Radiation Drying Research Articles

Infrared radiation drying of parboiled rice: Influence of temperature and grain bed depth in quality aspects

AbstractThe main objective of this study was to optimize the infrared radiation (IR) drying of parboiled rice on the temperatures of 70, 100, and 130°C and grain bed depth of 5, 10, and 15 mm. The effects of the temperature and grain bed depth on drying kinetics, head rice yield (HRY), milling and color parameters, and cooking properties were evaluated using response surface methodology. The drying temperature and bed depth presented a significant effect on HRY, whiteness, transparency, milling degree, L*, C*, relative crystallinity, cooking time, leached amylose, solubilized protein, and hardness. The longer exposure times to IR resulted in grains with an increase in the intensity of endosperm fissures and lower HRY. There is a tendency that the best condition to dry parboiled rice with IR is at higher temperatures and lower grain bed depth.Practical applicationsThe present study optimized infrared radiation drying of parboiled rice as a function of the drying temperature and grain bed depth. The results provide scientific support on making decision during industrial rice processes. Severe infrared radiation drying conditions can reduce the HRY, increase cooking time, and intensify undesired sensory attributes.

Transition to Elliptic Equations in the Study of Asymptotic Modes of Electromagnetic Drying

The initial boundary value problem for calculating the temperature and moisture content fields for electromagnetic drying of a sample with a capillary-porous structure and arbitrary geometry is formulated. An algorithm has been developed for numerical investigation of time-asymptotic fields of heat and mass transfer that occur after the decay of transients. It is shown that in the transition to asymptotics, the original non-stationary initial boundary value problem for two related parabolic equations can be replaced by two independently solvable stationary boundary value problems for elliptic equations. Due to the change in the problem statement, the algorithm for numerical study of the electromagnetic drying process is significantly simplified, becomes convenient for correction and debugging, and the results obtained using it, allowing for visual interpretation, allow us to determine the effect on drying of each of the various parameters and functions included in the mathematical model. In turn, this makes it possible to solve the problems of organizing optimal modes of radiation drying by simple means.

Infrared radiation drying of Moringa oleifera grains for use in water treatment

ABSTRACT This study aimed to evaluate the effects of using infrared radiation in the hot-air drying of Moringa oleifera grains on the inner dryer and grain temperatures, energy consumption, and grain quality. An experiment was conducted in a factorial scheme in 2013 to identify the optimum values of the air temperature (30 to 58 ºC) and infrared radiation application time (2.0 to 4.8 min) on moisture content, drying time, drying rate, inner dryer air temperature, grain temperature, energy consumption and quality of grains used as a natural coagulant for water treatment. The results obtained were moisture content from 4.40 to 4.76% wet basis; drying time from 0.50 to 2.00 h; drying rates from 0.70 × 10-3 to 2.05 × 10-3 kgwater kg-1 dry matter min-1; inner dryer air temperatures from 42.24 to 61.82 ºC; grain temperatures from 56.32 to 76.19 ºC; energy consumptions of the fan from 0.05 to 0.20 kWh, electrical resistances from 1.41 to 4.49 kWh; resistances of the infrared heaters from 0.48 to 1.56 kWh; water turbidities from 1.36 to 5.76 NTU; grain protein contents from 34.93 to 37.93%; and peroxide value of grains from 0.009 to 0.052 meq kg-1. Both evaluated factors increased the inner dryer air temperature and grain temperature. The electrical resistances contributed the most to the energy consumption. However, the infrared radiation reduced this consumption. The drying performed with air temperature of 44 °C and infrared radiation time of 3.4 min resulted in the highest protein concentration in the Moringa oleifera L. grains and in greater removal of the water turbidity in the water treatment.

Comparison of quality aspects and energy consumption of restructured taro and potato chips under three drying methods

AbstractDue to a high variety of health effects, nutritive snacks based on carbohydrate and dietary fibers are receiving growing attention in snack food production. The restructured chips were prepared by mixing of rose powder and other ingredients into restructured taro (TR) and potato (PR). Restructured (TR) and (PR) chips were dried using freeze‐drying (FD), infrared radiation drying (IRD), and hybrid infrared‐assisted freeze‐drying (IRFD) in this study. Investigation of three drying methods in terms of the main quality parameters, namely color, odor, texture, water activity, expansion ratio (ER), and bulk density as well as other quality aspects and energy consumption of two kinds of chips were compared. FD took the highest energy consumption and longest processing time together with the lowest drying rate among them. IRFD chips had the lowest water activity (aw), the total color difference (ΔE), and the highest overall acceptability score of sensory evaluation among them. IRFD had higher crispness and lower energy consumption than FD alone. Moreover, there were no significant differences in crispness between IRFD and commercial chips. IRFD chips contributed better product quality over IRD chips. Results of this work showed that IRFD method has the potential to keep high‐quality aspects for dried restructured chips with saving energy consumption.Practical applicationsInfrared‐assisted freeze‐drying (IRFD) can save 25–29% of drying time and 43–46% of the total energy consumption in comparison of FD with keeping high‐quality aspects and better product quality than IRD. IRFD method is a novel method for making food products with better color, maintains high‐quality, and less drying time. The research found that hybrid IRFD can produce high‐quality aspects as well as save time and energy consumption for large‐scale industrial production of restructured chips and various food products.

Effect of contact ultrasonic power on moisture migration during far‐infrared radiation drying of kiwifruit

AbstractIn order to explore the effect of direct contact ultrasound (DCU) on moisture migration during far‐infrared radiation (FIR) drying of kiwifruit, the drying characteristics, microstructure, water status, and moisture change of kiwifruit slices during drying were investigated based on scanning electron microscopy (SEM), low‐field nuclear magnetic resonance (LF‐NMR), and magnetic resonance imaging (MRI). The results showed that the drying time at ultrasonic power of 54 W was 40% shorter than that without DCU application. SEM observation verified that higher ultrasonic power could produce more and larger microcapillaries in the microstructure of kiwifruit slices, which was beneficial for moisture migration. LF‐NMR detection indicated that water mobility and distribution in kiwifruits changed during drying. The relative proportion of free water in kiwifruits decreased from 70 to 0% with the prolongation drying time at different ultrasonic powers, the removal time for free water at ultrasonic power of 54 W was 57% shorter than that without DCU application during FIR drying, and higher ultrasonic power could accelerate the shifting of water in different states. MRI results illustrated that the DCU application at higher ultrasonic power could promote moisture migration and water removal during FIR drying, and then increase drying rate.Practical applicationsDrying is a commonly utilized process method in food and agricultural industry. Far‐infrared radiation (FIR) drying, as one of the modern drying methods, has desirable advantages including high‐energy efficiency and uniform heating. However, it has unsatisfied promoting effect on internal mass transfer. Ultrasound has significant positive effect on moisture diffusion and water removal. In this study, direct contact ultrasound (DCU) was applied in FIR drying of kiwifruit slices. The study verified that the DCU application in FIR drying could promote drying rate, produce loose microstructure, and shorten drying time significantly. The increase in ultrasonic power could accelerate moisture migration and mass transfer to facilitate water removal. Therefore, DCU application with higher ultrasonic power is beneficial to increasing drying rate and reducing drying time of FIR drying, and FIR drying technology combined with DCU is promising in food industry and can be developed for other food products.

Effects of far-infrared radiation temperature on drying characteristics, water status, microstructure and quality of kiwifruit slices

Far-infrared radiation (FIR) drying is an advanced technique that has recently been applied in food processing. In order to reveal the effects of FIR temperature on dehydration process and quality characteristics of kiwifruit slices, FIR drying experiments on kiwifruit slices were conducted. Low-field nuclear magnetic resonance, scanning electron microscopy, colorimeter and chemical analysis were applied to explore the dynamic water states, microstructure, color changes and nutritional components of kiwifruit slices at different FIR temperatures. The results showed that drying time reduced by 57.9% and average drying rate increased by 137.5% as FIR temperature increased from 120 to 280 °C. The water mobility and distribution in kiwifruits changed with the extension of drying time, and increasing FIR temperature could accelerate the migration and removal of moisture. Higher FIR temperature could produce more cavities and larger channels in dried samples. An increase in FIR temperature decreased L* but increased a* values of dried kiwifruits and affected total phenolic content, total flavonoids content and Vitamin C content. Therefore, FIR drying is a promising method to improve drying rate as well as protect product quality of kiwifruit slices.

Comparison of mass and heat transfer properties of kelp when dried by radiation or conduction using a novel superheated steam system with built-in heat recovery unit

Kelp is an aquatic product that must be dried after harvest to prevent spoilage. This study tested a novel system for drying kelp. It utilized superheated steam for heating and could recover the latent heat of the exhausted steam, for further drying of the product. The system was tested in four drying modes, including single-face radiation drying mode (SRDM), double-face radiation drying mode (DRDM), single-face conduction drying mode (SCDM), and combined conduction and radiation drying mode (CCRDM). A one-dimensional semi-empirical mathematical model was used to predict the change in the moisture content and temperature of kelp during drying in each of the four drying modes. The drying characteristics of standardized kelp samples in each drying mode were investigated and the efficiency of heat recovery was assessed and compared. The change in moisture content and surface temperature of kelp during drying in each of the four drying modes was also predicted. The results showed that the drying characteristic of the kelp differed significantly depending on the drying mode. The CCRDM was determined as the optimal drying method and exhibited the best drying characteristics, including the highest kelp surface temperature, shortest drying time, and fastest drying rate. Compared to SRDM, DRDM and SCDM, CCRDM recovered, 83.3, 79.5, and 4.5% more energy from the system, and was the most energy efficient among 4 operation modes. Compared with changes in moisture, the changes in the surface temperature of kelp were more accurately predicted during drying.

Cinética del secado de coco por radiación

El coco es una fruta que puede aprovecharse completamente desde su parte líquida hasta su parte sólida, considerando la parte alimenticia y los residuos. La parte sólida puede utilizarse directamente como alimento, también puede ser procesado para su uso posterior. El secado es un proceso necesario para su conservación, por lo tanto se evaluó el secado por radiación para establecer la relación entre rapidez y temperatura del proceso. Se utilizaron las temperaturas de 60, 80,100 y 120 °C. El coco fue extraído, molido y homogenizado manualmente. Se utilizó un deshidratador con transmisión de calor por radiación en cuatro temperaturas de proceso. El contenido de humedad fue determinado por la pérdida de masa hasta obtener peso constante en una capa delgada de producto. Se determinó que durante secado, el contenido de humedad es exponencialmente decreciente y el modelo matemático de Midilli se ajustó adecuadamente con un coeficiente de determinación (R2) mayor al 94 %. El efecto de la temperatura en la rapidez del proceso se ajustó con la ecuación de Arrhenius. Se determinó que la energía de activación del proceso de secado por radiación en coco fue de 60,7 kJ/mol. La relación matemática de la rapidez del secado es una doble exponencial que depende directamente de la temperatura y el tiempo de secado.

Radiation-convective conveyor drying of basalt - bentonite cardboard

The manuscript presents the results of the research of the kinetics of radiation drying of basalt-bentonite cardboard. It has been established that in the case of high-temperature radiation drying of cardboard, the value of the reduced first critical moisture content in the area with low values – 0.17 is observed; compared to the same indicator for convective drying of slabs 50 and 100 mm thick - 0.41 and 0.20, respectively. This feature of the process allows you to raise the temperature in the first drying chamber to 570-600°C without fear of local overheating of the material. It was noted that at the stage of the falling drying speed, which is largely implemented in the second drying chamber, in order to avoid local overheating of the material, the temperature in the chamber is limited to 440°C. The decrease in the temperature level of the process in the second drying chamber is compensated for by the active gas-dynamic environment, in which the average speed of the drying agent in the inlet action zone can reach values of ± 5 m/s. The results of the controlled operation of the pilot conveyor drying installation are given. Its satisfactory specific energy indicators are noted, which for the same type of installations can reach values of 1200-2000 kcal/kg of moisture. In conclusion, it is noted that, in addition to the traditional positions of the heat balance of the plant, an energy-efficient modernization of a conveyor drying plant should include reducing losses with a spent drying agent, with recuperative losses through walling structures, with unorganized gas exchange in the drying chamber, and such positions as efficient drying agent with the optimization of its gas dynamics in the drying chamber.

Evaluation of sensory, textural, and nutritional attributes of shiitake mushrooms (Lentinula edodes) as prepared by five types of drying methods

AbstractThe effect of freeze drying (FD), far‐infrared radiation drying (FIRD), heat pump drying (HPD), hot air drying (HAD), and hot air combined instant controlled pressure drop drying (DIC) were compared on the drying efficiency and quality attributes of dried shiitake mushrooms. The results showed that in comparison with the HPD, HAD, and DIC, the FIRD shiitake mushroom exhibited better appearance with less shrinkage and lower ΔE (6.10), lower hardness (34.82 N), and higher rehydration ratio (7.55), which were more resemble to those of the FD sample. Besides, a significantly higher (p < 0.05) retention of protein was found in the FD and FIRD sample (2.47 mg/g and 2.30 mg/g), as well as higher retention of polysaccharide (1.79 mg/g and 1.39 mg/g). In addition, FIRD shiitake mushroom were superior to FD product in terms of saving drying time as 66.25% and exhibiting maximum numbers of flavor components, among which specific sulfides showed the highest percentage (24.59%). Therefore, the FIRD dried shiitake mushroom obtained a better overall quality among the products dried by the five drying methods.Practical applicationsShiitake mushrooms are wildly planted edible fungi, which are consumed mostly in dried form around the word. Recently, the demand of efficient application have promoted an increasingly use of novel drying technologies in mushroom processing. This study presents comprehensive evaluations on some vital quality attributes of shiitake mushrooms using five drying methods that already commercialized in China. FIRD was more suitable to produce dried shiitake mushrooms with desirable appearance and texture, as well as relatively rich flavor and nutrients.

Characterization of water status and water soluble pectin from peaches under the combined drying processing

Characterization of water status and water soluble pectin (WSP) from peach were evaluated after different stage of combined drying in which osmotic dehydration (OD) was considered as the pre-treatment prior to instant controlled pressure drop (DIC) - assisted infrared radiation drying (IRD) (IR-DIC). Results showed that the contents of free water and immobilized water decreased to 0 g after the combined drying. The content of bound water increased after IRD treatment. The residual PME activity in peach slices was 153.3–179.6% after OD treatment, while, the PG were totally inactivated after IRD. The degree of esterification (DE), WSP content and average molar mass (Mw) decreased significantly (from 75.00 to 43.74, from 156.00 to 74.91 mg/g AIR and from 2.28 to 0.49 × 105 Da, respectively) after the combined drying. The neutral sugar of WSP was mainly composed by galactose, arabinose and rhamnose, whose contents decreased after the combined drying. However, OD treatment would slow down the degradation. There was a low peak at 1740 cm−1 in FT-IR spectrum observed for WSP after IRD and DIC treatment, which might illustrate the degradation of WSP during the combined drying.

Convective and infrared drying assisted by capillary drainage of spirulina: a real possibility to reduce the energy consumption

The aim of this work was to investigate the energy efficiency of infrared radiation drying (labeled IR) and hot air drying (labeled HA) of spirulina assisted by capillary drainage (labeled DC). Capillary drainage effect was introduced by a porous material (filter paper) placed under a thin layer of spirulina biomass of 3 mm thickness. Infrared drying experiments were performed using a laboratory IR-30 moisture analyzer while convective drying experiments were realized in a pilot-scale drying tunnel. The spirulina was dried at two initial moisture contents on dry basis; 5 kg/kg and 7 kg/kg. For both infrared and convective processes, the drying temperature range was 50 to 80 °C and the air velocity was 0.5 m/s. The air humidity was not controlled but calculated for each temperature from the dry and wet bulb temperatures. The drying kinetic coefficients were identified by fitting the falling rate drying period data by Lewis semi-empirical model. According to our results, the capillary drainage provided a real possibility to dry faster and thus reduces the energy consumption for both infrared and convective drying processes. The time reduction percentage, averaged over the range of the operating conditions, was around 60% for infrared drying and 40% for convective drying. Moreover, the mean maximum drying rate was much higher for IR-DC drying (2.091.10−3 kg/kg s−1) than HA-DC drying (1.115.10−3 kg/kg.s−1). As concerns, the kinetic drying coefficient, this parameter was significantly increased by the presence of the porous material essentially for infrared drying.

Effect of different drying methods on the product quality and bioactive polysaccharides of bitter gourd (Momordica charantia L.) slices

In this study, three drying methods, namely, hot-air drying, freeze drying (FD), and infrared radiation drying (ID), were applied to dry bitter gourd (Momordica charantia L.) slices. Results showed that the drying methods had significant influences on appearance, color, rehydration ratio, and microstructure of dried bitter gourd. FD provided high-quality dried bitter gourd products due to the uniform honeycomb network and less collapsed structure. Three water-soluble bitter gourd polysaccharides (BPS-H, BPS-F, and BPS-I) were obtained from the bitter gourd dried using the three drying methods. The three polysaccharides exhibited similar preliminary structural characteristics with different monosaccharide compositions and molecular weights. BPS-I obtained from ID-dried bitter gourd had higher sugar and uronic acid contents than BPS-H and BPS-F. BPS-I exhibited stronger antioxidant activities and bile acid-binding capacity in vitro than BPS-H and BPS-F. Moreover, BPS-F and BPS-I showed significant α-amylase inhibitory activities in vitro.

Contact ultrasound strengthened far-infrared radiation drying on pear slices: Effects on drying characteristics, microstructure, and quality attributes

In order to investigate the feasibility and the enhancing effect of contact ultrasound application during far-infrared radiation (FIR) drying, a contact ultrasound strengthened FIR (CUFIR) drying equipment was fabricated and used, and CUFIR drying experiments on pear slices were carried out to explore the synergetic effects of ultrasound power and FIR heating on drying characteristics, microstructure, and quality of dried pear products. The results show that the application of contact ultrasound could be obviously helpful to accelerate internal mass transfer in pear slices and improve the drying rate of FIR drying, and higher ultrasound power could lead to stronger strengthening effect. The enforcing effect of ultrasound increased at higher FIR power, and weakened with the reduction of moisture content during CUFIR drying. The Deff values ranged from 4.76 × 10−10 m2/s to 13.94 × 10−10 m2/s in this study and the increase of both FIR power and ultrasound power had significant and positive influence on the increasing of Deff values. With scanning electrical microscope (SEM), it was observed that the improvement of ultrasound power could enlarge the size of microcapillaries and even generate new micropores and microchannels on the ultrasound-treated surface and in the organism structure of pear slices. The increase of ultrasound power could improve total phenolic content (TPC) and total flavonoids content (TFC) of pear slices at FIR powers of 100 and 220 W. Yet, the application of contact ultrasound with ultrasound power of 60 W had negative influence on TPC and TFC at FIR power of 340 W. Although the ascorbic acid content (AAC) reduced as FIR powers increased during FIR drying without contact ultrasound assistance, the increase of ultrasound power could improve AAC at all FIR powers. The CUFIR drying at ultrasound power of 60 W and FIR power of 220 W achieved the lowest energy consumption. Therefore, the application of FIR drying combined with contact ultrasound is a promising method to improve drying rate as well as protect product quality.

Effects of infrared radiation drying and heat pump drying combined with tempering on the quality of long‐grain paddy rice

AbstractThe objectives of this study were to study the effects of two drying methods, infrared radiation (IR) drying and heat pump (HP) drying, combined with tempering in the glassy state on the quality of long‐grain paddies (O. sativa L. subsp. indica) and the effects of intermittent ratios (δ = 0, 1, 2, 3, 4) on the milling properties and texture profiles of the paddies. The tempering temperature was set at 60 °C, according to the glass transition temperature (Tg) of the paddy rice, which was determined to be 58 ± 2 °C using low‐field nuclear magnetic resonance (LF‐NMR) technology. The results showed that, compared with HP drying, IR drying resulted in a higher drying rate and was more effective, but the rate of moisture reduction was more uniform under HP drying. The tempering process had positive effects on the milling and texture profile analysis (TPA) properties of the paddy rice. Overall, intermittent ratios of δ = 3 and δ = 2 are recommended for HP drying and IR drying, respectively. However, no significant differences in the effects of different drying methods and intermittent ratios on water diffusion in the paddy rice were found through MRI analysis.

Influence of infrared drying on storage characteristics of brown rice

The aim of this study was to improve storage characteristics of brown rice by using infrared radiation drying (IRD) through comparison with hot air drying (HAD) and ambient air drying (AAD). After heating by IR from 20 °C to 60 °C within 58 s, 2.17 percentage points moisture of rough rice (initial moisture content is 25.0 ± 0.2% in dry basis) were removed without adverse effect on germination capacity of husked brown rice. Compared with AAD, IRD slowed down the increase in yellowness, water uptake and volume expansion ratio of brown rice by 47.9%, 41.0% and 37.9% after four months of storage, and decreased the temperature range and enthalpy of gelatinization, the peak and breakdown viscosities. These changes might due to the higher stabilization effect of IRD on the microstructure and thermal properties of proteins and starch granules than AAD. IRD is an effective method to improve storage stability of brown rice.

ПОВЫШЕНИЕ ЭФФЕКТИВНОСТИ ПРОЦЕССОВ РЕКТИФИКАЦИИ БЕНЗОЛА И ВЛАГОУДАЛЕНИЯ ИЗ КУБОВОГО ОСТАТКА ДЛЯ ЕГО УТИЛИЗАЦИИ

When rectifying benzene, bottoms residue is formed, which is a composition of non-hydrated aromatic hydrocarbons. Its utilization is possible by using it in the printing industry for the production of solvents, industrial oils, SO2 and sulfuric acid, soot, carbon black. In addition, alkaline waters from benzene rectification are used to remove carbonate deposits from oil wells, as well as additives to road tar, etc. For convenience of storage, transportation and use, it is advisable to obtain alkaline waters in dry form. Due to the fact that alkaline waters are a surfactant, a variant of drying by means of coating the working surface by foam extruders with a volumetric IR energy supply is chosen for it. As a result of the carried out experimental studies, their analysis and mathematical processing, there have been obtained approximating equations of dependence of specific productivity of the process on influencing factors, as well as equations of dependence of the IR drying rate of alkaline waters on their moisture content. On the basis of empirical study of kinetic regularities of radiation drying of alkaline waters, a method is chosen and a rational regime for the process is justified; mathematically adequate dependences of the specific productivity and the rate of moisture removal from the influencing factors are obtained. Compared with spray drying, specific yield of the finished product is 3 times higher with IR drying and amounted to 24 kg/(m3 ∙ h)) with 20% reduction in energy costs. It has been stated that for organizing a rational method of drying alkaline waters from benzene rectification, it is expedient to maintain the following regime parameters of dehydration: С н = 0.5 kg/kg, Ер = 3.23 kW/m 2, d н = 4 mm

INVESTIGATION OF INFRARED DRYING OF POMEGRANATE BY-PRODUCTS

In the present study, infrared radiation drying, representative of the innovative drying method, was chosen to perform comparative study at different infrared power levels. Infrared drying of pomegranate by-products was dried at 88, 104, 125, 146 and 167 W power levels. The results showed that the infrared power has a significant effect on the drying characteristics of pomegranate by-products. Drying time was reduced from 270 to 60 min as the infrared power level increased from 88 to 167 W. The falling-rate period proved to be the main stage of infrared drying. Three thin-layer drying models (Aghbashlo et al., Jena & Das and Midilli & Kucuk) were fitted to the experimental data. The drying data (moisture ratio versus drying time) were successfully fitted to Aghbashlo et al. model. Fick’s law of diffusion was used to determine the effective moisture diffusivity, which varied between 3.296×10 −9 to 1.431×10 −8 m 2 /s. Activation energy was estimated by a modified Arrhenius type equation as 4.424 kW/kg.

Alternative Manufacturing Concepts for Solid Oral Dosage Forms From Drug Nanosuspensions Using Fluid Dispensing and Forced Drying Technology

Flexible manufacturing technologies for solid oral dosage forms with a continuous adjustability of the manufactured dose strength are of interest for applications in personalized medicine. This study explored the feasibility of using microvalve technology for the manufacturing of different solid oral dosage form concepts. Hard gelatin capsules filled with excipients, placebo tablets, and polymer films, placed in hard gelatin capsules after drying, were considered as substrates. For each concept, a basic understanding of relevant formulation parameters and their impact on dissolution behavior has been established. Suitable matrix formers, present either on the substrate or directly in the drug nanosuspension, proved to be essential to prevent nanoparticle agglomeration of the drug nanoparticles and to ensure a fast dissolution behavior. Furthermore, convection and radiation drying methods were investigated for the fast drying of drug nanosuspensions dispensed onto polymer films, which were then placed in hard gelatin capsules. Changes in morphology and in drug and matrix former distribution were observed for increasing drying intensity. However, even fast drying times below 1 min could be realized, while maintaining the nanoparticulate drug structure and a good dissolution behavior.

Effect of drying methods on physico-chemical properties and antioxidant activity of Dendrobium officinale

The present study aimed to investigate the effect of different drying methods, i.e., sun drying (SD), hot air drying (AD), vacuum drying (VD), infrared radiation drying (IR), and freeze drying (FD) on the physico-chemical properties of Dendrobium officinale. The results revealed that different drying methods showed significant differences in the color retention, water soluble polysaccharide content, total phenolic content, total flavonoid content, fatty acids, and antioxidant activities. FD, VD, IR and AD led to higher retention of bioactive compounds and better antioxidant activities, and FD showed the best. However, with respect to the water-soluble polysaccharides content, the characteristic components in D. officinale, AD was better than FD. The results showed that the quality of D. officinale depends on the drying method applied. Considering the retention of polysaccharide content and drying processing duration, AD is a promising treatment for D. officinale.