Hong-Wei Xiao | China Agricultural University (original) (raw)
Papers by Hong-Wei Xiao
Tang, Glass transition and state diagram for freeze-dried Lentinus edodes mushroom, Thermochimica... more Tang, Glass transition and state diagram for freeze-dried Lentinus edodes mushroom, Thermochimica Acta
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The drying characteristics of yam slices under different constant relative humidity (RH) and step... more The drying characteristics of yam slices under different constant relative humidity (RH) and step-down RH levels were studied. A mass transfer model was developed based on Bi-Di correlations containing a drying coefficient and a lag factor to describe the drying process. It was validated using experimental data. Results showed that the drying air with constant RH levels of 20%, 30%, and 40%, temperature of 60 oC and air velocity of 1.5 m/s had insignificant effect on drying time. This phenomenon was likely attributed to the fact that higher RH lead to rapidly increment of sample’s temperature. Afterwards, higher sample’s temperature could provide an additional driving force to water diffusion and thereby promoted the moisture movement which could minimize the negative effect of lower drying rate in the initial drying stage. Applying air with 40% RH for 15 min in the initial stage achieved the desired color and reduced the drying time by 25% compared to the drying time under continuous dehumidification from an initial RH of 40%. Using the developed Bi-Di correlation, the estimated Biot number, effective moisture diffusivity and mass transfer coefficient ranged from 0.1024 to 0.1182, from 1.1133×10-10 to 8.8144×10-9 m2/s and from 1.8992×10-9 to 1.7364×10-7 m/s, respectively. A rather high correlation coefficient of determination (R2 ranged from 0.9871 to 0.9971) was determined between the experimental and predicted moisture contents. The present findings contributed to a better understanding of the effect of relative humidity on drying characteristics. The developed Bi-Di correlation provided a new method to determine the effective diffusivity of moisture in drying.
The influences of different osmotic solution pretreatments (sucrose, glucose and maltose with con... more The influences of different osmotic solution pretreatments (sucrose, glucose and maltose with concentration of 45%) on the volatile compounds, phenolic compounds and other physicochemical parameters in frozen mangoes were studied. Volatile and phenolic compounds were measured using SPME/GC-MS and HPLC method, respectively. The results revealed that compared with untreated frozen mango, some volatile compounds (e.g. alcohols, aldehydes and some terpenes and esters) increased significantly and there were more compounds identified in osmo-dehydrofrozen samples. These changes positively affected mango aroma and resulted in higher sensory scores for osmo-dehydrofrozen samples. In addition, data on phenolic compounds showed that dehydrofrozen samples pretreated in glucose and sucrose had higher q-hydroxybenzoic acid and quercetin contents, respectively, while samples pretreated in maltose showed higher q-coumaric acid and sinapic acid contents compared with untreated frozen samples. The current work indicates that osmo-dehydrofreezing can improve the retention of phenolic and aromatic compounds in frozen mango.
Because the eggplant widely planted all over the country, but the moisture content and the shelf ... more Because the eggplant widely planted all over the country, but the moisture content and the shelf life of fresh eggplant is high and short, so harvest eggplants should be dried and dehydrated in time. But how to achieve high quality dried products is one of the important direction in drying research. Chemical impregnation process is a novel pretreatment technology, ethanol as a chemical with the advantages of penetration fast, easy to evaporate, no chemical residues and harmless to the human body, and which has been applied to the pretreatment of fruit and vegetable. In order to improve the drying quality of eggplant slices and shorten the drying time, the eggplant slices were dipped in ethanol before hot air drying. The effects of different drying temperature (45, 55, 65℃)，pretreatment of ethanol concentration (0, 5%, 15%) and slice thickness (1.0, 1.5, 2.0 cm) on drying rate, color, rehydration ratio and micros microscopic structure were investigated throught orthogonal experiments in this paper. Results showed that drying temperature, ethanol concentration of pretreatment and sample thickness have significant effects on the drying processing. In addition, the sample thickness was most significant, followed by drying temperature, and ethanol concentration of pretreatment．The drying time decrease with the increase of temperature, increases with the increase of the slice thickness of the eggplant, increased then decrease with the increase of the alcohol concentration. The whole drying process occurred in falling rate period. According to Fick′s Second Law, the water effective diffusion coefficient (Deff) was determined and the Deff ranged from 2.74×10-9 m2/s to 7.75×10-9 m2/s．The sample thickness has greater impact on rehydration ratio compared with sample thickness and ethanol concentration. Furthermore, the rehydration ratio decreased as the thickness increased. The ethanol concentration has important influence on color parameters of dried eggplant slices, but the effect of eggplant thickness and temperature on the colour and lustre is not significant, which is far less the ethanol concentration of pretreatment effects on the colour and lustre. And the pretreatment with ethanol also can change the microstructure and appearance quality of the dried samples. After eggplant is dipped with low concentration of ethanol, the moisture of which will be faster evaporated and send out of the eggplant internal free water in the drying, improve the drying rate; And after eggplant is impregnated with high concentration of ethanol, ethanol makes eggplant internal nutrient composition change, which make its structure more compact, and prevent moisture migration in the process of drying. Taking account of the drying rate and quality attributes, drying at 55℃, with ethanol concentration of 15%, and sample thickness of 1.5 cm was recommended as the most favorable conditions for eggplant slices drying. The present findings indicated that ethanol dipping pretreatment can not only enhance drying rate but also improve color attributes of dried products. The results provide a theory reference for the rapid drying of high quality eggplant slices.
摘 要：为了开发植物源脐橙贮藏保鲜技术，该文研究了川芎提取液在离体和活体条件下对采后脐橙的主要致腐菌意大 利青霉和指状青霉的抑制作用，以及对贮藏期脐橙品质和生理生化的影响。结果显示：在离体条件下... more 摘 要：为了开发植物源脐橙贮藏保鲜技术，该文研究了川芎提取液在离体和活体条件下对采后脐橙的主要致腐菌意大 利青霉和指状青霉的抑制作用，以及对贮藏期脐橙品质和生理生化的影响。结果显示：在离体条件下，川芎提取液对 2 种供试菌种有显著的抑制作用(P<0.05) ，最低抑菌质量浓度均为 25.00 mg/mL；在活体条件下，川芎提取液能有效抑制 2 种病原菌在脐橙上的生长，且质量分数为 4%效果较好，与体积分数为 50%乙醇处理的对照相比，差异显著(P<0.05) ； 在脐橙采后贮藏中，川芎提取液对脐橙的防腐保鲜效果与其质量分数相关，其中质量分数为 4%的效果较好，与蒸馏水处 理的对照相比，能够显著(P<0.05)降低采后脐橙的腐烂率、失重率和丙二醛含量，延缓总酸的下降，以及诱导过氧化 物酶活性上升，有利于维持可溶性固形物和总糖质量分数，而对维生素 C 和果皮色泽的变化无显著影响(P>0.05) 。结果 表明，川芎提取液用于脐橙贮藏保鲜切实可行，研究结果为脐橙天然保鲜剂的开发及脐橙在贮藏、运输和销售期间防腐 保鲜提供参考。
Medicinal herbs are economically and nutritionally important plants, which are rich in health-pro... more Medicinal herbs are economically and nutritionally important plants, which are rich in health-promoting compounds. Herbs are the backbone of both the traditional Chinese and Indian medicine, which has long history as part of their culture. Ensuring the quality of herbs is a crucial step for integrating the traditional medicine into science-based modern medicine. Drying is an essential technique in preservation of herbs as it affects directly the quality attributes of the dried products, whereas many producers lose much profit due to poor drying techniques. So, employing a suitable drying technology and selection of appropriate drying conditions are very important for producing high quality herb products. The aim of this article is to summarize the advances in drying technologies of medicinal plants, describe the current status and identify future research opportunities. The current work provides more data and information for selecting optimum technology for herb drying and would trigger innovative drying technologies to enhance drying kinetics and quality of herb drying.
Box type hot air dryer was widely used for agriculture products because of its simple structure a... more Box type hot air dryer was widely used for agriculture products because of its simple structure and convenient operation. How to shorten drying time, reduce energy consumption and improve products’ quality becomes one of the important directions of research. As to the material which is easily to be crusting in the surface, It is expected that with high relative humidity pretreatment and after that the relative humidity can be reduced to enhance drying rate. In this circumstance, the temperature and moisture gradient between sample and drying air become consistent and high efficient drying process could be achieved. However, it is difficult to confirm the magnitude of the relative humidity of each step and its keeping time in step down drying process. It is expected that material’s temperature and relative humidity of the hot air were the main two factors that have a significant influence on the drying process. High hot air drying temperature leads to high material’s temperature so that drying time can be reduced. Material’s internal moisture movement towards surface can be accelerated because of material temperature increment. Besides, the vapor partial pressure difference between material’s surface and drying medium can be increased by reducing drying relative humidity, which can improve drying rate. In addition, material’s temperature and relative humidity of drying hot air were the two aspects which reflect the mass transfer and heat transfer of the drying procedure. High relative humidity can increase material’s temperature but decrease drying rate. Conversely, low relative humidity may increase drying rate but hinder increment of material’s temperature. The material’s temperature curve during drying combined with drying procedure can be divided to initial preheating period, medium-term temperature increment period and late drying period. So according to material’s temperature, drying period can be specified and then relative humidity can be controlled so that drying process can be optimized. In this paper, the control of relative humidity was designed for internal recycle hot air drying technology. In initial pre-heating period, relative humidity was set at a high value. And the material’s temperature was raised rapidly. When the material’s temperature slowly increment trend was detected by the auto control program, the drying process transit to medium- term drying procedure. In this period, material’s temperature was kept at a specific value with the moisture removing fan open. When the material’s temperature began to increase, moisture removing fan was closed to heat material. When material’s temperature approached to drying hot air temperature or material’s temperature can’t rise rapidly, drying process transited to late drying period. Carrot was adopted to test the performance of the auto control relative humidity program. The experiment result showed that in the way of self adaptive control of relative humidity, the max maximum deviation of relative humidity was 1% in the preheating period and the material keeping drying temperature under dehumidifying increased gradually. The max error between the set temperature and achieved temperature was 0.8 oC。In the last drying period, the drying end time judge by the moisture content in 15 min was 9 min later than judging by weighing method. Drying time was reduced by 19.7% compared to the drying conditions of 50% relative humidity in the initial period and 20% in the late period as well as the drying condition of 50% relative humidity pretreatment and removing moisture continuously afterwards. The present work come up with a new way of control relative humidity in internal recycle hot air drying technology, which is useful for enhancing drying rate.
In current work, the drying kinetics and evolution of sample's core temperature and moisture dist... more In current work, the drying kinetics and evolution of sample's core temperature and moisture distribution of yam slices during convective hot air drying were investigated. In the terms of drying kinetics, the effect of drying temperature (50, 55, 60, 65, 70 o C), relative humidity (20%, 30%, 40%, 50%) and sample thickness (5, 7, 9 mm) on drying characteristics of yam slices were studied. Results indicated that all the three factors had significant influence on the drying kinetics, whereas drying temperature gave the most significant effect, followed by relative humidity and sample thickness. Moisture effective diffusivity and activation energy were calculated and it was found that the diffusivity was in the range of 5.5454×10 -10 to 1.0804×10 -9 m 2 /s and the activation energy was 29.528 kJ/mol. Heat and mass transfer models were developed based on the finite element method to calculate the core temperature and moisture distribution of yam slices during drying.
Recently, infrared radiation heating has been widely applied in different thermal processing syst... more Recently, infrared radiation heating has been widely applied in different thermal processing systems in food industry.
It has several advantages such as high efficiency, low energy consumption, and high quality of dried products. In addition, the
heating power generated from infrared radiation can penetrate into food materials. But the electric radiant infrared heater, such
as ceramic infrared heater and gas-fired infrared radiator, has the some drawbacks e.g., large structure and high heating
temperature, which lead to higher energy consumption of infrared drier. In order to explore the drying characteristics of carbon
fiber and develop a new heating technology of infrared drying, the drying characteristics of banana slices, apple slices, carrot
slices and agaric were investigated in a carbon fiber infrared heating. The material internal temperature, ambient temperature,
ambient humidity of drying process were detected during drying process. Result indicated that: 1) Far-infrared waves in the
rage of 1-30 μm could be launched by the carbon fiber heating board, and main infrared waves were concentrated in the rage of
5-15 μm. The surface temperature of carbon fiber board was in the range of 84-92℃. Fruits and vegetables could be quickly
dried in this form of infrared drying. Under the radiation power of 1.1 kW/m2 and the radiation distance of 8 mm, the drying
time of 3 kinds of fruit slices (20 mm×20 mm×11 mm) and agaric (approximately 6-8 g) was about 270-300 min; 2) Carrot
slices with size of 20 mm×20 mm and 5-11 mm thickness were dried under the radiation power of 1.1 kW/m2. It was found
that the internal temperature increased with the increase of the thickness. 3) Under the radiation power of 1.1 kW/m2, at the
radiation distance of 4, 8 and 12 mm, the drying time of 11 mm thick carrot slices was 240, 320 and 450 min, respectively and
the drying time increased with the increase of the radiation distance. The adjustment of the distance between the heat source
and the material could enhance convection heat transfer, and the temperature of the medium inside the dryer could also be
effective in decreasing the drying time without causing quality degradation. 4) Samples were dried in 5 modes: infrared drying,
infrared + dehumidification drying, infrared + cold air drying, infrared + hot air drying, hot air drying. The energy
consumption of infrared drying of the carbon crystal fiber infrared plate was lower, and the energy consumption of the infrared
+ cold air drying mode was only 7.68% of the traditional hot air drying at temperature of 55℃. “Infrared+ hot air” drying
could effectively shorten the drying time and reduce the energy consumption, which were 60% and 49.39% of the hot air
drying at 55℃, respectively. In addition, reducing the humidity of drying chamber at the initial drying stage and keeping low
air velocity could accelerate drying process. This phenomenon was probably due to the fact that with air velocity increasing,
the cooling effect is enhanced, which can reduce the material’s temperature. In summary, the carbon crystal fiber infrared plate
can be used in fruits and vegetables drying as the heating source, which has the advantages of higher heating rate, compact
radiation distance, lower energy consumption and simple structure. The findings of the current work provide theoretical basis
for the practical application of carbon fiber heating infrared plate in drying.
Thin-layer air impingement drying kinetics of American ginseng slices were investigated under dif... more Thin-layer air impingement drying kinetics of
American ginseng slices were investigated under different
drying temperatures (35, 40, 45, 50, 55, 60, and
65°C), air velocities (3, 6, 9, and 12 m/s), and sample
thicknesses (1, 2, 3, and 4 mm). Results indicated that
the drying time is more significantly affected by drying
temperature followed by sample thickness and air
velocity. Drying rate curves illustrated that the whole
drying process happened in the falling rate period.
Additionally, from initial drying to the moisture content
of about 0.5 kg/kg, the drying rate increased with the
increase of drying temperature and air velocity or
decreased with the increase of sample thickness. The
moisture effective diffusivity (Deff) was determined both
neglecting shrinkage and considering shrinkage. The
drying activation energy of American ginseng slices
was 46.64 kJ/mol determined by Arrhenius relationship.
The moisture effective diffusivity and drying
activation energy of American ginseng slices were
compared to other biomaterials and related issues
were also discussed. The current work is useful for
designing air impingement drying system, evaluating
and saving energy consumption of American ginseng
slices.
Drying is one of the most common processing methods of fruits and vegetables. Enhancing drying ra... more Drying is one of the most common processing methods of fruits and vegetables. Enhancing drying rate and dried products’ quality as well as energy efficiency is very tempting for drying industry. Recently, lots of investigations illustrated that drying temperature, air velocity and sample’s thickness have a significant effluence on drying process. High drying temperature and velocity can extensively reduce drying time and enhance drying rate. However, few investigations taking into account hot air relative humidity (RH) as important drying parameter in drying process. Some literatures showed that decreasing RH would lead to a steeper moisture ratio decreasing slope. Whereas, some researches pointed out that there was no effect of RH on the drying rate in specified range of RH. In general, high RH can contribute to a rapid increase of product temperature. It is expected that with high RH pretreatment, the temperature and moisture tend to be equivalent and after that the relative humidity can be reduced to enhance drying rate. In this circumstance, the temperature and moisture gradient between sample and drying air become consistent and high efficient drying process could be achieved. Drying process refers to heat and mass transfer efficient, energy consuming and products quality. Theoretical models, semi-theoretical and empirical models were widely used to describe drying process. However, those models neglect fundamentals of the drying process and their parameters have no physical meaning and they do not help in the optimization. Recently, Weibull model was used to describe drying process because of its applicability. Based on Weibull model, the relationship between scale parameters as well as shape parameters and drying process can be developed. So in current work, carrot slabs were used to explore the drying characteristic under different constant drying RH and under step down drying RH with constant drying temperature and constant air velocity. Result showed that under constant RH, drying time was decreased as reducing RH and drying time under 20% RH was reduced by 27.6% compared to that of 50%RH. Drying rate would rise up in the initial drying period and then drop afterwards. Additionally, drying rate is more rapidly under low RH. However, material’s temperature would be the highest under 50%RH drying condition. Besides, under step down RH drying condition, when 50%RH was kept 30 min and then was changed to20%RH, the drying time was saved by 18.5% compared to constant 20%RH drying condition. When 50%RH was kept 30 min or more than 30 min, there were two accelerating periods of drying rate. The material’s temperature would decrease as RH decreased because of moisture evaporates. Weibull model can fit the drying curves under different conditions accurately. The scale parameter ranged from 1.864 to 2.803 and shape parameter ranged from 1.296 to 1.713. So there is a lag period according to shape parameter value. Based on Weibull model, the moisture effective diffusivitye were calculated in the range of 1.10×10-8~2.15×10-8 m2/s. Taking rehydration ratio, color value, drying time and energy consuming into account, 50%RH keeping for 30 min and then reduced to 20%RH was proposed as the favorable condition for drying carrot slabs. The present work contributes to a better understanding of the effect of relative humidity on drying characteristics of carrot slabs, which is useful for enhancing drying rate and dried products’ quality as well as energy efficiency
Tang, Glass transition and state diagram for freeze-dried Lentinus edodes mushroom, Thermochimica... more Tang, Glass transition and state diagram for freeze-dried Lentinus edodes mushroom, Thermochimica Acta
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The drying characteristics of yam slices under different constant relative humidity (RH) and step... more The drying characteristics of yam slices under different constant relative humidity (RH) and step-down RH levels were studied. A mass transfer model was developed based on Bi-Di correlations containing a drying coefficient and a lag factor to describe the drying process. It was validated using experimental data. Results showed that the drying air with constant RH levels of 20%, 30%, and 40%, temperature of 60 oC and air velocity of 1.5 m/s had insignificant effect on drying time. This phenomenon was likely attributed to the fact that higher RH lead to rapidly increment of sample’s temperature. Afterwards, higher sample’s temperature could provide an additional driving force to water diffusion and thereby promoted the moisture movement which could minimize the negative effect of lower drying rate in the initial drying stage. Applying air with 40% RH for 15 min in the initial stage achieved the desired color and reduced the drying time by 25% compared to the drying time under continuous dehumidification from an initial RH of 40%. Using the developed Bi-Di correlation, the estimated Biot number, effective moisture diffusivity and mass transfer coefficient ranged from 0.1024 to 0.1182, from 1.1133×10-10 to 8.8144×10-9 m2/s and from 1.8992×10-9 to 1.7364×10-7 m/s, respectively. A rather high correlation coefficient of determination (R2 ranged from 0.9871 to 0.9971) was determined between the experimental and predicted moisture contents. The present findings contributed to a better understanding of the effect of relative humidity on drying characteristics. The developed Bi-Di correlation provided a new method to determine the effective diffusivity of moisture in drying.
The influences of different osmotic solution pretreatments (sucrose, glucose and maltose with con... more The influences of different osmotic solution pretreatments (sucrose, glucose and maltose with concentration of 45%) on the volatile compounds, phenolic compounds and other physicochemical parameters in frozen mangoes were studied. Volatile and phenolic compounds were measured using SPME/GC-MS and HPLC method, respectively. The results revealed that compared with untreated frozen mango, some volatile compounds (e.g. alcohols, aldehydes and some terpenes and esters) increased significantly and there were more compounds identified in osmo-dehydrofrozen samples. These changes positively affected mango aroma and resulted in higher sensory scores for osmo-dehydrofrozen samples. In addition, data on phenolic compounds showed that dehydrofrozen samples pretreated in glucose and sucrose had higher q-hydroxybenzoic acid and quercetin contents, respectively, while samples pretreated in maltose showed higher q-coumaric acid and sinapic acid contents compared with untreated frozen samples. The current work indicates that osmo-dehydrofreezing can improve the retention of phenolic and aromatic compounds in frozen mango.
Because the eggplant widely planted all over the country, but the moisture content and the shelf ... more Because the eggplant widely planted all over the country, but the moisture content and the shelf life of fresh eggplant is high and short, so harvest eggplants should be dried and dehydrated in time. But how to achieve high quality dried products is one of the important direction in drying research. Chemical impregnation process is a novel pretreatment technology, ethanol as a chemical with the advantages of penetration fast, easy to evaporate, no chemical residues and harmless to the human body, and which has been applied to the pretreatment of fruit and vegetable. In order to improve the drying quality of eggplant slices and shorten the drying time, the eggplant slices were dipped in ethanol before hot air drying. The effects of different drying temperature (45, 55, 65℃)，pretreatment of ethanol concentration (0, 5%, 15%) and slice thickness (1.0, 1.5, 2.0 cm) on drying rate, color, rehydration ratio and micros microscopic structure were investigated throught orthogonal experiments in this paper. Results showed that drying temperature, ethanol concentration of pretreatment and sample thickness have significant effects on the drying processing. In addition, the sample thickness was most significant, followed by drying temperature, and ethanol concentration of pretreatment．The drying time decrease with the increase of temperature, increases with the increase of the slice thickness of the eggplant, increased then decrease with the increase of the alcohol concentration. The whole drying process occurred in falling rate period. According to Fick′s Second Law, the water effective diffusion coefficient (Deff) was determined and the Deff ranged from 2.74×10-9 m2/s to 7.75×10-9 m2/s．The sample thickness has greater impact on rehydration ratio compared with sample thickness and ethanol concentration. Furthermore, the rehydration ratio decreased as the thickness increased. The ethanol concentration has important influence on color parameters of dried eggplant slices, but the effect of eggplant thickness and temperature on the colour and lustre is not significant, which is far less the ethanol concentration of pretreatment effects on the colour and lustre. And the pretreatment with ethanol also can change the microstructure and appearance quality of the dried samples. After eggplant is dipped with low concentration of ethanol, the moisture of which will be faster evaporated and send out of the eggplant internal free water in the drying, improve the drying rate; And after eggplant is impregnated with high concentration of ethanol, ethanol makes eggplant internal nutrient composition change, which make its structure more compact, and prevent moisture migration in the process of drying. Taking account of the drying rate and quality attributes, drying at 55℃, with ethanol concentration of 15%, and sample thickness of 1.5 cm was recommended as the most favorable conditions for eggplant slices drying. The present findings indicated that ethanol dipping pretreatment can not only enhance drying rate but also improve color attributes of dried products. The results provide a theory reference for the rapid drying of high quality eggplant slices.
摘 要：为了开发植物源脐橙贮藏保鲜技术，该文研究了川芎提取液在离体和活体条件下对采后脐橙的主要致腐菌意大 利青霉和指状青霉的抑制作用，以及对贮藏期脐橙品质和生理生化的影响。结果显示：在离体条件下... more 摘 要：为了开发植物源脐橙贮藏保鲜技术，该文研究了川芎提取液在离体和活体条件下对采后脐橙的主要致腐菌意大 利青霉和指状青霉的抑制作用，以及对贮藏期脐橙品质和生理生化的影响。结果显示：在离体条件下，川芎提取液对 2 种供试菌种有显著的抑制作用(P<0.05) ，最低抑菌质量浓度均为 25.00 mg/mL；在活体条件下，川芎提取液能有效抑制 2 种病原菌在脐橙上的生长，且质量分数为 4%效果较好，与体积分数为 50%乙醇处理的对照相比，差异显著(P<0.05) ； 在脐橙采后贮藏中，川芎提取液对脐橙的防腐保鲜效果与其质量分数相关，其中质量分数为 4%的效果较好，与蒸馏水处 理的对照相比，能够显著(P<0.05)降低采后脐橙的腐烂率、失重率和丙二醛含量，延缓总酸的下降，以及诱导过氧化 物酶活性上升，有利于维持可溶性固形物和总糖质量分数，而对维生素 C 和果皮色泽的变化无显著影响(P>0.05) 。结果 表明，川芎提取液用于脐橙贮藏保鲜切实可行，研究结果为脐橙天然保鲜剂的开发及脐橙在贮藏、运输和销售期间防腐 保鲜提供参考。
Medicinal herbs are economically and nutritionally important plants, which are rich in health-pro... more Medicinal herbs are economically and nutritionally important plants, which are rich in health-promoting compounds. Herbs are the backbone of both the traditional Chinese and Indian medicine, which has long history as part of their culture. Ensuring the quality of herbs is a crucial step for integrating the traditional medicine into science-based modern medicine. Drying is an essential technique in preservation of herbs as it affects directly the quality attributes of the dried products, whereas many producers lose much profit due to poor drying techniques. So, employing a suitable drying technology and selection of appropriate drying conditions are very important for producing high quality herb products. The aim of this article is to summarize the advances in drying technologies of medicinal plants, describe the current status and identify future research opportunities. The current work provides more data and information for selecting optimum technology for herb drying and would trigger innovative drying technologies to enhance drying kinetics and quality of herb drying.
Box type hot air dryer was widely used for agriculture products because of its simple structure a... more Box type hot air dryer was widely used for agriculture products because of its simple structure and convenient operation. How to shorten drying time, reduce energy consumption and improve products’ quality becomes one of the important directions of research. As to the material which is easily to be crusting in the surface, It is expected that with high relative humidity pretreatment and after that the relative humidity can be reduced to enhance drying rate. In this circumstance, the temperature and moisture gradient between sample and drying air become consistent and high efficient drying process could be achieved. However, it is difficult to confirm the magnitude of the relative humidity of each step and its keeping time in step down drying process. It is expected that material’s temperature and relative humidity of the hot air were the main two factors that have a significant influence on the drying process. High hot air drying temperature leads to high material’s temperature so that drying time can be reduced. Material’s internal moisture movement towards surface can be accelerated because of material temperature increment. Besides, the vapor partial pressure difference between material’s surface and drying medium can be increased by reducing drying relative humidity, which can improve drying rate. In addition, material’s temperature and relative humidity of drying hot air were the two aspects which reflect the mass transfer and heat transfer of the drying procedure. High relative humidity can increase material’s temperature but decrease drying rate. Conversely, low relative humidity may increase drying rate but hinder increment of material’s temperature. The material’s temperature curve during drying combined with drying procedure can be divided to initial preheating period, medium-term temperature increment period and late drying period. So according to material’s temperature, drying period can be specified and then relative humidity can be controlled so that drying process can be optimized. In this paper, the control of relative humidity was designed for internal recycle hot air drying technology. In initial pre-heating period, relative humidity was set at a high value. And the material’s temperature was raised rapidly. When the material’s temperature slowly increment trend was detected by the auto control program, the drying process transit to medium- term drying procedure. In this period, material’s temperature was kept at a specific value with the moisture removing fan open. When the material’s temperature began to increase, moisture removing fan was closed to heat material. When material’s temperature approached to drying hot air temperature or material’s temperature can’t rise rapidly, drying process transited to late drying period. Carrot was adopted to test the performance of the auto control relative humidity program. The experiment result showed that in the way of self adaptive control of relative humidity, the max maximum deviation of relative humidity was 1% in the preheating period and the material keeping drying temperature under dehumidifying increased gradually. The max error between the set temperature and achieved temperature was 0.8 oC。In the last drying period, the drying end time judge by the moisture content in 15 min was 9 min later than judging by weighing method. Drying time was reduced by 19.7% compared to the drying conditions of 50% relative humidity in the initial period and 20% in the late period as well as the drying condition of 50% relative humidity pretreatment and removing moisture continuously afterwards. The present work come up with a new way of control relative humidity in internal recycle hot air drying technology, which is useful for enhancing drying rate.
In current work, the drying kinetics and evolution of sample's core temperature and moisture dist... more In current work, the drying kinetics and evolution of sample's core temperature and moisture distribution of yam slices during convective hot air drying were investigated. In the terms of drying kinetics, the effect of drying temperature (50, 55, 60, 65, 70 o C), relative humidity (20%, 30%, 40%, 50%) and sample thickness (5, 7, 9 mm) on drying characteristics of yam slices were studied. Results indicated that all the three factors had significant influence on the drying kinetics, whereas drying temperature gave the most significant effect, followed by relative humidity and sample thickness. Moisture effective diffusivity and activation energy were calculated and it was found that the diffusivity was in the range of 5.5454×10 -10 to 1.0804×10 -9 m 2 /s and the activation energy was 29.528 kJ/mol. Heat and mass transfer models were developed based on the finite element method to calculate the core temperature and moisture distribution of yam slices during drying.
Recently, infrared radiation heating has been widely applied in different thermal processing syst... more Recently, infrared radiation heating has been widely applied in different thermal processing systems in food industry.
It has several advantages such as high efficiency, low energy consumption, and high quality of dried products. In addition, the
heating power generated from infrared radiation can penetrate into food materials. But the electric radiant infrared heater, such
as ceramic infrared heater and gas-fired infrared radiator, has the some drawbacks e.g., large structure and high heating
temperature, which lead to higher energy consumption of infrared drier. In order to explore the drying characteristics of carbon
fiber and develop a new heating technology of infrared drying, the drying characteristics of banana slices, apple slices, carrot
slices and agaric were investigated in a carbon fiber infrared heating. The material internal temperature, ambient temperature,
ambient humidity of drying process were detected during drying process. Result indicated that: 1) Far-infrared waves in the
rage of 1-30 μm could be launched by the carbon fiber heating board, and main infrared waves were concentrated in the rage of
5-15 μm. The surface temperature of carbon fiber board was in the range of 84-92℃. Fruits and vegetables could be quickly
dried in this form of infrared drying. Under the radiation power of 1.1 kW/m2 and the radiation distance of 8 mm, the drying
time of 3 kinds of fruit slices (20 mm×20 mm×11 mm) and agaric (approximately 6-8 g) was about 270-300 min; 2) Carrot
slices with size of 20 mm×20 mm and 5-11 mm thickness were dried under the radiation power of 1.1 kW/m2. It was found
that the internal temperature increased with the increase of the thickness. 3) Under the radiation power of 1.1 kW/m2, at the
radiation distance of 4, 8 and 12 mm, the drying time of 11 mm thick carrot slices was 240, 320 and 450 min, respectively and
the drying time increased with the increase of the radiation distance. The adjustment of the distance between the heat source
and the material could enhance convection heat transfer, and the temperature of the medium inside the dryer could also be
effective in decreasing the drying time without causing quality degradation. 4) Samples were dried in 5 modes: infrared drying,
infrared + dehumidification drying, infrared + cold air drying, infrared + hot air drying, hot air drying. The energy
consumption of infrared drying of the carbon crystal fiber infrared plate was lower, and the energy consumption of the infrared
+ cold air drying mode was only 7.68% of the traditional hot air drying at temperature of 55℃. “Infrared+ hot air” drying
could effectively shorten the drying time and reduce the energy consumption, which were 60% and 49.39% of the hot air
drying at 55℃, respectively. In addition, reducing the humidity of drying chamber at the initial drying stage and keeping low
air velocity could accelerate drying process. This phenomenon was probably due to the fact that with air velocity increasing,
the cooling effect is enhanced, which can reduce the material’s temperature. In summary, the carbon crystal fiber infrared plate
can be used in fruits and vegetables drying as the heating source, which has the advantages of higher heating rate, compact
radiation distance, lower energy consumption and simple structure. The findings of the current work provide theoretical basis
for the practical application of carbon fiber heating infrared plate in drying.
Thin-layer air impingement drying kinetics of American ginseng slices were investigated under dif... more Thin-layer air impingement drying kinetics of
American ginseng slices were investigated under different
drying temperatures (35, 40, 45, 50, 55, 60, and
65°C), air velocities (3, 6, 9, and 12 m/s), and sample
thicknesses (1, 2, 3, and 4 mm). Results indicated that
the drying time is more significantly affected by drying
temperature followed by sample thickness and air
velocity. Drying rate curves illustrated that the whole
drying process happened in the falling rate period.
Additionally, from initial drying to the moisture content
of about 0.5 kg/kg, the drying rate increased with the
increase of drying temperature and air velocity or
decreased with the increase of sample thickness. The
moisture effective diffusivity (Deff) was determined both
neglecting shrinkage and considering shrinkage. The
drying activation energy of American ginseng slices
was 46.64 kJ/mol determined by Arrhenius relationship.
The moisture effective diffusivity and drying
activation energy of American ginseng slices were
compared to other biomaterials and related issues
were also discussed. The current work is useful for
designing air impingement drying system, evaluating
and saving energy consumption of American ginseng
slices.
Drying is one of the most common processing methods of fruits and vegetables. Enhancing drying ra... more Drying is one of the most common processing methods of fruits and vegetables. Enhancing drying rate and dried products’ quality as well as energy efficiency is very tempting for drying industry. Recently, lots of investigations illustrated that drying temperature, air velocity and sample’s thickness have a significant effluence on drying process. High drying temperature and velocity can extensively reduce drying time and enhance drying rate. However, few investigations taking into account hot air relative humidity (RH) as important drying parameter in drying process. Some literatures showed that decreasing RH would lead to a steeper moisture ratio decreasing slope. Whereas, some researches pointed out that there was no effect of RH on the drying rate in specified range of RH. In general, high RH can contribute to a rapid increase of product temperature. It is expected that with high RH pretreatment, the temperature and moisture tend to be equivalent and after that the relative humidity can be reduced to enhance drying rate. In this circumstance, the temperature and moisture gradient between sample and drying air become consistent and high efficient drying process could be achieved. Drying process refers to heat and mass transfer efficient, energy consuming and products quality. Theoretical models, semi-theoretical and empirical models were widely used to describe drying process. However, those models neglect fundamentals of the drying process and their parameters have no physical meaning and they do not help in the optimization. Recently, Weibull model was used to describe drying process because of its applicability. Based on Weibull model, the relationship between scale parameters as well as shape parameters and drying process can be developed. So in current work, carrot slabs were used to explore the drying characteristic under different constant drying RH and under step down drying RH with constant drying temperature and constant air velocity. Result showed that under constant RH, drying time was decreased as reducing RH and drying time under 20% RH was reduced by 27.6% compared to that of 50%RH. Drying rate would rise up in the initial drying period and then drop afterwards. Additionally, drying rate is more rapidly under low RH. However, material’s temperature would be the highest under 50%RH drying condition. Besides, under step down RH drying condition, when 50%RH was kept 30 min and then was changed to20%RH, the drying time was saved by 18.5% compared to constant 20%RH drying condition. When 50%RH was kept 30 min or more than 30 min, there were two accelerating periods of drying rate. The material’s temperature would decrease as RH decreased because of moisture evaporates. Weibull model can fit the drying curves under different conditions accurately. The scale parameter ranged from 1.864 to 2.803 and shape parameter ranged from 1.296 to 1.713. So there is a lag period according to shape parameter value. Based on Weibull model, the moisture effective diffusivitye were calculated in the range of 1.10×10-8~2.15×10-8 m2/s. Taking rehydration ratio, color value, drying time and energy consuming into account, 50%RH keeping for 30 min and then reduced to 20%RH was proposed as the favorable condition for drying carrot slabs. The present work contributes to a better understanding of the effect of relative humidity on drying characteristics of carrot slabs, which is useful for enhancing drying rate and dried products’ quality as well as energy efficiency
Japanese paddy farmlands rewilding threatens biodiversity. It is found that as the abandonment of... more Japanese paddy farmlands rewilding threatens biodiversity. It is found that as the abandonment of paddy farmlands continues, biodiversity is declining as farmland species, e.g. aquatic weeds, invertebrates, and amphibians and wetland birds are threatened by habitat loss (N. Katayama et al. Agricultural Systems 132, 73-84; 2015). For example, the population of wetland birds such as egrets, shorebirds, and herons have decreased extensively as a consequence of the disappearing of artificial paddy wetlands, which provide rich habitats for such birds (N. Katayama et al. Agriculture, Ecosystems and Environment 214, 21-30; 2015).