Effects of Germination Process and Drying Temperature on Gamma-Aminobutyric Acid (GABA) and Starch Digestibility of Germinated Brown Rice

In this work, germination method, germination time, and drying temperature were investigated for their effects on gamma-aminobutyric acid (GABA) and starch digestibility. The germination method and germination time influenced the GABA and dietary fiber contents as well as starch and glucose, but both factors did not provide a faster hydrolysis of starch for germinated brown rice because of the dietary fiber. When the germinated samples were dried by a hot-air fluidized bed dryer at 130 or 150°C, the GABA content was not decreased and the amylose-lipid complexes occurred. Dissociation temperature of the complexes was given in a range of 100–117°C, which was lower than that of complexes in the non-germinated paddy. Thus, the amylose-lipid complexes in the germinated samples obtained at high temperature lost some crystalline structure when cooked by the boiling method. The corresponding rate of starch hydrolysis or glycemic index of the germinated samples changed insignificantly from that of the shade-dried germinated sample or non-germinated brown rice which was dried in shade.     

Enhancement of γ-aminobutyric acid in germinated paddy by soaking in combination with anaerobic and fluidized bed heat treatment

Enhancement of γ-aminobutyric acid (GABA) in germinated grain could be induced via environmental stresses. Soaking in combination with anaerobic treatment (SA) as well as soaking in combination with anaerobic and heat treatment (SAH) are proposed in this work to increase the GABA content in germinated paddy; the results were compared with that obtained via a conventional germination (soaking) method (CS). The quality of germinated rice prepared from paddy (GP) by CS, SA and SAH after shade drying and fluidized bed drying in terms of the GABA content, number of fissured kernels and textural property was also investigated. The results showed that the GP prepared via SAH had the highest GABA content. The GABA contents in GP prepared by CS, SA and SAH increased 15, 25 and 29 times as compared to that of the un-germinated brown rice, respectively. However, SAH resulted in the higher number of fissured kernels as compared with CS and SA. After fluidized bed drying at 150 °C, the GABA content in GP did not decrease, but the number of fissured kernels of the fluidized bed dried samples was higher than that of the shade-dried samples. However, the head brown rice yield of the fluidized bed dried samples was higher than that of the shade-dried samples. Hardness and stickiness of the fluidized bed dried samples prepared by the three germination methods were not significantly different; exception held nevertheless for the hardness value of the complete kernels obtained via CS.     

Optimal Operating Conditions to Produce Nutritious Partially Parboiled Brown Rice in a Humidified Hot Air Fluidized Bed Dryer

V-type amylose–lipid complexes present in partially parboiled rice can decrease starch digestibility. Formation of such complexes can be accomplished using high-temperature fluidized bed drying; the degree of the complexes depends on the thermal condition. The effects of drying media (hot air and humidified hot air), operating conditions (drying air temperature and relative humidity [RH]), and the initial moisture content on the degree of V-type crystallinity and subsequent starch digestibility (or glycemic index, GI) and brown rice texture were examined experimentally. The results showed that paddy drying with humidified hot air (HHA) requires a longer time than hot air (HA). Higher drying air temperature, RH, and initial moisture content of paddy yield higher degrees of starch gelatinization and V-type amylose–lipid complexes. The brown rice dried by HA or HHA had lower starch digestibility and a harder texture than the reference sample. Within the range of parameters studied, to obtain the lowest GI for the dried brown rice, paddy at an initial moisture content of 33% (db) should be dried by HHA at 150°C and 6.4% RH.     

Effects of germination time and drying temperature on drying characteristics and quality of germinated paddy

Germination time and drying temperature are very important parameters affecting the quality of the germinated paddy (GP) since the microstructure of starch granules is modified during germination. The experimental results showed that the germination time increasing from 60 to 68 h provided more loosely-packed starch granules, lower hardness of cooked GP, higher γ-aminobutyric acid content (GABA) and larger number of fissured GP after drying. However, the modified microstructure did not cause a difference between drying curves at each germination time. Prediction results of the moisture content from the two-layer model were in good agreement with the experimental results and also showed that the effective moisture diffusion coefficient values of husk were significantly lower than those of germinated brown rice. Drying at a higher drying temperature could reduce the number of fissured GP more significantly. The hardness of cooked GP samples and their GABA contents obtained from drying temperatures changed insignificantly from that of the shade-dried GP. The sensory analysis results revealed that the texture of GP was better than that of the rice without germination and the longer germination time provided the adverse effect on the fermentation odour and texture.     

Effect of Fluidized Bed Drying Temperature on Various Quality Attributes of Paddy

Abstract

As reported by many researchers, it was found that fluidized bed paddy drying using high drying air temperatures of over 100°C affected the head rice yield and whiteness of dried rice. However, only a few studies on fluidized bed paddy drying with drying air temperatures below 100°C were so far reported. The main objective of this work was therefore to study the effect of fluidized bed drying air temperature on various quality parameters of Suphanburi 1 and Pathumthani 1 Indica rice. Paddy was dried from the initial moisture contents of 25.0, 28.8, and 32.5% dry basis to 22.5 ± 1.2% dry basis using inlet drying air temperatures between 40 and 150°C at 10°C/step. After fluidized bed drying, paddy was tempered and followed by ambient air aeration until its final moisture content was reduced to 16.3 ± 0.5% dry basis. The results showed that the head rice yield of Suphanburi 1 was significantly related to the inlet drying temperature and initial moisture content whilst there was no significant relationship between the head rice yield, drying temperature and initial moisture content for Pathumthani 1. The whiteness of the two rice varieties was slightly decreased with increase in drying air temperature and initial moisture content. It was also found that the hardness of both cooked rice varieties exhibited insignificant difference (p < 0.05) comparing to rewetted rice, which was gently dried by ambient air aeration in thin layer. The thermal analysis by DSC also showed that partial gelatinization occurred during drying at higher temperatures. Using inlet drying air temperatures in the range of 40–150°C therefore did not affected the quality of cooked rice and paddy. The milling quality of paddy was also well maintained.     

Influence of hot air fluidized bed drying on quality changes of purple rice

The influence of drying using a fluidization technique on the quality of purple rice was investigated in this study. The results demonstrated that the initial moisture of rice was 28.3% dry basis (db). Compared to the sun-dried or reference purple rice samples, the influence of drying at temperatures ranging from 100 to 150°C did not affect the quality of color, anthocyanin content, total phenolic content, or antioxidant activity. At this initial moisture level, samples should be dried at 150°C air because such temperatures yield the highest drying rate. Drying at this temperature also causes an increase in the head purple rice yield because of the gelatinization of starch. In the case of an initial moisture content of 33.3% (db), the drying temperature should not exceed 130°C.     

Modeling heat and mass transfer–induced stresses in germinated brown rice kernels during fluidized bed drying

A study of stress distribution inside a germinated brown rice (GBR) kernel during drying is important to understand the fissure formation of GBR and hence control the drying process in order to improve the quality of GBR. In this study, a finite element method performed in three dimensions in conjunction with the heat and mass balance of the drying system was developed to describe moisture, temperature, and stress distributions inside GBR kernels during fluidized bed drying. The modeling was carried out using the coupling of heat and mass transfer and validated with experimental data at 90–150°C. The results of moisture and temperature predictions agreed well with the experiments. During drying, tensile stress occurred at the layers close to surface and compressive stress occurred at the inner portion of a kernel. The tensile and compressive stresses increased to the highest value at about 30 s of drying, corresponding to the highest moisture gradient, and then decreased afterwards. The tensile and compressive stresses were higher at a higher drying temperature. These stress prediction results corresponded to the experiments, which show more severe GBR fissuring at higher drying temperatures.     

Corn,Rice, and Wheat Seed Drying by Two-Stage Concept

Corn, rice, and wheat seeds with an initial moisture content (IMC) of 20–25% wb were dried to moisture content below 18% wb at 40–80°C in a fluidized bed dryer (FBD) and spouted bed dryer (SBD) and the seeds with IMC 18% wb were dried to below 14% wb at air temperatures 18–30°C and relative humidity 60–70% by an in-store dryer (ISD). As a result, it appears that a two-stage drying concept is feasible in drying high-moisture-content seeds due to the high germination rate of dried seeds. Nonetheless, the drying temperature must be carefully selected. A drying temperature of 40°C was clearly safe for all samples, whereas more than 90% of wheat seeds still germinated after drying at 60°C in FBD. Furthermore, drying seeds with IMC 18% wb by ISD was safe under specified drying conditions.     

Effects of High-Temperature Fluidized Bed Drying and Tempering on Kernel Cracking and Milling Quality of Vietnamese Rice Varieties

Studies on the effects of high-temperature fluidized bed drying and tempering on physical properties and milling quality of two long-grain freshly harvested Vietnamese rice varieties, A10 (32±1% wet basis moisture) and OM2717 (24.5±0.5% wet basis moisture), were undertaken. Rice samples were fluidized bed dried at 80 and 90°C for 2.5 and 3.0 min, then tempered at 75 and 86°C for up to 1 h, followed by final drying to below 14% moisture (wet basis) at 35°C by thin-layer drying method. Head rice yield significantly improved with extended tempering time to 40 min. Head rice yield tended to increase with decreasing cracked (fissured) kernels. The hardness and stiffness of sound fluidized bed dried rice kernels (in the range of 30–55 N and 162–168 N/mm, respectively) were higher than that of conventionally dried ones (thin layer dried at 35°C). The color of milled rice was significantly (P < 0.05) affected by high-temperature fluidized bed drying, but the absolute change in the value was very small.     

A New Model and Quality of Unfrozen and Frozen Cooked Rice Dried in a Microwave Vibro-Fluidized Bed Dryer

This study aimed to develop a suitable drying model for microwave vibro-fluidized bed drying in a single-mode applicator (MVFB-SMA drying) of cooked rice with and without prefreezing treatment and to investigate the effects of prefreezing treatment and drying temperature (110–185°C) on quality of dried cooked rice. During the process of drying cooked rice from 60 to 10% (wet basis), results indicated that drying rate increased, whereas drying time decreased with prefreezing treatment and increased drying temperature. The drying rate and drying time of unfrozen and frozen cooked rice ranged from 0.196 to 0.497 g water/g dry matter/min and 0.228 to 0.554 g water/g dry matter/min; and from 7 to 2.5 min and 5.5 to 2 min, respectively. A new model was proposed in this study (MR = exp(?k t ⁿ ) + bt + c) to compare with 11 commonly used drying models. The new model describes the MVFB-SMA drying data most satisfactorily. The values of effective diffusivity were between 1.70 × 10^?7 and 5.72 × 10^?7 m²/s for the unfrozen sample and between 1.99 × 10^?7 and 5.86 × 10^?7 m²/s for the frozen sample. Their activation energy values were 23.66 and 21.19 kJ/mol, respectively. Prefreezing treatment provided a whiter product with a less uniform porous structure and higher bulk density. Slower ability to rehydrate was also observed for the frozen cooked rice dried at 160 and 185°C. An increase in drying temperature resulted in changes in whiteness, microstructure, bulk density, and rehydration capability. No prefreezing treatment and drying at 160°C seemed to be the optimal process condition for cooked rice, ensuring whiteness, a porous structure, low bulk density, and high rehydration capability.     

Influences of Pretreatments and Drying Process Including Fluidized Bed Puffing on Quality Attributes and Microstructural Changes of Banana Slices

Healthy snacks have received more attention because of their low fat content. Color and texture are important to snack quality. Effects of chemical pretreatment, thickness, blanching, and puffing temperature on quality of banana slices were therefore investigated. Banana slices (2.5 and 3.5 mm thickness) were chemically treated by citric acid and sodium metabisulfite, blanched, and dried at a temperature of 90°C to an intermediate moisture content of 25% db. They were then puffed in a fluidized bed dryer at 160 and 180°C for 2 min and dried again at the same drying temperature as the first drying step. Blanching, puffing temperature, and thickness strongly affected the degree of shrinkage, effective moisture diffusivity, morphology, textural properties such as hardness and crispiness, and color, but the chemical treatment did not affect those qualities. Blanching can improve the product appearance; the color was uniform and shiny throughout the surface and golden yellow. However, the textural attributes of the blanched sample had higher hardness and less crispiness than those of unblanched sample.     

Rapid Drying of Parboiled Paddy Using Hot Air Impinging Stream Dryer

A method for rapid drying of parboiled paddy via the use of an impinging stream dryer was proposed and assessed. The effects of the drying air temperature, number of drying cycles, as well as time of tempering between each drying cycle on the moisture reduction, head rice yield, and whiteness index of the dried parboiled paddy were studied. The drying experiments were carried out at drying air temperatures of 130, 150, and 170°C; inlet air velocity of 20 m/s; impinging distance of 5 cm; and paddy feed rate of 40 kg_{dry_paddy}/h. Parboiled paddy was dried for up to seven cycles. Between each drying cycle the parboiled paddy was tempered for a period of either 0 (no tempering), 15, 30, 60, or 120 min. After impinging stream drying, paddy was ventilated by ambient air flow until its moisture content reached 16% (db). Moisture reduction of the paddy was noted to depend on both the impinging stream drying temperature and tempering time. Drying at a high temperature along with tempering for a suitable period of time could maintain the head rice yield of the paddy at a level similar to that of the reference parboiled paddy. To avoid discoloration and low head rice yield, parboiled paddy should not be dried at a temperature higher than 150°C and should be tempered for at least 30 min.     

Improving head rice yield of glutinous rice by novel parboiling process

Most commercial parboiled rice is produced from high-amylose content rice. Glutinous rice, which is lacking in amylose content, is generally consumed in Southeast Asian countries. Rare study of parboiling glutinous rice has been observed. In this study, glutinous rice was improved in head rice yield by a novel parboiling process. Two rough glutinous rice, rice department 6 (RD6) and black glutinous rice (BGR) cultivars, were soaked in hot water at 70?±?5°C for 3?h. The ricer 3moisture content after soaking was 50–52% (d.b.), it was dried with hot air and superheated steam (SHS) at 110, 130, and 150°C in a fluidized bed dryer. The results show that SHS at all drying temperatures can improve the high head rice yield in both parboiled glutinous rice cultivars better than hot air drying. Higher temperature drying caused L* value to decrease but the b* value increases in RD6, whereas in BGR, all color values decreased and ΔE* was increased when the drying temperature increased. Increasing drying temperature presented a softer texture of both glutinous rice cultivars. Upper 130°C, completed gelatinization of both varieties can be obtained and seen by scanning electron microscope and differential scanning calorimeter (DSC). This technique of using high-temperature fluidized bed drying can produce completely parboiled glutinous rice in a single process instead of two conventional processes, steaming and drying, in series.     

Effect of airflow rate on drying air and moisture content profiles inside a cross-flow drying column

Rice at 20.5 and 16.3% initial moisture contents (IMCs) was dried using 57°C/13% RH air at airflow rates (Qs) of 0.36, 0.46, and 0.56 (m³/s)/m² for 30, 60, and 90?min, respectively, in an experimentally simulated cross-flow drying column. Q significantly affected the drying air and rice moisture content profiles within the drying column; for a particular drying duration, the range of MCs within the column decreased as Q increased. Q also impacted the extents of intra-kernel material state gradients created and thus had potential impacts on kernel fissuring and consequent head rice yield reduction. In addition, the impact of Q on the above-mentioned profiles was dependent on the rice IMC.     

Attrition of Victorian brown coal during drying in a fluidized bed

Analyzing the attrition of Victorian brown coal during air and steam fluidized bed drying, the change in particle size distribution over a range of initial moisture contents (60% to 0%) and residence times (0 to 60 minutes) was determined. Dried at a temperature of 130°C with a fluidization velocity 0.55 m/s and an initial particle size of 0.5–1.2 mm, both fluidization mediums show a shift in the particle size distribution between three and four minutes of fluidization, with a decrease in mean particle size from 665 µm to around 560 µm. Using differential scanning calorimetry (DSC), the change in particle size has been attributed to the transition between bulk and non-freezable water (approximately 55% moisture loss) and can be linked to the removal of adhesion water, but not to fluidization effects. This is proved through the comparison of air fluidized bed drying, steam fluidized bed drying, and fixed bed drying—the fixed bed drying is being used to determine the particle size distribution as a function of drying. The results show the three drying methods produce similar particle size distributions, indicating that both fluidization and fluidization medium have no impact upon the particle size distribution at short residence times around ten minutes. The cumulative particle size distribution for air and steam fluidized bed dried coal has been modeled using the equation P_d = A₂ + (A₁ ? A₂)/(1 + (d/x₀)^p), with the resultant equations predicting the effects of moisture content on the particle size distribution. Analyzing the effect of longer residence times of 30 and 60 minutes, the particle size distribution for steam fluidized bed dried coal remains the same, while air fluidized bed dried coal has a greater proportion of smaller particles.     

Evolution of mechanical properties of parboiled brown rice kernels during impinging stream drying

Information on mechanical properties of parboiled brown rice kernels upon impinging stream drying, which is important for effective control of kernel fissure and head rice yield, is reported. Experiments were performed at the drying temperatures of 130, 150, and 170°C; inlet air velocity of 20?m/s; impinging distance of 5?cm and paddy feed rate of 40?kg_{dry_paddy}/h. Parboiled paddy was dried for up to seven cycles. Between each drying cycle, the paddy was tempered for a period of either 0 (without tempering) or 30?min. The moisture evaporation rate was noted to be very high during the first two drying cycles and rapidly dropped in the later drying cycles. When tempering was included after a particular drying cycle, the drying rate in a subsequent cycle was higher than without tempering. At the kernel moisture contents immediately after drying of 25.3–47.5% (d.b.), the drying temperature and existence of tempering did not affect the mechanical properties although microcracks were formed in the kernels. However, both factors played a more important role on the mechanical properties when the kernels were evaluated at 16% (d.b.). The head rice yield correlated well with the tensile strength of the kernels.     

Change of mechanical properties related to starch gelatinization and moisture content of rice kernel during fluidized bed drying

Rice fissuring during the drying process is a major problem affecting rice quality. To alleviate this critical issue, it is necessary to understand the change of mechanical properties and the drying kinetics of paddy during drying. The objective of this work is therefore to study the drying characteristics and changes of mechanical properties, i.e., breaking force (F), ultimate tensile strength (UTS), and apparent modulus of elasticity (AMOE) during fluidized bed drying. Suphanburi 1 paddy variety with three initial moisture contents (Mi) of 29.5, 30.2, and 42.8% dry basis was used as the raw material, which was dried at drying air temperatures (Ta) of 110, 130, and 150?°C. A three-point bending method was used for testing the mechanical properties with a texture analyzer. The experimental results showed that the breaking force and the ultimate tensile strength of paddy during drying were more strengthened with higher drying temperatures and higher initial moisture content while its apparent modulus of elasticity was changed only with the moisture content. However, both operating parameters positively affected the apparent modulus of elasticity when evaluated at a 16% dry basis. The maximum changes in F, UTS, and AMOE concerning the initial moisture content were 25.1, 25.2, and 19.5%, respectively. Besides, the maximum changes in F, UTS, and AMOE concerning drying temperatures during drying were 14.2, 14.3, and 13.5%, respectively. The improvement of the mechanical properties could be attributed to the starch gelatinization of which the degree was higher in cases of higher initial moisture content and higher drying temperatures. The empirical models of ultimate tensile strength and apparent modulus of elasticity were developed and related to intermediate moisture content and the degree of starch gelatinization.     

Evaluation of new parboiled rice process using humidified hot air fluidized bed drying

This study aims to experimentally investigate the drying characteristics and quality of a paddy dried by hot air (HA) and humidified hot air (HHA) fluidization technique. Qualities such as head rice yield (HRY), white belly, degree of gelatinization (DSG), and color of dried paddy were evaluated. A paddy with an initial moisture content of 14% d.b. was soaked in hot water at a temperature of 70?°C for 5?h then dried at a temperature of 130,150, and 170?°C, relative humidity in the range of 0.3–12%, an air velocity of 3.9 m/s, and a bed height of 10?cm. The results showed that the drying time of the paddy in the HHA condition took longer than the HA drying condition. Because HHA provided a higher grain temperature and a slow rate of drying, the degree of starch gelatinization was significantly higher when compared to HA. The subsequent HRY was relatively higher than using HA drying. However, the color of the sample obtained from the HHA condition was relatively browner, but the parboiled rice product still had a light brown color for the drying temperature range used in this study. To produce parboiled rice, HHA could be operated up to the temperature of 170?°C, relative humidity of 6%, and DOM of 10%.     

Study on quality attributes and drying kinetics of instant parboiled rice fortified with turmeric using hot air and microwave-assisted hot air drying

Abstract

This study investigated the quality and drying kinetics of instant parboiled rice fortified with turmeric (IPRFT) by using hot air (HA) and microwave-assisted hot air (MWHA) drying. The cooked long grain parboiled rice (LGPR) fortified with turmeric was dried with HA at temperatures of 65, 80, 95, and 110?°C. The microwave power density of 0.588 Wg^?1 was incorporated for drying with MWHA. Drying was performed until the dried IPRFT reached 16% (d.b.) of moisture content. The quality of the dried IPRFT was evaluated in terms of color, total phenolics content (TPC), total antioxidant capacity (TAC), rehydration ratio, volume expansion ratio, texture and microstructure. The results showed that the incorporation of microwave power with HA drying helped to reduce the drying time by 50% compared to conventional HA drying. A prediction of the moisture ratio by using the Page model provided the best R² and RMSE in drying kinetics. The drying conditions had small effects on the color, TPC, TAC, and microstructure of the dried IPFRT. The rehydration ratio, volume expansion ratio and texture of the rehydrated IPFRT showed minimal variations from changes in the drying conditions. The TPC and TAC of the dried IPRFT clearly increased compared to the TPC and TAC of the initial LGPR.     

Test Model for Studying Sun Drying of Rough Rice Using Far-Infrared Radiation

ABSTRACT

The effect of heat input, mixing at regular intervals, airflov over the surface and the relative humidity were investigated within a radiation chamber. Likening to sun drying as practiced in the tropics, the chamber was constructed to study the direct radiant heat drying of rough rice under various bed thicknesses. Graphic results showing the variations of rough rice surface temperature during the experiments are presented. Comparisons are also made between the relative contributions of bed depth and mixing on the drying rate. A non-mixed bed of 3 cm dried just as fast as a 6 cm mixed bed although moisture content was nonuniform in the former case. After drying, the grains were dehusked by hand and examined for physical defects like cracks. Possible constraints involved in drying thick beds of rough rice under direct radiation were investigated with the aim of defining suitable strategies for improving actual sun drying.