Effects of rice harvest moisture on kernel damage and milled rice surface free fatty acid levels

ABSTRACT:  Surface free fatty acid (FFA) on milled rice is a key factor in determining rice quality and acceptability to the brewing industry. Rice FFA oxidizes, causing off-flavors and odors to develop, compromising the brewing quality of milled rice. The effect of harvest moisture (13%, 16%, and 20%), harvester type (1688 Case and 9500 John Deere), and rice variety (Cocodrie and Bengal) on harvest damaged rough rice and milled rice surface FFA after drying to 12% moisture and 6 mo rough rice storage was examined. The Case harvester produced more damaged kernels than the John Deere harvester, but this was not reflected in surface FFA development. There were no significant FFA differences in variety or harvester type. Rice harvested at a higher moisture content (20%) produced significantly greater FFA values, with a peak near 0.1%, than rice harvested at lower moisture contents (13% and 16%), which had FFA values near 0.08%. Retention of bran by damaged kernels at high harvest moisture probably was responsible for promoting surface FFA development, but if bran was lost at lower harvest moistures, surface FFA, development was limited. Harvest moisture affected milled rice FFA, although rough rice was dried to 12% immediately after harvesting.     

日本寒冷地带北海道抑制粳稻生成白未熟粒的栽培法（网络首发、推荐阅读）

白未熟粒的多发会使整粒率下降,降低检查等级,因此急需抑制其发生。白未熟粒中,乳白粒和基部未熟粒的发生率存在品种间差异。切除止叶减少光合作用,增肥导致每平方米稻谷数量的增加,疏植和育苗时高温引起早期异常抽穗所致的齐穗不良,以及收割时期的延迟等会造成白未熟粒的增多。此外倒伏还会导致青未熟粒、白未熟粒增多。在初期生长良好的情况下,从分蘖期开始的深水灌溉抑制了过剩的分蘖产生,增加了粒重和糙米产量,使糙米品质得以提高。由于成熟期的土壤过于干燥,因腹白粒产生引起的品质降低和千粒重减少会导致减产。从抽穗期到齐穗期10天后的茎叶到稻谷的每粒稻谷非结构性碳水化合物（NSC）流转量,以及粗糙米产量减去同一流转量的每粒稻谷NSC增加量越多,这些白未熟粒的产生就越少。为避免白未熟粒的多发,必须使施肥量、种植密度、育苗温室的温度管理、移植时期、成熟期的土壤水分和收割时期合理化,促进初期生长,用深水抑制过剩的分蘖。通过改善以上的栽培方法,以及1990年代中期后在共同干燥调制储藏设施中使用色选机选别糙米,北海道的一等米比例超过了日本全国的平均水平。     

优质籼米地下仓储藏过程中品质变化

为探索成品粮绿色、安全的储藏方法,在南方高温高湿地区,利用地下仓储藏黄花粘和籼优998两种优质籼米,定期检测水分、碎米总量、小碎米率、垩白粒率、黄粒米、直链淀粉、品尝评分值、色泽气味、不完善率、害虫虫口密度等指标。实验结果显示,实验期间,大米水分呈小幅下降;2种大米不生虫时间长达13个月;小碎米率、色泽气味等指标无显著性变化;碎米总量、黄粒米、不完善粒含量小幅增加,直链淀粉含量逐渐增加,但均未导致大米质量等级下降;垩白粒率显著增加,品尝评分值显著下降,且均造成大米质量定等下降。根据国家标准《大米》的规定,籼优998于储藏3个月后,质量定等由二级降为三级,储藏6个月后,已不属于优质籼米,黄花粘于实验结束后仍为优质籼米三级。说明地下仓具有良好的保湿、保鲜和害虫抑制效果,优质籼米耐储性能与储藏条件和品种均相关。     

Effects of Combine Harvesting on Head Rice Yield and Chaff Content of Long and Short Grain Paddy Harvest in Sri Lanka

Paddy harvesting is the process of collecting the mature rice crop from the field which consists of activities such as cutting, handling, threshing and cleaning. Cutting, threshing and cleaning plays an important role to reduce postharvest losses. Lower performance of traditional harvesting process, labour shortage, reduced turn-around time and use of high yielding varieties have inevitably forced farmers to shift into mechanical grain harvesting in Sri Lanka. Rice milling is carried out to produce an edible polished or white rice product from harvested rough rice. Head rice yield is considered for marketing purposes because broken rice has low price in the market. Field survey was conducted in Polonnaruwa, Ampara and Hambanthota districts to identify most popular types of combine harvesters operating in the above districts. Paddy samples were collected from harvest of two most popular models of combine harvester in triplicate. Paddy sample of 1m² area from every paddy field were harvested separately by manual harvesting followed by manual threshing and cleaning in laboratory as control sample of relevant paddy field. Moisture content of the paddy grains were measured in the paddy field using digital moisture meter before harvesting. Paddy samples were subjected to sun drying until the moisture content come down to 14±1% before the quality analysis in the laboratory. Each paddy sample was analyzed for moisture content, chaff percentage and head rice yield percentage (HRY). Paddy was milled using laboratory scale rubber roll sheller and abrasive polisher. Chaff content percentage was measured by adding 100 ml of paddy to water and volume of chaff was measured using graduated cylinder. HRY was calculated dividing the weight of grain partials, which are larger than the ³/₄ of the grain, by weight of paddy sample. HRY between the two combine harvesting machine models evaluated were not significantly different at p<0.05 and also it was not significantly dependent on the harvesting methods such as combine harvesting and manual harvesting. The chaff content was significantly higher in model-2 in comparison to control sample for long grain paddy while model-1 was not significantly different with control sample for short grain paddy.     

CONDUCTION HEATING of HIGH MOISTURE ROUGH RICE III. CHANGES IN MILLING and COOKING QUALITIES

The effects of high temperature conduction heating on the milling and cooking qualities of rough rice having moisture in the range 18–30% wet basis were investigated. the results showed an increase in head rice yields of heat-treated samples accompanied by a reduction in milled rice whiteness and improvement in cooked-rice texture. Heat treatments of rough rice corresponding to fungal inactivation level of 95% gave the highest head rice yields and acceptable level of reduction in the whiteness of milled rice. the observed increase in the firmness of cooked-rice kernels and a reduction in their stickiness due to conduction heating appeared to resemble the natural aging of fresh rough rice.     

日本の寒地，北海道のうるち米における白未熟粒発生を抑制する栽培法（日文）（网络首发、推荐阅读）

白未熟粒の多発生は,整粒歩合を低下させ検査等級を下げるため,抑制する必要がある。白未熟粒,その中でも乳白粒と基部未熟粒の発生率に品種間差異があった。白未熟粒は,止葉切除による光合成の減少,増肥とそれによるm2当たり籾数の増加,疎植および育苗時の高温で生じる早期異常出穂による穂揃い不良,および刈り取り時期の遅延により増加した。倒伏により青未熟粒?白未熟粒は多くなった。初期生育が良好な場合,分げつ期からの深水灌漑は過剰分げつ発生を抑制し,粒重と玄米収量を増加させ,玄米品質も向上させた。登熟期の土壌の過乾燥により,腹白粒発生による品質低下や千粒重減少による減収を生じた。これら白未熟粒の発生は,出穂期から出穂揃い期10日後までの茎葉から籾への非構造性炭水化物（NSC）の1籾当たり転流量および粗玄米収量から同転流量を減じた1籾当たりNSC増加量が多いほど,少なかった。白未熟粒の多発生回避には,施肥量,栽植密度,育苗ハウスの温度管理,移植時期,登熟期の土壌水分および刈り取り時期を適正化し,初期生育を促進し,過剰分げつを深水で抑制する必要があった。以上の栽培法改善と,1990年代後半以降からの共同乾燥調製貯蔵施設での色彩選別機を使った1等米調製により,北海道の1等米比率は全国平均を上回るようになった。     

The breakage susceptibility of raw and parboiled rice: A review

Rice (Oryza sativa L.) is one of the most important cereals in the world. Before it is consumed, it is common to remove the hull, bran and germ from the rough rice kernel which is either parboiled or not. During such processing, rice kernels are subjected to mechanical stresses which cause some rice grains to break. A main challenge of the rice industry is to minimize the quantities of broken rice. We here review the factors impacting the breakage susceptibility of rice kernels. Their tendency to break is primarily determined by fissures, chalkiness, immaturity and rice kernel dimensions, properties which are both cultivar and rice grain history dependent. The intensity of processing of any given rice feedstock determines the actual level of broken rice kernels. If performed properly, parboiling, a three-step hydrothermal treatment consisting of soaking, heating and drying of rough rice, substantially reduces the level of broken kernels.     

Effect of pre-harvest flooding of paddy on the milling and cooking quality of rice

The physico-chemical, milling, pasting and cooking characteristics of six cultivars of paddy, viz PR-106, PR-109, PR-103, Java, PR-108 and Basmati-370, as affected by flooding were investigated. A significant reduction in 1000-kernel weight and bulk density of paddy rice in damaged samples was observed. The kernels in flood-affected samples became soft and developed fissures which contributed to low head rice recoveries. The milled rice from them had lower kernel weight and protein content but showed higher amylose and ash content. The diastatic activity of these samples was higher. Amylographic characteristics showed no effect on the gelatinisation time and temperature in most of the samples. Peak viscosity and setback were affected in all samples, and the effect was variable among different varieties. The flood-affected samples showed lower cooking time and higher gruel solids loss, and were rated poorer organoleptically.     

Quality Evaluation of Milled Aromatic Rice from India, Thailand, and the United States

Five aromatic and two nonaromatic milled rice samples were used to compare the quality of U.S. produced aromatic rice with that of India and Thailand. Jasmine (Thailand) was whiter than all other rice samples tested. Della rice samples (U.S.) were not as white as Basmati (India). Della AR (Arkansas) was less red and less yellow than Della LA (Louisiana). While the uncooked kernels of Della were as long as Basmati or Jasmine, the greater length: width ratio caused Basmati to appear longer than Della. Della and Jasmine were greater than Basmati in 1000 kernel weight. Della samples were classified as having intermediate to high intermediate gelatinization temperature, medium gel consistency, intermediate amylose content and cooking quality, which are characteristic of typical U.S. long grain nonaromatic rice. A sensory panel could not detect a flavor difference between Della AR and either Basmati or Jasmine.     

Corn silage management I: effects of hybrid,maturity, and mechanical processing on chemical and physical characteristics

Two experiments were conducted to evaluate the effects of hybrid, maturity, and mechanical processing of whole plant corn on chemical and physical characteristics, particle size, pack density, and dry matter recovery. In the first experiment, hybrid 3845 whole plant corn was harvested at hard dough, one-third milkline, and two-thirds milkline with a theoretical length-of-cut of 6.4 mm. In the second experiment, hybrids 3845 and Quanta were harvested at one-third milkline, two-thirds milkline, and blackline stages of maturity with a theoretical length-of-cut of 12.7 mm. At each stage of maturity, corn was harvested with and without mechanical processing by using a John Deere 5830 harvester with an onboard kernel processor. The percentage of intact corn kernels present in unprocessed corn silage explained 62% of variation in total tract starch digestibility. As the amount of intact kernels increased, total tract starch digestibility decreased. Post-ensiled vitreousness of corn kernels within the corn silage explained 31 and 48% of the variation of total tract starch digestibility for processed and unprocessed treatments, respectively. For a given amount of vitreous starch in corn kernels, total tract starch digestibility was lower for cows fed unprocessed corn silage compared with processed corn silage. This suggests that processing corn silage disrupts the dense protein matrix within the corn kernel where starch is embedded, therefore making the starch more available for digestion. Particle size of corn silage and orts that contained corn silage was reduced when it was processed. Wet pack density was greater for processed compared with unprocessed corn silage.     

Comparison of sensory properties of popcorn from various types and sizes of kernel

Three rice‐type popcorns (red, white and yellow) and one pearl‐type popcorn (yellow) were used in this study. All types were sized into three fractions (5 < D < 6 mm, 6 < D < 7 mm and D > 7 mm) by screening with round‐hole sieves. Samples were tested for popping quality and suitability for popping, and the sensory properties of the popcorns were evaluated. A popcorn popper with a maximum operating temperature of 226 °C was used for popping the samples (25 g). Both kernel type and size affected the expansion volume and the number of unpopped kernels. Yellow pearl‐type (YPT) and white rice‐type (WRT) popcorns showed good popping performance. The popping properties of the smallest‐sized kernels were better than those of the other fractions. Popcorn type significantly affected the flake size uniformity, flake shape uniformity, flake colour, crispness and taste of the products. Analysis of variance (ANOVA) and principal component analysis (PCA) showed that that kernel size was of great importance for the expansion volume, which was negatively correlated with number of unpopped kernels, 1000‐kernel weight and diameter ratio and positively correlated with flake size, kernels per 25 g, crispness and tenderness. © 2001 Society of Chemical Industry     

Effects of rice flour size fractions on gluten free rice bread

Fractionation (F-1, F-2, and F-3) of semi-dry milled rice flour (SDMRF) was performed using air-classification wheel speeds (ACWS, 1,000, 2,000, and 3,000 rpm) to identify suitable size fractions for preparation of gluten-free rice bread (GFRB). Characteristics and effects of fractions on GFRB were investigated. Fractions had higher water absorption indices than unfractionated flour (control). Fractions were smaller in size, and the amount of damaged starch was larger for higher ACWS values. The F-1 fraction had higher peak viscosities and specific volumes than other fractions. The F-3 fraction had lower values. GFRB prepared using the F-1 fraction had a lighter air-cell structure and lower hardness than control bread. From sensory evaluations, the particle size of SDMRF affected the appearance of GFRB. GFRB prepared using the F-1 fraction had more uniform and smaller air-cells. The quality of GFRB can be improved by controlling the particle size of flour.     

Effect of drying and tempering on rice fissuring analysed by integrating intra-kernel moisture distribution

The fissure generation of one short- and two long-grain rough rice dried at different air conditions for 15, 30 and 60 min, and respectively, tempered at 20, 30, 40 and 50 °C for tempering duration ranging from 0 to 330 min was analysed by integrating moisture gradients in rice kernels. Results indicated that drying and tempering processes had significant effects on the moisture gradient and rice fissuring. The percentage of fissured kernels increased with increasing drying time and decreasing tempering time. The tempering duration required for long-grain rice was shorter than that for short-grain rice to prevent kernel fissuring. Higher tempering temperatures can effectively eliminate moisture gradients and then lower the rice fissuring generation. Tempering at 50 °C reduced fissuring incidence by 32 to 50% compared to tempering at 20 °C. Moreover, short-grain rough rice was very susceptible to fissure whereas long-grain rough rice with a high amylose content was much more fissure-tolerance.     

Milling of rice grains: The roles of starch structures in the solubility and swelling properties of rice flour

Rice flours with different particle sizes and degrees of damaged starch granules were produced by hammer milling and cryogenic milling of rice grains, where degradation of starch molecules was evident in the hammer‐milled flours, but not in the cryogenically milled flours. The solubility and swelling properties of the resulting rice flours were determined in cold (30°C) and hot water (90°C). The cold‐ and hot‐water starch solubility was strongly correlated with the degree of damaged starch granules, and weakly with the particle size of rice flour. No evident correlations were observed between starch solubility and the molecular structures, indicating that molecular degradation by milling process was not the only precondition of increased starch solubility. Possible mechanism for the observed correlations is that increasing surface area and/or exposure of loosely packed inner part of starch granules with increasing degree of damaged starch granules allowed more starch molecules to leach out in cold and hot water. Furthermore, the cold‐water swelling of rice flour was strongly correlated with the degree of damaged starch granules, possibly due to the rapid hydration of damaged starch granules, whereas the hot‐water swelling did not show any correlations with flour particle size and granular and molecular starch structures. The results have provided better insights in the relationship between starch structures and solubility and swelling properties of rice flour, which can be used to improve the manufacture and selection criteria of rice flour for better products.     

Influence of malathion resistance status on survival and growth of Tribolium castaneum (Coleoptera: Tenebrionidae), when fed on flour from insect-resistant and susceptible grain rice cultivars

The effect of insecticide resistance on the potential for control of stored product insect pests based on plant resistance was evaluated. Flours made from three rice cultivars (cvs.) that showed resistance or susceptibility to feeding by Tribolium castaneum were studied, using two strains, resistant and susceptible to the organophosphate insecticide, malathion. Flours made from rough, brown and milled rice were used to help identify the locus of any cultivar resistance mechanisms. The insect-resistant (Dawn) and moderately resistant (Lebonnet) cvs. had fewer eggs laid and caused greater mortality of the insects than the susceptible cultivar (cv.) (IR8). For all cvs., flour from brown rice was the most suitable for insect survival, whereas the highest larval weights were found in milled and the lowest in rough rice flours. On the other hand, the highest mortality of the susceptible strain occurred in milled rice flours. The larvae resistant to malathion survived significantly better than those of the susceptible strain, when fed on flour from the insect-resistant cv. (Dawn). The cause of this positive interaction between the insecticide resistance status of T. castaneum and the grain resistance is not known. The mechanism of malathion resistance occurring in this strain is enhanced malathion-specific carboxylesterase activity but it is not known how this can confer survival benefits, when the insect feeds on flour from the resistant cv. These results could have practical implications for the efficacy of stored product pest control using varietal resistance in situations where insecticide resistance is prevalent.     

Sorption equilibrium moisture and isosteric heat of cold plasma treated milled rice

To promote industrial adoption of cold plasma as a sustainable and safe processing technology for rice, data on equilibrium moisture content (EMC) for cold plasma treated milled rice of five Chinese varieties were collected by a gravimetric method at 11–96% equilibrium relative humidity (ERH) and a temperature range of 15–35 °C. Nine models were fitted well to the sorption data, with the modified Guggenheim–Anderson–deBoer equation (3-MGAB), modified Henderson equation (MHE), and a polynomial equation being the best fits. At a constant ERH, the EMC was negatively correlated with temperature, whereas there was a strong effect of temperature on the sorption isotherms of the milled rice. Initially, the isosteric heats of sorption for the cold plasma treated rice decreased rapidly with increasing sample moisture content (MC); however, when MC was higher than 15% of the wet basis (w.b.), further increases in MC caused a slight decrease in heat sorption values. The heat of vaporization of the milled rice approached the latent heat of pure water at a moisture content of ~17.5% w.b., which was ~2500 kJ/kg. The isosteric heat of sorption values of the milled rice predicted by the modified Chung-Pfost equation (MCPE) and MHE models negatively correlated with temperature. At 70% ERH, the safe-storage MC of the cold plasma treated rice were ≤14.5% w.b. at 25 °C. In comparison to the untreated milled rice, the cold plasma treated rice with 120 W for 20 s and 60 s significantly decreased the water contact angle and increased kernel broken index, without significantly changing the appearance quality of milled rice. The cold plasma treated rice with 120 W-20 s had insignificantly higher EMC than that of 120 W-60 s at the studied temperature range. This study demonstrates that helium cold plasma treatment insignificantly changed hygroscopic property of milled rice whilst maintaining the appearance quality.     

Development of Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae) on rice milling components and by-products: Effects of diet and temperature

Development of Tribolium castaneum (Herbst), the red flour beetle, was assessed on different rice components and their various by-products (i.e., diets) commonly found in rice mills, in two separate experiments. In the first experiment, eggs did not develop through to the adult stage on rough rice hulls, paddy rice dust, and milled rice dust, while eggs developed to the adult stage to some extent on rice flour, milled whole kernels, brown rice, milled broken kernels, and bran. For the diets where development occurred, the lowest percentage was on brown rice, and adults that emerged on brown rice had smaller elytra compared to adults emerging on the other diets. In the second experiment, 1–2-day old neonates were exposed on the diets listed above and held at 22, 27, 32, and 37 °C. At all temperatures, development to the pupal and adult stages was slowest on rice flour. At 22 °C, development to those stages took about twice as long compared to development at 27 °C. As temperature increased developmental times were reduced. Even though neonates developed slowest on rice flour adult emergence rates were not affected. Predictive models were used to estimate potential population development on the diets. At 22 and 27 °C, adult size as measured by elytra length was greatest when they developed on bran, while body weight was generally lowest for adults that developed on brown rice. Results show that T. castaneum can utilize rice components and by-products produced during the rice milling process, although not all components or by-products were optimal for development, and emphasis should be placed on cleaning and sanitation to remove food sources to limit infestations. Mill managers can use these results to show the importance of sanitation, and potentially improve overall pest management programs inside the mill.     

应用近红外光谱技术快速测定粳稻品种的直链淀粉含量

应用近红外光谱法以稻谷、糙米、精米、糙米粉和精米粉为扫描材料分别建立了粳稻直链淀粉含量的预测模型。结果表明采用光谱预处理的校正效果比不采用预处理的好,用偏最小二乘法(PLS)获得的粳稻稻谷、糙米、精米、糙米粉、精米粉的回归模型和交叉验证结果为:最优校正决定系数(R2)和交叉检验均方误差(RMSECV)分别为0.8136、2.74,0.8864、2.56,0.8915、2.59,0.9261、2.26,0.9505、1.83,粉碎性样品的误差比整粒样品的误差小。育种实践中,低世代可选用糙米、高世代可选用糙米粉或精米粉作为扫描样本测定稻米直链淀粉含量。     

Physicochemical Differences Between Milled Whole Kernel Rice and Milled Broken Rice

The purpose of this study was to demonstrate the existence of distinct differences between selected physicochemical properties of head and broken milled rice. Polyuronic acids were found to affect hardness of the rice kernels. The broken kernels were measurably softer than intact kernels for all cultivars. Values for alkali spreading and amylographic pasting properties indicated that broken kernels were more porous, and exhibited lower peak and setback viscosities than intact kernels. This suggests differences in the relative amounts of amylose and amylopectin in head rice and brokens. A protein-phytin complex may be more prominent in broken kernels than head rice.     

Stability of Ethanol-Extracted Brown Rice to Hydrolytic and Oxidative Deterioration

Brown rice kernels extracted with EtOH at 7°C for 60 min were the most stable to lipolytic hydrolysis; free fatty acids (FFA) level in these kernels increased from 1.0–1.4% during 6 mo storage at 36°C. At lower extraction temperatures and times, kernels were less stable to lipolytic hydrolysis. The higher the temperature of extraction, the more susceptible kernels were to oxidative deterioration during storage; extraction time was not a factor. Kernels extracted with recycled EtOH were no more susceptible to oxidation than those extracted with fresh EtOH.