Quality Attributes of Germinated High-Amylose and Waxy Rice in Superheated Steam and Hot Air Drying

In this work, the effects of amylose content, drying medium, and drying temperature on the fissure, texture, and glycemic index of germinated paddy (GP) were investigated. The amylose content, drying temperature, and drying medium affected the degree of starch gelatinization and percentage of fissure kernels significantly. Hot air drying at 130 and 150°C insignificantly influenced the hardness of Phitsanulok 2 GP with high amylose content after cooking compared to that of shade-dried GP, and the drying temperatures significantly affected the hardness and stickiness of RD6 GP without amylose content. Superheated steam drying caused a significant change in textural properties for both paddy varieties because of complete starch gelatinization. The high-amylose paddy had higher gamma-aminobutyric acid and lower glycemic index than nonamylose paddy. Drying temperature and drying media did not change the gamma-aminobutyric acid and glycemic index of both GP varieties in comparison to their shade-dried samples.     

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.     

Characteristics of Rice Dried in Superheated-Steam Fluidized-Bed

Characteristic properties of rice in a superheated-steam fluidized-bed dryer have been investigated using RVA, DSC, and SEM. The experimental results have shown that the reduction in moisture content from 41-42.5 to 25% d.b. using steam temperatures of 150-170°C was initially linear with drying time followed by the exponential decay when the moisture content was below 25% d.b. During the latter period, the water transport was controlled by the internal diffusion. Condensation of steam, along with the use of high temperature, enabled the development of gel layer as obvious from SEM. The formed gel layer caused the very low effective diffusivity when compared with the case of no gel formation in paddy kernel. The pasting properties and DSC measurements have shown that paddy dried at a higher temperature and a thinner bed depth provided a greater extent of gelatinization during the drying time, the first factor showing a profound effect. Kinetics of gelatinization is reasonably described by the zero-order reaction. For the paddy quality, the head rice yield was 70% higher than the reference value and color of white rice became yellow and low luminous after reducing moisture content to 18% d.b. The percentage of white belly was less than 1.5%.     

SUPERHEATED STEAM IMPINGEMENT DRYING OF TORTILLA CHIPS

Low-fat snack products are the driving forces for the drying of tortilla chips before frying. Super-heated steam impingement drying of foods has the advantage of improved energy efficiency and product quality. The temperature profile, drying curves, and the physical properties (shrinkage, crispiness, starch gelatinization and microstructure) of tortilla chips dried at different superheated steam temperatures and heat transfer coefficients were measured. Results indicated that the steam temperature had a greater effect on the drying curve than the heat transfer coefficient within the range of study. The microstructure of the samples after steam drying showed that higher steam temperature resulted in more pores and coarser appearance. The modulus of deformation and the shrinkage of tortilla chips correlated with moisture content. A higher steam temperature caused less shrinkage and a higher modulus of deformation. The pasting properties showed that samples dried under a higher steam temperature and a higher heat transfer coefficient gelatinized less during drying and had a higher ability to absorb water. Comparison of the superheated steam drying and air drying revealed that at elevated temperatures the superheated steam provided higher drying rates. Furthermore, there was a less starch gelatinization associated with air drying compared to superheated steam drying.     

SUPERHEATED STEAM IMPINGEMENT DRYING OF TORTILLA CHIPS

ABSTRACT

Low-fat snack products are the driving forces for the drying of tortilla chips before frying. Super-heated steam impingement drying of foods has the advantage of improved energy efficiency and product quality. The temperature profile, drying curves, and the physical properties (shrinkage, crispiness, starch gelatinization and microstructure) of tortilla chips dried at different superheated steam temperatures and heat transfer coefficients were measured. Results indicated that the steam temperature had a greater effect on the drying curve than the heat transfer coefficient within the range of study. The microstructure of the samples after steam drying showed that higher steam temperature resulted in more pores and coarser appearance. The modulus of deformation and the shrinkage of tortilla chips correlated with moisture content. A higher steam temperature caused less shrinkage and a higher modulus of deformation. The pasting properties showed that samples dried under a higher steam temperature and a higher heat transfer coefficient gelatinized less during drying and had a higher ability to absorb water. Comparison of the superheated steam drying and air drying revealed that at elevated temperatures the superheated steam provided higher drying rates. Furthermore, there was a less starch gelatinization associated with air drying compared to superheated steam drying.     

Effects of High-Temperature Drying on Physicochemical Properties of Various Cultivars of Rice

Abstract

Three varieties of paddy rice, namely Langi and Amaroo from Australia and Chainart I from Thailand, were dried from high initial moisture content of about 27% down to 13–14% wet basis using a two-stage drying system. A fluidized bed dryer reduced the moisture content down to 18%. Drying experiments were carried out at 100, 125, and 150°C. Further moisture content reduction down to 14% was achieved by shade drying. As a result of these treatments, head rice yield increased proportionally with the drying temperature. In contrast to that, the yellowness, measured by colorimeter in terms of b value, showed an opposite trend. Starch characteristics were studied by Rapid Visco Analyser (RVA), x-ray diffraction, and differential scanning calorimetry (DSC). Pasting properties were affected by the drying temperature. The peak viscosity and break down were decreasing with the increase of drying temperature in all varieties while the setback values were increasing in Langi and Amaroo only. All starch samples displayed the typical A type x-ray diffraction pattern. The apparent crystallinity determined by x-ray diffraction was reduced with increasing drying temperature. The gelatinization peak shifted to higher temperature while the endothermic enthalpy of gelatinization decreased with increasing drying temperature.     

Novolac resin–poly(ethyl methacrylate) interpenetrating polymer networks: Morphology and mechanical and thermal properties

Full interpenetrating networks (IPNs) and semi‐IPNs of Novolac (phenolic) resin and poly(ethyl methacrylate) (PEMA) were prepared by the sequential mode of synthesis. These were characterized with respect to their mechanical properties, that is, ultimate tensile strength (UTS), percentage elongation at break, modulus, and toughness. Thermal properties were studied by DSC and thermogravimetric analysis (TGA). The morphological features were studied through polarizing light microscopy (PLM). The effects of variation of the blend ratios on the above‐mentioned properties were examined. There was a gradual decrease of modulus and UTS with consequent increases in elongation at break and toughness for both types of IPNs with increasing proportions of PEMA. An inward shift and lowering (with respect to pure phenolic resin) of the glass‐transition temperatures of the IPNs with increasing proportions of PEMA were observed, thus indicating a plasticizing influence of PEMA on the rigid and brittle matrix of crosslinked phenolic resin. The TGA thermograms exhibit two‐step degradation patterns. Although there was an apparent increase in thermal stability at the initial stages, particularly at lower temperatures, a substantial decrease in thermal stability was observed in the regions of higher temperatures. The surface morphology as revealed by PLM clearly indicates two‐phase structures in all the full and semi‐IPNs, irrespective of PEMA content. The matrix–PEMA domain interfaces are quite sharp at higher concentrations of PEMA. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 412–420, 2003     

Effects of Simultaneous Parboiling and Drying by Infrared Radiation Heating on Parboiled Rice Quality

An infrared (IR) radiation heating and vibrating apparatus was used to study a simultaneous parboiling and drying process. Physicochemical properties such as milling yield, color, and pasting properties of parboiled paddy were evaluated. Radiation intensity levels of 46.7 kW/m², variable exposure time, and rice samples at fixed initial moisture contents (IMC) of 30 and 32% wet basis (wb) were used. It was discovered that the radiation intensity of 46.7 kW/m² and 32% wb moisture content yielded a quality level similar to that of conventional steam-parboiled rice. The head rice yield (HRY) of IR paddy slightly decreased with increased exposure time. The HRY of IR heating was more than 60% compared to HRY values of 67.68 to 69.34% for conventional steam-parboiled rice. The b-values of 23 to 25 for IR samples showed lighter yellowness than the 29.7 b-value of conventional steam-parboiled rice. The pasting properties of all IR samples showed lower viscosity compared to the raw-milled rice samples but higher than conventional steam-parboiled rice. Initial moisture content of paddy affected the degree of starch gelatinization (SG) by differential scanning calorimetry (DSC). Under IR heating for 18 min of exposure time, the 32% wb IMC sample showed SG at 80.15% compared to SG at 59.02% with the 30% wb IMC sample. Hence, while employing simultaneous parboiling and drying with IR heating for an exposure time of 18 min, the sample retained more parboiled flavor as a result of a higher degree of starch gelatinization. The sample showed lower HRY, but yellowness was within the acceptable range. Energy requirement for producing 1 ton of parboiled paddy by the IR heating process is lower than the conventional steam-parboiled process but statistically nonsignificant (P > 0.05). However, the process time was reduced to one third of the conventional process, leading to improved quality. In addition, initial investment cost was minimal because a steam generator was not required.     

Water sorption kinetics of spaghetti at different temperatures

The water sorption kinetics of spaghetti was measured in the temperature range of 20-90 °C to investigate the temperature dependencies of an equilibrium moisture content and an initial rate of water sorption. The dependencies indicated the mechanism of water sorption: the equilibrium moisture content is limited by the state of starch gelatinization and the initial rate of water sorption is governed by the water diffusion through the pores of the spaghetti regardless of the starch gelatinization. The empirical equations were proposed to predict the amount of loss of the spaghetti mass during water sorption which results in the quality loss of cooked spaghetti and the moisture content which affects the mechanical properties and an optimal immersion time. The equation of the moisture content, taking the effect of starch gelatinization into consideration, has the initial diameter of spaghetti, immersion time, and temperature of immersed water as parameters to predict under any conditions.     

Modification of novolac resin by interpenetrating network formation with poly(butyl acrylate)

Interpenetrating networks (IPNs) of novolac (phenol formaldehyde) resin and poly(butyl acrylate) (PBA) were prepared by a sequential mode of polymerization. Both full IPNs and semi‐IPNs of different compositions were synthesized and characterized with respect to their mechanical properties, that is, their modulus, ultimate tensile strength (UTS), elongation‐at‐break percentage, and toughness. Their thermal properties were examined with differential scanning calorimetry and thermogravimetric analysis (TGA). A morphological study was performed with an optical microscope. The effects of the variation of the blend ratios on the aforementioned properties were studied. There was a gradual decrease in the modulus and UTS with a simultaneous increase in the elongation‐at‐break percentage and toughness for both types of IPNs as the proportions of PBA were increased. With increasing proportions of PBA, the glass‐transition temperatures of the different IPNs underwent shifts toward a lower temperature region. This showed a plasticizing influence of PBA on the rigid and brittle phenolic matrix. TGA thermograms depicted the classical two‐step degradation for the phenolic resin. Although there was an apparent increase in the thermal stability at the initial stage (up to 350°C), particularly at lower temperatures, a substantial decrease in the thermal stability was observed at higher temperatures under study. In all the micrographs of full IPNs and semi‐IPNs, two‐phase structures were observed, regardless of the PBA content. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 2407–2417, 2005     

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.     

A Superheated-Steam Fluidized-Bed Dryer for Parboiled Rice: Testing of a Pilot-Scale and Mathematical Model Development

This article describes the testing of a pilot-scale superheated-steam fluidized-bed dryer for parboiled rice along with development of a mathematical model for predicting the changes in temperature of steam and moisture content of parboiled rice during drying. Based on the obtained results, it was found that the superficial velocity of steam from 1.3 to 1.5 times of the minimum fluidization velocity had no significant effect on the drying rates of rice. The energy consumption for reducing the moisture content of paddy from 0.43 to 0.22 kg/kg dry basis was approximately 7.2 MJ/kg water evaporated. Drying temperature caused the appreciable change of parboiled rice qualities as characterized by water adsorption, whiteness and pasting viscosities, white belly, and hardness. Soaking paddy at a temperature of 70°C for 7–8 h before drying was sufficiently enough for producing parboiled rice, with no white belly. The gelatinization of starch during drying resulted in higher head rice yield of the product as compared to that of raw paddy.     

A Superheated-Steam Fluidized-Bed Dryer for Parboiled Rice: Testing of a Pilot-Scale and Mathematical Model Development

This article describes the testing of a pilot-scale superheated-steam fluidized-bed dryer for parboiled rice along with development of a mathematical model for predicting the changes in temperature of steam and moisture content of parboiled rice during drying. Based on the obtained results, it was found that the superficial velocity of steam from 1.3 to 1.5 times of the minimum fluidization velocity had no significant effect on the drying rates of rice. The energy consumption for reducing the moisture content of paddy from 0.43 to 0.22 kg/kg dry basis was approximately 7.2 MJ/kg water evaporated. Drying temperature caused the appreciable change of parboiled rice qualities as characterized by water adsorption, whiteness and pasting viscosities, white belly, and hardness. Soaking paddy at a temperature of 70°C for 7-8 h before drying was sufficiently enough for producing parboiled rice, with no white belly. The gelatinization of starch during drying resulted in higher head rice yield of the product as compared to that of raw paddy.     

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.     

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%.     

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.     

Synthesis and characterization of sequential interpenetrating polymer networks of novolac resin and poly(ethyl acrylate)

Interpenetrating polymer networks (IPN) of Novolac/poly(ethyl acrylate) have been prepared via in situ sequential technique of IPN formation. Both full and semi IPNs were characterized with respect to their mechanical properties that is, ultimate tensile strength (UTS), percentage elongation at break, modulus, and toughness. Physical properties of these were evaluated in terms of hardness, specific gravity, and crosslink density. Thermal behavior was studied by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). The morphological features were observed by an optical microscope. There was a gradual decrease in modulus and UTS, with consequent increases in elongation at break and toughness for both types of IPNs with increasing proportions of PEA. An inward shift and lowering (with respect to pure phenolic resin) of the glass transition temperatures of the IPNs with increasing proportions of PEA were observed, thus, indicating a plasticizing influence of PEA on the rigid, brittle, and hard matrix of crosslinked phenolic resin. The TGA thermograms exhibit two‐step degradation patterns. An apparent increase in thermal stability at the initial stages, particularly, at lower temperature regions, was followed by a substantial decrease in thermal stability at the higher temperature region under study. As expected, a gradual decrease in specific gravity and hardness values was observed with increase in PEA incorporation in the IPNs. A steady decrease in crosslink densities with increase in PEA incorporation was quite evident. The surface morphology as revealed by optical microscope clearly indicates two‐phase structures in all the full and semi IPNs, irrespective of acrylic content. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci, 2006     

ON THE DRYING MECHANISM OF SHRINKAGE MATERIALS

Effects of moisture content on Liquid transport properties (Permeability and suction pressure) and mechanical properties (Young's modulus, yield stress and tensile strength) of drying shrinkage materials (Kibnshi, IIaido and mixed clay) were measured and a strong dependence was found. When glass beads are added to the Kibushi, permeability increase and Young's modulus and yield stress decrease in spite of the same suction pressure and tensile strength. Changes in local moisture content and stress during drying was calculated by using finite-element method, taking into account the stress gradient in addition to the pressure gradient due to osmotic suction.     

ON THE DRYING MECHANISM OF SHRINKAGE MATERIALS

ABSTRACT

Effects of moisture content on Liquid transport properties (Permeability and suction pressure) and mechanical properties (Young's modulus, yield stress and tensile strength) of drying shrinkage materials (Kibnshi, IIaido and mixed clay) were measured and a strong dependence was found. When glass beads are added to the Kibushi, permeability increase and Young's modulus and yield stress decrease in spite of the same suction pressure and tensile strength. Changes in local moisture content and stress during drying was calculated by using finite-element method, taking into account the stress gradient in addition to the pressure gradient due to osmotic suction.     

Properties of aminosilane grafted moisture curable poly(vinyl chloride) formulations

The reaction of plasticized PVC with [N-(2-amino ethyl)-3aminopropyl trimethoxy silane] yielded silane-grafted PVC that was crosslinked by a hydrolytic mechanism. It was found that crosslinking resulted in improvement of mechanical properties (tensile strength and elongation at break) specially at temperatures higher than 80°C. Properties at 130°C were substantially enhanced, showing a fourfold increase in ultimate tensile strength (UTS), and a twofold increase in elongation at break. There was a unique relationship between UTS at 130°C and gel content irrespective of processing conditions, with UTS starting to increase sharply around 30% gel content, and reaching a plateau at about 60%. Also, the softening temperature was improved. The crosslinked material had a higher softening temperature (up to 165°C, compared with 95°C for the compound without crosslinking agent), indicating that the hydrolytic crosslinking of PVC yielded a material with improved properties.