Convective air,microwave, and combined drying of potato pre-treated by pulsed electric fields

Abstract

The effects of pulsed electric field (PEF) treatment on drying of potato have been investigated. The convective air (CA) (T?=?50?°C), microwave (MW), and combined (CA?+?MW or MW?+?CA) drying was applied. The drying curves, progression of temperature inside samples, microstructure, and capillary imbibition capacity of untreated (U) and PEF treated samples were compared. The PEF treatment noticeably affected the CA and MW drying characteristics and structure of dried samples. It reflected impact of electroporation on the heat and mass transfer processes during the different drying periods. The different progressions of temperatures inside U and PEF samples for the MW mode of drying were revealed. The highest and smallest rehydrations were observed for the U samples for individual CA and MW modes of drying, respectively. The observed behavior was explained accounting for the absence of starch gelatinization for the CA mode of drying and presence of it for the MW mode of drying.     

Comparison of Three Different Frequency Drying Methods for Barley Chewable Tablets

The effect of 27 MHz radio-frequency (27 RF), 915 MHz microwave (915 MW), and 2450 MHz microwave (2450 MW) on drying of barley chewable tablets was examined experimentally. It was observed that the dielectric constant was decreased with the moisture content reduction. Penetration depths of samples treated with 27 RF were the highest. The quality of products was evaluated according to color, temperature, ferric-reducing power, and DPPH scavenging. 2450 MW played a positive role in improving antioxidant properties. The comprehensive view is that radio-frequency technology may be a promising drying method for food processing.     

Design and performance evaluation of a pilot-scale pulsed vacuum infrared drying (PVID) system for drying of berries

Abstract

The objective of current work was to develop a new pilot-scale pulsed vacuum infrared drying (PVID) system for the drying of berries. The system design and drying performance evaluation for grape and goji berries are reported here. The PVID system consisted of three major sections, including infrared heating section, vacuum section, and a controlling section. Electrical infrared (IR) emitter was made with carbon fiber sheet at the thickness of 2–4?mm, which emitted IR wavelength of 1–30?μm. The control system was used to achieve paused pressure by switching the drying chamber pressure between atmospheric pressure (101?kPa) and vacuum (3–10?kPa) successively and maintaining the pressure for different time periods. Grapes and goji berries were dried in a single layer at three different temperatures (55, 65, and 75?°C) with an atmospheric duration ranging from 1 to 12?min and vacuum duration from 10?min to constant vacuum. The drying characteristic and quality of PVID dried berries were investigated and compared with that of hot air (HA) dried berries. Results showed that the IR heating temperature, atmospheric duration, and vacuum duration had significant effects (p?<?.05) on the drying time. The optimum drying conditions for grapes and goji berries were IR heating at 65?°C, vacuum duration of 15?min, and atmospheric duration of 4 and 2?min, respectively. The corresponding drying time is nearly 720?min for grapes, and 450?min for goji berries. The PVID dried grapes and goji berries had more attractive color than that of HA dried ones. These findings demonstrated that PVID should be a promising method to produce high-quality dried berries. This study laid a good foundation for scaling up the technology in the future.     

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.     

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.     

Hot air drying of purple-fleshed sweet potato with contact ultrasound assistance

A drying technique using a combination of a contact ultrasound apparatus and a hot air dryer is developed to investigate the strengthening effect of contact ultrasound on hot air drying. The effects of drying parameters such as ultrasound power and drying temperature on drying characteristics, effective moisture diffusivity (D_eff), microstructure, glass transition temperature (T_g), rehydration ratio, and color difference are discussed. The results show that the application of contact ultrasound causes a significant acceleration of internal mass transfer, and higher ultrasound power applied leads to faster drying rate. The effect of ultrasound power on drying rate decreases along with the reduction of moisture content during drying process. The increase in drying temperature significantly reduces drying time but has a little negative influence on the strengthening effect of ultrasound. D_eff values range from 1.0578?×?10^?10 to 5.4713?×?10^?10?m²/s in contact ultrasound-assisted hot air drying of purple-fleshed sweet potato and increase significantly with an increase in drying temperature as well as ultrasound power. The microstructure of purple-fleshed sweet potato is greatly different at different ultrasound powers during contact ultrasound-assisted hot air drying and shows more microchannels and dilated intercellular spaces in the cross-section of purple-fleshed sweet potato micrographs at higher ultrasound power. Contact ultrasound application during hot air drying could improve the mobility of water and consequently reduce glass transition temperature. Lower color difference and higher rehydration ratio could be achieved as drying temperature decreases and ultrasound power increases. The increase in contact ultrasound power could reduce energy consumption of drying process up to 34.60%. Therefore, contact ultrasound assistance is a promising method to enhance hot air drying process.     

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%.     

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.     

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 the condition of spray-drying on the properties of the polypeptide-rich powders from enzyme-assisted aqueous extraction processing

Abstract

Enzyme-assisted aqueous extraction processing (EAEP) is an environmentally friendly technology that simultaneously extracts both oil and protein. It has shown to be commercial feasibility for high oil recovery (～97%) and favorable protein functionality properties. The present study used soy skim, the liquid co-products obtained using EAEP to produce a polypeptide-rich spray-dried powder. The effects of inlet drying air temperature (140?°C, 160?°C, 180?°C and 200?°C), feed flow rate (3, 6, 9, and 12?mL/min), and solids concentration (25%, 30%, 35%, and 40%) on the properties of the polypeptide-rich powders were investigated. Water activity (a_w), color characteristics, bulk density, Carl Index (CI), Water Solubility Index (WSI), micro-morphology, peptide distribution, and antioxidant capacity were significantly affected by different spray-drying parameters. The results of antioxidant capacity test showed that the spray drying conditions significantly affected the antioxidant capacity of the polypeptide-rich powders. The polypeptide molecular weight size and distribution, the composition of the peptide chain, and the cross-linking with other substances could all affect its antioxidant capacity. Overall, good quality polypeptide-rich powders in terms of physicochemical characteristics, micro-morphology, and functional properties can be produced by spray-drying at an inlet temperature of 160?°C, a feed flow rate of 6?mL/min, and solids concentration of 35%.     

Preparation of goat milk powder with Lactobacillus casei L61 and antioxidant peptides: optimization of the composite thermal protectants and evaluation of storage stability

Abstract

The Lactobacillus casei L61 has great ability for producing antioxidant peptides. For reducing the mortality of L. casei L61 in spray drying process, the Box-Behnken design (BBD) was adopted to optimize the composite thermal protective agent formula. The results exhibited that the composite thermal protective agent formula of L. casei L61 contained glucose at 6.03% (w/v), skim milk at 18.98?g/L, and glycerol at 12.50?mL/L. Under the optimal conditions, the average survival of L. casei L61 in the fermented goat milk reached 14.58?±?0.72% after heat treatment at 75?°C for 10?min, which was higher than the control (13.14%). The average hydroxyl free radical scavenging activity of L. casei L61 reached 85.09?±?0.98%, which was not significantly different from the predicted value (86.83%). Therefore, the BBD is feasible for optimizing the composite thermal protective agent formula of L. casei L61. Under the optimal conditions with the inlet air temperature of 130?°C and feed rate of 4.5?mL/min, the maximum viable counts and survival rate of L. casei L61 were 7.46?×?10⁸ cfu/g and 23.41?±?1.28%, respectively. More importantly, the storage stability of antioxidative probiotic goat milk powder was predicted by temperature acceleration test. The shelf life of antioxidative probiotic goat milk powder was estimated to be 352?days at 4?°C and 117?days at 25?°C, embodying the great long-term stability. This study provides a technical reference for industrialized production of probiotic goat milk powder.     

EFFECT OF DRYING METHOD ON MESOPOROSITY OF RESORCINOL-FORMALDEHYDE DRYGEL AND CARBON GEL

Resorcinol-formaldehyde hydrogels were synthesized by sol-gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution. RF cryogels, RF xerogels, and RF xerogels (MW gels) were respectively prepared from RF hydrogels by freeze drying, hot air drying, and microwave drying. Carbon cryogels, carbon xerogels and carbon MW gels were subsequently obtained by pyrolyzing RF drygels in an inert atmosphere. Freeze drying and microwave drying were effective to prepare mesoporous RF drygels and carbon gels. RF cryogels and carbon cryogels showed high mesoporosity over wide ranges of the molar ratio of resorcinol to catalyst (R/C) and the ratio of resorcinol to water (R/W) used in sol-gel polycondensation. Although RF xerogels had a few mesopores, carbon xerogels had no mesopores. RF MW gels and carbon MW gels showed mesoporosity if appropriate values of R/C and R/W were selected.     

EFFECT OF DRYING METHOD ON MESOPOROSITY OF RESORCINOL–FORMALDEHYDE DRYGEL AND CARBON GEL

Resorcinol–formaldehyde hydrogels were synthesized by sol–gel polycondensation of resorcinol with formaldehyde in a slightly basic aqueous solution. RF cryogels, RF xerogels, and RF xerogels (MW gels) were respectively prepared from RF hydrogels by freeze drying, hot air drying, and microwave drying. Carbon cryogels, carbon xerogels and carbon MW gels were subsequently obtained by pyrolyzing RF drygels in an inert atmosphere. Freeze drying and microwave drying were effective to prepare mesoporous RF drygels and carbon gels. RF cryogels and carbon cryogels showed high mesoporosity over wide ranges of the molar ratio of resorcinol to catalyst (R/C) and the ratio of resorcinol to water (R/W) used in sol–gel polycondensation. Although RF xerogels had a few mesopores, carbon xerogels had no mesopores. RF MW gels and carbon MW gels showed mesoporosity if appropriate values of R/C and R/W were selected.     

Concentration and Drying of Tea Polyphenols Extracted from Green Tea Using Molecular Distillation and Spray Drying

The purpose of this study was to develop a method of combining molecular distillation and spray drying to concentrate and dry tea polyphenols extracts. Molecular distillation and spray drying of tea phenols extracts were performed using an orthogonal array design. The order of importance that influenced molecular distillation was distillation temperature > flux > rotational speed. The optimal conditions for concentration by molecular distillation were 70°C distillation temperature, 10 mL/min flux, and 1,200 n/min rotational speed. Inlet temperature was found to be the most important determinant of spray drying. The order of importance that influenced the spray drying was inlet temperature > feed flux > wind capacity > feed concentration. The optimal conditions for drying of tea polyphenols extracts by spray drying were determined as follows: 170°C distillation temperature, 3 mL/min feed flux, 30% feed concentration, and 30 m³/h wind capacity. Results of this study indicated that the combination of molecular distillation and spray drying was very suitable for the concentration and drying of tea polyphenols extracts. Using this approach to process tea polyphenol extracts can not only maintain the quality of tea polyphenols but also save time and energy.     

Effect of Different Drying Methods and 24-Month Storage on Water Activity,Rehydration Capacity,and Antioxidants in Boletus edulis Mushrooms

This article evaluates the effect of air drying, freeze drying, and 24-month storage at 4 and 20 ^° C on unblanched and blanched Boletus edulis . Water content and activity were lower in freeze-dried mushrooms than in air-dried mushrooms, whereas rehydration capacity showed the opposite tendency. Drying resulted in substantial losses of the following antioxidants: total flavonoids (4–7%), vitamin C (2–36%), β-carotene (26–32%), and total tocopherols (72–81%); total polyphenols increased during air drying (7–17%) and decreased during freeze drying (5–7%). Antioxidant activity increased 1–33% during drying. Storage led to further changes in the quality of dried mushrooms. After 24 months, no vitamin C or tocopherols were detected, and water content and activity were moderately high.     

Kinetics of ultrasound pretreated apple cubes dried in fluidized bed dryer

Abstract

This work evaluated the effect of ultrasonic pretreatment on the production of dehydrated apples (Malus domestica L. var Granny Smith) in a fluidized bed dryer. Cube-shaped apple samples were subjected to ultrasound in an ultrasonic bath and dried in a fluidized bed drier. The experimental design evaluated the effect of ultrasound pretreatment time (0 to 30?min) on the soluble solids loss during pretreatment and on the drying time. The ultrasonic pretreatment was carried out in a bath ultrasound operating at 25?kHz and outputting 55?W/m³ of power density. Distilled water was applied in the pretreatment to produce low-calorie apple cubes. Fluidized bed drying was carried out at 30, 40, and 50?°C. Fick’s law was used to model the drying process and to determine the apparent water diffusivity. The soluble solid loss ranged between 8.7 and 21.2% during the pretreatment, and the apparent water diffusivity during air drying ranged from 1.09?×?10^?6 to 2.81?×?10^?6 m²/min. Ultrasound pretreatment increased the apparent water diffusivity up to 58%. Apple cubes subjected to 20?min of ultrasound pretreatment and dried at 50?°C presented the highest apparent water diffusivity and dried to achieve a water activity of 0.4 in 100?min.     

Influence mechanism of radio frequency heating on moisture transfer and drying stress in larch boxed-heart square timber

Abstract

Radio frequency heating combined with convection (RF/C) drying of larch boxed-heart square timber and its influence on drying kinetics such as rate, moisture content distribution, and stresses was explored. Results revealed that RF heating increased the drying rate and in RF/C drying was twice as high as in conventional drying. Below fiber saturation point, RF heating reduced internal moisture gradients, especially around moisture content of 20%. The effect of RF heating on moisture transfer was strongly associated with moisture content. Specifically, above the fiber saturation point, RF heating played a minor role in moisture transfer however, it reached maximum around fiber saturation point and thereafter, it largely decreased with moisture content. RF heating relieved some drying stresses during RF/C drying and reduced residual stresses in the timber surface layers. Furthermore, it changed the original development pattern of drying stresses in conventional drying.     

Drying Foodstuffs with Superheated Steam

Abstract

A thin-layer superheated steam drier was constructed with the objective of determining the drying characteristics, drying rates, and the effect of superheated steam on product quality in thin-layers. Results from superheated steam drying experiments with sugar-beet pulp, potatoes, Asian noodles, and spent grains indicate that drying times and rates increase with increasing steam temperature. For sugar-beet pulp it was also found that these changes were more significant than increases seen by hot-air drying under the same conditions and that drying rates were not affected by velocity for hot air but were increased for superheated steam. When quality aspects were examined, superheated steam dried Asian noodles saw both beneficial changes to recovery, adhesiveness, and gumminess while parameters of maximum cutting stress, resistance to compression, and surface firmness saw deleterious effects. Spent grains saw high levels of starch gelatinization and retention of fibre content.

     

Ultrasound-assisted fluidized bed drying of paddy: Energy consumption and rice quality aspects

Several studies have been conducted on equipping conventional fluidized bed with some technologies to increase drying efficiency and its performance. The objective of this study was to investigate the influence of high-power ultrasound (HPU) on fluidized bed drying of paddy in terms of drying kinetics, grain quality (percentage of cracked kernels and bending strength of grain kernels), and specific energy consumption (SEC). To decrease the initial moisture content of paddy from 26.5?±?0.5% (kg/kg, d.b) to the final moisture content of 13?±?0.5% (kg/kg, d.b), the experiments were conducted in a factorial design at three levels of ultrasound power densities (11.1, 14.6, and 18.7?kW/m³), four levels of frequencies (20, 25, 28, and 30?kHz), and three levels of drying air temperatures (30, 40, and 50°C). Application of HPU in conjunction with conventional fluidized bed drying led in 23% decrease in drying time as well as improvement in grain quality, in terms of percentage of cracked kernels and bending strengths. In addition, SEC reduced approximately by 22%, as HPU applied at selected drying condition.     

Microstructural evolution and micromechanical properties of thermally sprayed hydroxyapatite coating

ABSTRACT

The effects of preheating and annealing processes on the micromechanical features of thermally sprayed hydroxyapatite (HA) coatings were investigated. The results indicated that subsequent heat treatment at 700°C for 60?min promotes the development of a crystalline HA coating. The EDS line scan showed that the oxygen content was homogeneous along the thickness direction from the coating surface to the titanium–HA interface, whereas the calcium and phosphorus concentration gradually decreased at 7?μm from the interface. From the roughness profiles, the coatings on preheated substrates gave lower roughness compared to the coatings at room temperature. According to the nanoindentation results, the sample preheated at 300°C after annealing at 700°C exhibited an elastic modulus of 108.1?±?6?GPa and hardness of 5.97?±?0.3?GPa, which were almost 3% lower and 171% higher than the bare substrate, respectively.