Microwave Finish Drying of Osmotically Dehydrated Cranberries

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Microwave Finish Drying of Osmotically DehydratedCranberriesC. Beaudry a; G. S. V. Raghavan a; T. J. Rennie aa Department of Agricultural and Biosystems Engineering, Macdonald Campus ofMcGill University. Sainte Anne-de-Bellevue. Canada

First Published on: 15 December 2003To link to this article: DOI: 10.1081/DRT-120025509URL: http://dx.doi.org/10.1081/DRT-120025509

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©2003 Marcel Dekker, Inc. All rights reserved. This material may not be used or reproduced in any form without the express written permission of Marcel Dekker, Inc.

MARCEL DEKKER, INC. • 270 MADISON AVENUE • NEW YORK, NY 10016

DRYING TECHNOLOGY

Vol. 21, No. 9, pp. 1797–1810, 2003

Microwave Finish Drying of Osmotically

Dehydrated Cranberries

C. Beaudry, G. S. V. Raghavan,* and T. J. Rennie

Department of Agricultural and Biosystems

Engineering, Macdonald Campus of McGill University,

Sainte Anne-de-Bellevue, Canada

ABSTRACT

Combined microwave and hot-air drying characteristics was studied

for the drying of cranberries that had been previously partially

dehydrated by osmosis in a high fructose corn syrup (76�Brix). A

750W 2450MHz microwave oven was used to dry cranberry samples

from 57% to 15% moisture content using three different power

densities (0.75, 1.0, 1.25W/g of initial cranberries) and two different

power cycles (30 s On/30 s Off and 30 s On/60 s Off ). All com-

binations of these variables were tested in triplicate. Quality of the

cranberries was measured using a universal testing machine, chroma-

meter, and with the use of a taste test panel. Drying times ranged

from 2.2 to 5.0 h. Power times and power cycles affected the drying

*Correspondence: G. S. V. Raghavan, Department of Agricultural and

Biosystems Engineering, Macdonald Campus of McGill University, 21 111

Lakeshore Road, Sainte Anne-de-Bellevue, QC, H9X 3V9, Canada; E-mail:

[email protected].

1797

DOI: 10.1081/DRT-120025509 0737-3937 (Print); 1532-2300 (Online)

Copyright & 2003 by Marcel Dekker, Inc. www.dekker.com

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time and the quality of the dried cranberries. Lower power densities

resulted in cranberries with higher quality. High power densities

(125W/g) resulted in the burning of some cranberries.

Key Words: Postharvest; Quality; Dehydration.

INTRODUCTION

Over the last few decades, it has been recognized that microwaveheating can lead to potential economic, engineering, and social benefits.[1]

Many researchers have shown the advantages of using microwavesin drying processes.[2–8] Radio frequency (RF) and microwaves (MW)are forms of electromagnetic wave energy, which are used in industrialapplications, such as drying of foodstuffs, wood, papers, and textile.Radio frequency and microwaves have a penetrating effect on theproduct, causing volumetric heating. Materials, that are absorbers andtransmitters of microwaves, are said to be dielectric, and when subjectedto microwaves, heat is generated throughout the material. The amount ofheat generated is dependant on such factors as the frequency and strengthof the electromagnetic field and the dielectric properties of the materialbeing heated.[3] The resulting energy is absorbed throughout the volumeof the material being dried. In fact, it is the increase in internal pressurethat drives out the moisture from the interior of the material to thesurface where evaporation occurs.[1,9] Radio frequency and microwaveheating is therefore often combined with conventional drying means inorder to enhance drying rates.

Power Density and Cycling Period

When applying microwave energy in a drying process, differentparameters need to be considered. For example, the amount of generatedmicrowaves according to the quantity of material being dried and themode (continuous or pulsed) in which microwaves are supplied tothe material are important factors. The power density is used to referto the amount of generated microwaves according to the mass of materialbeing dried. Power density is commonly expressed in units of Watts pergram of wet material (W/g).[10]

Microwaves can be generated via two different modes: by usingeither a pulsed or a continuous mode. However, research has shownthat continuous heating does not accelerate the rate of water removal

1798 Beaudry, Raghavan, and Rennie

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when critical moisture content is reached, and that there is no overalladvantage of using a continuous mode over a pulsed one.[5] In some casespulsed heating has been shown to be more energy efficient.[11] When usingpulsed heating, the microwave generator is turned off for a specificamount of time, and thus different power-on and power-off times canbe used. Yongsawatdigul and Gunasekaran[5] examined two power-ontimes (30 and 60 s) and three power-off times (60, 90, 150 s) whenmicrowave-vacuum drying cranberries. They determined that a power-on time of 30 s and a power-off time of 150 s were the most suitablesettings for maximum drying efficiency.

Dehydrated cranberries, especially those osmotically dehydrated orsugar infused, have recently become of interest to the food industry asthey can be added as a valuable ingredient to cookies, cakes, cereals,and other products due to the presence of natural colorants, mainlyanthocyanins, which fall into a class of antioxidants.

Convective drying of osmotically pretreated cranberries offers qualityand energy advantages over drying of raw cranberries.[12] The addition ofmicrowave energy to the drying process could be an alternative forenhanced drying rates.

OBJECTIVES

The objectives of this study were to evaluate the drying characteris-tics of osmotically dehydrated cranberries using a dielectric method,where microwaves and hot-air are combined to dry osmoticallydehydrated cranberries; to determine the appropriate microwave powerdensity and cycling period; and to perform a quality evaluation on thedried samples.

MATERIALS AND METHODS

All tests were performed on cranberries (Vaccinium macrocarpon) ofthe Stevens cultivar, which were grown on sandy soils and floodharvested. The fresh fruits were frozen after harvesting and werecompletely thawed by immersion in water at room temperature for 1 hjust prior to osmotic dehydration. The fruits were cut in half anddehydrated through osmosis, by placing the fruits in high fructose cornsyrup (76�Brix) at a 1:1 fruit to sugar ratio, at ambient temperature for24 h, as had been previously found to be the best conditions (unpublishedmaterial). The fruits were then rinsed with warm tap water and gently

Osmotically Dehydrated Cranberries 1799

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dried with towels. The samples were then refrigerated at 2�C until usedfor drying. The mean initial moisture content of fresh (thawed) cranber-ries was 88.0% (wet basis), and the mean moisture content of theosmotically dehydrated cranberries was 57% (wet basis) before drying.

Microwave Drying

The tests were performed using a custom designed laboratory scaleconvective and microwave dryer, shown in Fig. 1. The dryer wasequipped with a 750W, 2450MHz microwave generator (item 1).Generated microwaves traveled through rectangular waveguides to themain cavity (item 6). A circulator (item 2) absorbed the reflected micro-waves from the main cavity. Item 3 shows two power meters indicatingboth the incident and reflected power. Incident power was set accordingto the tested power density, which was based on the initial mass of thesample. Reflected power was maintained manually around zero duringthe experiments, via three tuning screws inserted in the top of the wave-guide assembly (item 4). Heated air was continually blown on the sampleplaced as a single layer on the sample holder (item 7), by a 0.25 kWblower (item 8) placed underneath the drying cavity. Three 2 kW-electrical heaters (item 9) were used to raise the air temperature. Thetemperature and velocity of the air were maintained constant throughout

1. MW Generator2. Circulator3. Power Meters4. Tuning Screws5. Strain Gauge6. MW Cavity7. Sample Holder8. Blower9. Heaters

6

8

1

32

9

7

4

5

Figure 1. Schematic of the experimental set-up for microwave and hot-air drying

of cranberries.


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the tests, at 62�C and 1m/s, respectively. The sample mass (initially 125 g)was monitored during the drying process, as the sample holder wasequipped with a strain gage (item 5). The inlet and outlet air temperaturewas measured with Type-K thermocouples, and the temperature of thesample was measured using a digital fiber optic thermometer (NortechFibronic Inc., Canada). All temperature, power, and mass data wererecorded by a data acquisition system (HP34970A—Data Acquisition/Switch Unit, Hewlett-Packard, USA). A computer program was writtenin HPVEE to monitor the drying process. The sample was removed whenit reached a moisture content of 15% (wet basis) and refrigerated at4� 1�C until quality evaluation was performed, one week later.

Power Density and Cycling Period

In order to determine appropriate power density and cycling period,combinations of these parameters were studied. Upon determiningthe critical limit of power density based on burning of the samples(approximately 1.5W/g), the selected power densities were 0.75, 1.0,and 1.25W/g based on the sample’s initial mass. Two different cyclingperiods were tested, 30 s On/30 s Off (30/30) and 30 s On/60 s Off (30/60).Osmotically dehydrated cranberries were dried under the six combina-tions of power density and cycling period, and all experiments werereplicated twice. The dried cranberries were then subjected to qualityevaluation.

Quality Evaluation

Three methods were selected to evaluate the quality of the driedcranberries. A sensory evaluation of the samples was performed, alongwith the measurement of its surface color and texture.

Sensory evaluation of a produce, though subjective, is an importantpart of quality evaluation since it represents the same procedure thatwould be used by a consumer. The hedonic scale that was used for thesensory evaluation of the dried cranberries is shown in Table 1. The maindrawback of this method is the subjectivity of the judges involved. Dueto the large number of samples evaluated, it was difficult to include thesame judges for all tests. However, since the judges differed from test totest, the data obtained is not valid for statistical analysis, but is stillconsidered important since it gives an idea of the consumer’s preference


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to the different samples. The judges were asked to evaluate the overallappearance and the taste of the samples.

Objective measurements, including surface color and texture, weredetermined. The color of dried product is one of the main attributes toevaluate quality. The color of cranberries is caused by red anthocyaninsand yellow flavonoids.[5] The surface color of the samples was measured byusing a chromameter (Model CR-300X, Minolta camera Co. Ltd., Japan)equipped with a 5mm diameter measuring area. The measurement wastaken on the external side of the cut cranberries and the mean of threemeasurements at the same location was taken. Five different fruits fromthe same sample were randomly tested. Mean color values of cranberriesdried with different treatments were compared to those of fresh (frozen-thawed) cranberries as a standard. The data obtained were in terms oflightness (L*), redness (a*), and yellowness (b*), but was converted tohue angle (h�), and Chroma (C*), an index somewhat analogous to colorsaturation or intensity.[13] Color difference (�E ) was also calculated inorder to evaluate the change in color between the fresh (frozen-thawed)and the dried cranberries.[13]

The textural characteristics of the dried samples were determinedusing the Instron Universal Testing Machine (Series IX AutomatedMaterials Testing System 1.16). Compression tests, using a Kramershear press, were performed on 15 g samples (for the osmoticallydehydrated samples) and 4 g samples (for the control sample). Thesemasses were used in order to have a single layer of dried fruits in the66mm by 66mm Kramer shear press cavity. A 50 kN load cell was usedand the crosshead speed for all tests was 160mm/min. Three sampleswere used for each trial (i.e., combination of power density and cyclingperiod). Different parameters were obtained, including Young’s Modulusand the toughness of the tested samples.

Table 1. Sensory evaluation scale

(Hedonic scale).

Score Description

1 Like extremely

2 Like very much

3 Like

4 Neutral

5 Dislike

6 Dislike very much

7 Dislike extremely


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Experimental Design

All experiments were conducted in triplicate and the data weresubjected to analysis of variance (ANOVA). Differences were identifiedas significant or nonsignificant based on the Student–Newman–Keuls testand Duncan’s multiple range tests for each variable (i.e., combination ofpower density and cycling period). A significance level of 0.05 was used inall cases.

RESULTS AND DISCUSSIONS

Drying Time and Sensory Evaluation

Table 2 summarizes the results for the total drying time and sensoryevaluation from the six combinations of power densities and cyclingperiods tested. Figure 2 represents the drying curves of the six com-binations, where the mean of three replicates was plotted. A significantdifference (P<0.05) in drying time was observed among the six combina-tions, where the shortest and longest drying times were for power densityof 1.25W/g with cycling period 30/30 and for power density of 0.75W/gwith cycling period 30/60, respectively. The drying time associated withcycling period 30/30 was always significantly lower than that associatedwith cycling period 30/60 for the same power density. Furthermore, somecombinations led to similar drying times with different power levels. Forexample, a lower power density of 0.75W/g, with cycling period 30/30,

Table 2. Drying time and sensory evaluation of cranberries

dried with microwaves at different power densities and cycling

periods.

Power density and

cycling period (on/off )

Drying

time (h)

Overall

appearance Taste

0.75W/g (30/30) 3.3b,c 2.5 2.2

0.75W/g (30/60) 5.0a 2.6 2.4

1.00W/g (30/30) 2.5d 3.2 2.8

1.00W/g (30/60) 3.6b 2.9 2.4

1.25W/g (30/30) 2.2d 3.8 3.0

1.25 W/g (30/60) 2.9c 3.0 2.4

Duncan groupings: means with the same letters are not

significantly different.


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resulted in similar drying times compared to higher power density, suchas 1.0W/g with cycling period 30/60 and 1.25W/g with cycling period30/60. However, even though the data obtained from sensory evaluationwas not statistically valid, a general trend was observed where the overallappearance was less acceptable with an increased power density. This canbe due to the fact that a small quantity of fruits tended to burn at aspecific location on the sample holder when higher power densities wereused. This indicates a possible nonuniform distribution of microwavesinside the cavity. When evaluating taste scores, similar results areobtained, with samples that were the most and the least acceptable,based on taste score, were obtained at conditions of power density of0.75W/g with cycling period 30/30 and power density of 1.25W/g withcycling period 30/30, respectively. Once again, this can be due to thetendency of some cranberries to burn at higher power densities. It istherefore reasonable to conclude that under the experimental conditionstested in this study, the lowest power density with cycling periods such as30/30 are more appropriate to produce acceptable products. However,the ideal power density was not studied in this work. Heating uniformitycan be improved if the product is allowed to be mixed in the heatingcavity, such as with a spouted bed method, which may allow for higherpower densities before burning occurs.[7]

The total drying time for the combined microwave and hot airdrying ranged from 2.2 to 5.0 h in this study. Preliminary studies onhot air drying resulted in drying times of 12.6 h. The same equipment

10

15

20

25

30

35

40

45

50

55

60

0 50 100 150 200 250 300 350

Time, min

Moi

stur

e co

nten

t, %

wb

A: 1.25 W/g 30s ON 30s OFFB: 1.25 W/g 30s ON 60s OFFC: 0.75 W/g 30s ON 60s OFFD: 0.75 W/g 30s ON 30s OFFE: 1.00 W/g 30s ON 30s OFFF: 1.00 W/g 30s ON 60s OFF

A EF C

DB

Figure 2. Mean drying curve of cranberries dried using microwave at different

power densities and cycling period.


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was used for the hot air drying, except that the microwave heating wasnot used.

Color Characteristics

Mean color values of cranberries dried under different microwaveconditions were compared to fresh (frozen-thawed) cranberries as a stan-dard. The data obtained for lightness (L*), redness (a*), and yellowness(b*), along with the calculated hue angle (h�), Chroma (C*), and colordifference (�E ) are shown in Table 3. No significant difference (P<0.05)was observed in the values of hue angle and total color difference, but asignificant difference (P<0.05) was observed for the Chroma index basedon Duncan Groupings.

When looking at the mean color differences for the six differentconditions, one would expect the value for power density of 1.0W/gwith cycling period 30/60 to be significantly lower than the othervalues. However, statistical analysis of the values based on Duncangroupings showed no significant difference. This can be due to thevariation within the values, which is not shown when looking at meanvalues. It was determined, from visual observations, that some cranber-ries dried under higher power densities, had a tendency to burn, thuspresenting a more brown or black surface color. When measuring coloron cranberries within one sample, the fruits were randomly selected.Therefore, cranberries that started to burn may have been picked, thusleading to variation of data within the same sample.

A significant difference (P<0.05) was observed for the Chroma indexwithin the six combinations; however, no significant difference was

Table 3. Effect of power density and cycling period in microwave drying of

cranberry on the mean surface color.

Power density and cycling period L* a* b* h� C* �E

0.75 W/g (30/30) 33.7 32.8 16.0 25.6a 36.6a 6.2a

0.75 W/g (30/60) 33.5 32.4 14.9 24.3a 35.7a,b 6.2a

1.00 W/g (30/30) 31.0 27.4 11.9 23.3a 29.8b,c,d 5.9a

1.00 W/g (30/60) 33.2 32.0 13.8 23.3a 34.9a,b,c 2.4a

1.25 W/g (30/30) 32.5 25.0 12.5 26.5a 27.9d 6.4a

1.25 W/g (30/60) 29.6 26.8 10.8 21.9a 28.9c,d 6.6a

Frozen thawed cranberries 34.0 30.9 13.4 23.3a 33.8a,b,c,d —

Duncan groupings: means with the same letters are not significantly different.


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observed between the standard (frozen-thawed fruits) and those driedunder the six combinations of power density and cycling period.Therefore, it can be stated that under the tested conditions, a possibleeffect on surface color by different power density and cycling periods wasnot observed.

Textural Characteristics

Toughness and Young’s Modulus were used to describe texture ofthe dried samples. These values are shown in Table 4 and were comparedwith the toughness and Young’s modulus of commercially available driedcranberries. A significant difference (P<0.05) among treatments wasfound for both Young’s modulus and toughness.

Cranberries dried under a power density of 1.25W/g with cyclingperiod 30/30 had values significantly different (P<0.05) than commercialCraisinsTM for both toughness and Young’s modulus. Also, cranberriesdried under a power density of 1.0W/g with cycling period 30/60 had atoughness value significantly different (P<0.05) than that of commercialCraisinsTM. As shown in Table 4, all other combinations of power densityand cycling period under the conditions tested appeared to have no effecton textural characteristics. It would, therefore, be appropriate to select acondition that would result in similar textural characteristics than thoseof the commercial samples. These results, along with those from dryingtime, sensory evaluation, surface color, and energy consumption willresult in selection of appropriate conditions for microwave drying ofcranberries.

Table 4. Effect of power density and cycling period on dried cranberry textural

characteristics.

Power density and cycling period

Young’s

modulus (Mpa)

Toughness

(MPa)

0.75W/g (30/30) 11.0a,b 0.020a,b

0.75W/g (30/60) 9.7a,b 0.017b

1.00W/g (30/30) 10.9a,b 0.020a,b

1.00W/g (30/60) 12.1a 0.021a,b

1.25W/g (30/30) 11.6a 0.024a

1.25W/g (30/60) 11.4a,b 0.021a,b

Commercial CraisinsTM 8.9b 0.016b



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Energy Consumption

The analysis of energy consumption in microwave drying is closelyrelated to drying times. In microwave-vacuum drying of osmoticallydehydrated cranberries, Yongsawatdigul and Gunasekaran[5] determinedthe most favorable value of drying efficiency for microwave power-onand power-off times was 30 and 150 s, respectively. The mean value ofthe drying efficiency under these conditions was 2.66MJ/kg, whichrepresents an improvement of about 40–60% over conventional hot-airdrying and about 46% over continuous microwave-vacuum drying.Yongsawatdigul and Gunasekaran[5] used Eq. (1) in order to calculatethe drying efficiency of their process:

DE ¼tonPð1�mf Þ10

�6

Miðmi �mf Þð1Þ

where DE is the drying efficiency (MJ/kg of water), ton is the total amountof time of microwave power (s), P is the microwave power input (W),Mi isthe initial mass of the sample (kg), mi and mf are the initial and finalmoisture content (fraction). It should be noted that althoughYongsawatdigul and Gunasekaran[5] consider this a drying efficiency, itis actually an energy consumption rate. This equation consideredthe energy demand due to the use of microwave, but did not take intoconsideration the energy demand from the vacuum used in these experi-ments. Equation (1) has been used in this work to determine an energyconsumption rate. The energy requirements to heat up and blow the air forthe convective part of the drying process are not considered here. Theenergy consumption rate was determined for each combination of powerdensity and cycling period, and results are shown in Table 5. The highestmicrowave energy demands occurred with power densities of 1.0 and1.25W/g with cycling period 30/30. In both conditions, the total time ofmicrowave power was large, due to the cycling period when microwaveheating took place half of the total process time. It is interesting to notethat a lower power density did not necessarily mean lower microwaveenergy consumption. For example, the combination of 0.75W/g withcycling period 30/60 resulted in higher microwave energy demands thanconditions of 1.0W/g also with cycling period 30/60. This was due to thelonger drying time observed with the lower power density, therefore thelonger total amount of time for microwave heating. In fact, the combina-tion of power density of 1.0W/g with cycling period 30/60 was the onlycondition significantly different (P<0.05) than the highest microwaveenergy demand at 1.25W/g with cycling period 30/30. The total time of


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microwave heating increased by 0.9%when the cycle period changed from30/30 to 30/60 when the power density of 0.75W/g. For the power densitiesof 1.0 and 1.25W/g, the total microwave heating time decreased by 4.6 and10.1%, respectively, comparing the 30/30 to 60/60 modes. The total energyconsumption significantly dropped with increased power density if theenergy for heating the air is included. This energy was constant and thepower input to the heaters was much larger than the power from themicrowave heating (by an order of magnitude). These values were notadded into the energy consumption rate because the amount of airflowthrough the product was significantly higher then required, and wouldresult in meaningless, exaggerated values.

CONCLUSIONS

Distinct differences were observed in drying times according to thevarious conditions applied, where the shortest time was found for1.25W/g with cycling of 30 s On/30 s Off. However, other factors,along with drying time, were considered in order to select appropriateconditions for microwave drying of cranberries. Results from the sensoryevaluation, although not statistically valid, showed a clear appreciationof cranberries dried at 0.75W/g with 30 s On/30 s Off, based on both tasteand the overall appearance.

Even though a significant difference (P<0.05) was observed in theChroma index for the surface color evaluation of the dried cranberries,no difference was detected on the total color difference of the fruits dueto different power density and cycling periods. However, from visualobservations, cranberries dried under higher power densities had a

Table 5. Mean values of drying efficiency based on microwave (MW)

consumption for different combinations of power densities and cycling periods.

Power density and

cycling period

Total time of MW

power (s)

MW power

input (W)

Energy consumption

(MJ/kg water)

0.75W/g (30/30) 5,886 94 8.9a,b

0.75W/g (30/60) 5,940 94 9.0a,b

1.00W/g (30/30) 4,518 125 9.1a,b

1.00W/g (30/60) 4,308 125 8.7b

1.25W/g (30/30) 3,924 156 9.9a

1.25W/g (30/60) 3,516 156 8.9a,b



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tendency to burn, resulted in a more brown or black surface color, whichwas unacceptable to the consumer, based on sensory evaluation scores.

It was also determined that cranberries dried under power densitiesof 1.0W/g with cycling period 30/60 and 1.25W/g with cycling periods30/30 and 30/60 presented significantly different (P<0.05) texturalcharacteristics than commercially available dried cranberries, based onthe toughness of the samples. These conditions were therefore less appro-priate since the end product should somehow resemble the commercialproduct, which is well accepted by consumers.

The energy demand through microwave drying under different con-ditions is another factor to be considered when selecting appropriatedrying conditions. The lowest energy demands were observed for thefollowing conditions: 0.75W/g with cycling period 30/30, 1.0W/g withcycling period 30/60, and 1.25W/g with cycling period 30/60. Since theselast two conditions did not give favorable results for textural character-istics, the combination of 0.75W/g with cycling period 30/60 wasappropriate to dry cranberries in this study. This combination resultedin a reasonably short drying time, a clear appreciation of both taste andoverall appearance from judges, similar textural characteristics comparedto commercial product, along with one of the lowest energy demandsobserved. Further studies are required at lower power densities todetermine the quality of the dried product. Unfortunately, decreasingthe power density may increase the drying time to unacceptable levelsfor a hybrid drying system.

REFERENCES

1. Sanga, E.; Mujumdar, A.S.; Raghavan, G.S.V. Principles and appli-cations of microwave drying. In Drying Technology in Agriculture andFood Sciences; Mujumdar, A.S., Ed.; Elsevier Science Publishers:NY, 2000; 253–289.

2. Cohen, J.S.; Ayoub, J.A.; Yang, T.C. A comparison of conventionaland microwave augmented freeze-drying of peas. In Drying ‘92;Mujumdar, A.S., Ed.; Elsevier Science Publishers: NY, 1992; 585–594.

3. Garcia, A.; Iglesias, O.; Roques, M.; Bueno, J.L. Microwave dryingof agar gels: kinetics parameters. In Drying ‘92; Mujumdar, A.S., Ed.;Elsevier Science Publishers: NY, 1992; 595–606.

4. Tulasidas, T.N.; Raghavan, G.S.V.; Norris, E.R. Microwave andconvective drying of grapes. Transactions of the ASAE 1993, 36(6), 1861–1865.


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5. Yongsawatdigul, J.; Gunasekaran, S. Microwave vacuum drying ofcranberries. Part I: energy use and efficiency. Part II: qualityevaluation. Journal of Food Processing and Preservation 1996,20 (2), 121–156.

6. Venkatachalapathy, K.; Raghavan, G.S.V. Microwave drying ofosmotically dehydrated blueberries. Journal of Microwave Powerand Electromagnetic Energy 1998, 33 (2), 95–102.

7. Feng, H.; Tang, J. Microwave finish drying of diced apples in aspouted bed. Journal of Food Science 1998, 63 (4), 679–683.

8. Laguerre, J.C.; Tauzin, V.; Grenier, E. Hot air and microwavedrying of onions: a comparative study. Drying Technology 1999,17 (7&8), 1471–1480.

9. Feng, H.; Tang, J.; Cavalier, R.P.; Plumb, O.A. Heat and masstransfer in microwave drying of porous materials in a spoutedbed. J. AIChE 2001, 47 (7), 1499–1511.

10. Raghavan, G.S.V.; Silveira, A.M. Shrinkage characteristics ofstrawberries osmotically dehydrated in combination with micro-wave drying. Drying Technology 2001, 19 (2), 405–414.

11. Gunasekaran, S. Pulsed microwave-vacuum drying of foodmaterials. Drying Technology 1999, 17 (3), 395–412.

12. Grabowski, S.; Marcotte, M.; Poirier, M.; Kudra, T. Dryingcharacteristics of osmotically pretreated cranberries—energy andquality aspects. Drying Technology 2002, 20 (10), 1989–2004.

13. McGuire, R.G. Reporting of objective color measurements.Hortscience 1992, 27 (12), 1254–1255.


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Microwave Finish Drying of Osmotically Dehydrated Cranberries