Effects of parboiling and fluidized bed drying on the physicochemical properties of germinated brown rice

Changes in physicochemical properties of germinated brown rice (GBR) and parboiled germinated brown rice (PGBR) dried in a fluidized bed dryer at 110–150 °C were investigated. Results indicated that parboiling altered the properties of GBR owing to starch gelatinisation. The moisture content, yellowness, peak viscosity and hardness of PGBR increased, but internal fissured kernel, cooking time, water absorption and total solids loss decreased when compared to GBR. γ‐aminobutyric acid (GABA) content in GBR was 23.31 mg per 100 g and was reduced to 17.91 mg per 100 g in PGBR. The drying times required to reduce the moisture content of GBR and PGBR to 16% d.b. were 4.01–7.65 min and 5.11–9.50 min, respectively. Final moisture content, which is optimum to prevent internal fissures of dried GBR and PGBR, was 27–29% and 25–28% d.b., respectively. The same trend was observed in the physicochemical properties of GBR and PGBR when increasing drying temperature and time.     

Microwave drying of germinated brown rice: Correlation of drying characteristics with the final quality

Drying characteristics influence the formation of quality including visual color and gamma-aminobutyric acid (GABA) of germinated brown rice (GBR) subjected to microwave drying. In microwave drying, microwave intensities induced microscopic pores inside GBR to enhance the drying rate in initial stage, while rising temperatures caused gelatinization of starch granules to hinder the drying rate in later stage. The higher microwave intensity resulted in the greater non-uniformity of temperature inside the grain layer, which dominated the moisture content and final quality indexes of GBR. However, the coupling effects of temperature rising and moisture reducing failed to stimulate the glutamate decarboxylase (GAD) activity for the GABA synthesis, but may cause the degradation of GABA. The non-uniformity of microwave drying influenced the evaluation of GABA content in the dried GBR, and the suitable average grain temperature of 64–67 °C may retain relatively high GABA content. The critical temperature for preventing the serious browning and charred kernels inside the grain layer was 132 °C and 170 °C, respectively. Microwave intensity of 3–4 W/g may be suitable for drying of GBR considering high drying efficiency and product quality.     

Improvement in Storage Stability of Infrared-Dried Rough Rice

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.     

Effect of cooking and drying on the thermal conductivity of rice

The transient line source technique was used to determine the thermal conductivity of rice during cooking and drying of cooked rice. A temperature range of 50‐70°C, moisture content of 10‐70% (wet basis), bulk (packing) density range of 500‐850 kg/m³ and porosity range of 0.265‐0.7 were studied. Thermal conductivity increased with increasing temperature, moisture content and bulk density, and the values were in the range 0.082‐0.543 W/m °C. This value is comparable with the literature values for granular and gelatinized starch. The data on the effect of phase change due to gelatinization have also been included. The experimental values were statistically analyzed and empirical polynomial equations were developed in terms of temperature, bulk density, porosity and moisture content of rice during cooking and drying the cooked material.     

Effect of superheated-steam drying compared to conventional parboiling on chalkiness,head rice yield and quality of chalky rice kernels

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.     

Effect of ageing-induced changes in rice physicochemical properties on digestion behaviour following storage

The changes in rice grains structure and digestion behaviours were investigated following storage at 4 °C and 37 °C, respectively. Pasting study indicated that rice samples stored at 37 °C demonstrated a consistent increase in the time to peak viscosity of the Rapid ViscoAnalysis parameters, implying a quick ageing progress. Compared to the rice stored at 4 °C, aged rice (stored at 37 °C) showed a coarser morphology after cooking by SEM, suggesting a limited starch gelatinization. Consistently, ageing process led to a decrease in the leaching of starch molecules in cooking residual water, which further confirmed that starch granules in aged rice grain caused less hydration and swelling. The analysis of the amount of cell wall remnants showed that rice stored at 37 °C caused a significant increase in the amount of cell wall remnants along the storage at 37 °C, which might suggest that the cell wall structure of the rice grains became more lignified because of the ageing. Furthermore, the ageing process significantly reduced rice digestion kinetics both in rate and extent. Thus, it is assumed that ageing process leads to the cell walls becoming more strengthened and lignified, which makes the rice grain more organized in its structure, and subsequently reduces starch granules disruption and molecules leaching during the cooking. Therefore, this study suggests that the changes in digestion behaviours of rice are highly associated with the changes in rice physical and chemical properties occurred during storage and the ageing process might be another option for manipulating rice digestion properties.     

糯米的不同干燥方式对米酒酿造的影响

该实验探究了烘干、阴干两种不同的干燥方法对糯米的基本理化特性、糊化特性和发酵特性的影响。结果表明,与阴干糯米相比,烘干糯米含水量低1.1%、出饭率高5.9%、粗淀粉含量高1.55%、直链淀粉含量高0.14%。两种糯米淀粉糊化曲线显示,烘干糯米体系整体黏度低于阴干糯米,具有较高的衰减值和回生值,糊化温度略微下降。对比两种糯米31℃发酵48 h后酿造的米酒,烘干糯米米酒比阴干糯米米酒总糖含量高59.3%、总酸含量高16.5%,酒精度低2.1%vol。结果表明烘干糯米对比与阴干糯米具有更优良的发酵性能。     

Standardization of ginseng processing for maximizing the phytonutrients of ginseng

This study was designed to optimize the process conditions, such as steaming, drying, and extracting, for obtaining the maximum content of prosapogenin (Rg3, Rg2, Rh1, and Rh2) from red ginseng, which has antitumor and anti-cancer properties. The steaming process was performed in an autoclave and the drying and extracting processes were done in dryer and heat extractor, respectively, and content of each prosapogenin was analyzed by HPLC. In the steaming process, prosapogenin values did not show any significant increase at 80 or 90°C, but tended to increase sharply as the steaming period became longer at 100°C, and the maximum value was obtained at 100°C with 6 h of steaming without any significant difference between local Gyeonggi areas. Drying red ginseng at 70°C for 24 h was the optimal condition to enhance prosapogenin extraction without affecting the quality. Maximal crude saponin and prosapogenin contents were obtained using 70% ethanol as the solvent at 70°C in the extracting process. Using these standardization processes such as steaming, drying, and extraction, maximum prosapogenin values could be obtained at ginseng factories.

     

Development of Mobile Dryer for Freshly Harvested Paddy

Presently, due to an increase in usage of large scale mechanical threshers and combine harvesters, moisture content of freshly harvested paddy is being high as much as 18-24%. The mechanical threshers or combine harvesters with elevated capacity enable for both harvesting and threshing at once. Thus the paddy harvested all over persists with high moisture content that affects adversely in unit operations of paddy processing such as cleaning, storing, and milling. The research was conducted to overcome this problem by developing a mobile paddy dryer that can be used at field level for freshly harvested paddy. A mobile dryer, one ton capacity, was developed and tested for drying freshly harvested paddy. The performance of the mobile dryer was evaluated in terms of overall thermal efficiency, heat utilization factor, coefficient of performance, total heat efficiency and head rice yields. The overall thermal efficiency of this dryer was 46.83%. The average heating efficiencies namely heat utilization factor and total heat efficiency were 0.82 and 0.72 respectively. The coefficient of performance of the developed dryer was 0.18. The head rice yields of freshly harvested paddy after drying at 60 °C air temperature was of 73.78%. The overall drying performance of the dryer was found to be good.     

Effect of high-temperature fluidized-bed drying on cooking, textural and digestive properties of waxy rice

In this work, changes of the cooking and pasting properties as well as starch digestibility of waxy rice (RD6) during hot air fluidized bed drying were investigated. Re-moistened waxy rice at an initial moisture content of 28% dry basis (d.b.) was dried at 90-150 °C. Semi-dried waxy rice was tempered and dried again by ambient air until the moisture content reached 16% (d.b). It was found that the degree of gelatinization increased with an increase in the drying temperature. At 130 and 150 °C the appearance of some waxy rice kernels changed from opaque to translucent, indicating complete gelatinization. Thermal degradation of amylopectin granules during high-temperature drying caused the starch to be more rapidly digested; this led to lower peak viscosity and setback viscosity. In addition, waxy rice processed at higher drying temperatures (90-150 °C) could adsorb more water and exhibited larger loss of solids during soaking. Such effects subsequently led to samples with lower hardness and higher stickiness. Based on the sensory analysis results, however, waxy rice dried at the above temperatures, when cooked, did not significantly differ in overall acceptability from the reference waxy rice.     

高温流化改良红小豆蒸煮品质及其机理研究

为解决红小豆质地坚硬、蒸煮品质差、煮饭前需长时间浸泡的问题,采用高温流化技术对红小豆进行蒸煮品质改良,以满足其与白米煮饭时同煮同熟的需要。研究了补水量、流化温度、进料速度对红小豆吸水性能以及蒸煮硬度的影响,然后通过正交实验得到最佳工艺条件为:补水量10∶2、流化温度215℃、进料速度62 kg/h。经最佳工艺条件处理的红小豆吸水指数为194.03%、硬度为1 448.08 g,其蒸煮硬度与白米蒸煮硬度相近,达到了与白米煮饭同煮同熟的要求。通过SEM、XRD、DSC、RVA表征处理前后红小豆微观结构、热力学特性和糊化特性,发现高温流化的红小豆细胞间微孔直径增加、细胞壁破损、淀粉结晶度下降、淀粉热力学特性和糊化行为改变,这些变化可能是高温流化改良红小豆蒸煮品质的内在机理。     

Kinetic studies on cooking of tropical milled rice

Four aged tropical milled rices differing in amylose content and/or starch gelatinization temperature (GT) were presoaked for 30 min and cooked in calculated weights of water based on amylose content at 80, 90, 100, 110 and 120°C. Differences in cooking rates were evident below 100°C. Activation energy of cooking, derived from Arrhenius plots of cooking rate constant and reciprocal temperature, ranged from 76 to 121 kJ/mole at 80–90°C and 31–57 kJ/mole at 90–120°C. Cooking rates were lower and activation energy values were higher for intermediate GT samples than for low GT samples.     

Delayed drying interval of red rice: Effects on cooking properties,in vitro starch digestibility and phenolics content

Maintaining the cooking characteristics and bioactive compound contents in red rice is essential during the post-harvest stages. For this reason, this study aimed to evaluate the influence of delayed drying time interval of 3 and 6 days and temperature of 15 and 25 °C followed by storage for 12 months on the cooking properties, in vitro starch digestibility, and the phenolic contents of red rice. The increased the delayed interval duration reduced the protein solubility, rehydration capacity, and free phenolic contents, and increased the cooking time and hardness after cooking in a temperature-independent manner. These changes reduced the starch digestibility of red rice. Increased the delayed interval duration also reduced the proanthocyanidin contents, consequently changing the grain color (decreased luminosity and increased a1 values). Thus, a delay in the interval duration before drying of 3 days at 15 °C showed the best results about the rice characteristics among the evaluated parameters; these conditions may be utilized when immediate drying is not possible.     

Cooking qualities of parboiled rices produced at low and high temperatures

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.     

Changes in Specific Heat of Corn Starch Due to Gelatinization

Differential scanning calorimetry (DSC) was used to measure apparent specific heat and heat of gelatinization for corn starch at a 13.4 to 79.1% moisture and 30°C to 100°C. Apparent specific heat of granular and heated starch was determined as a function of moisture content, temperature, and gelatinization. Effect of gelatinization was maximum at 42.3% moisture (wet basis) where the ratio of starch/water caused the largest differences in apparent specific heats. The largest difference corresponded to a degree of gelatinization of 0.429. A model was developed to predict apparent specific heats and provided values with a ±2.57% standard error (compared to experimental values) for heated starch with partial gelatinization over the range from 13.4 to 79.1% moisture.     

Effect of postharvest handling on valerenic acids content of fresh valerian (Valeriana officinalis) root

Valerian (Valeriana officinalis) is a medicinal herb native to Europe and North Asia, the roots and rhizomes of which are used as a sedative for nervous tension, sleeplessness, anxiety and stress. The impact of washing and drying on the valerenic acids concentration in valerian roots was investigated. The valerenic acids content of roots that were washed, soaked or cut prior to drying was not significantly different from that of whole valerian roots that were dried without washing, but cutting markedly decreased the drying time. Increasing the drying temperature from 15 to 70 °C reduced drying time by 176 h, with a 23% loss of valerenic acids from 15 to 40 °C. A further 36% loss occurred from 40 to 50 °C but no further significant change was evident at higher temperatures. The use of a heat pump dryer reduced the drying time at 40 °C by 25% compared with a hot air drier operated at the same temperature with no significant difference in the level of valerenic acids. There was no significant change in the level of valerenic acids in fresh whole roots held at ambient conditions for 10 days but a considerable decrease in water content. Hence valerian growers can separate or soak roots prior to washing and can store fresh roots before drying without concern over loss of valerenic acids. However, drying at the lowest feasible temperature is recommended. Copyright © 2005 Society of Chemical Industry     

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.     

Gelatinization,Pasting Characteristics and Cooking Behaviour of Egyptian Rice Varieties in Relation to Amylose and Protein Contents

Gelatinization and pasting characteristics of milled powder of shortgrain rice varieties gave Amylograms which generally exhibited lower gelatinization temperatures and longer gelatinization times than long-grain varieties. Galatinization temperatures and peak viscosities were independent of amylose and protein contents; the drop in viscosity at 94 °C generally was negatively correlated with protein content but positively correlated with amylose content. The maximum volume-expansion ratio and water absorption ratio for short-grain varieties were lower than with the long-grain varieties, and the two ratios were also related to the amylose content. Apparently cooking period was the principle factor for controlling the degree of cooking.     

Gelatinization Properties of Navy Bean Starch

Gelatinization properties of navy bean (Phaseolus vulgaris) starch under different combinations of concentration (6, 8, 10 and 12%) and cooking temperature (75, 85 and 95°C) were studied using a rotational viscometer. The torque response due to swelling and/or breakdown of starch granules approached equilibrium after either a gradual increase or a relatively rapid increase to a peak followed by a decline during cooking. For every condition, the difference between the final torque values obtained for the rapid and the slow heating processes was not significant. In general, the viscosity of the paste increased as the starch concentration and/or cooking temperature increased. However, cooking temperature of 75°C did not cause a significant gelatinization or swelling of starch granules in pastes of 6 or 8% concentration. Maximum final viscosity values were obtained at 85°C for all starch concentrations except for a maxium at 95°C for 6%. Thixotropic breakdown was observed at 10 and 12% concentrations during initial shearing at 85 and 95°C. The threshold concentration for singnificant viscosity effects in this study was in the range of about 8 to 10% or 95°C. The calculated activation energy (14.5 Kcal.g⁻¹ mole⁻¹) of navy bean starch gelatinization was similar to values reported for rough rice and rice starches.     

Effect of cooking time and ingredients on the performance of different starches in white sauces

The effect of white sauce ingredients and increased cooking time at 90 °C on the degree of gelatinization of corn, waxy corn, rice, potato and modified waxy corn starches was studied. The changes in pasting properties, linear viscoelastic properties, and microstructure were determined. In all the native starches in water, a longer cooking time at 90 °C caused greater starch granule swelling and more leaching of solubilized starch polymers into the intergranular space. These effects were more noticeable in the waxy corn and potato starches. The potato starch was the most affected, with complete disruption of the starch granules after 300 s at 90 °C. The microstructural changes which transformed a system characterized by starch granules dispersed in a continuous phase (amylose/amylopectin matrix) into a system with an increase in the continuous phase and a decrease in starch granules were associated with a decrease in system viscoelasticity. The elastic moduli were higher in the sauce than in the starch in water system. However, with the exception of potato starch, the white sauce showed lower viscoelasticity than the starch in water system. The white sauce ingredients decreased the effect of cooking time on the starch gelatinization process, particularly in potato starch.