Rice degree of milling effects on hydration,texture, sensory and energy characteristics. Part 1. Cooking using excess water

The purpose was to assess the effect of degree of milling (DOM) on cooking kinetics, sensory attributes, and energy requirements when cooking rice in excess water. Commercial milling equipment was adjusted to produce parboiled and non-parboiled rice samples that were milled to varying DOMs, including brown rice lots having no milling. Surface lipid content (SLC) ranged from 0.15% to 0.55% for non-parboiled rice and from 0.40% to 0.95% for parboiled rice. The percentage gelatinized kernels, moisture content, peak force and sensory attributes were determined as a function of cooking duration for all samples. The cooking duration required to attain ‘well-cooked’ rice was determined, after which the energy required for cooking was measured. Within the SLC range tested, DOM did not affect cooking kinetics, texture and flavor of rice. Non-parboiled brown rice required the most energy, expressed as energy per unit mass of uncooked rice, to be cooked, followed by parboiled brown, parboiled milled and non-parboiled milled rice.     

Effects of parboiling,storage and cooking on the levels of tocopherols,tocotrienols and γ-oryzanol in brown rice (Oryza sativa L.)

Vitamin E and γ-oryzanol display a wide range of biological activities including hypocholesterolemic, anti-inflammatory and antioxidant activities. Although white rice is far more popular worldwide, consumption of brown rice is increasing, partially on account of the presence of bioactive compounds; however, the effects of parboiling, storage and cooking on them are not well-characterized. The effects of parboiling and a 6-month storage period on the contents of vitamin E and γ-oryzanol in three brown rice cultivars grown in three different locations in Brazil were investigated. Also, their levels in branded non-parboiled and parboiled brown rice were monitored before and after cooking. Vitamin E homologues and γ-oryzanol were separated by RP-HPLC equipped with PDA and fluorescence detectors. The average levels of total tocols and γ-oryzanol in the raw brown rice cultivars studied were 25 and 188 mg/kg, respectively. Of the vitamin E homologues, γ-tocotrienol contributed with 74% of total tocols, followed by α-tocopherol, α-tocotrienol and γ-tocopherol in minor quantities. The combined processes, parboiling, storage and cooking, led to an approximate 90% reduction in tocols and only γ-tocotrienol was detectable after any of the processes. Parboiling followed by storage resulted in an approximate 40% loss of γ-oryzanol. Cooking had almost no further effect over γ-oryzanol levels in parboiled rice previously stored for 6 months.     

EFFECT OF ARTISANAL PARBOILING METHODS ON MILLING YIELD AND COOKED RICE TEXTURAL CHARACTERISTICS

ABSTRACT

One of the main objectives of artisanal rice parboiling is to reduce the levels of broken grains (brokens) on milling. Rice samples that had been parboiled using different regimes of soaking temperatures and steaming times were analyzed for their physical properties and cooked rice textures. It was established that inappropriate soaking and steaming regimes resulted in greater levels of brokens than raw‐milled paddy. Consequently, in artisanal parboiling, the initial soaking temperature should be about 90C and the steaming time should be more than 8 min, ideally, about 12 min. On cooking, more severely parboiled rice samples had firmer textures than mildly parboiled samples. The commercially parboiled sample and the more severely laboratory‐parboiled samples required a rice‐to‐water ratio of 1:3, while the raw‐milled sample and the mildly parboiled ones required a 1:2½ rice‐to‐water ratio for optimum cooking.

PRACTICAL APPLICATIONS

Artisanal rice parboiling is carried out mainly to reduce the levels of broken grains and increase the yield of milled rice in many countries. If this is carried out very well, there are economic benefits as more rice of better quality is available to be sold. This study provides information on optimum processing conditions, i.e., initial soaking temperature of about 90C and a steaming time of about 12 min. The study also provides recommendations on optimum cooking conditions, i.e., rice‐to‐water ratio, for the variably parboiled rice samples.     

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.     

Effects of parboiling and infrared radiation drying on the quality of germinated brown rice

This research investigated the physicochemical properties, bioactive compounds, and microstructure of brown rice (BR) and non-parboiled and parboiled germinated brown rice (GBR and PGBR). The GBR and PGBR were treated by sun, hot-air oven, or infrared irradiation (IR) drying. The results showed that IR drying enhanced the bioactive compounds of non-parboiled GBR, including γ-aminobutyric acid, α-tocopherol, and total phenolic compounds, while γ-oryzanol and antioxidant activity were comparable to BR. Meanwhile, IR drying significantly improved the head rice yield (HRY) of PGBR while reducing fissured grains. Parboiling also affected the color values of rice grains, suggesting the diffusion of husk color into endosperm and the formation of brown polymers by the Maillard reaction. In addition, IR drying altered the internal structure of rice grains, resulting in abundant intercellular voids. Specifically, the IR-dried non-parboiled GBR significantly enhanced essential bioactive compounds and improved HRY while maintaining the color of standard BR.     

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.     

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.     

Cooking rice in excess water reduces both arsenic and enriched vitamins in the cooked grain

This paper reports the effects of rinsing rice and cooking it in variable amounts of water on total arsenic, inorganic arsenic, iron, cadmium, manganese, folate, thiamin and niacin in the cooked grain. We prepared multiple rice varietals both rinsed and unrinsed and with varying amounts of cooking water. Rinsing rice before cooking has a minimal effect on the arsenic (As) content of the cooked grain, but washes enriched iron, folate, thiamin and niacin from polished and parboiled rice. Cooking rice in excess water efficiently reduces the amount of As in the cooked grain. Excess water cooking reduces average inorganic As by 40% from long grain polished, 60% from parboiled and 50% from brown rice. Iron, folate, niacin and thiamin are reduced by 50–70% for enriched polished and parboiled rice, but significantly less so for brown rice, which is not enriched.     

Ohmic heating for cooking rice: Electrical conductivity measurements,textural quality determination and energy analysis

In this study, an innovative technique, namely ohmic heating was applied in rice cooking and compared with conventional method using electric rice cooker. Four types of rice samples including white rice of two varieties (KDML105 and Sao Hai), brown rice and germinated brown rice of one variety (KDML105) were used. Electrical conductivities of mixtures between rice samples and 0.1 M salt solution at various ratios were measured. Empirical models were developed for predicting electrical conductivities of rice samples as a function of temperatures. Textural properties of cooked rice samples and energy consumption were compared between ohmic and conventional cooking methods. The purposes of this work were to (1) study the possibility of applying ohmic method in rice cooking and (2) compare between cooking rice by ohmic and conventional method. The results revealed that it is possible to apply ohmic method for cooking all rice samples by using 0.1 M salt solution in the mixtures. The electrical conductivities of white rice (KDML105), white rice (Sao Hai), brown rice and germinated brown rice (KDML105) mixtures were 0.246–0.900, 0.375–1.005, 0.617–1.370 and 0.485–1.182 S/m respectively. The rice cooked by ohmic method had significantly different textural properties from that cooked by electric rice cooker. The magnitude of difference depended on the rice types. The electrical energy consumption of ohmic cooking system was approximately 73–90% of energy required for conventional rice cooker.     

Functional Properties as Affected by Laboratory‐Scale Parboiling of Rough Rice and Brown Rice

ABSTRACT: Rough rice (RR) is the conventional feedstock for parboiling. The use of brown rice (BR) instead of RR is gaining interest because it results in shorter processing time and lower energy requirement. This study compared the functional properties of milled parboiled rice under different parboiling conditions from RR and BR. Presoaked RR and BR from cultivars Bolivar, Cheniere, Dixiebelle, and Wells were parboiled under mild (20 min, 100 °C, 0 kPa) and severe (20 min, 120 °C, 98 kPa) laboratory‐scale conditions. Head rice yield improved on the RR and BR samples subjected to severe parboiling and was comparable to that of a commercially parboiled sample. Mild parboiling of BR resulted in lower head rice yields. Parboiling generally resulted in decreased head rice whiteness, decreased apparent amylose, increased total lipid, and sparingly changed protein content. Under the same parboiling conditions, the extent of starch gelatinization was higher for BR compared to RR as manifested by some distinct differences in pasting and thermal properties. The cooking characteristics (water uptake ratio, leached materials, and volumetric expansion) and cooked rice texture (hardness and stickiness) of RR and BR subjected to severe parboiling were fairly comparable. Differences in parboiled rice functional properties due to cultivar effect were evident.     

Quality changes in HTST processing of rice parboiling

Paddy soaked to saturation level, when treated at a high temperature for a short time in a mechanical sand roaster is parboiled and dried in a single pass of 47 s duration. The extent of drying depends on the sand temperature. The sand temperature is critical as it decides the associated quality changes in the milled rice. Even at a sand temperature of 125°C, paddy could fully be parboiled but with mild effect. The parboiling became severe at high temperatures. Roasting the soaked paddy at 250°C, reduced the cooking time of the resultant milled rice. A sand temperature of 125–150°C was considered suitable for producing normal parboiled rice by this technique.     

Iron fortification and parboiled rice quality: appearance,cooking quality and sensory attributes

BACKGROUND: Iron (Fe) fortification of parboiled rice increases both Fe concentration and bioavailability in milled grains (i.e. white rice). The aim of the present study was to evaluate parboiled rice fortified with 250 and 450 mg Fe kg^?1 paddy rice for its pre‐cooking appearance, cooking quality, basic sensory attributes and overall acceptance in comparison with unfortified parboiled rice in Thailand and local parboiled rice in Bangladesh. RESULTS: Fe fortification at 250 mg Fe kg^?1 paddy rice significantly elevated Fe concentration in white rice to as high as 19.1 mg Fe kg^?1 white rice, compared with 6.2 mg Fe kg^?1 white rice for unfortified parboiled rice, without any adverse impact on consumer acceptance based on the current preliminary assessment. The added Fe was well retained in the cooked rice, with significant residual value for human intake. Panellists in Thailand and Bangladesh did not detect significant differences in the acceptability of parboiled rice fortified at 250 mg Fe kg^?1 paddy rice compared with unfortified and local parboiled rice respectively. However, Fe fortification of parboiled rice at the higher level of 450 mg Fe kg^?1 paddy rice significantly intensified the yellow colour of the grain and changed the off‐flavour, chewiness and flakiness of the cooked Fe‐fortified parboiled rice. This resulted in a low acceptability ranking of parboiled rice fortified at 450 mg Fe kg^?1 paddy rice by panellists in both Thailand and Bangladesh. CONCLUSION: Fe fortification of parboiled rice at an appropriate level (e.g. 250 mg Fe kg^?1 paddy rice) is dosage‐effective and acceptable to rice consumers. Consumer acceptability of Fe‐fortified parboiled rice is closely related to pre‐cooking appearance, cooking quality and sensory attributes. Copyright © 2009 Society of Chemical Industry     

基于食味计评价杂交籼稻食味品质

为探讨不同蒸煮条件对西南两个生态点杂交籼稻食味品质的影响,以分别种植于云南永胜和四川大邑的9 个品种中籼杂交稻为材料,利用米饭食味计分析不同蒸煮条件（7 个水米质量比（1.3∶1、1.5∶1、1.6∶1、1.9∶1、2.1∶1、2.4∶1、2.7∶1）、4 个浸泡时间（0、15、30、60 min）、3 个蒸煮时间（20、30、40 min）和3 个焖饭时间（0、15、30 min））对稻米米饭食味品质的影响。结果表明：稻米米饭的食味品质为蒸煮条件、品种、生态点及其互作效应共同作用的结果,米饭外观和食味值均受三者极显著影响（P＜0.01）;蒸煮条件与生态点、品种与生态点及三者的互作效应均极显著影响米饭食味品质（P＜0.01）。米饭食味计分析结果显示,云南永胜等光温充足稻区以水米质量比2.1∶1、浸泡30 min、蒸煮30 min以及焖制15 min蒸煮米饭的食味品质较好;四川大邑等高湿寡照稻区以水米质量比2.1∶1、浸泡15 min、蒸煮30 min以及焖制15 min蒸煮米饭的食味品质较好。9 个品种中‘内5优39’米饭食味品质最好,且在各水米质量比间变异较小,‘宜香优2115’米饭食味品质次之,而‘中优295’和‘F优498’米饭的食味品质较差,‘F优498’和‘天优华占’米饭食味品质在各蒸煮条件间变异系数较大。总体来看,云南生态点的稻米米饭外观更好,而四川生态点稻米米饭在特定蒸煮条件下食味值更高。     

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.     

不同储藏年限稻谷的品质及蒸谷米加工适应性分析

为了解不同储藏年限的稻谷加工蒸谷米的品质变化,为蒸谷米加工原料的选择提供依据。以不同储藏年限的籼稻、粳稻各40 份样品为研究对象,将其加工成蒸谷米,并对蒸谷米的蒸煮特性、外观及其制备米饭的食用品质与质构特性等指标进行测定,采用描述统计分析、方差分析、主成分分析等方法对蒸谷米的品质指标进行分析,采用聚类分析探讨稻谷的蒸谷米加工适应性。结果表明：随着原料稻谷储藏年限的延长,蒸谷米吸水率、体积膨胀率均呈上升趋势,与储藏1 年的稻谷相比,储藏4 年的籼稻和粳稻加工成的蒸谷米吸水率分别增加49.1%和35.9%,体积膨胀率分别增加70.6%和66.6%;米汤pH值、碘蓝值和固形物含量均无显著变化;感官评价总分均降低,米粒色泽加深,外观结构变差,米饭的适口性、滋味均降低,其中籼型蒸谷米的感官品质较粳型蒸谷米好;蒸谷米米饭质构特性各指标中除硬度、咀嚼性呈上升趋势以及粳型蒸谷米米饭的黏着性呈下降趋势外,其他各项指标无显著变化。在感官品质评价的基础上,引入质构特性指标分析,对蒸谷米的品质进行综合评价;并利用主成分分析,构建了蒸谷米品质评价的数学评价模型;再对综合评分进行聚类分析得出品质分类,并统计各储藏年份的样品数量,由此证实籼稻加工蒸谷米适应性优于粳稻,且储藏1、2 年的籼稻加工蒸谷米品质较好。     

Microstructure of olbyeossal,partially milled parboiled glutinous rice made by modified parboiling method

The microstructure of partially milled parboiled glutinous rice (PMPGR) before and after cooking was investigated using scanning electron microscopy to identify the changes in the microstructure due to parboiling treatments. Parboiling was performed in two different ways: conventional and modified. The conventional parboiling method involved soaking at room temperature for 24 h, followed by steaming and drying. The modified parboiling method involved tumbling to replace soaking of the rice grains, tempering, retorting, and drying. The microstructures of the PMPGR made using both methods were compared. The modified parboiling method significantly changed the microstructure of the rice, but cooking did not cause considerable changes in the microstructure of PMPGR.     

Studies on Expanded Rice. Physicochemical Basis of Varietal -Differences

Extent of expansion of milled parboiled rice when heated varied widely among 35 varieties. Expansion correlated strongly with the amylose content, being maximum at 27% total amylose and/or 13.5% hot-water-insoluble amylose. In general rice quality type II gave the highest expansion. Protein content had a small negative correlation. Mineral content of the milled grain had no effect, The influence of grain gelatinization temperature is uncertain. Overall shape of the rice grain remained largely unchanged after expansion.     

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.     

干法、半干法和湿法磨粉工艺制备的糙米米线品质研究

采用干法、半干法和湿法3种方式将糙米磨粉制备糙米米线,干法粉碎强度10～40 Hz,半干法调节含水量为20%～35%及湿法料液比为1∶1、1∶2、1∶3、1∶4,研究了3种磨粉方式对糙米米线蒸煮品质和质构性质的影响,并分析了糙米磨粉颗粒细度及损伤淀粉含量与糙米米线蒸煮品质的相关性。结果表明,磨粉方式及磨粉工艺条件显著影响糙米米线的蒸煮、质构和感官品质,糙米磨粉颗粒细度与糙米米线最佳蒸煮时间显著正相关,与糙米米线断条率显著负相关。糙米磨粉损伤淀粉含量与糙米米线最佳蒸煮时间、硬度显著负相关,损伤淀粉含量与糙米米线断条率显著正相关。干法粉碎强度10、半干法水分调节含量20%、30%和35%、湿法粉碎料液比1∶3～1∶4时,糙米米线的品质较好。     

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.