Industrial Crops and Products 70 (2015) 417426

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Industrial Crops and Products

jo ur nal home p age: www.elsev ier .com/ locate / indcrop

Effect o neconvec mon the

Somayeha Department ob LUNAM, ONIR

a r t i c l

Article history:Received 12 JaReceived in reAccepted 15 M

Keywords:ElectrohydrodConvective dryButton mushroomTextureRehydration ratioColor

an itwo v/s) onh, co.4 m/V2.ment

p 0.001 on moisture content, shrinkage, rehydration ratio, and shear strength, but no signicant dif-ference was observed in the color of the dried mushroom slices. The advantages of the mushroom slicesdried at a higher voltage or air ow velocity included a higher drying rate, porosity and rehydrationratio and a lower remaining moisture content. However, the higher voltage or air velocity caused thedevelopment of a wrinkled and broken structure, leading into more shrinkage and shear strength.

2015 Elsevier B.V. All rights reserved.

1. Introdu

Drying isit representHashinaga, logical stabchemical reing, storagein weight aproduct undtant to notisimultaneoMartnez etof the convedrawbacks,and qualityof convectiat least 10%fore, the se

CorresponE-mail add

http://dx.doi.o0926-6690/ ction

one of the oldest techniques for food preservation ands an important aspect of food processing (Bajgai and2001a). It has been widely used to provide microbio-ility, to minimize many deteriorative problems due toactions (Ochoa-Martnez et al., 2012), to reduce pack-, and transportation costs due to a substantial reductionnd volume of a product, and to enable storability of theer ambient temperatures (Doymaz, 2014). It is impor-ce that products of low-cost and high-quality are notusly provided by traditional drying methods (Ochoa-

al., 2012). For instance, convective drying, which is onentional and extensively used drying method, has many

including low energy efciency, long processing time, deterioration (Wu et al., 2014). The energy efciencyve dryers is often below 50% and drying accounts for

of industrial energy demand (Jin et al., 2014). There-lection of an appropriate drying method is of great

ding author. Tel.: +98 3153292069; fax: +98 3153232701-2.ress: Taghian@iaush.ac.ir (S. Taghian Dinani).

importance and innovative drying techniques and dryers must bedesigned and studied in order to decrease the energy cost of thedrying process (Doymaz, 2014) and increase the nal quality ofproducts.

One of the innovative drying methods is electrohydrodynamic(EHD) drying, which has been developed only recently (Bai et al.,2013). The main mechanism involved in EHD is the production ofan electric wind, also termed as corona wind. To produce coronawind, a high voltage is employed between two electrodes withconsiderably different radii of curvature, for example, between apin and a plate (Ould Ahmedou et al., 2009) or between a wireand a plate and a moist sample is placed between them. Coronawind produced in an electrostatic eld impinges on the moist sur-face and disturbs the saturated air layer; this phenomena results inevaporation enhancement and consequently heat transfer augmen-tation (Kamkari and Alemrajabi, 2010). However, EHD drying has adrawback of long drying time (Bai et al., 2013) and earlier studieshave shown that EHD drying method is highly effective at the rststage of drying, i.e., the constant-rate period or surface evaporationstage, and like most drying methods, its effectiveness decreasesas the drying process advances in time (Tansakul and Lumyong,2008). In this study, in order to compensate the drawbacks of thetwo described convective and EHD drying methods, a hybrid or

rg/10.1016/j.indcrop.2015.03.0472015 Elsevier B.V. All rights reserved.f voltage and air ow velocity of combitive-electrohydrodynamic drying systephysical properties of mushroom slices

Taghian Dinania,, Michel Havetb

f Food Science, Shahreza Branch, Islamic Azad University, Shahreza, IranIS, GEPEA (CNRS UMR 6144), Rue de la Graudire, BP 82225, 44322 Nantes, France

e i n f o

nuary 2015vised form 13 March 2015arch 2015

ynamicing

a b s t r a c t

Electrohydrodynamic (EHD) drying isconvective-EHD drying system with velocity (at two levels of 0.4 and 2.2 mage, rehydration ratio, shear strengtThe eight drying treatments (30 kV025 kV2.2 m/s, 20 kV2.2 m/s and, 0 kshowed that these eight drying treatd

nnovative drying method. For this investigation, a combinedariables of voltage (at four levels of 0, 20, 25 and 30 kV) and

drying kinetics, remaining moisture content, porosity, shrink-lor, and microstructure of mushroom slices was envisaged.s, 25 kV0.4 m/s, 20 kV0.4 m/s, 0 kV0.4 m/s, 30 kV2.2 m/s,2 m/s) were carried out at 45 C for a period of 5 h. ANOVAs had a signicant effect with p 0.01 on porosity and with

418 S. Taghian Dinani, M. Havet / Industrial Crops and Products 70 (2015) 417426

tal set

combined cto dry mushimportanceconsiderabland Prasadbutton musmushroom Mushroomsriorate sootemperaturjected to soshelf life forous methoddifferent qunutritional,dried mush

Thereforthe inuenEHD dryingand 30 kV) the physicakinetics, redration ratidrying.

2. Materia

2.1. Experim

A schemEHD dryingthis gure, (15 15 cmer and a bl(Model CV

e (Model

esse, Ottth, NcharorizorateFig. 1. Scheme of the experimen

onvective-EHD drying system was designed and usedroom slices. Mushrooms are edible fungi of commercial

and their cultivation and consumption have increasedy due to their nutritional value, delicacy, and avor (Giri, 2007). Out of 38,000 known mushroom varieties, thehroom (Agaricus bisporus) is the most widely cultivatedthroughout the world (Taghian Dinani et al., 2014c).

are highly perishable commodities and begin to dete-

balancger (MsystemSefelecElizabethe disxed ha perfon after harvest, with a shelf life of 12 days at roome (Doymaz, 2014). Therefore, mushrooms must be sub-me forms of preservation to prolong their commercial

off-season use (Lespinard et al., 2009). Among numer-s of mushroom processes, drying is widely used andality attributes such as optical, structural, rehydration,

and sensory properties can be used for judgment ofrooms (Taghian Dinani et al., 2014c).e, the main goal of the present study was to investigatece of technical parameters of combined convective-

system, such as voltage (at four levels of 0, 20, 25,and air velocity (at two levels of 0.4 and 2.2 m/s) onl properties of mushroom slices, including the dryingmaining moisture content, porosity, shrinkage, rehy-o, shear strength, color, and microstructure after 5 h of

ls and methods

ental set-up

atic diagram of the experimental set-up for convective- of mushroom slices is shown in Fig. 1. As shown inthe convective system is equipped with a wind tunnel2 internal dimensions and 190 cm long), a dehumidi-ower (Model ML 180, Munters, Kista, Sweden), a heater16-21-1MTXL, VEAB Heat Tech AB, Sweden), a digital

(to be driedtrode and generate ththe wire elsupply andstudy, fourcombinatioelectric elset-up wasbottom walfrom the inthe top of twind tunne2 cm) and ithe dehumthe heater, and relativair is blownand 2.2 m/smotor, the the openingair velocityCalc, Shore127 cm fromin each holeover time aof 10 s.-up.

odel Radwag, PS 600/C/2, Radom, Poland), a data log- AOIP, Evry, France), and a personal computer. The EHDntially consists of a high-voltage power supply (Modelersweier, Germany) and a wire (Alpha Wire Company,ew Jersey, United States) with a diameter of 0.15 mm asge electrode, which is suspended horizontally across antal grounded metallic plate (14.6 20 cm2), on which

d plate (14.4 20 cm2) and blanched mushroom slices

) are placed. The discharge gap between the wire elec-the grounded electrode was set at 6 cm. In order toe corona discharge needed to form the corona wind,ectrode was connected to the DC high-voltage power

was charged with a direct high voltage. In the present voltage levels of 0, 20, 25, and 30 kV were used. Then of these voltages and the electrode gap generated and strength range from 0 to 5 kV/cm. The described EHD

combined with the wind tunnel via an opening at thel of the tunnel, measuring 15 cm 21 cm, 150 cm awaylet that was tted with the grounded plate placed onhe digital balance underneath the wire electrode. Thel is made of extruded polystyrene material (thickness ofs open to atmosphere on one side. Air is supplied fromidier and blower and its temperature is increased bywhich provides air at a controlled temperature of 45 Ce humidity of around 10% to the tunnel. In this study,

into the wind tunnel at two desired velocity levels (0.4) and because the blower is driven by a constant speedair speed into the test section is controlled by adjusting

of the two valves which are opposite the blower. The is measured with an anemometer (Model TSI Veloci-view, Minnesota, United States) in ve holes located at

the entry of the tunnel and at ve depths of the tunnel. During drying, the weight changes of mushroom slicesre recorded using the data logger with a sampling rate

S. Taghian Dinani, M. Havet / Industrial Crops and Products 70 (2015) 417426 419

2.2. Sample preparation

Fresh button mushrooms (Agaricus bisporus) were acquired froma shop in Nantes, France. Initially, mushrooms graded accordingto uniform running tapbe removedrooms were(Model SOFblanched inunder runnslices was experimentuniformly pon the groucross-ow nel was opetemperaturor 2.2 m/s),ued for 5 h during all mushroom mination ofshear strenEach dryingexperimentetitions.

2.3. Proced

2.3.1. DeterThe moi

at least in tand dried mthe oven (Mweight was(Model Radcontent on dry matter et al., 2014a

2.3.2. DryinThe dryi

tent, whichwere comp

DR = M1 t2

where DR it2 are the dmoisture cotimes t1 and

2.3.3. PorosPorosity

P = s as

where P is tent density 2012). The weight of tto the equaent volumepycnometetilled water

of solid density was taken by a gas pycnometer (AccuPyc 1330,Micromeritics Instrument Crop., Norcross, USA), with compressedhelium (Taghian Dinani et al., 2014b). The average values of threerepetitions for apparent density and two repetitions for solid den-

s cal

Shrin volh dryd, insed age w

VfV0

S is tf theal vot thralue

Rehyed me (Moeake

at 50). Aftpape

surfation

(Dua

m m

m an, resent a

Colorve ster oter sith aweenlizedoomL0*s. Ahang7),inpo

a2 +00.17

(

(L0 subsblanent f

Shearar slus

Y/Stcolor and size were subjected to mild washing under water so that foreign matters adhered to them would. Then, the middle white section of the cleaned mush-

sliced into slices of 5-mm thick using an electric slicerRACA, Morangis, France). The mushroom slices were

boiling water for 2 min and then were cooled quicklying tap water. The excess water on the surface of theremoved by blotting-off with tissue paper. For every, approximately 65 g of blanched mushroom slices wereut on the perforated plate as a thin layer and placednded metallic plate for exposure to the EHD eld andof air. Before each drying experiment, the wind tun-rated without load for 30 min to reach to the desirede (45 C), relative humidity (around 10%), velocity (0.4

and steady-state conditions. The drying was contin-and the samples were continuously exposed to dryingexperiments. After each drying treatment, the driedslices were kept in sealed polyethylene bags for deter-

the remaining moisture content, shrinkage, porosity,gth, rehydration ratio, color, and their microstructure.

experiment were conducted twice and within each all measurements were conducted at least in two rep-

ures

mination of moisture contentsture content of the mushroom slices was determinedriplicate by the oven method. Representative blanchedushroom slices were randomly taken out and dried inemmert, Schwabach, Germany) at 70 C until a constant

obtained. Weighing was performed on a digital balancewag, AS 220/C02, Radom, Poland) and then the moisturea dry basis and wet basis was expressed as kg water/kgand kg water/kg product, respectively (Taghian Dinani).

g rateng rates calculated from the change in moisture con-

occurred in each consecutive time interval (Pillai, 2013),uted using Eq. (1):

M2 t1

(1)

s the drying rate (kg water/kg dry matter min), t1 andrying times (min) during drying and M1 and M2 are thentent (kg water/kg dry matter) of mushroom slices at

t2, respectively (Perea-Flores et al., 2012).

ity was calculated using the following equation:

(2)

he porosity in percentage and a and s are the appar-and solid density in kg/m3, respectively (Nowacka et al.,apparent density of the samples was calculated by thehe sample, m, and the apparent volume, V, accordingtion of a = m/Va (Karathanos et al., 1996). The appar-

of the mushroom slices was determined by the liquidr technique using a Pyrex glass pycnometer with dis-

as the reference liquid. Furthermore, the measurement

sity wa

2.3.4. The

of eacmethouid. Bashrink

S = V0

whereume othe nAt leasmean v

2.3.5. Dri

balancglass b60 minFrancetissue on therehydrEq. (4)

Rreh =

wheredrationtreatm

2.3.6. Abo

and afmamexed wity betnormamushreters (featurecolor c(Eqs. (5(Hosse

CH =[

BI = 10

E =[

whereseven treatm

2.3.7. She

TA.XTPdale, Nculated for each treatment.

kageumes of both blanched and dried mushroom slicesing treatment were measured by the displacement

which distilled water was used as the reference liq-on the measurements of the sample volume, volumeas calculated using Eq. (3) (Nowacka et al., 2012):

100 (3)

he shrinkage of the mushroom slices (%), V0 is the vol- blanched mushroom slices before drying (cm3), Vf islume of the mushroom slices at the end of drying (cm3).ee repetitions were performed for each sample and the

was calculated.

dration ratioushroom slices were weighed using an electronic digitaldel Radwag, AS 220/C02, Radom, Poland), then put into

rs containing 150 ml distilled water to be rehydrated forC in a water bath (Polystat, Bioblock Scientic, Illkirch,

er 1 h, they were moved from the water, dried off withr in order that their excess water would be removedace, and weighed (Taghian Dinani et al., 2014b). The

ratio (Rreh) of the sample was calculated according ton et al., 2011):

m0

0(4)

d m0 are the weight of the sample after and before rehy-pectively. Three repetitions were performed for eachnd mean value was calculated.

urface, color measurement of mushroom slices beforef each drying treatment was conducted using a chro-pectrophotometer (Model CM 3500d, Minolta, Japan)n 8-mm-diameter aperture. To reduce the heterogene-

different raw samples, the L*, a*, and b* values were by subtracting the initial values from values of dried

slices. In this study, all three color retention param-L*, a0*a* and b0*b*) were considered as the colorlso, the chroma (CH), browning index (BI), and totale (DE) were calculated from the L*, a* and b* values

respectively) to describe the color change during dryingur et al., 2013):

b2]0.5

(5)

a + 1.75L5.645L + a 3.012b 0.31

)(6)

L)2 + (a0 a)2 + (b0 b)2]0.5

(7)

cript 0 indicates blanched mushroom slices. At leastched and dried mushroom slices were used for eachor maximum accuracy.

strengthtrength of mushroom slices was measured using aTexture Analyzer (Texture Technologies Corp., Scars-

able Micro Systems, Godalming, Surrey, UK), equipped

420 S. Taghian Dinani, M. Havet / Industrial Crops and Products 70 (2015) 417426

with a 5 kg load cell with a sensitivity of 0.1 g at room tem-perature. The probe was cylindrical with a puncture diameter of3.2 mm and pre-test, test and post-test probe speeds were 60, 100,and 600 mm/min, respectively. The probe was penetrated into themushroom slices placed over a 6.1 mm diameter hole generatedin a plate (100.2 90.0 mm2 dimensions), and the force deforma-tion curve was developed and analyzed using the software textureexponent 5, 1, 0, 0. (Stable Micro System Ltd., Surrey, UK). The max-imum force was calculated by making one puncture in each sampleaccording to the following equation:

SS = FDL

(8)

where F is maximum resistance force (N), D is probe diameter (m),L is slice thickness (m) and SS is shear strength (N/m2). The meanvalue of shear strength from at least ve measurements was calcu-lated for ea

2.3.8. ScannThe inte

ity and texinterior struing treatmealuminum bscope (EVO

2.4. Statisti

In this sblock desigprocessing and air velotions on ncontent, pocolor. A muusing Fishe95% condeXVI softwaFurthermorison betweconvective-20 kV0.4 mtwo pure cIn order ttreatmentswere used.mean stan

Fig. 2. Variation of drying rate with moisture content (kg water/kg dry matter) ofmushroom slices at different combined convective-EHD drying treatments.

ults

rying

2 deter/kned c, 20,). Throceshe p

averith

h. In hade dry

1.40 kV0ore, creas

ush inteertianvec

pleass tadecshro

for 2 comir veegarsult

Ahmedou et al. (2009) and Ramachandran and Lai (2010)

Table 1GLMANOVA lices.

Fvalue

ear strength Color parameters

L* a* b* C* BI* E*

Voltage .985n.s 3.097n.s 1.890n.s 1.083n.s 1.147n.s 0.793n.s 0.902n.s

Velocity .460*** 0.678n.s 5.893* 6.228* 6.647* 8.566* 6.037*

Voltage ve .154** 0.551n.s 3.041n.s 1.404n.s 1.434n.s 1.597n.s 1.395n.s

n.s: not signi* p 0.05; s

** p 0.01; v*** p 0.001; ch treatment (Taghian Dinani et al., 2014b).

ing electron microscopyrior structure is very important in rehydration abil-ture properties of dried products. To investigate thecture of button mushroom slices during different dry-nts, a small piece of sample was cut and kept on anase and photographed using a scanning electron micro--40, Zeiss, Germany) (Pei et al., 2013).

cal analysis

tudy, a factorial experiment in a randomized completen (RCBD) was used to investigate the effects of the twoparameters (voltage at four levels of 0, 20, 25, and 30 kVcity at two levels of 0.4 and 2.2 m/s) and their interac-al product qualities, such as their remaining moisturerosity, shrinkage, rehydration ratio, shear strength andltifactor ANOVA procedure and a multiple range testrs least signicant difference (LSD) procedure at thence level were performed by the Statgraphics Centurionre (StatPoint Technologies, Inc., Warrenton, VA, USA).e, complete randomized design was used for compar-en eight drying treatments consisting of six combinedEHD drying treatments (30 kV0.4 m/s, 25 kV0.4 m/s,/s, 30 kV2.2 m/s, 25 kV2.2 m/s, 20 kV2.2 m/s) and

onvective treatments (0 kV0.4 m/s and 0 kV2.2 m/s).o assess signicant differences among these eight, the aforementioned statistical method and software

The results reported in this study are presented asdard deviation (SD).

3. Res

3.1. D

Fig.(kg wacombiages (02.2 m/sEHD pthan tlowestmin)) wafter 50.4 m/saveraghigh asand 30Therefage inwhen mvoltageow inthe cothe samand mRattanthe mutimes mentshigh astant rThis reof Ould

results for the effect of voltage and air velocity on quality attributes of mushroom s

Responses

Moisture content Porosity Shrinkage Rehydration ratio Sh

5.340* 3.857* 11.712** 10.825** 049.645*** 43.417*** 28.678*** 76.006*** 86

locity 6.648** 5.490* 9.864** 17.839*** 12

cant.ignicant correlation.ery signicant correlation.extremely signicant correlation.and discussion

rate

picts the drying rate variation versus moisture contentg dry matter) of the mushroom slices under differentonvective-EHD drying treatments at four levels of volt-

25, and 30 kV) and two levels of air velocities (0.4 andis gure shows that the mushroom slices exposed tos at low air velocity of 0.4 m/s were dried much fasterure convective treatment of 0.4 m/s0 kV, having theage drying rate (0.023 0.001 (kg water/kg dry matterthe decrease of moisture content to only 81.90 1.49%other words, increasing voltage at the low air velocity of

a major effect on enhancing the drying rate so that theing rate ratios of mushroom slices for 5 h would be as, 1.56, and 1.78 times for 20 kV0.4 m/s, 25 kV0.4 m/s,.4 m/s treatments compared to 0 kV0.4 m/s treatment.

the average drying rate increased as the applied volt-ed at the low air velocity of 0.4 m/s (Fig. 2) becauseroom slices dry at a low cross-ow velocity and a largensity, the electric body force will be superior over the

(Lai et al., 2004). In this way, corona wind improvestive heat transfer coefcient and evaporation rate on

surface exposed to convective ow, resulting in heatransfer enhancement in the sample (Chaktranond andho, 2010). However, the average drying rate ratios ofom slices for 5 h were as high as 1.08, 1.03, and, 0.970 kV2.2 m/s, 25 kV2.2 m/s, and 30 kV2.2 m/s treat-pared to the 0 kV2.2 m/s treatment. Therefore, for thelocity of 2.2 m/s, the drying rate remained fairly con-dless of the corona wind production in EHD process.coincides with what has been found in other studies

S. Taghian

Dinani,

M.

Havet

/ Industrial

Crops and

Products 70

(2015) 417426

421

Table 2Effect of voltage on quality attributes of mushroom slices.

Variable Responses

Voltage (kV) Moisturecontent (%)

Porosity (%) Shrinkage (%) Rehydrationratio

Shear strength(106 N/m2)

Color parameters

L* a* b* C* BI* E*

0 49.64 37.37a 18.89 10.98b 78.33 14.86b 2.18 0.95c 10.30 10.20a 1.63 0.85a 1.77 1.37a 5.83 5.08a 5.87 5.12a 15.55 12.75a 6.47 5.06a20 40.66 25.96ab 24.32 7.09a 86.87 5.86a 2.46 0.56bc 10.72 7.44a 1.40 0.96ab 2.39 1.08a 8.48 2.78a 8.60 2.89a 21.76 8.39a 9.00 2.79a25 32.54 24.71bc 25.52 6.42a 90.39 5.64a 2.53 0.36b 10.52 5.60a 0.64 0.59ab 2.75 0.70a 7.48 1.48a 7.66 1.25a 19.77 0.75a 8.06 1.22a30 21.86 5.33c 24.69 1.35a 92.38 1.90a 2.87 0.11a 12.59 2.46a 0.17 0.23b 1.78 0.50a 9.33 3.95a 9.41 3.84a 21.27 7.27a 9.56 3.79a

Data are shown as the mean standard deviation (SD). For each response in this table, means in each column not sharing the same lowercase letters are signicantly different (p 0.05).

Table 3Effect of air velocity on quality attributes of mushroom slices.

Variable Responses

Velocity (m/s) Moisturecontent (%)

Porosity (%) Shrinkage (%) Rehydrationratio

Shear strength(106 N/m2)

Color parameters

L* a* b* C* BI* E*

0.4 54.21 25.01a 18.29 6.15b 82.14 11.61b 2.13 0.62b 6.10 4.46b 1.12 1.08a 1.75 0.93a 5.97 2.99a 6.06 2.93a 14.95 5.85a 6.53 2.83b2.2 18.15 5.49b 28.42 3.30a 91.85 1.38a 2.88 0.13a 15.97 3.26a 0.80 0.66a 2.60 0.86b 9.58 3.08b 9.71 3.09b 24.23 7.28b 10.02 3.04a

Data are shown as the mean standard deviation (SD). For each response in this table, means in each column not sharing the same lowercase letters are signicantly different (p 0.05).

422 S. Taghian Dinani, M. Havet / Industrial Crops and Products 70 (2015) 417426

Fig. 3. Effect slices after 30case letters ar

who pointea high air v

3.2. Remain

Table 1 depicts thaaction of von the remResults shoslices treateless than thwhile theremoisture coages (Tabledried mushthan that oobtained bythe remainisignicantlgure that moisture conot signicof 20 kV0.greater thawhile the Emean of 15.the largest room slices30 kV2.2 mindicate tha30 kV voltaas treatmenof the nal with 0 kV030 kV0.4 mTherefore, tage increasthe low croing rate inctransfer rating force (Tvelocity is athe water when the aturbed by ta large vapsample sur

ffect os the micant

r (eve ratV2.22.2 more, tsingiffer

n of 009)

rosit

osityto tshowse o

ana evi

oomlices6 3e por

diff kV.4 m/entsthat tionslicesty incs 2 anlicesoltae inof different treatments on nal moisture content (%) of mushroom0 min. Data are shown as the mean SD. Means with different lowere signicantly different (p 0.05).

d out the suppression of corona wind by cross-ows atelocity.

ing moisture content

obtained by the factorial statistical analysis methodt the voltage (p 0.05), velocity (p 0.001), and inter-oltage and velocity (p 0.01) had an evident impactaining moisture content of the dried mushroom slices.w that remaining moisture content of the mushroomd at 30 and 25 kV voltages were signicantly (p 0.05)ose of mushroom slices treated at 20 and 0 kV voltages

was no signicant difference between the remainingntent of the mushroom slices dried at 25 and 30 kV volt-

2). In addition, the remaining moisture content of theroom slices of 2.2 m/s was signicantly (p 0.001) lessf mushroom slices treated at 0.4 m/s (Table 3). Results

CRD statistical analysis presented in Fig. 3 shows thatng moisture content of the dried mushroom slices wasy affected by treatments (p 0.001). It is seen from this0 kV0.4 m/s treatment had the maximum remainingntent with a mean value of 81.90 1.49%, which wasantly different from the remaining moisture content4 m/s treatment (63.09 2.90%), but was signicantlyn the remaining moisture content of other treatmentsHD treated mushroom slices of 25 kV2.2 m/s with a84 11.06% had the minimum moisture content. In fact,water loss after 5 h of drying occurred in the mush-

treated at 25 kV2.2 m/s, 0 kV2.2 m/s, 20 kV2.2 m/s,/s, and 30 kV0.4 m/s processes. Therefore, the resultst the moisture content of the EHD-treated samples at

ge and the low air velocity of 0.4 m/s reduced as muchts at the high air velocity of 2.2 m/s. The average ratiosmoisture content of the mushroom slices dried for 5 h

Fig. 4. Eshown aare sign

transfeaveragby 0 k30 kVTherefslices uof the dventioet al., 2

3.3. Po

Porpared Fig. 4 respontisticalhad anmushrroom sto 30.3that thicantlyand 300 kV0treatmcates interacroom porosi(Tableroom s30 kV vincreas.4 m/s treatment to 20 kV0.4 m/s, 25 kV0.4 m/s, and/s treatments were as high as 1.30, 1.66, and 3.63 times.he nal moisture content decreased as the applied volt-ed from 0 kV to 30 kV for the experiments conducted atss-ow of 0.4 m/s. This result is consistent with the dry-rease of these treatments. The improvement in masse could be attributed to the corona wind as a key driv-aghian Dinani et al., 2014d). In fact, when a low airpplied and the electric body force is not strong enough,vapor is mostly conned to the boundary layer. Butpplied voltage increases, the boundary layer is per-he strong corona wind; leading to the production ofor concentration gradient between the water in theface and the air above and the increase of the mass

and 30 kV v0 kV voltagindicate thavelocity waslices treate2.2 m/s, in cair velocityvoltage or athe surfacetion of thesthe higher pthe more wFrom Figs. as water isf different treatments on porosity of dried mushroom slices. Data areean SD. For each response, means with different lower case letters

ly different (p 0.05).

aporation) rate (Huang and Lai, 2010). However, theios of the moisture content of the mushroom slices dried

m/s treatment to 20 kV2.2 m/s, 25 kV2.2 m/s, and/s treatments were 0.96, 1.10, and 0.82 times (Fig. 3).he enhancement in the moisture removal of mushroom

2.2 m/s air velocity remained fairly constant regardlessent intensity of the corona wind application due to pre-the corona wind by a high air velocity (Ould Ahmedou.

y

is dened as volume fraction of total pores com-he total volume of a sample (Russo et al., 2013).s a comparison between mean values of porosity

f the dried mushroom slices obtained by CRD sta-lysis method. This gure shows that the treatmentsdent impact on the porosity response of the dried

slices (p 0.01). The porosity for the dried mush- ranged from 9.56 1.79% for 0 kV0.4 m/s treatment.59% for 25 kV2.2 m/s treatment. The results indicatesosity value for 25 kV2.2 m/s treatment was not signif-

erent from 20 kV2.2 m/s, 0 kV2.2 m/s, 30 kV2.2 m/s,0.4 m/s treatments. Moreover, the porosity value fors treatment was signicantly different from all of other

(Fig. 4). One-way ANOVA presented in Table 1 indi-the voltage (p 0.05), velocity (p 0.001), and the

of velocity and voltage (p 0.05) affected the mush- porosity signicantly. The results conrm that thereases as the voltage and drying air velocity increasesd 3, respectively). In fact, the porosity of the dried mush-

at 0 kV was signicantly less than that at 20, 25, andges (p 0.05). In addition, a 28.74%, 35.10%, and 30.70%

the porosity of the mushroom slices treated at 20, 25,

oltages in comparison to the porosity of those treated ate was calculated, respectively. Furthermore, the resultst the porosity of the dried mushroom slices of 2.2 m/ss signicantly (p 0.001) more than that of mushroomd at 0.4 m/s velocity. A 55.38% increase in the porosity ofomparison to that of mushroom slices treated at 0.4 m/s, was calculated. In fact, fast drying obtained at a higherir velocity (Fig. 2) has led to a mechanical stabilization of

(Sturm et al., 2012), resulting in more porosity produc-e treatments (Taghian Dinani et al., 2014b). In addition,orosity of these drying treatments can be attributed toater evaporation and production of more empty holes.3 and 4, it can be concluded that porosity increases

removed from the sample. Yan et al. (2008) reported

S. Taghian Dinani, M. Havet / Industrial Crops and Products 70 (2015) 417426 423

Fig. 5. Effect oare shown as letters are sign

mango poring air-dryiin this studslices.

3.4. Shrinka

One-wayslices shrindried by 0 klowed by 2shrinkage owas the higity, and therespectivelythese factorResults showas signicbut there wues of the was a 10.90mushroom in comparisvoltage (Taage for diffamount of wet al., 2011)that of othetreatment wtheir moisttioned leveet al. (2012)ture is remet al. (2012age of the the cell struture contenshrinkage oconvective to cell wall2001a) accoing. Alemrabetween thing by EHDsignicant, ing was lesshrinkage oture. This re

ffect SD. Foifferen

ffect SD. Foiffere

reported that the ultrasound treated apples exhibited higherage and simultaneously higher porosity than untreated sam-hese simultaneous phenomena are consistent with our

hydration ratio

VA established the existence of a signicant differencemean values of the rehydration ratio of the dried mush-slices among different treatments (p 0.001). As seen in

the rehydration ratio of the mushroom slices dried by.4 m/s treatment was the lowest, but that of those dried2.2 m/s treatment was the highest. This gure also indi-hat the rehydration ratio value for 0 kV0.4 m/s treatmentgnicantly different from all other rehydration ratio val-rthermore, 0 kV2.2 m/s treatment was not signicantlyf different treatments on shrinkage of dried mushroom slices. Datathe mean SD. For each response, means with different lower caseicantly different (p 0.05).

osity increase with a moisture content decrease dur-ng; this result is in consistent with the results obtainedy for combined convective-EHD drying of mushroom

ge

ANOVA indicates that treatments affect the mushroomkage (p 0.001) signicantly. The mushroom slicesV0.4 m/s treatment showed the lowest shrinkage, fol-0 kV0.4 m/s and 25 kV0.4 m/s treatments while thef the dried mushroom slices by 25 kV2.2 m/s treatmenthest. For the main factors of the voltage and air veloc-ir interaction, values of p 0.01, p 0.001 and p 0.01,, were obtained from an ANOVA test; therefore, alls have a signicant effect on the shrinkage response.w that shrinkage of the dried mushroom slices of 0 kVantly (p 0.01) less than 20, 25, and 30 kV voltages,as no signicant difference (p 0.05) in the mean val-shrinkage of 20, 25, and 30 kV voltages. In fact, there%, 15.40%, and 17.93% increase in the shrinkage of theslices dried at 20, 25, and 30 kV voltages, respectively,on to the shrinkage of mushroom slices dried at 0 kVble 2). It was reported that the magnitude of shrink-erent foods is affected by several factors, such as theater removed and drying conditions (Gumeta-Chvez

. In fact, although the shrinkage of 0 kV was lower thanr voltages (Table 2) or the shrinkage of 0 kV0.4 m/sas much lower than that of other treatments (Fig. 5),

ure content was much higher than that of other men-ls and treatments after 5 h of drying. Ochoa-Martnez

reported that the shrinkage increases linearly as mois-oved. This linear trend has been reported by Ponkham), too. Segura et al. (2014) reported that the shrink-

Fig. 6. Emean cantly d

Fig. 7. Emean icantly d

(2012)shrinkples; tstudy.

3.5. Re

ANOin the room Fig. 6,0 kV0by 0 kVcates twas siues; fuapple wall cell is a function of the water content incture and signicant shrinkage occurred at the mois-t, equal or less than 50%. Another reason for extensivef the EHD-convective treatments, in comparison to puredrying, may be associated with the cellular collapse due

and cell membrane damages (Bajgai and Hashinaga,rding to Fig. 8, which will be discussed in the follow-jabi et al. (2012) reported that although the differencee moisture content of the carrot slices after 5 h of dry-

process at 24 1 C and oven drying at 55 C was notthe shrinkage of the dried carrot slices using EHD dry-s than that using oven drying. In their study, lowerf EHD process may have been due to its low tempera-sult is not in agreement with our study. Nowacka et al.

different fr25 kV2.2 mstatistical athe rehydravoltage (p ity and volincreased rshows that30 kV voltadried at 0, 2ference (p mushroomand 11.85%treated at 0of different treatments on rehydration ratio. Data are shown as ther each response, means with different lower case letters are signi-t (p 0.05).

of different treatments on shear strength. Data are shown as ther each response, means with different lower case letters are signif-nt (p 0.05).om 20 kV2.2 m/s, 30 kV0.4 m/s, 30 kV2.2 m/s, and/s treatments. The results obtained by the factorialnalysis method presented in Table 1 indicate thattion ratio values were signicantly inuenced by the

0.01), velocity (p 0.001), and the interaction of veloc-tage (p 0.001). Increasing the voltage and velocityehydration ratio of the dried mushroom slices. Table 2

the rehydration ratio of the mushroom slices dried atge was signicantly (p 0.01) more than that of those0, and 25 kV voltages, but there was no signicant dif-

0.05) in mean values of the rehydration ratio of the slices dried at 0 and 20 kV voltages. A 24.04%, 14.28%,

reduction in rehydration ratio of the mushroom slices, 20, and 25 kV voltages, respectively, in comparison

424 S. Taghian Dinani, M. Havet / Industrial Crops and Products 70 (2015) 417426

Fig. 8. Scanninent drying trea

to that of thAlso, Table room slicesmore than a 35.21% incomparisonhigher rehytheir more had the lowcompared tdrying, alonple to devea higher amJadhav et a

ples, more water is absorbed by the highly porous structure; thisresult is in agreement with the present study. Another reason forthe higher rehydration capacity of the mushroom slices dried at

voltages and velocities might be due to their lower remain-istur.4 m/e to

ear s

s cletrease ohich

howsrang4 1

in highering mo0 kV0are abl

3.6. Sh

It iferent responure, walso sslices to 19.0resultsg electron micrographs of button mushroom slices dried with differ-tments of (A) 0 kV0.4 m/s, (B) 30 kV0.4 m/s, and (C) 30 kV2.2 m/s.

ose treated at 30 kV voltage, was calculated (Table 2).3 shows that the rehydration ratio of the dried mush-

of 2.2 m/s air velocity was signicantly (p 0.001)that of those dried at 0.4 m/s air velocity; moreover,crease in the rehydration ratio of 2.2 m/s air velocity in

to 0.4 m/s air velocity was calculated. A reason for thedration capacity of these samples can be attributed toporous structures. For instance, 0 kV0.4 m/s treatmentest porous structure and the lowest rahydraion ratio

o other drying treatments (Figs. 3 and 6). In fact, fasterg with higher voltage or air velocity, caused the sam-lop a porous structure, increasing its ability to absorbount of water during rehydration (Wang et al., 2014).

l. (2010) reported that during the rehydration of sam-

for 0 kV0.25 kV0.4 mstrength vaferent fromThe resultsshow that tby the veloage (p 0.0strength vathere was nstrength ofIncreasing vslices; in addried at 2.2that of muincrease in to 0.4 m/s athat shear scontent andIt was repoincreased wture of beanvice versa (

3.7. Color

Color inof the prodstatistical aference betparametersthat the room slicesinuenced interactionwere signiever, they interactiona* and for 0.4 m/s yellow coloparison to tthat the Cby the air icantly involtage (p the C* an(p 0.05); me content. For instance, the mushroom slices dried ats retain high moisture content (Fig. 3) and therefore,absorb less water (Fig. 6).

trength

ar from the data presented in Fig. 7 that the dif-tments had a signicant effect on the shear strengthf the dried mushroom slices (p 0.001). This g-

is obtained by CRD statistical analysis method, that the shear strength of the dried mushroomed from 1.56 106 N/m2 for 0 kV0.4 m/s treatment06 2.46 106 N/m2 for 0 kV2.2 m/s treatment. Thethis gure indicate that the shear strength value4 m/s treatment was not signicantly different from/s and 20 kV0.4 m/s treatments; moreover, the shear

lue for 0 kV2.2 m/s treatment was not signicantly dif- that for 20 kV2.2 m/s and 25 kV2.2 m/s treatments.

obtained by the factorial statistical analysis methodhe shear strength values were signicantly inuencedcity (p 0.001) and the interaction of velocity and volt-1); whereas, the effect of the voltage on the shearlues was not signicant (p 0.05) (Table 1). Therefore,ot a signicant difference in mean values of the shear

all investigated levels of voltage (p 0.05) (Table 2).elocity increased shear strength of the dried mushroomdition, the shear strength value of the mushroom slices

m/s air velocity was signicantly (p 0.001) more thanshroom slices dried at 0.4 m/s air velocity. A 161.80%the shear strength of 2.2 m/s air velocity, in comparisonir velocity, was observed (Table 3). Figs. 3, 5, and 7 showtrength increase is related to the decrease of moisture

increase of the shrinkage of the dried mushroom slices.rted for drying cocoa sample beans that their hardnessith the decrease in moisture content, because the struc-s were soft and swollen at high moisture content, and

Hii et al., 2012).

uences consumers acceptability and the market valueucts (Wang et al., 2014). The results obtained by CRDnalysis method shows that there was no signicant dif-ween the values of L*, a*, b*, C*, E*, and BI*

in different drying treatments (p 0.05). Table 1 showsL* values (the lightness reduction of the dried mush-

in comparison to blanched mushroom slices) wereneither by the voltage and air velocity nor by their

(p 0.05). This table also shows that the a* and b*cantly inuenced by the air velocity (p 0.05); how-were not signicantly inuenced by the voltage and

of the velocity and voltage (p 0.05). In fact, absoluteb* values for 2.2 m/s were obviously more than thoseair velocity, which means an increase in the red andrs of the dried mushroom slices, respectively, in com-he blanched mushroom slices. In addition, Table 1 shows*, BI*, and E* values were signicantly inuenced

velocity (p 0.05); nonetheless, they were not signif-uenced by the voltage and interaction of velocity and

0.05). Table 2 shows that increasing velocity increasedd BI* absolute values of the dried mushroom slicesoreover, a 60.23% and 62.07% increase in C* and BI*

S. Taghian Dinani, M. Havet / Industrial Crops and Products 70 (2015) 417426 425

absolute values of 2.2 m/s air velocity, respectively, in comparisonto 0.4 m/s air velocity were calculated. In this study, the value of C*was positive and more than C0*, indicating that the treated sam-ples were more saturated, possibly because of the loss of waterand the conAlso, BI* duction of the Maillard(Hosseinpoity showed be attributenon-enzymated at its lothe E for 2this observablanched m1999), appland Hashinshowed no to oven dryience betweslices at 2045 C for boin this papresults; howences in thetime, and Emushroom (EHD) dryinobtained leslices as thedifference battributed t

3.8. Morph

The mic0 kV0.4 m/observed uFig. 8. The uture can be o(Fig. 8A) altIn addition,at 30 kV0.4C). These nelular tissue due to mor30 kV0.4 mstructure intion is in linconvective-parison to 0

4. Conclus

In this stconvective-the effects oels of air veproperties otent, porosiand microssummarize

Drying rate at the low air velocity of 0.4 m/s increases as the volt-age increases because drying rate can be enhanced by the coronadischarge electrostatic eld.

At 0.4 m/s cross-ow, the enhancement in water evaporationasedelociorati

by tstronnto ar streemai, she

and unifoushr

a scahrin

withdrati

refoross-suchty anmproemean bmpaher s

wled

cial tped t

nces

abi, A.uationot cyliu, M.,mber.R., Hang Tec.R., Hang Tecond, ncem

and l, I., 20237, Jiangacterirod. P., Prasaowav521.

-Chvbay-Fee atro

ngemega, F., ) dry

Law, Ca beanpour, Sputer ng dry., Lai

trosta.B., V

r cabin607.centration of pigments (Ochoa-Martnez et al., 2012).increased as drying proceeded. It means that the pro-brown pigments in the sample tissue emerges from

reaction and samples shrinkage during drying processur et al., 2013). The treatments dried at 2.2 m/s air veloc-a greater color change (Table 3); this phenomenon cand to either a higher concentration of pigments or theatic (Maillard) browning reaction, which was acceler-wer moisture content (Vsquez-Parra et al., 2013). Also,.2 m/s increased more than that for 0.4 m/s air velocity,tion denotes a greater color change from the referenceushroom slices. HEF-dried whey protein (Xue et al.,

e slices (Hashinaga et al., 1999), Japanese radish (Bajgaiaga, 2001a), and spinach (Bajgai and Hashinaga, 2001b)discoloration in the HEF-drying method in comparisonng. Our results show that there was no signicant differ-en combined convective-EHD drying of the mushroom, 25, and 30 kV voltages and pure convective drying atth air velocity of 0.4 and 2.2 m/s. The results presenteder is different from these results. Compared to theseever, this difference might be caused by the differ-

experimental conditions such as temperature, dryingHD systems. Our previous study showed that puttingslices in hot air combined with an electrohydrodynamicg system at 60 C until constant moisture content wasd into an increase in E value of the dried mushroom

voltage increased (Taghian Dinani et al., 2014b). Thisetween our previous study and the present one can beo the previously mentioned reasons.

ology of mushrooms

rostructure of the button mushroom slices dried ats, 30 kV0.4 m/s, and 30 kV2.2 m/s treatments weresing a scanning electron microscopy as presented inniform honeycomb network and less collapsed struc-bserved in the mushroom slices treated at 0 kV0.4 m/shough this honeycomb network was lled with water.

the morphologies of the dried mushroom slices treated m/s and 30 kV2.2 m/s have been shown in Fig. 8(B andtworks are relatively dense with more collapse of cel-and shrinkage and their ber structures arrange tightlye water removal. In other words, dehydrated slices by/s and 30 kV2.2 m/s treatments show a more wrinkled

comparison to those by 0 kV0.4 m/s. This observa-e with the nding which indicates that these combinedEHD treatments depict a high shrinkage value in com-

kV0.4 m/s treatment.

ion

udy, a setup for experimental investigation of combinedEHD drying of mushroom slices was constructed andf four levels of voltage (0, 20, 25, and 30 kV) and two lev-locity (0.4 and 2.2 m/s) on drying kinetics and physicalf mushroom slices, including remaining moisture con-ty, shrinkage, rehydration ratio, shear strength, color,tructure after 5 h were investigated. The results can bed as follows:

increair vevapwind

The led isheathe rratioC*,

The of mwithless slledrehy

Thelow crslices (porosias an ienhancslices ction coin anot

Ackno

Spedevelo

Refere

Alemrajevalcarr

Bai, Y., Qcucu

Bajgai, TDryi

Bajgai, TDryi

Chaktranenhasizes

Doymaz23, 7

Duan, Z.charBiop

Giri, S.Kmicr512

GumetaGariAgavarra

Hashina(EHD

Hii, C.L.,coco

Hosseincomduri

Huang, MElec

Jadhav, Dsola600 with an increase in the applied voltage; but using thety of 2.2 m/s reduced the electric eld effect on theon enhancement due to the suppression of the coronahe high air velocity.ger corona wind produced by higher voltage intensity

higher level of moisture removal, shrinkage, porosity,ngth, and rehydration ratio of mushroom slices. Also,ning moisture content, porosity, shrinkage, rehydrationar strength, E*, and the absolute values of a*, b*,BI* increased with an increase in the air velocity.rm honeycomb network and less collapsed structureoom slices dried at 0 kV0.4 m/s, which are observednning electron microscopy, can be used to explain thekage of the dried mushroom slices while their pores are

water and therefore, it can be used to explain their lesson ratio and porosity.

e, due to the advantages of the combination of 0.4 m/sow and high applied voltage for drying mushroom

as the increase of the drying rate, moisture removal,d rehydration ratio), this combination can be offeredved method for drying mushroom slices. In addition,nts in the drying rate and quality of the dried mushroome simultaneously achieved with low energy consump-red to the conventional methods that are investigatedtudy (Taghian Dinani and Havet, 2015).

gment

hanks are addressed to Christophe Coudel (Oniris) whohe experimental set-up.

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Effect of voltage and air flow velocity of combined convective-electrohydrodynamic drying system on the physical propertie...1 Introduction2 Materials and methods2.1 Experimental set-up2.2 Sample preparation2.3 Procedures2.3.1 Determination of moisture content2.3.2 Drying rate2.3.3 Porosity2.3.4 Shrinkage2.3.5 Rehydration ratio2.3.6 Color2.3.7 Shear strength2.3.8 Scanning electron microscopy

2.4 Statistical analysis

3 Results and discussion3.1 Drying rate3.2 Remaining moisture content3.3 Porosity3.4 Shrinkage3.5 Rehydration ratio3.6 Shear strength3.7 Color3.8 Morphology of mushrooms

4 ConclusionAcknowledgmentReferences