during milling.     

Effect of the Enzymatic Removal of Endosperm Cell Wall on the Gelatinization Properties of Aged and Unaged Rice Flours

Endosperm cell walls of the milled rice flour derived from aged and unaged rice were degraded and removed selectively using several commercial enzymes. Amylography of these cell wall degraded flours showed that the distinct difference between the gelatinization properties of aged rice flour and unaged rice flour had disappeared after the removal of the cell wall. The possible role of “structure-maintaining components” in the formation of the characteristic cooking properties of the aged rice during storage is discussed based on these results and also on the microscopic observation of the gelatinization process of the flour.     

稻谷吸湿性应力裂纹分形模型的动力学分析

将稻谷裂纹的生成看作籽粒内微缺陷扩展而成,建立了裂纹扩展分形模型,给出了分形模型背景下裂纹扩展的判据,推导出吸湿情况下断裂面的表面能,分析了分形模型的动力学特性。结果表明:吸湿性裂纹扩展路径通过淀粉颗粒,且宏观扩展方向受分形效应影响;分形效应降低了微裂纹扩展不规则程度;在吸湿膨胀情况下,淀粉对稻谷抗裂能力影响的本质是淀粉平均相对分子质量Mr存在差异,由于淀粉颗粒的Mr与直链淀粉含量的非线性关系的存在,使得裂纹率与直链淀粉的线性相关性并不显著。     

SENSORY TEXTURE PROFILE, GRAIN PHYSICO-CHEMICAL CHARACTERISTICS AND INSTRUMENTAL MEASUREMENTS OF COOKED RICE

Three samples of raw-milled rice, and 4 differently parboiled rices were used to study and to relate sensory perception to instrumental measurements. Variance analysis showed that some physico-chemical characteristics indicated great differences among rice samples: thickness of cooked grain, length/width ratio, water uptake, elastic recovery, white core rate and amylose and protein contents. The most discerning sensory attributes were: elasticity, stickiness, pastiness, mealiness, length of grain, firmness, crunchiness, time in mouth, brittle texture and juiciness. The correlation circle of the principal component analysis (PCA) showed high correlation between some sensory characteristics and instrumental measurements. Melting texture, surface moistness, juiciness, were positively correlated with water uptake (r = 0.70, 0.61, 0.71). Granular texture, crunchiness, brittleness and mealiness were significantly affected by white core presence (r = 0.81, 0.74, 0.86, 0.83). Elasticity was dependent upon elastic recovery and firmness measured by the Viscoelastograph, but not linearly. Length of cooked grain was correlated with the length/width ratio of raw grain (r = 0.83). Pastiness, compactness, stickiness were slightly influenced by the thickness of raw grain (r = 0.81, 0.67, 0.72). To a weaker extent, the sensory firmness was associated with the firmness measured by extrusion force using an Ottawa cell (r = 0.58). PCA showed greatdifferences in texture between rices. Two of the parboiled rices were very elastic, another was firm, granular, crunchy and mealy. The remaining two, cooked longer, were moister and more melting. Among the 3 samples of raw-milled rices, differences in grain length feeling and melting-granular-brittle characteristics. were distinguished.     

Incidence of open crack formation in short-grain polished rice during soaking in water at different temperatures

The incidence of open crack formation in short-grain polished rice during soaking in water at different temperatures was investigated. Rice with a moisture content of 10.4% (wet basis) was soaked in distilled water for 90 min at 15 °C, 25 °C or 35 °C, and the rate of open crack formation and the moisture content of the rice during soaking were measured. Results show that the rate of open crack formation increased with decreasing the soaking temperature. A model based on the relationship between the tensile stress calculated from the moisture gradient in a rice grain and the tensile strength calculated from the average moisture content of a rice grain provided a reliable qualitative estimate of the difference in the rate of open crack formation at different temperatures. It can be concluded that water diffusion into rice grains should be accelerated to prevent the formation of open cracks.     

4种典型谷物中酚类化合物的抗氧化和抗癌细胞增殖活性

将荞麦、大麦、小麦、水稻4种全谷物用70%(v/v)乙醇水浸提后,经AB-8大孔吸附树脂富集/分离,分别得到4种全谷物酚类提取物,测定其总酚和总黄酮含量,并运用高效液相质谱联用(HPLC-MS)法鉴定酚类化合物组成。在此基础上,通过体外法测定4种谷物的抗氧化能力和抗Caco-2细胞增殖能力,并探讨多酚含量与活性之间的相关性。结果表明:4种谷物酚类提取物中总酚和总黄酮含量从高到低的顺序均依次为:荞麦>大麦>水稻>小麦。从4种全谷物中成功确定了21种酚类化合物。4种谷物酚类化合物均具有一定的抗氧化能力和抗Caco-2细胞增殖能力,其强弱顺序均为:荞麦>大麦>水稻>小麦,而且其总酚含量与抗氧化和抗Caco-2细胞增殖活性之间以及抗氧化活性与抗Caco-2细胞增殖活性之间均具有良好的相关性。     

Strikingly high content of grain protein in solution‐cultured rice

A greenhouse experiment was conducted to investigate the nutritional quality of solution‐cultured rice. Five rice cultivars, different in grain amylose content and protein content, were grown under 10, 40 and 80 mg l^?1 nitrogen levels during the period of July 2003 to October 2003. In comparison to their original seeds, the solution‐cultured rice Oryza sativa L grain had strikingly higher protein content across all the cultivars and nitrogen levels, and remarkably lower amylose content in the waxy and low amylose cultivars, which might be due to the sufficiently stable nitrogen supply and well‐controlled temperature and humidity. The highest grain protein content was 163.6 g kg^?1 in this experiment, which is the highest reported rice grain protein content. The residual nitrogen concentration was greater than 12.39 g kg^?1 in the roots, 8.95 g kg^?1 in the stems, and 21.97 g kg^?1 in the flag leaves across all the cultivars and nitrogen treatments at harvesting. The rice grain had a narrow range of grain carbon content and hydrogen content. The average grain carbon and hydrogen contents for all the rice samples were 42.95 ± 0.15 (n = 60) and 6.81 ± 0.04 g kg^?1 (n = 60), respectively. The solution cultured rice grain was characterized with lower carbon–nitrogen mole ratio and lower hydrogen–nitrogen mole ratio, which could be mainly attributed to the increased protein content. The response of plant nitrogen, grain protein and amylose concentration to the supplemental nitrogen level varied with the cultivars. The results in this study suggested that solution culture technology could improve the production potential of rice. Copyright © 2005 Society of Chemical Industry     

用纤维素酶处理改良陈米饭食味的研究

借鉴了前人关于大米在陈化过程中胚乳细胞发生一系列变化的研究,用纤维素酶降解陈米细胞壁以促使细胞内容物析出,发现是一种切实有效的提高陈米饭食味的方法。     

Schallemissionen während der Holztrocknung

The relation between drying conditions and acoustic emisions from micro cracks have been observed on small end grained and straight grained pieces of freshly cut pine. The emission rates are related to the loss of moisture and the temperature depression due to the desorption process. In cach test series only one sample parameter has been varied: length, width, heartwood or sapwood. This stresses the particular influence of the end grain on the development of surface cracks. The drying conditions were about 40 C and 40% relative humidity, sufficiently severe to cause. above all, surface cracks. The presented studies are a basis for further investigating. The aim of this study is to develop a technique in which the dyring run is controlled by the acoustic emissions of a sample board which represents the charge being dried.     

A REASSESSMENT OF THE PATTERN OF ENDOSPERM HYDROLYSIS (MODIFICATION) IN GERMINATED BARLEY

Microscopic and enzymic studies of germinated barley have confirmed that excised barley embryos can produce α-amylase because the peripheral areas of the scutellar tissue contain aleurone cells. In contrast, the aleurone-free tissue of the scutellum is incapable of producing significant quantities of α-amylase. The potential of excised embryos to develop α-amylase is not correlated with the in vivo elongation of the scutellar epithelial cells in the grain because these cells do not elongate in excised embryos. Detailed anatomical studies revealed that the highly insoluble Intermediate layer of cell wall material, which is located between the embryo and the starchy endosperm, is broken-down asymmetrically, thus confirming that enzymic modification of the endosperm is under aleurone rather than scutellar control, in germinated barley. Other studies which have sited the scutellum of barley as inducing symmetric break-down of the endosperm have not linked structural changes, in vivo, with fluorescent or non-fluorescent staining patterns. Some of these studies have failed to recognise the possibility that grains such as sorghum and rice may have a different pattern of endosperm break-down from that of barley.     

Differences in Hollow Volumes in Cooked Rice Grains with Various Amylose Contents as Determined by NMR Micro Imaging

The presence of hollows in cooked rice grains found before in the cultivar Koshihikari was confirmed for 4 more cultivars with various amylose contents. The size, shape, and total volume of hollows differed between cultivars. Hollow volumes increased with grain volume and length before 100 °C was reached, but subsequently decreased during prolonged boiling. The previously proposed mechanism, describing sealing by gelatinized starch of cracks formed during soaking, seemed accurate for all 5 cultivars. Based on the hypothetical model of their formation, a relationship between amylose content and hollow formation was assumed. However, no correlation existed between final hollow volume and shape on 1 side and individual parameters such as flour gelatinization and amylose content on the other side.     

Aflatoxins in stored maize and rice grains in Liaoning Province, China

Aflatoxin contamination and its relationship to storage length in stored maize and rice in Liaoning Province, northeastern China, was investigated. Aflatoxins in 110 samples collected from an area of 14.68 million km² covering storage length from 1 yr to over 10 yr were determined by high-performance liquid chromatography with fluorescence detection. The results showed that almost all samples collected contained aflatoxins. The average contents in maize, whole grain rice and brown rice were found to be 0.99, 3.87 and 0.88 μg kg⁻¹, respectively. Three-fourths of the total aflatoxins in whole grain rice (3.87 μg kg⁻¹) could be removed by dehusking to as low as 0.88 μg kg⁻¹ in brown rice. No significant aflatoxin increase was observed in whole grain rice and brown rice over a 10-yr storage period. In maize, the amount of aflatoxins was significantly higher in 2-yr than 1-yr sample. Aflatoxin G₁ was detected as the major type of aflatoxin in over 40% of all stored grain samples tested and over 92% of rice samples examined. The aflatoxin content in maize and rice is much lower than the regulated maximum amount allowed in foodstuffs in China and other countries. We concluded that these grains are safe for human and livestock consumption and for trading.     

Analysis of phenolic compounds and antioxidant activity with H4IIE cells of three different rice grain varieties

The phenolic content and the antioxidant capacity of ethanolic extract of rice grains were examined using three different rice (Oryza sativa L. var. japonica) varieties, Jakwangchalbyeo (red pericarp glutinous rice), Hwasunchalbyeo (white pericarp glutinous rice), and Ilpumbyeo (white pericarp non-glutinous rice). Quantitative high performance liquid chromatography (HPLC) analyses showed that Jakwangchalbyeo contains the highest amount of total phenolic substances. Radical scavenging activities measured by the 1,1-diphenyl-2-picryl hydrazyl (DPPH) assay were 87.5% (Jakwangchalbyeo), 45.0% (Hwasunchalbyeo), and 50.0% (Ilpumbyeo). The results suggest a positive correlation between the phenolic content and the antioxidation capacity. Antioxidant activity in the ethanolic extract of rice grain was further assessed with 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) cell viability assay and fluorescence-activated cell sorting (FACS) analysis of H4IIE cells treated with hydrogen peroxide (H₂O₂). Hwasunchalbyeo and Ilpumbyeo extracts showed no significant effects on H₂O₂-induced oxidative stress. Jakwangchalbyeo extract increased cell viability by up to 82% and 74% after 5- and 24-h treatments at 100 μg/mL, respectively. Consistent with the results of DPPH and MTT assays, dichlorofluorescein (DCF) fluorescence was further reduced when H₂O₂ was applied with Jakwangchalbyeo extract. In conclusion, red pericarp Jakwangchalbyeo grain extracts exerted significantly higher inhibitory effects on H₂O₂-induced oxidative stress in H4IIE cells than did other white pericarp rice grain extracts.