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。     

Effect of milling on mineral and trace element composition of raw and parboiled rice.

The effect of milling on the mineral and trace element composition of raw and parboiled grain samples of 16 varieties of rice was investigated. Varietal, locational and seasonal differences in the nutrient composition of brown rice were noted. The mean values for different nutrients per 100 g brown rice were total ash 1.37 g, phosphorus 349 mg, magnesium 157 mg, calcium 18 mg and iron 2.16 mg and in μg per g samples, zinc 14.3, manganese 11.0, copper 2.39, molybdenum 0.775 and chromium 0.088. Parboiling per se had no effect on the composition of brown rice. The degree of milling and the initial concentration of the nutrient in the grain determined the magnitude of loss on milling both in raw and parboiled grain. Percent losses of different nutrients on 5 and 10% milling of raw rice respectively were total ash 40, 62; iron 51, 67; magnesium 40, 64; calcium 36, 57; iron 54, 64; copper 26, 45; manganese 48, 56; molybdenum 24, 34; chromium 57, 69; and zinc only 2.8, 4.6. Zinc in rice grain was uniformly distributed and a major portion of other nutrients was concentrated in the outermost 2.5% surface layers of the grain. Parboiling appeared to have altered the distribution of some nutrients in rice grain except for zinc, magnesium and copper. Milling losses for other nutrients were therefore significantly lower in parboiled than in raw rice.     

Effect of parboiling on thiamin, protein and fat of rice

Parboiling decreased the thiamin content of rice. Nevertheless, milled parboiled rice contained more thiamin than milled raw rice at the same degree of milling because parboiling caused thiamin to diffuse inwardly. Both the degree of loss and the degree of diffusion depended on the severity of the heat treatment. Bran-polish of parboiled rice had a higher fat and protein content than bran-polish of raw rice at the same degree of milling because the starchy endosperm of parboiled rice had a greater resistance to milling and so the bran and the germ were more effectively removed. Milled parboiled rice tended to have lower protein content than milled raw rice. Starch content was lower in bran-polish from parboiled rice.     

不同储藏时间米糠制备膳食纤维对米粉糊化和凝胶性质的影响

将米糠储藏0、1、3、5、10 d后制备的米糠不溶性膳食纤维(rice bran insoluble dietary fiber,RBIDF)添加到米粉中,研究不同储藏时间米糠制备的RBIDF对米粉糊化和凝胶性质的影响。结果表明,当RBIDF添加量相同时,随着米糠储藏时间的延长,米粉的峰值黏度呈先上升后略微下降的趋势,在米糠储藏第5天时达到最大值,回生值逐渐上升,峰值时间和糊化温度先下降后上升,分别在米糠储藏5 d和3 d达到最小值;储能模量在米粉凝胶形成阶段和米粉凝胶形成后阶段都呈上升趋势,损耗角正切在米粉凝胶形成后阶段先减小后增大,在米糠储藏5 d达到最小值;硬度、回复性、胶着性、咀嚼度先增大后减小,黏附性先减小后增大,均在米糠储藏3 d达到极值。相关性分析结果表明,米糠毛油酸值与米粉的峰值黏度呈显著(P 0. 05)正相关,与峰值时间和糊化温度呈极显著(P 0. 01)负相关,与回生值和米糠储藏时间呈极显著(P 0. 01)正相关。     

稻谷水热加工过程中镉迁移规律研究

目的研究稻谷在蒸谷米水热加工过程中镉的迁移规律。方法以蒸谷米小试装置及生产线采集样品为研究对象,在优化碾米时间的基础上,在排除水分含量差异对测定结果的前提下,利用统计分析考察水热工艺(浸泡和蒸煮)对稻谷各部分(稻壳、米糠和精米)镉含量的影响。结果由实验数据推断,在水热过程中,镉的迁移主要发生在稻谷的内部,且主要是在浸泡时从精米向米糠迁移富集,而蒸煮工艺则对镉的分布变化影响很小;经过浸泡,精米中的镉含量可降低约40%;推测热水的浸泡一方面使胚乳淀粉分子间游离的镉部分溶出,一方面促使镉向络合能力更强的米糠蛋白迁移,最终导致其分布发生明显变化。结论该研究为在稻谷加工过程中实现重金属镉的消减提供了科学依据。     

Effect of processing on thiamin and riboflavin contents of some high-yielding rice varieties of punjab

Six high-yielding varieties of rice (Oryza sativa L) were taken and subjected to 6 and 8% degree of milling. The raw rice and the parboiled rice were analysed microbiologically for thiamin and riboflavin contents. Milled parboiled rice contained more thiamin and riboflavin that milled raw rice at both the levels of milling because parboiling of paddy results in inward diffusion of water-soluble vitamins to the endosperm. The thiamin content of brown rice is reduced after parboiling. The loss may be due to the partial decomposition of thiamin during the stages of parboiling, but the riboflavin content of brown rice is found to be increased after parboiling.     

Some physical properties of paddy and rice and their interrelations

Grain dimensions, density, bulk density, porosity and angle of repose of paddy and rice were studied with respect to (a) varietal difference, (b) effect of moisture content, and (c) effect of degree of milling.

• (a) Grain breadth and thickness were mutually correlated; all dimensions of milled rice were closely related to those of the corresponding paddy. Density was nearly constant at 1.452 g/ml in all rice varieties; in paddy, the value was around 1.182 g/ml for round varieties and around 1.224 g/ml for others. Bulk density varied appreciably in both rice (0.777–0.847) and paddy (0.563–0.642 g/ml), and so did porosity (41–46% in rice, 46–54% in paddy). These were related to the grain shape (l/b ratio); the more round the grain, the greater was the bulk density and the lower the porosity and vice versa. Angle of repose was relatively constant in different varieties of rice (average 37.5°) and paddy (average 36.5°).
• (b) With increasing moisture content, in rice, density decreased linearly; but the bulk density decreased twice as fast and the porosity increased owing to a concurrent progressive increase in the frictional property which decreased the degree of grain packing. In paddy, with increasing moisture content, density and bulk density increased, showing the presence of void space between the husk and the kernel; the angle of repose also increased moderately, but the porosity remained nearly constant.
• (c) Density of rice increased slightly with milling; but bulk density, porosity and angle of repose were markedly affected by the degree of milling. In general, with progressive milling, bulk density decreased at first and then increased, while porosity and angle of repose changed in reverse fashion—the changes being more pronounced in parboiled rice than in raw rice. Thus brown rice packed well and flowed freely; rice of intermediate polish, particularly parboiled rice, had poor packing and flow properties; and fully milled rice again packed and flowed well. The primary change in these was in frictional property, which affected the porosity and hence the bulk density. The frictional property in turn was related primarily to the surface fat content of the rice. The surface fat increased sharply on initial milling, more in parboiled rice, and then gradually disappeared on full milling.

     

Effect of stabilization of rice bran on the extractability and recovery of proteins

The extractability profile of rice bran proteins under different conditions were studied to determine optimal conditions of extraction. Milling and differential sieving of rice bran increased the protein content in fine fraction by 7%. Maximum extractability of protein from defatted rice bran at pH 11.0 was 72%, out of which 70% could be precipitated at isoelectric pH 4.0. Increasing the time of extraction or using sodium chloride, sodium dodecyl sulfate or sodium hexametaphosphate were not effective in extracting more protein. The extraction and precipitation profiles of proteins from acid stabilized rice bran were comparable to untreated rice bran. However, it was very low for heat stabilized and parboiled rice bran. Denaturation of protein due to heat treatment affected the extractability of protein. Protein contents of protein concentrates obtained from untreated rice bran and acid stabilized rice bran were in the range of 71–73% whereas protein concentrates from heat stabilized rice bran and parboiled rice bran had lower protein contents of 39.5 and 54.5%, respectively.     

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.     

蒸谷米糠蛋白功能特性研究

研究在不同温度和不同pH值条件下,酶解提取的蒸谷米糠蛋白（PRBP）溶解性、乳化性和泡沫性,并和大豆分离蛋白（SPI）做比较。结果发现：在不同温度下,蒸谷米糠蛋白的溶解性、乳化性、泡沫性随温度增加,先升高后下降。而乳化稳定性和泡沫稳定性一直下降;在不同pH值下,蒸谷米糠蛋白的溶解性、乳化性、泡沫性与泡沫稳定性随pH值增加,先降低、后升高,而乳化稳定性先升高后降低;大豆分离蛋白的乳化性和泡沫性好于蒸谷米糠蛋白。     

INFLUENCE OF PARBOILING AND FREEZING CONDITIONS ON TEXTURAL PROPERTIES OF CALIFORNIA COOKED RICE

The textural properties of thawed samples of cooked parboiled, long (Cal Belle) and short (S201) grain rice varieties were evaluated using an Instron Universal Testing Instrument (Model 1122). In general, the parboiling treatments resulted in a significant increase of hardness but a significant decrease in stickiness of both long and short grain cooked rice when freezing conditions were pooled. Freezing increased hardness and decreased stickiness of long grain cooked parboiled rice significantly regardless of parboiling conditions, however, it did not decrease the stickiness of short grain cooked parboiled rice significantly. The long grain rice was harder and less sticky than the short grain rice when cooked regardless of treatments used. Hardness was negatively correlated with stickiness indexes (r =?0.819, P < 0.001).     

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.     

Effect of stabilisation treatment of rice bran on functional properties of protein concentrates

The functional properties of differently dried protein concentrates prepared from unstabilised, acid-stabilised, heat-stabilised and parboiled rice bran were evaluated. Freeze-dried protein concentrates from all types of bran exhibited similar nitrogen solubilities. Both cabinet-and roller-dried protein concentrates had lower nitrogen solubilities than freeze-dried samples except for cabinet-dried concentrate from heat-stabilised bran. The functional properties (bulk density, water and fat absorption, emulsification and foaming capacity) of protein concentrates prepared from acid-stabilised rice bran were not significantly different from those prepared from untreated bran. Freeze-dried protein concentrates from both heat-stabilised and parboiled rice bran had low water absorption capacity and high fat absorption capacity. Cabinet-dried samples did not exhibit any foaming or emulsification capacity, thereby indicating a greater extent of denaturation. Thus, the study indicated that in addition to stabilisation treatment functionality was also influenced by the drying technique employed.     

Nutritive value of raw,parboiled, stabilised and deoiled rice bran for growing chicks

The proximate analysis of different types of rice bran (raw, parboiled, stabilised and deoiled) showed wide differences in the oil, fibre, ash and available carbohydrate contents. Free fatty acids in the fat extracted from the raw, parboiled and stabilised rice brans were 500.6, 277.8 and 163.1 g kg^?1 respectively. Palmitic, oleic and linoleic acids constituted about 94.5% of the total fatty acids in oils extracted from those rice bran types. In chick growth trials, the average metabolisable energy of raw, parboiled, stabilised and deoiled rice brans was found to be 12.34, 11.67, 12.11 and 9.08 MJ kg^?1 DM, respectively. The bodyweight gain of broiler chicks over a period of 6 weeks was depressed by 183, 79, 49 and 200 g when the level of the respective brans was raised from 200 to 400 g kg^?1 in the diet. However, the food and protein conversions were significantly depressed at both levels of rice bran in the diets.     

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%).     

超临界流体萃取与二乙醇胺法综合制备米糠油

以市购米糠为原料,采用超临界流体萃取法提取米糠油,并对毛糠油的简化精炼工艺进行研究。原料经微波预处理降低解脂酶活性后,利用超临界CO2分段萃取,先后控制条件15MPa、32℃、1.0h和35MPa、40℃、4.0h获得毛糠油Ⅰ、Ⅱ。用二乙醇胺处理毛糠油Ⅱ,通过单因素实验和正交实验得出二乙醇胺法精炼毛糠油的最佳条件为:二乙醇胺加入量为油重的9%,精炼温度为50℃,振荡时间为15min。在此条件下精炼毛糠油,油脂酸价可降至0.85mgKOH/g,酸价降低率达到94.33%。超临界流体萃取与二乙醇胺法精炼综合处理所得米糠油清澈、透明,谷维素含量为1.73%,色度达到了国家标准。     

The functional effectiveness of reprocessed rice bran as an ingredient in bakery products

Rice bran, as a coproduct of the rice milling industry, is yet to be efficiently utilized for human consumption. Despite its excellent nutrition, its hypoallergenicity and recently claimed nutraceutical properties, it is mainly utilized for animal feed or simply discharged. It is of interest to incorporate this healthy ingredient back into our diet. In these studies, rice bran was processed by drum-drying and pin-milling. This processing step increased hydration capacity and removed grittiness by decreasing mean particle size from 444 to 72 microns and producing a desirable monomodal size distribution. There are no reported studies addressing differences in rice bran composition in food applications and specifically their effect on bread quality. Thus, we were interested in examining the functional properties of bread made with processed full-fat (FFRB) and defatted (DFRB) bran from three cultivars (long, medium and short grain rice) and to compare them to a control. For 10% and 20% replacements of wheat flour, respectively, loaf volume increased 2% for FFRB and decreased 6% for DFRB and decreased by 6% for FFRB and 17% for DFRB. Loaf volume was highest with medium rice bran and this was attributed to its lowest fiber content and highest starch content among three varieties. Texture profile analysis showed no significant differences as far as cohesiveness and springiness, but bread hardness, gumminess and chewiness increased with increased levels of rice bran and was higher for DFRB bread than for FFRB. Measurements of texture determined that there was no detrimental effect in adding 10% FFRB to the bread and a very slight hardening of the loaves with the 20% FFRB, when compared to the control. It was found that FFRB gave better textural characteristics than DFRB overall and differences amongst different rice bran varieties were not significant.     

微波处理米糠贮存过程中其油脂酸值变化的研究

采用不同微波方式处理米糠,通过常温贮存试验观察其油脂酸值的变化。结果表明:不同来源的米糠其油脂酸值上升的趋势不同,可能与米糠中酶的活性有关;第1阶段贮存试验中,米糠1#开始2 d内油脂酸值(KOH)增加了3.89 mg/g,米糠3#油脂酸值(KOH)增加了17.4 mg/g,而经微波处理后米糠1#开始5 d内油脂酸值(KOH)仅增加了0.69 mg/g;在第2阶段贮存试验中,未经处理的米糠4#在贮存98 d内油脂酸值(KOH)增加了104.56 mg/g,而经微波处理7的米糠4#油脂酸值(KOH)仅增加了11.97 mg/g,微波处理4的米糠4#油脂酸值(KOH)增加了34.85 mg/g;比较表明微波处理能较好地稳定米糠。