Milling breakage susceptibility and mechanical properties of parboiled brown rice kernels

Parboiling, a hydrothermal treatment of paddy or brown rice, impacts both head rice yield and texture and nutritional characteristics of cooked rice. Here, milling breakage susceptibility of parboiled brown rice was investigated on both bulk and kernel level. Brown rice was parboiled by soaking at 40, 55 or 65 °C and steaming at 106, 120 or 130 °C. The breakage susceptibility and changes in starch and proteins of bulk samples were related to the properties of individual rice kernels. An increase in milling breakage susceptibility from 1% to 11% corresponded to a decrease in average bending force of individual kernels from 34.9 to 14.6 N. Furthermore, both white bellies and fissured parboiled rice grains were more breakage susceptible. Their average bending force was respectively 14.1 N and 17.6 N compared to an average of 39.6 N for intact parboiled rice grains. Whereas the level of proteins extractable with sodium dodecyl sulfate containing medium had no impact, the degree of starch gelatinization was critical in determining the presence of both white bellies and fissured parboiled rice grains. More in particular, complete starch gelatinization ensured the absence of white bellies and minimized fissuring in the parboiled end-product, thereby decreasing milling breakage susceptibility.     

蒸谷米糠膨化工艺的研究

考察了膨化方式、原料水分、入料温度、机膛温度等工艺条件对蒸谷米糠膨化效果的影响.实验结果表明,湿法和干法膨化均可获得较好的膨化效果,最佳工艺条件为:干法,原料水分控制在8％ ～9％,入料温度50C,机膛温度100 ～ 110℃;湿法,原料水分控制在6％ ～7％,入料温度60℃,机膛温度120 ～130℃.蒸谷米糠膨化料在实验室模拟浸出卖验中获得了较好的浸出效果.     

Studies on parboiled rice—Part 3: Characteristics of parboiled rice on recooking

The apparent solubility and cookwater loss of samples of parboiled rice, subjected to various steam treatments, were measured after recooking the rice in boiling water. Both parameters were reduced according to the severity of treatment received, the reduction of apparent solubility being the most marked.The results showed a highly significant, negative linear correlation (r = 0.972) between apparent solubility and the relative amount of complexed amylose in the starch. This confirmed the suggestion made in Part 1 of this paper that complexed amylose was responsible for the resistance of the starch towards solubilisation.Estimation of the amylose and amylopectin released into the cooking water and solubilised inside the kernel revealed that both fractions were insolubilised to a similar extent. It was proposed that amylose was insolubilised by complexing with free fatty acids and the amylopectin insolubilised by interaction with the complexed amylose.     

蒸谷米生产工艺简析

介绍了中粮(江西)米业有限公司的蒸谷米生产工艺。     

Studies on parboiled rice: Part 1—Comparison of the characteristics of raw and parboiled rice

Various properties of raw and parboiled rice were compared in an effort to elucidate the factors responsible for the changes induced by parboiling.The parboiled rice was less prone to disintegration on cooking, the kernels remaining well separated and less sticky than the non-parboiled sample. The solids leached into the cooking water and the extent of solubilisation of the kernels on cooking were both considerably lowered by parboiling. Amylograms of flour prepared from the rice revealed that this was due to the resistance of the starch in the parboiled rice to swelling and solubilisation in hot water.From the results of X-ray diffraction spectra it was concluded that the behaviour of parboiled rice is influenced by the presence of an insoluble helical amylose complex and not, as is generally assumed, by retrogradation.     

Comparative studies on the physicochemical properties and microstructure of raw and parboiled rice

The protein and mineral salts of rice were found to have increased while water-soluble substances were found to have decreased as a result of parboiling. Parboiling resulted in marked changes in the amylograph properties of rice paste, as well as increasing its resistance to alkali dispersion. The grains were shorter but wider, with lower water absorption and swelling capacity during cooking than those of raw-milled rice.The differences in ultrastructure between dry and cooked raw-milled and parboiled rice were studied with a scanning electron microscope. Complete deformation of the starch granules was evident in the raw-milled rice after cooking for 9 × 10² and 12 × 10² s, while those of parboiled rice showed great resistance to deformation. Variations in the over-cooked grains of both raw-milled and parboiled rice were studied.     

Studies on parboiled rice—Part 2: Quantitative study of the effects of steaming on various properties of parboiled rice

A study was made of the effect of steaming on the solubilisation of the starch in paddy rice and the relative crystallinity and milling yields of the dried product.The rates of gelatinisation and solubilisation of the starch were extremely dependent on steaming pressure. Solubilisation continued long after gelatinisation was completed and was a more useful index of processing treatment. The relative crystallinity due to amylose complex formation was highly significantly and positively correlated (r = 0·960) with the extent of solubilisation achieved during steaming. Slight steaming markedly increased milling breakage and yields were only improved in relation to unprocessed rice after the starch had been completely gelatinised.     

Swelling and solubility behaviour of parboiled rice flour

Parboiled rice flour swelled and dissolved more than raw rice flour in water at temperatures below 70°C, but less than raw rice at higher temperatures. This difference between raw and parboiled rice increased with an increasing degree of parboiling. A sample of parboiled rice produced by dry-heating soaked paddy in hot sand behaved differently; but when it was wetted and tempered to favour reassociation of starch, its properties fell in line with normal steam-parboiled rice. The above behaviours of raw and parboiled rice flour were similar to those of corresponding whole-grain rice. They also reinforce the earlier suggestion of starch reassociation in conventional parboiled rice.     

蒸谷米快速浸泡工艺研究

研究不同浸泡工艺包括温度-时间、微波、酸碱溶液、低浓度乙醇、酶对稻谷吸水率的影响,结合蒸谷米外观品质及米饭质构分析,筛选有效的快速浸泡工艺。结果表明,在稻谷∶水为1∶1(g/mL)、温度60~70℃、浸泡4~5 h时,便达到浸泡工艺要求,吸水率达到30%;能显著提高稻谷吸水率的方法是质量比5%的纤维素酶浸泡4 h,吸水率达30.07%;能显著缩短浸泡时间方法是5 min、700 W微波浸泡,吸水率为31.69%。且2种浸泡工艺对蒸谷米的外观品质和米饭质构无不良影响,有望作为蒸谷米快速浸泡工艺进行应用。     

Limited multilayer desorption of brown, parboiled rice

Two mathematical models, the BET-equation and the Caurie-equation, are used to analyse experimental desorption isotherms of two long-grain varieties of brown, parboiled rice at different temperatures. Monolayer moisture contents and maximum number of sorbed water layers, estimated by the Caurie-model, decrease with increasing temperature. From the temperature dependence of the desorption isotherms, isosteric heats of desorption are calculated. For both varieties, the differential heats of desorption are already very small (1.4 kJ/mol) at a moisture content of 20%. Thus, additional moisture behaves almost like pure water.     

蒸谷米浸泡工艺参数初探

通过研究浸泡温度、浸泡时间、浸泡压力对蒸谷米含水量的影响,采用正交试验优化蒸谷米浸泡工艺参数,经过中试试验修正的工艺参数为:浸泡温度55℃、浸泡压力400kPa、浸泡4 h.     

蒸谷米糠制油工艺方案简析

针对蒸谷米的特性,简要介绍了蒸谷米糠油厂工艺方案确定过程中需注意的问题,以期为新建蒸谷米糠制油厂和日后的生产管理提供参考。     

Effect of soaking medium on the physicochemical properties of parboiled glutinous rice of selected Laotian cultivars

The effect of various soaking mediums, viz. water (control), 3% NaCl and 0.2% acetic acid, and without soaking on the physicochemical properties of parboiled selected glutinous (TDK8 and TDK11) and non-glutinous (Doongara) was investigated in the present study. Results showed that the chemistry of soaking had a significant effect on the head rice yield (HRY), grain hardness, crystallinity, color, pasting and thermal properties, textural attributes, and glycemic index of these rice varieties. Soaking with NaCl and acetic acid significantly increased the grain hardness and HRY than control and without soaking treatments. Acetic acid and NaCl soaking significantly affected crystalline regions of starch resulting in reduced crystallinity in X-ray diffraction analysis and thermal endotherms in DSC analysis. NaCl soaking induced swelling of starch granules resulting in high peak and final viscosities. However, acetic acid restricted swelling resulting in reduced peak and final viscosities. NaCl and acetic acid soakings also resulted in increased hardness and adhesiveness of cooked grains than normal water soaked and un-soaked parboiled rice samples. Interestingly, change in textural attributes was prominent in parboiled glutinous rice. The color difference value for fresh parboiled samples was significantly lower for acetic acid soaked samples compared to NaCl soaked and un-soaked samples probably due to bleaching effect of acetic acid. Moreover, parboiling also resulted in significant reduction in glycemic index of glutinous rice. These findings revealed the potential application of parboiling with modified soaking techniques to improve the grain quality.     

蒸谷米生产中干燥工序工艺参数的研究

以糙米为原料进行干燥工序工艺参数的研究。通过对快速干燥温度和时间、慢速干燥温度和时间以及缓苏时间进行单因素试验和正交试验,最终确定干燥工序的最佳工艺参数为快速干燥温度为70℃、快速干燥时间60 min、缓苏时间为40 min、慢速干燥温度65℃和慢速干燥时间40 min。     

Physical properties of parboiled wheat and bulgur produced using spouted bed and microwave assisted spouted bed drying

The main objective of this study was to compare the spouted bed and microwave assisted spouted bed drying on affecting physical properties of parboiled wheat and bulgur. Drying was performed at different temperatures (50 °C, 70 °C, 90 °C) and microwave powers (288 W, 624 W). Bulk and apparent density, bulk and apparent porosity, sphericity, color, microstructure and pore size distribution of parboiled wheat were investigated after drying. Yield and water absorption capacity were determined in bulgur samples. The effect of air temperature on physical properties of product except color was not significant in spouted bed drying. More porous structure was observed in wheat samples dried in microwave assisted spouted bed compared to air dried ones. Sphericity and bulk density were higher when high temperature was combined with high microwave power. In microwave assisted spouted bed drying, similar yield value but lower water absorption capacity of bulgur were observed as compared to spouted bed drying.     

A comparative study on the physicochemical,cooking and textural properties of fortified rice kernels prepared from raw and parboiled rice

Fortified rice kernels (FRK) are extruded rice-shaped kernels manufactured by blending broken rice flour and vitamin–mineral premix. In this study, four parboiled and three raw rice with intermediate amylose content (20–24%) were processed to manufacture FRK. The system parameters (torque and die pressure), physicochemical properties (length, lightness, water absorption index and water solubility index), cooking properties (cooking time, solid loss, elongation) and textural properties of FRK were analysed and correlated using the Pearson correlation coefficient. The torque and die pressure were 16.76–22.76 Nm and 92.56–136.41 bar, respectively. Compared to raw rice, the parboiled rice showed the highest torque, die pressure and axial expansion in uncooked FRK while longer cooking times, higher elongation ratio and hardness; lesser water absorption ratio and solid loss in cooked FRK. The raw rice FRK showed higher lightness. There was a significant difference between all FRK for water absorption index (1.74–2.52) and water solubility index (2.06–3.53%).     

The bioavailability of iron fortified in whole grain parboiled rice

The present study was to evaluate the bioavailability of iron (Fe) fortified in parboiled rice grain, expressed as Fe uptake by Caco-2 cells after in vitro digestion. The bioavailability of Fe-fortified in the rice grain was closely and positively correlated with increasing concentrations of Fe in the grains of the three cultivars (r = 0.96∗∗). The uptakes of the Fe-fortified in parboiled rice milled for 120 s (34.2, 47.7 and 107 ng ferritin mg protein⁻¹ in three cultivars, respectively) were well above those of the unfortified raw (6.1, 4.9 and 5.7 ng ferritin mg protein⁻¹) or parboiled rice (4.7, 3.6 and 4.4 ng ferritin mg protein⁻¹), the high Fe rice line IR68144-2B-3-2-2 (4.0 ng ferritin mg protein⁻¹) and popular Jasmine rice cultivar KDML 105 (3.9 ng ferritin mg protein⁻¹). Increasing milling time and rinsing the Fe-fortified parboiled rice decreased Fe bioavailability, due to their negative effects on total Fe concentrations in the parboiled rice grains, but uptakes were still well above that of their unfortified raw or parboiled rice grains. Rinsing or washing the Fe-fortified and milled rice grains decreased the bioavailability to 85 ng ferritin mg protein⁻¹ in the YRF cultivar, compared to about 100 ng ferritin mg protein⁻¹ in its non-rinsed grains. Dilute acid-extractable (DAE) Fe was linearly, positively correlated with the uptake of Fe assessed by the in vitro digestion/Caco-2 cell technique (r = 0.90∗∗), which can be used as a rapid method for optimizing levels of bioavailable Fe to be fortified in the parboiled rice by parboiled-rice mills if this Fe-fortification technique should be adopted in south and southeast Asia.     

蒸谷米超高压浸泡工艺条件优化

利用超高压浸泡生产蒸谷米,在单因素实验的基础上,利用Box-Benhnken中心组合实验和响应面分析法,确定了提升蒸谷米品质的最适工艺条件:浸泡水用量为35%,浸泡压力为150 MPa,浸泡水温度为35℃,保压时间为7 min,此条件下,整精米率为71.38%、蛋白质质量分数为9.06%、维生素B_1含量为0.40 mg/100 g、维生素B_2含量为0.14 mg/100 g。与普通精白米相比较,蛋白质、维生素B_1、维生素B_2含量均极显著性升高(P0.01)。     

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.