Microwave Drying of Scots Pine Lumber:Structure Changes,Its Effect on Liquid Permeability

Microwave(MW)drying method was adopted to enhance the liquid permeability of Scots pine lumber.Structure changes were characterized by stereoscope microscope,scanned electron microscope(SEM)and transmission electron microscope(TEM)examination.Pore parameters before and after MW treatment were detected by mercury intrusion porosimetry(MIP)method,and the effect of structure changes on liquid permeability were analyzed.As stereoscope microscope,SEM and TEM examination results showed,macro and micro checks mainly developed at intercellcular of tracheids,intercellular of ray parenchyma and tracheid,while these checks extend main along the radial-longitudinal plane.Pit border destruction,aspirated pits’orus translocation and micro-checks in tracheid cell wall were also observed.MIP test shown that pore volume and pore area increased as macro and micro checks generated to form new cavities.Microstructure changes would increase the quantity of pores or enlarge the pore diameter.Liquid flow pathways increased as macro and micro checks generated,aspirated pits reopened to form new pathways;liquid flow efficiency improved as porosity,pore volume and pore diameter increased which facilitated the liquid flow.

Optimization of Process Parameters of Continuous Microwave Drying Raspberry Puree Based on RSM and ANN-GA

To improve drying uniformity and anthocyanin content of the raspberry puree dried in a continuous microwave dryer,the effects of process parameters(microwave intensity,air velocity,and drying time)on evaluation indexes(average temperature,average moisture content,average retention rate of the total anthocyanin content,temperature contrast value,and moisture dispersion value)were investigated via the response surface method(RSM)and the artificial neural network(ANN)with genetic algorithm(GA).The results showed that the microwave intensity and drying time dominated the changes of evaluation indexes.Overall,the ANN model was superior to the RSM model with better estimation ability,and higher drying uniformity and anthocyanin retention rate were achieved for the ANN-GA model compared with RSM.The optimal parameters were microwave intensity of 5.53 W•g^(-1),air velocity of 1.22 m·s^(-1),and drying time of 5.85 min.This study might provide guidance for process optimization of microwave drying berry fruits.

Structural and functional properties of hydrolyzed/glycosylated ovalbumin under spray drying and microwave freeze drying

Ovalbumin(OVA),the main protein in egg white,affects most of the functional properties of egg white protein in food processing.The aim of this study was to investigate the effects of spray drying(SD)and microwave freeze drying(MFD)on the preparation of hydrolyzed/glycosylated ovalbumin(HGOVA)and provide useful information on the applications of egg protein powders in the food industry.Results demonstrated that the structure of HGOVA was considerably changed,and its functional properties were improved compared with those of native OVA.SD and MFD processing did not lead to dissociation of HGOVA subunits.SD-HGOVA exhibited higher protein solubility,emulsifying activity,foaming capacities,and gel hardness than MFD-HGOVA.However,MFD-HGOVA was better than the SD-HGOVA in terms of color,emulsion stability,foam stability,water/oil absorption capacity,and thermal stability.Selection of an appropriate drying method could enhance the potential applications of HGOVA in the food industry.

Process Parameter Study on Microwave-assisted Foam-mat Drying Properties of Corn Soaking Water

In order to study the microwave-assisted foam-mat drying properties of corn soaking water and optimize process parameters, a quadratic regression orthogonal rotary method was used to analyze the influence of microwave power, material weight, material thickness and drying time on moisture content（dry basis）, color value and protein content. Results showed that the primary and secondary sequence of parameters with regard to moisture content（d. b.） was drying time, microwave power, material weight and material thickness; the primary and secondary sequence of parameters with regard to color value was material weight, drying time, microwave power and material thickness; the primary and secondary sequence of parameters with regard to protein content was drying time, material weight, microwave power and material thickness. Optimum conditions were obtained as microwave power of 560 W, material weight of 46.88 g, material thickness of 6.20 mm and drying time of 8.01 min. The results might provide the theoretical basis and technical support for the microwave-assisted foam-mat drying of corn soaking water to produce yeast protein power.

Drying Characteristics of Microwave-assisted Foam Drying of Corn Soaking Water

To improve the industrial utilization of corn soaking water, the yeast protein powder was produced by microwave-assisted foam drying. Firstly, preparation experiments were carded out, which included the foaming characteristic experiments of fermentation broth and that about the effects of carbon and nitrogen ratio on solid content in the fermentation broth. Secondly, the drying characteristics experiment of corn soaking water was studied, which selected the microwave power, material amount and thickness as the influencing factors for the single experiment. The results showed that the final moisture content （d.b.） and drying rate were significantly affected by those factors.

A valid evaluation method for UPLC fingerprint analysis and moisture ratio prediction model:application to microwave vacuum drying of Radix isatidis extract

Background:Drying is a necessary component of traditional Chinese medicine extracts.The heating principle of microwave vacuum drying is different from that of the conventional heat method.However,at present,there is paucity of information on the drying process of traditional Chinese medicine extract by microwave vacuum drying,and the results of such process are unclear.Methods:To study the dynamic changes in the chemical characteristics of microwave vacuum drying under different drying conditions,ultrahigh-performance liquid chromatography fingerprint profiles were established using Radix isatidis extract as a model drug and analyzed using similarity analysis,partial least squares-discriminant analysis,and semi-quantitative analysis.In addition,a backpropagation artificial neural network model was developed to predict the moisture ratio of the drying process.Results:Qualitative results showed that the similarity between different drying conditions was greater than 0.95,and 2 amino acid components(peaks 5 and 6)affected by process fluctuations were screened out.The quantitative results showed that the mass concentration of component 1 fluctuated after drying,while that of component 2 increased.The optimal backpropagation artificial neural network model structure used to predict the moisture ratio was 5-4-1,with regression and mean squared error values of 0.996 and 0.0003,respectively,after training,which were well fitted and had a strong approximation ability.Conclusion:Upon comparison of fingerprints and the evaluation of statistical methods,common components of Radix isatidis extract had little variation under different drying conditions,and the selected components provided a reference for the establishment of process evaluation indexes.The establishment of backpropagation artificial neural network provides a theoretical basis for the application of microwave vacuum drying technology and online monitoring of moisture ratio.

Effect of different drying methods on the taste and volatile compounds,sensory characteristics of Takifugu obscurus

Pufferfish is prone to deterioration due to abundant nutrients and high moisture content.Drying technology can extend the shelf life and enhance the flavor quality of aquatic products.The study investigated the effect of hot air drying(HAD),microwave vacuum drying(MVD)and hot air assisted radio frequency drying(HARFD)on the taste and volatile profiles of Takifugu obscurus.Different drying methods had significant influence on the color,rehydration,5’-nucleotides,free amino acids and volatile components(P<0.05).The results showed that HAD and HARFD could promote the flavor of T.obscurus by producing higher equivalent umami concentration(EUC)values,which were about two times of MVD group,and more pronounced pleasant odor according to sensory analysis.HAD is more appropriate for industrial application than HARFD and MVD considering the economic benefits.This study could provide a reference for the industrial application of drying T.obscurus.

Using vibrational infrared biomolecular spectroscopy to detect heat-induced changes of molecular structure in relation to nutrient availability of prairie whole oat grains on a molecular basis

Background： To our knowledge, there is little study on the interaction between nutrient availability and molecular structure changes induced by different processing methods in dairy cattle. The objective of this study was to investigate the effect of heat processing methods on interaction between nutrient availability and molecular structure in terms of functional groups that are related to protein and starch inherent structure of oat grains with two continued years and three replication of each year.Method： The oat grains were kept as raw（control） or heated in an air-draft oven（dry roasting： DO） at 120 °C for 60 min and under microwave irradiation（MIO） for 6 min. The molecular structure features were revealed by vibrational infrared molecular spectroscopy.Results： The results showed that rumen degradability of dry matter, protein and starch was significantly lower（P 〈0.05） for MIO compared to control and DO treatments. A higher protein α-helix to β-sheet and a lower amide I to starch area ratio were observed for MIO compared to DO and/or raw treatment. A negative correlation（-0.99, P 〈 0.01）was observed between α-helix or amide I to starch area ratio and dry matter. A positive correlation（0.99, P 〈 0.01） was found between protein β-sheet and crude protein.Conclusion： The results reveal that oat grains are more sensitive to microwave irradiation than dry heating in terms of protein and starch molecular profile and nutrient availability in ruminants.

Microwave drying kinetics and quality characteristics of corn

In recent years,microwave(MW)drying has gained popularity as an alternative drying method for a wide variety of food and agricultural products because of increasing concerns over product quality and production costs.However,the determination of drying kinetics that accurately describes microwave drying characteristics is crucial for the optimization of operating parameters,performance improvement of the drying system and product quality.The objective of this study was to investigate the drying kinetics and the quality characteristics of corn kernels,especially the effects of different initial moisture contents(18.3%,26.3%,34.3%and 42.3%db),MW power levels(70,175 and 245 W)and exposure time(80 s and 120 s)on the drying kinetics,drying rate and various key quality parameters.The results indicated that the increased drying rate at higher power levels(P3,245 W)reduced the drying time considerably but increased stress crack index and reduced germination.In addition,it reduced bulk density,true density and thousand grain weight(TGW).The germination rate of corn was the highest at MW power level P1(70 W),with the lowest drying rate and observed to decrease with increase in initial moisture content.The reduction in exposure time decreased stress crack index and increased germination rate,bulk density and true density.The correlation analysis among drying rate,germination,stress-crack index(SCI),bulk density,true density and TGW showed that increasing drying rate could lead to an increase in SCI and decrease in germination,bulk density and true density.

Evolution of pore structure during microwave freeze-drying of Chinese yam

In order to reduce the energy consumption of freeze drying(FD),microwave freeze drying(MFD)can be used to dry Chinese yam.Porosity is a critical factor influencing transport mechanism,and can be considered as an important index to reflect the changes of structure of MFD foods.In this study,the changes of pore structure during the process of MFD Chinese yam were investigated by SEM and mercury porosimetry.The results showed that some closed pores could transform to open pores in drying process,and the open porosity showed a rising trend throughout the drying process.The pore size distribution range was about 10 nm to 10^(6) nm throughout the drying process.In the early stage of drying,the pore size was mainly in the range of 10-10^(4) nm,and then the pore size and the number of pores reduced.In the middle and late drying stages,the size of large pores increased again.

Microstructure changing and moisture removing of lychee during microwave vacuum drying

Micrographs of lychee pericarp and pulp during microwave vacuum drying were tested and analyzed in order to illuminate the microstructure change of lychee and effect of the change on moisture removing in lychee.The results showed that the pericarp consisted of three parts:outer layer with cuticle,inter layer and inner layer.Outer layer and inter layer cells are easily destroyed than inner layer because of small and intact inner layer cells.Furthermore,micrographs showed that the moisture content of pulp keep constant with the temperature increasing at first 40 min due to the inner layer cells prevent the moisture removing from pulp.The long tubular structure of pulp cell would become break and lost over time,because the intercellular spaces reduced and the moisture removing was slow down in pulp.Meanwhile,the microstructure of lychee dried with temperature control was better than that without temperature control.

Effects of different pretreatments on the pore structure of Chinese yam during microwave freeze drying

In order to explore the effects of different pretreatments on the pore structure of Chinese yam during Microwave Freeze Drying(MFD),the samples were treated by typical drying pretreatments including osmosis,blanching and ultrasound,and compared with the untreated samples.The results showed that the pretreatment had significant impacts on the porosity of MFD Chinese yam.Ultrasonic pretreatment could obtain the highest open porosity,and the internal pore network structure of the material showed a uniform sponge shape.The shape of pores obtained by blanching pretreatment was the most irregular.The pore network structure obtained by different pretreatments could result in various product texture and rehydration,which implied that pretreatment methods should be carefully selected according to actual requirements.All these pretreatments could improve the open porosity of MFD Chinese yam,which result in a better rehydration capability.Among them,ultrasonic treatment is worth further investigating.

Comparative analyses/evaluation of the textural properties of naproxen sodium tablets and powders prepared using microwave and other drying techniques

The properties of oral tablets are normally related to the properties of the powders they contain.Characterization of oral tablets is important for the development of tablets with rapid and safe release of the active ingredient.In this study,a new formulation of naproxen sodium was prepared and dried using microwave drying (MWD) and the following conventional drying techniques:freeze-drying (FD),vacuum drying (VD),and convective drying (CD).The reference drug powder (RDP) and dry granules MWG,CDG,VDG,and FDG,which were dried using MWD,CD,VD,and FD,respectively were compressed to form tablets labeled RF-TAB,MW-TAB,CD-TAB,VD-TAB,and FD-TAB,respectively.The dry granules and prepared tablets were characterized using Fourier transform infrared spectrometry,scanning electron microscopy,and X-ray diffraction.This study aimed to explore the correlation between the textural characteristics of the tablets and their respective powders for different drying methods.Although the morphologies of the dry particles were irregular,the prepared tablets were smooth and flat with few cracks.Drying increased the amorphous nature of the granules but decreased their crystallinity.The crystallinities of all tablets,except those prepared by VD,decreased after compression.In summary,the characteristics of the prepared tablets were acquired from their respective powders.

In flue nee of microwave drying and con venti onal drying methods on the mechanical properties of naproxen sodium drug tablets

Tablets are one of the most comm only used solid dosage forms taken by patients.The preparati on of high-quality tablets requires an understanding of the preparation process and elucidation of how the physical and mechanical properties change as a function of the preparation process.This work aims to investigate the impact of microwave irradiation drying and conventional drying methods(including freeze,convective and vacuum drying)on the hardness,tensile strength and friability of tablets made from a multi-component formulation containing naproxen sodium,microcrystalline cellulose,and polyvinylpyrrolidone.The results show that tablets subjected to microwave drying had the secondhighest tensile strength and hardness of 1.296 MPa and 67 N,respectively.The tablets subjected to vacuum drying had the lowest tensile strength and hardness of 1.21 MPa and 64 N,respectively.The friability index values for the tablets derived from the microwave and freeze-drying methods were<1%,while those for the tablets subjected to convective drying and vacuum drying methods were>l%.Microwave drying was observed to be an efficient method to produce naproxen sodium-containing tablets with satisfactory mechanical properties.These findings confirm that the drying method plays an essential role in the improvement or degradation of the mechanical properties of tablets.

Mathematical modeling of microwave drying of crashed cotton stalks for man-made composite material

Drying characteristics,energy consumption and drying kinetics modeling of crashed cotton stalks dried in a microwave dryer were investigated in this research.A microwave dryer with an output power of 1000 W and 2450 MHz was employed,and the effects of material load ranging from 50 g to 250 g on drying time,drying rate,drying efficiency and specific energy consumption were evaluated.The results showed that drying rate decreased with drying duration.A rising rate period was followed by a falling rate period and the overall drying process occurred in the falling rate period.Six mathematical models were used to fit the drying rates data of crashed cotton stalks,and Midilli et al.model was found the best prediction model by comparing R2,RMSE andχ^(2)values between experimental and predicted moisture ratios.With decrease in material load from 250 g to 50 g,effective moisture diffusivity increased from 2.8668×10^(-8)m^(2)/s to 7.9817×10^(-8)m^(2)/s.Results also indicated that drying efficiency and specific energy consumption significantly increased with the increase of the material load.Average drying efficiency and specific energy consumption varied in the range of 7.52%-19.78%and 12.49-35.90 MJ/kg water,respectively.There were a lowest energy consumption of 10.99 MJ/kg water and a highest drying efficiency of 17.13%at the material load level of 250 g.

Differences in breaking behavior of rice leaves under microwave and naturally drying processes

In order to fight for good farming time or harvest in bad weather,combine harvester will produce more broken leaves when threshing high moisture content rice,which will seriously hinder the grain cleaning effect.In this study,the breaking behavior of rice leaves under different microwave drying time and drying power was studied.Firstly,based on the appearance of freshly rice leaves undergoing microwave drying,the changing property of moisture content,weightlessness rate and temperature rise of rice leaves were tested and analyzed.Secondly,the tensile breaking force of freshly rice leaves under different microwave drying time and drying power was tested and compared with the tensile breaking force of naturally dried rice.Finally,the optimal microwaves parameters of rice leaves after drying which could result in greater breaking force than the natural drying state were obtained.The result showed that microwave drying method will reduce the moisture content of rice leaves and change the microstructure,which would affect the tensile-breaking property of rice leaves.The maximum tensile breaking force of rice leaves appeared at microwave dried power 70 W for 5-8 min and at microwave dried power 210 W for 3-4 min.The tensile breaking property of rice leaves at microwave dried power 350 W for 6-8 min were the weakest,which was lower than that of fresh rice leaves.Therefore,the optimal microwave drying parameters of rice leaves will provide a basis for the application of microwave technology in the threshing process.

Comparative study on the effects and efficiencies of three sublimation drying methods for mushrooms

Freeze drying(FD)yields the best quality of dried mushrooms but needs long drying time and higher cost.Air drying(AD)gives relatively poor product quality.In order to achieve faster drying along with high product quality,microwave freeze drying(MFD)and atmospheric freeze drying(AFD)were developed to dry mushrooms.By comparison of three sublimation drying processes,it was concluded that FD could lead to the best product quality,but cost the highest energy consumption.AFD mushrooms had the worst quality and longest drying time,but the lowest energy consumption.Compared with FD and AFD,MFD could get relatively acceptable quality and drying efficiency.As a result,MFD can be used to replace traditional FD,and AFD also should be popularized because of its low energy consumption.