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1.

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.  相似文献   

2.
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.  相似文献   

3.
Four rice cultivars (Ayutthaya 1, Khao Bahn Nah 432, Plai Ngahm Prachin Buri, and Prachin Buri 2) that usually have a major problem with chalkiness were processed by applying superheated-steam drying and conventional parboiling methods. The main objectives were: (1) to determine the possibility of applying superheated-steam drying to solve the chalkiness and low head rice yield problems and (2) to compare the properties of rice produced using superheated-steam drying and the conventional parboiling process. Both the initial moisture content and superheated-steam drying temperature significantly affected head rice yield. The higher moisture helped to increase starch gelatinization leading to a stronger rice structure and subsequently an increased head rice yield. The rice samples dried in the superheated-steam dryer using an initial moisture content of paddy at 32% w.b. for 6 h under a steam pressure of 1.2 bar and at three drying temperatures (120, 140, 160 °C) had higher milling quality than the conventionally parboiled rice samples. The darker color of the superheated-steam-dried samples was their main drawback. Both parboiling and superheated-steam drying could clearly lessen the percentage of chalky rice kernels compared to the raw paddy. The parboiled rice and superheated-steam-dried rice had more nutrients than normal white rice.  相似文献   

4.
The enzymes amylase, protease, phosphatase and β-glucosidase in rough rice (paddy) were activated during the soaking step of parboiling. The extent of activation of these enzymes varied with the soaking duration and the parboiling methods adopted. Highest activities were observed in the cold soaking method followed by the double steaming and household methods. β-Glucosidase activity was eliminated in the presteaming stage of the double steaming process. Hot soaking inactivated all these enzymes. The steam in the parboiling process inactivated the enzymes partly while the pressure parboiling process inactivated them totally. Studies with purified enzymes also revealed the activation of enzymes during soaking. Enzyme activity contributes to the loss of solids during soaking and also to the characteristic odor of parboiled rice.  相似文献   

5.
Resistant starch (RS) content could be altered by the processing method, including pre-treatment, cooking method and storage conditions. This study determined the influence of RS formation in white rice (WR), brown rice (BR) and parboiled germinated brown rice (PGBR) as affected by various pre-treatment and processing conditions. This is the first report to chemically and structurally analyse WR, BR and PGBR of the same rice variety using X-ray diffraction, DSC and SEM. The results showed that the PGBR prepared by a non-soaking process cooked with steaming and stored cold contained RS content (92.1 mg/g, wet basis) followed by BR processed by soaking, steamed and then stored cold (91.8 mg/g, wet basis). The formation of RS3 as not affected by the parboiling and germination process compared to WR and BR. Reheating reduced resistant starch content by changing the RS structure conformation from crystalline to amorphous under higher temperatures. Moreover, the scanning electron microscope revealed that WR, BR and PGBR of the same rice variety show similar starch granule and microstructure patterns but slightly different in thermal conductivity value.  相似文献   

6.
7.
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.  相似文献   

8.
The cooking characteristics of parboiled rice are related to (i) its hydration behaviour at temperatures above and below the gelatinisation point; (ii) to kernel elongation on cooking; and (iii) to the extent of amylose solubility. These properties differ among samples, depending on the parboiling conditions. Samples were prepared by parboiling paddy at 70, 80, 90, 100, 110 and 120°C. The kernel elongation on cooking and the amount of soluble amylose in the gruel were then determined. The water uptake values for raw and parboiled rice samples were determined by hydrating them at room temperature (25-30), 60 and 98°C (boiling temperature) for optimal cooking times. The rate of hydration at temperatures below the gelatinisation point increased on parboiling and, conversely, a reverse pattern above this point. Close correlations existed between the temperature of parboiling and the properties studied. The different properties studied also correlated well. The temperature of parboiling influenced the linear elongation of the kernel after cooking. The soluble amylose content was negatively correlated with the temperature of parboiling. Though the hydration properties of different parboiled samples differed among themselves, depending on the degree of parboiling, they fell into two distinct classes, viz. the samples parboiled at a temperature close to the gelatinisation point having cooking qualities similar to raw rice, and above this point qualities differing from raw rice. The water uptake values at room temperature and at 60°C, and the ratio of water uptake at 98°C and optimum cooking time to that at 60°C were found to be useful in differentiating the parboiled rices into the two classes.  相似文献   

9.
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.  相似文献   

10.
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.  相似文献   

11.
Instant rice produced from a conventional process consisting of the cooking, washing and drying steps possesses poorer eating quality compared with that of freshly cooked rice. The objective of this work was therefore to study the effects of cooking, pretreatment and drying methods on microstructure, textural properties and starch digestability of instant rice after rehydration; jasmine white rice was chosen as a test material. Conventional boiling method and electric rice cooking were selected as the methods to prepare cooked rice. In the case of boiling, cooked rice was frozen at −20 °C or cooled at 4 °C for 24 h prior to drying, while the cooked rice from an electric rice cooker was washed with ambient or cool water for 30 s prior to drying. After pretreatment the cooked rice was dried either by freeze drying or hot air drying at 80 °C. Based on the scanning electron microscopic results it was found that the cooking, pretreatment and drying methods all affected the rice morphology. The hardness and stickiness of instant rice after rehydration were lower for samples prepared from the rice cooker than those of freshly cooked rice, while both textural properties appeared to be improved significantly for the samples from boiling. The texture of the freeze-dried products was not different from that of the air-dried one. The freezing pretreatment provided the texture and glycemic index of instant rice after rehydration similar to those of the freshly cooked rice. On the other hand, the cooling pretreatment resulted in the harder texture and higher glycemic index of the samples.  相似文献   

12.
The effects of heat–moisture treatment (HMT) (120 °C for 10, 30 and 60 min) on paddy rice grains before parboiling, on head rice yield (HRY), pasting and thermal properties, and colour and cooking characteristics of parboiled rice were studied. The results indicated that the HMT performed intensifies the changes in grains after parboiling, impacting pasting and thermal properties, which results in rice kernels with yellowish colouration and greater cooking time. HMT increased the temperatures of gelatinisation, with increasing HMT time from 10 to 60 min and reduced the gelatinisation enthalpy. HMT also affected the pasting properties of rice flours, reducing setback and viscosity and increased their stability to heat and mechanical agitation. The HMT performed in rice grains before the parboiling process with 60 min of the treatment decreased the HRY and increased the level of metabolic defects only in the treatment with 60 min.  相似文献   

13.
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.  相似文献   

14.
A procedure for in situ analysis of rice cooking was developed in this study. Grain softening during soaking and cooking of selected rice varieties (fresh and aged TDK8, TDK11, and Doongara) were subjected to in situ analysis by using a thermally controlled sample block (thermal mechanical compression test) attached to a texture analyzer. This technique measures the changes in the mechanical properties of intact rice grain during cooking continuously. The results obtained from the thermal mechanical compression test technique were validated against two standard and conventional procedures viz; analyzing the pasting properties of rice flours by rapid visco analyzer and microscopic observations during the cooking of rice grains. The technique developed in this study was found valid for in situ analysis of rice cooking. This technique can be used for a sample size as small as 0.50 g.  相似文献   

15.
利用响应面分析法研究大米蒸煮方式及参数对米饭物性的影响,为米饭的制作及食味的调节与改善提供参考。在常压蒸煮方法下研究大米加水、浸泡、蒸煮条件对米饭物性的影响确定各因素的水平范围,然后进行响应面设计与模型分析。通过响应面分析法建立了常压蒸煮法下大米加水量(水米比),浸泡时间和蒸煮方式三因素与米饭黏硬比的二次回归模型,方差分析证明了模型的可靠性。实验结果表明:水米比、浸泡时间和蒸煮方式及它们的交互作用对米饭黏硬比影响显著,三个因素对黏硬比的影响强弱依次为:蒸煮方式、水米比、浸泡时间。水米比与蒸煮方式的交互作用对米饭黏硬比的影响最显著,浸泡时间与蒸煮方式次之,而水米比与浸泡时间影响最小。  相似文献   

16.
稻谷水热加工过程中镉迁移规律研究   总被引:1,自引:0,他引:1  
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。  相似文献   

17.
The effect of steaming conditions (mild, intermediate and severe) during parboiling of five different long-grain rice cultivars (brown rice cultivars Puntal, Cocodrie, XL8 and Jacinto, and a red rice) on rice colour, and Maillard precursors and indicators was investigated. Rice colour increased with severity of parboiling conditions. Redness increased more than yellowness when parboiling brown rice. Parboiling turned red rice black. It changed the levels of glucose, fructose, sucrose, and maltose. Losses of the non-reducing sugar, sucrose were caused by both leaching into the soaking water and enzymic conversion, rather than by thermal degradation during steaming. Concentrations of the reducing sugars, glucose and fructose, in intermediately parboiled rice were higher than those of mildly parboiled rice. After severe parboiling, glucose levels were lower than those of intermediately parboiled rice, while fructose levels were higher. These changes were ascribed to the sum of losses in the Maillard reaction (MR), formations as a result of starch degradation and isomerisation of glucose into fructose. It was clear that the ε-amino group of protein-bound lysine was more affected by parboiling conditions and loss in MRs, than that of free lysine. Low values of the MR indicators furosine and free 5-hydroxymethyl-2-furaldehyde (HMF) in processed brown and red rices were related to mild parboiling, whereas high furosine and low free HMF levels were indicative of rices being subjected to intermediate processing conditions. High furosine and high free HMF contents corresponded to severe hydrothermal treatments. The strong correlation (r = 0.89) between the free HMF levels and the increase in redness of parboiled brown rices suggested that Maillard browning was reflected more in the red than in the yellow colour.  相似文献   

18.
大米通电加热特性的研究   总被引:2,自引:0,他引:2  
研究了大米的通电加热工艺,并研究了大米通电加热后微观结构的变化,并与传统的加热方式进行了比较。结果表明大米经浸泡12h后,通电加热蒸煮20min口感最佳,通电加热蒸煮的米粒口感明显好于电炉加热。通电加热后的米粒微观结构与电炉加热的米粒微观结构有明显差异,通电加热的米粒糊化程度高于电炉加热。  相似文献   

19.
Infrared radiation heating has a promising potential in improving drying rate and food safety, but its effect on the storage stability of rough rice is not known. The objective of this study was to develop an infrared drying (IRD) method to improve the storage stability of rough rice during storage. The effects of IRD on the physicochemical properties of stored rough rice were compared with those of hot air drying (HAD) and ambient air drying (AAD). Freshly harvested M206 rice was dried to a targeted moisture content of 16 % (d.b.) by using IRD, HAD, and AAD. The dried rice samples were then stored at 35.0?±?1.0 °C and a relative humidity of 65.0?±?3.0 % for up to 10 months. The physicochemical and cooking properties of rice samples were periodically determined over the storage duration. Compared with AAD, the yellowness index, water uptake, and volume expansion ratio of the rough rice dried with IRD and stored for 4 months were reduced by 26.3, 76.3, and 14.5 %, respectively. After 10 months of storage, the change in hardness of cooked IR-dried rice was significantly reduced by 22 % compared to that of samples dried with AAD. IRD likely caused a slight denaturation of protein and annealing of starch that was located on the surface layer of rice kernels, resulting in decreased gelatinization temperature, enthalpy, and viscosity, and reduced the changes in microstructure, but retained cooking characteristics after storage. Therefore, IRD is recommended as a promising technique that achieves high rice drying efficiency and improved storage stability.  相似文献   

20.
Parboiling was investigated to improve the long-term oxidative stability of milled white rice beyond its current application to paddy brown rice. White rice was steamed at 105°C for 20 min, 120°C for 5 min, or 120°C for 20 min without soaking in water, followed by drying at 70°C for 3 h. During oneyear storage at 25 and 4°C, acid value as an index of oxidative deterioration of rice remained relatively constant in parboiled rice samples, while significant increases were observed in raw rice with higher acid values at 25°C compared with 4°C. This indicates that the parboiling improved the oxidative stability of white rice over the long period of time even at room temperature, therefore it can be an efficient alternative to retard the oxidative deterioration of white rice.  相似文献   

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