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.     

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.     

Technological properties of microwave parboiled rice

Two rice varieties, a short grain (Giza 175) and a long grain (Giza 181), were parboiled by soaking in water at 80–85 °C for 1.5 h and then dried in the microwave oven for 3, 5, 6 and 8 min. The effect of such parboiling treatment on milling output and technological properties (cooking and eating quality) of milled rice were studied. There was a negative significant correlation between head rice and the drying time and a positive correlation between the drying time and the broken grains. The effect of such treatment on the chemical composition of milled parboiled rice, i.e. amylose, protein, fat and ash contents, showed that the amylose content of Giza 175 variety significantly decreased while not affect in Giza 181 variety. No significant differences were obtained in protein, fat and ash contents by increasing drying time. Microwave drying was more pronounced on Giza 175 variety rather than Giza 181 one. However, the optimum cooking time of the parboiled samples of the two varieties was not affected as a result of increasing the microwave drying time.     

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。     

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.     

Staling of cake prepared from rice flour and sticky rice flour

MiGao, prepared from rice flour and sticky rice flour, is a kind of steam cooked Chinese cake. Staling of MiGao resulted in loss in texture and eating quality. Moisture content, water activity, texture, differential scanning calorimetry thermograms and sensory quality of MiGao, were monitored and were found to be significantly affected by cake staling when stored at room temperature for up to 5 days. The moisture content decreased after 2 days of storage and during the following days the crumb moisture content remained practically unchanged. Firmness was developed mainly during the first day of storage, remained at a similar level from day 2 to 3 and increased slightly after the third day of storage. A decrease in sensory quality and acceptability of the MiGao was observed during storage. Differential scanning calorimetry was used to follow changes of starch retrogradation in MiGao crumb. Amylopectin recrystallisation in MiGao continued to increase during storage.     

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.     

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。     

Hydration,swelling and solubility behaviour of rice in relation to other physicochemical properties

Water uptake at 90°C and above in 16 rice cultivars, representing eight cooking-quality types, showed positive correlation (P≤0.001) with the surface area of the grain, while at 60°C it was negatively related to amylose (P≤0.01), and gelatinisation temperature (P≤0.001), and positively to equilibrium moisture content on soaking (P≤0.001). The swelling and solubility curves for all varieties showed a two-stage swelling pattern. Swelling at 60°C was positively correlated (P≤0.001) with water uptake at 60 and 70°C, while swelling at 70°C, and solubility at 60 and 70°C, showed highly negative correlation (P≤0.001 and P≤0.01, respectively) with water uptake at high temperatures. Waxy rices showed distinct differences from non-waxy rices in their hydration, swelling and solubility behaviour. They swelled more but solubilised less than the non-waxy rices at 96°C.     

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.     

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.     

A study on the acceptability and consumer attitude towards parboiled rice

Despite nutritional claims and other advantages that parboiled rice possesses, its consumption is still low in Brazil mainly because of the local preference for milled rice. In the first part of this study, the acceptability of five commercial brands of parboiled and milled rice was assessed by 100 consumers and similar acceptance levels were observed, evidencing that consumers might not reject parboiled rice for its sensory properties. In the second part, 286 consumers were surveyed about their eating habits and attitude towards rice, focusing especially the nutritional value, sensory and convenience aspects of parboiled rice. In the survey 35% of the respondents were unaware of parboiled rice. Cluster analysis performed on data grouped consumers in one segment with positive attitude and in two other segments with negative attitude towards parboiled rice. Segmentation was mainly because of negative beliefs about the sensory characteristics of the product, although its nutritional claims were unknown to most respondents, revealing the need of marketing efforts focused on informing consumers the health benefits and convenience of eating parboiled rice.     

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.     

Comparative properties of cakes prepared from rice flour and wheat flour

Received: 20 September 1999     

Production of high-fructose rice syrup and high-protein rice flour from broken rice

The objective of this study was to develop a process for the production of both high-fructose rice syrup and high-protein rice flour from broken rice. The rice flour was obtained from broken rice by using either a dry or wet milling method. The glucose produced from the slurry of various raw materials by treating with α-amylase and glucoamylase was compared. Results indicated that cassava and corn starch were better raw materials than rice flour. However, the filtered residue of liquefied rice slurry could be recovered as high-protein rice flour. The particle size of rice flour had a small effect on the glucose yield. The orthogonal-array table (L₂₇) method of experimental design was employed to determine optimum conditions for liquefaction. The glucose yield based on starch was 90.8±3.6% under the following optimum conditions α-amylase, 0.12%; rice flour, 20%; temperature, 96°C; time, 90 min. The filtrate from liquefied rice slurry was saccharified at 60°C with three different concentrations of glucoamylase. The higher the enzyme concentration, the shorter the time required to reach the maximum yield. After saccharification, the glucose solution was decolourised, desalted and concentrated to 40% d.s. and then isomerised to fructose at 60°C under continuous operation by using immobilised glucose isomerase packed in a column. The isomerised syrup was then purified and concentrated to 71% d.s. The final high-fructose rice syrup contained 50% glucose, 42% fructose and 3% maltose. After liquefaction, the rice slurry was centrifuged and the precipitate was dried by either spray or drum drying. The composition of these two high-protein rice flours was almost the same and the protein content was about three times as high as the raw material. There were significant differences in surface structure of rice flour and high-protein rice flours, as observed by the scanning electron microscope.     

Folic acid fortification of parboiled rice: Multifactorial analysis and kinetic investigation

Folic acid fortification of parboiled rice has been systematically studied to obtain quantitative insights into the role of key process variables. Parboiling was conducted with brown rice soaked at 70 °C for 1, 2 and 3 h with four different fortificant concentrations added and dried parboiled rice was milled for three durations (i.e. 0, 60 and 120 s). Both residual folate concentration in treated parboiled rice and pH of the soaking water after soaking stages were measured. Multifactorial model was developed to describe the residual folate retention behaviour and suggested that both soaking and milling were significant factors in folic acid fortification. The optimum soaking time was deduced to be 1.97 h. Folate retention rate followed a 1st order kinetics while the rates of natural rice hydrolysis and folate uptake were both time-dependent.     

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.