super heated steam drying

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Journal of Food Engineering 80 (2007) 1023–1030

Comparative study of different combined superheated-steamdrying techniques for chicken meat

Adisak Nathakaranakule *, Worawit Kraiwanichkul, Somchart Soponronnarit

School of Energy and Materials, King Mongkut’s University of Technology Thonburi, 91 Pracha u-tid Road, Bangkok 10140, Thailand

Received 14 December 2005; received in revised form 4 April 2006; accepted 10 April 2006Available online 13 October 2006

Abstract

The purpose of this study was to compare and evaluate different drying techniques for chicken meat, which was aimed as an ingredientfor ready-to-eat noodle. Two multi-stage drying techniques, i.e., superheated steam drying in the first stage followed by heat pump dryingin the second stage (SSD/HP), and superheated steam drying in the first stage followed by hot air drying in the second stage (SSD/AD),were proposed. The effects of superheated steam temperature and moisture content of chicken at the end of the first-stage drying on thedrying kinetics and quality of the dried product viz. color, shrinkage, rehydration ability were then evaluated. The results were also com-pared with those of purely superheated steam drying. SSD/HP was found to be the most suitable drying method for drying chicken as aningredient for ready-to-eat noodle.� 2006 Published by Elsevier Ltd.

Keywords: Color; Heat pump drying; Hot air drying; Microstructure; Rehydration behavior; Shrinkage; Superheated steam drying

1. Introduction

Dried chicken, either in sliced or in cubic form, can beused as an ingredient for ready-to-eat noodle. Hot air dry-ing is generally used to dry chicken for this purposealthough it is well known that this drying technique leadsto much quality degradation, in terms of both physical orchemical (nutritional) properties. Attempts have thereforebeen made recently to find alternative drying technologiesto produce dried products of higher quality. Among thetechnologies, the use of two-stage drying, which combinethe advantages of two drying techniques, such as combinedsuperheated steam drying and heat pump drying or com-bined superheated steam and hot air drying can be adopted(Namsanguan, Tia, Devahastin, & Soponronnarit, 2004).

Superheated steam has been used for drying severalproducts due to its many advantages, either from the dry-

0260-8774/$ - see front matter � 2006 Published by Elsevier Ltd.

doi:10.1016/j.jfoodeng.2006.04.067

* Corresponding author. Tel./fax: +662 427 9062.E-mail address: [email protected] (A. Nathakaranakule).

ing kinetics or product quality point of view (Li, Seyed-Yagoobi, Moreira, & Yamsaengsung, 1999; Namsanguanet al., 2004; Tarnawski, Mitera, Borowski, & Klepaczka,1996; Tang & Cenkowski, 2000).

This drying technique is an airless drying which usedhigh-temperature steam to transport heat to a product,making moisture inside evaporate from the product at itsboiling point with no diffusional resistance. Although dry-ing with high-temperature superheated steam leads toincreased drying rates and effective diffusion coefficients ofthe drying products (Prachayawarakorn, Soponronnarit,Wetchacama, & Jaisut, 2002; Li et al., 1999; Uengkimbuan,Soponronnarit, Prachayawarakorn, & Nathakaranakule,2005 Rordprapat, Nathakaranakule, Tia, & Soponronnarit,2005), the product quality, e.g., color and texture as well asnutritional quality, is much damaged. Two-stage dryingsuch as superheated steam drying in the first stage followingby heat pump drying in the second-stage (SSD/HP) orsuperheated steam drying in the first stage following byhot air drying in the second stage (SSD/AD) was found tobe an alternative drying technology as it can combine the

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Fig. 2. A Schematic diagram of the heat pump dryer.

1024 A. Nathakaranakule et al. / Journal of Food Engineering 80 (2007) 1023–1030

advantages of different drying techniques to improve theproduct quality (Namsanguan et al., 2004; Uengkimbuanet al., 2005).

In this study, two-stage drying techniques viz. SSD/HPand SSD/AD were proposed for drying chicken meat(breast section). The effects of superheated steam tempera-ture and moisture content of chicken at the end of the first-stage drying on the drying kinetics and quality of the driedchicken in terms of its color, shrinkage and rehydrationability were evaluated. The results were also compared withthose of purely superheated steam drying.

2. Materials and methods

2.1. Experimental setup

Details of the close-loop superheated steam dryer areshown in Fig. 1. The drying system consisted of four maindevices, i.e., a boiler with a steam generating capacity of31 kg/h, a 13.5-kW heater, a 0.3 · 0.3 · 0.1 m3 cabinetdryer, and a backward-curve blade centrifugal fan, whichwas driven by a 2.2 kW motor, to circulate steam throughthe drying system. The steam flow rate was controlled byvarying the revolution speed of the fan via a PID control-ler. The dryer was operated at the pressure slightly abovean atmospheric pressure.

The heat pump dryer, as shown in Fig. 2, composed oftwo main circuits, i.e., a heat pump and a dryer circuits.The heat pump circuit was operated with R-22 as a refrig-erant. It comprised of a 2.1-kW compressor, an 8.3-kWinternal and external condenser, a 6.2-kW evaporator,and a throttling valve. The dryer circuit composed of a for-ward-curve blade centrifugal fan, which was driven by a0.75 kW motor, air duct and a 0.83 · 0.6 · 0.74 m3 dryingchamber.

Fig. 1. A Schematic diagram of the superheated steam dryer. (1) Boiler;(2) Heater; (3) Drying chamber; (4) Blower.

Fig. 3. A Schematic diagram of the hot air dryer. (1) Blower; (2) Motor;(3) Blower inlet; (4) Drying Chamber; (5) Product tray; (6) Exit air duct;(7) Return air duct; (8) Chamber door; (9) Air control valve.

The hot air drying system was a fixed tray type, shownin Fig. 3, and was composed of a forward-curve blade cen-trifugal fan, which was driven by a 0.75 kW motor, a 4-kWheater and a 0.52 · 0.52 · 0.52 m3 cabinet dryer.

2.2. Materials

Chicken breast was purchased from a local supermarketand was sliced longitudinally to its muscle line into a pieceof 0.03 m thick by an electric slicer. The chicken piece wasthen cut to a size of 0.3 · 0.3 m2. Sixteen pieces of slicedchicken breast were used in each drying experiment.

Fig. 4. Drying curve of chicken undergoing superheated steam drying.MR ¼ X t�X eq

X i�X eqwhere Xt = moisture content of chicken meat at time t (%

d.b.), Xi = initial moisture content of chicken meat (% d.b.), Xeq = equi-librium moisture content of chicken meat (% d.b.).

Fig. 5. Temperature evolution of chicken during purely superheatedsteam drying.

A. Nathakaranakule et al. / Journal of Food Engineering 80 (2007) 1023–1030 1025

2.3. Methods

All experiments were setup by first warming the super-heated steam drying system with hot air to the desired dry-ing temperature in order to prevent the steam condensationwithin the system. Saturated steam was then fed into thesystem and was heated by the heater to become super-heated steam at the desired drying temperature before pass-ing through the drying chamber, within which the chickenmeat was placed on a tray, and circulated throughout thesystem by the blower. Some excess steam generated insidethe system as a result of the drying process was releasedfrom the system to maintain the system pressure.

For two-stage drying experiments, the heat pump andhot air dryers were also warmed up to the desired dryingtemperature before placing partially dried chicken meatobtained from the first-stage superheated steam dryer. Dry-ing was continued in each second-stage dryer until thechicken meat reached its desired final moisture contentsof around 0.11 kg/kg d.b.

The experiments were divided into three parts, i.e.,solely superheated steam drying (SSD), combined super-heated steam and heat pump drying (SSD/HP) and com-bined superheated steam and hot air drying (SSD/AD).Superheated steam drying experiments were conducted atthe temperatures of 120, 140 and 160 �C. In the case oftwo-stage drying experiments chicken was dried by super-heated steam to an intermediate moisture contents of either42.8% or 66.7% (d.b.) prior to introducing the meat intothe selected second-stage dryer. Both heat pump and hotair drying experiments were conducted at a constant dryingtemperature of 55 �C.

Measured qualities of the dried chicken were color,shrinkage and rehydration behavior. The color of the driedchicken was measured in Hunter system using a colorime-ter (JUKI, JP7100, Japan). The shrinkage of the driedchicken was measured by a volumetric replacement methodusing toluene as a working liquid. Percentage of shrinkagewas calculated as follows:

%shrinkage ¼ V 0 � VV 0

� 100;

where V0 is the initial volume of chicken, m3; and V is thevolume of dried chicken, m3.

The dried chicken was rehydrated in warm water withan initial temperature of 90 �C.

The change in mass of rehydrated chicken was measuredat one-minute interval for 10 min. The percentage of rehy-dration of the dried chicken was then calculated as follows:

%rehydration ¼ Mt �Md

Md� 100;

where Mt is the mass of rehydrated chicken at time t, kg;and Md is the mass of dried chicken, kg.

Finally, texture of the dried chicken was analyzed byscanning electron microscope (JEOL, JSM-5600LV, JEOLLtd., Japan) with an accelerating voltage of 10 kV.

3. Results and discussion

3.1. Drying kinetics of chicken meat

Fig. 4 shows the drying curves of chicken meat undergo-ing purely SSD at different temperatures. It is seen fromthis figure that the drying rate of chicken undergoingSSD increased with the drying temperature. This is dueto high heat transfer rate to the drying chicken at higherdrying temperature. As seen in Fig. 5, which shows thetemperature evolution of chicken meat undergoing SSD,the chicken temperature rose rapidly during the first thirtyseconds of drying and remained at 100 �C (more or less thesaturation temperature of steam at the operating pressure)for some time before continuously increasing to the set-point drying temperature. The rapid increase in tempera-ture was caused by the steam condensation (observablyoccurred at the beginning of drying). The constant-temper-

Fig. 8. Drying curve of chicken undergoing superheated steam drying andcombined superheated steam and heat pump drying at intermediate


ature period was found to be extended at lower dryingtemperatures.

This phenomenon implied that there was more conden-sation occurring at lower than at higher drying tempera-tures. Therefore, the time needed to evaporate the filmcondensate was longer. This effect of steam condensationwas also reported by Rordprapat et al. (2005), who studiedpaddy drying in a superheated steam fluidized bed dryer. Inboth two-stage drying techniques studied, the drying ratesof chicken during the superheated steam period were alsosimilar to that of purely SSD, as shown in region 1 of Figs.6–11.

The effective moisture diffusion coefficient of chickenmeat undergoing SSD, SSD/HP and SSD/AD wasassumed to be a function of temperature following theArrhenius equation:

Fig. 6. Drying curve of chicken undergoing superheated steam drying andcombined superheated steam and heat pump drying at intermediatemoisture contents of 42.8% and 66.7% d.b. and at superheated steamtemperature at 120 �C.

Fig. 7. Drying curve of chicken undergoing superheated steam drying andcombined superheated steam and heat pump drying at intermediatemoisture contents of 42.8% and 66.7% d.b. and at superheated steamtemperature at 140 �C.

moisture contents of 42.8% and 66.7% d.b. and at superheated steamtemperature at 160 �C.

Fig. 9. Drying curve of chicken undergoing superheated steam drying andcombined superheated steam and hot air drying at intermediate moisturecontents of 42.8% and 66.7% d.b. and at superheated steam temperature at120 �C.

Fig. 10. Drying curve of chicken undergoing superheated steam dryingand combined superheated steam and hot air drying at intermediatemoisture contents of 42.8% and 66.7% d.b. and at superheated steamtemperature at 140 �C.

Fig. 11. Drying curve of chicken undergoing superheated steam dryingand combined superheated steam and hot air drying at intermediatemoisture contents of 42.8% and 66.7% d.b. and at superheated steamtemperature at 160 �C.


Deff ¼ D0 exp�Ea

RT

� �ð1Þ

where D0 and Ea were calculated by fitting the analyticalsolution of Fick’s second law of diffusion to the experimen-tal data at different temperature; a thin slab geometry wasassumed for a chicken meat slice.

MR ¼ 8

p2

X1m¼0

1

ð2mþ 1Þ2exp �ð2mþ 1Þ2p2 Deff :t

L2

� � !ð2Þ

The values of D0, Ea and Deff of each superheated steamtemperature of superheated steam and two-stage dryingtechniques are shown in Table 1.

Region 2 of Figs. 6–11 illustrates the effect of intermedi-ate moisture content (moisture content at the end of thefirst stage drying) on the drying rate of chicken meat driedeither by heat pump dryer or hot air dryer in the secondstage. As shown in Figs. 6–11, chicken meat dried from

Table 1Effective moisture diffusion coefficients of chicken meat

Drying process Deff

(·10�8 m2/s)D0

(·10�6 m2/s)Ea

(kJ/kg)

SSD 120 �C 2.71 2.04 4362.145SSD 140 �C 4.64SSD 160 �C 7.74SSD 120 �C + HP (66.7% d.b.) 2.43 1.00 3714.812SSD 140 �C + HP (66.7% d.b.) 4.05SSD 160 �C + HP (66.7% d.b.) 6.17SSD 120 �C + HP (42.8% d.b.) 2.54 1.00 3605.083SSD 140 �C + HP (42.8% d.b.) 4.19SSD 160 �C + HP (42.8% d.b.) 6.99SSD 120 �C + AD (66.7% d.b.) 2.23 1.00 3874.369SSD 140 �C + AD (66.7% d.b.) 3.65SSD 160 �C + AD (66.7% d.b.) 5.30SSD 120 �C + AD (42.8% d.b.) 2.42 1.00 3661.969SSD 140 �C + AD (42.8% d.b.) 3.97SSD 160 �C + AD (42.8% d.b.) 6.70

an intermediate moisture content of 66.7% d.b. dried fasterin the second stage than that dried from 42.8% d.b. This isbecause when chicken meat was dried to an intermediatemoisture content of 42.8% d.b., it was exposed to a highertemperature environment during the first stage dryinglonger than that dried to an intermediate moisture contentof 66.7% d.b. This led protein in chicken with an interme-diate moisture content of 42.8% d.b. denatured and formedgel matrix more than the sample with an intermediatemoisture content of 66.7% d.b. As a result, it was more dif-ficult to remove the moisture inside the sample with anintermediate moisture content of 42.8% d.b. than thatinside the sample with an intermediate moisture contentof 66.7% d.b. However, the differences in the drying ratesbetween the two cases became less obvious when the mois-ture content of chicken was lower, as shown in region 3 ofFigs. 6–11. This is due to the fact that removal of moisturefrom the product at lower moisture contents becameincreasingly difficult, irrespective of the structure of thedrying material was.

The effects of the second-stage drying methods on thedrying rates of chicken are shown in Figs. 6–8 for the caseof heat pump drying and in Figs. 9–11 for the case of hotair drying. As is seen in these figures, SSD/HP was ableto dry chicken meat to the desired moisture content fasterthan SSD/AD. This is due to the advantage of the low rel-ative humidity environment in the heat pump drying sys-tem in accelerating the drying rate even at lower dryingtemperatures.

3.2. Colors

The colors of dried chicken are represented in terms of L

(lightness), a (redness) and b (yellowness) values. Theexperimental results of the colors of dried chicken meatin Table 2 show that the redness of chicken dried by purelySSD increased with the drying temperature. The values ofredness were also higher than that of chicken dried by bothcombined two-stage drying techniques. However, the val-ues of lightness and yellowness of chicken dried by SSDwere lower than those achieved from both combined two-stage drying techniques. These trends of color changesare attributed to the long exposure time of chicken to hightemperature environment when drying with SSD, resultingin more browning of sugar-amine, which was the result ofthe reaction between amine groups of muscle proteins andavailable reducing sugars in the connective tissue ofchicken (Forrest, Aberle, Hedrick, Judge, & Merkel,1975). By comparing between both two-stage drying tech-niques, it was found that chicken dried by SSD/AD hadstatistically higher redness values than those dried bySSD/HP, while the lightness and yellowness values ofchicken obtained from both combined techniques weremore or less the same. This is due to the longer drying timeof hot air drying than in the case of heat pump drying,making the chicken exposed to the drying medium longerand resulting in higher values of redness. The intermediate

Table 2Colors of dried chicken meat

Drying process Color parameter

L a b

SSD 120 �C 33.15 ± 2.81a 5.97 ± 0.45c 12.30 ± 0.57a

SSD 120 �C + AD (66.7% d.b.) 44.41 ± 0.74c,d 2.38 ± 0.17a,b 13.96 ± 0.12d

SSD 120 �C + AD (42.8% d.b.) 42.05 ± 3.65b,c 2.38 ± 0.49a,b 13.82 ± 0.42c,d

SSD 120 �C + HP (66.7% d.b.) 45.23 ± 0.13d 2.08 ± 0.07a 13.83 ± 0.13c,d

SSD 120 �C + HP (42.8% d.b.) 43.96 ± 3.08b,c,d 2.06 ± 0.39a 13.75 ± 0.44c,d

SSD 140 �C 35.09 ± 0.39a 7.56 ± 0.57d 12.30 ± 0.25a

SSD 140 �C + AD (66.7% d.b.) 43.10 ± 1.72b,c,d 2.43 ± 0.46a,b 13.79 ± 0.10c,d

SSD 140 �C + AD (42.8% d.b.) 40.70 ± 0.63b 2.37 ± 0.10a,b 12.88 ± 0.14b

SSD 140 �C + HP (66.7% d.b.) 40.78 ± 0.50b 2.25 ± 0.35a 12.92 ± 0.34b

SSD 140 �C + HP (42.8% d.b.) 41.25 ± 1.10b,c 2.12 ± 0.73a 13.69 ± 0.25c,d

SSD 160 �C 34.79 ± 0.54a 10.95 ± 0.91e 12.16 ± 0.17a

SSD 160 �C + AD (66.7% d.b.) 45.43 ± 2.11d 2.45 ± 0.12a,b 13.23 ± 0.13b,c

SSD 160 �C + AD (42.8% d.b.) 41.56 ± 1.60b,c 2.94 ± 0.14b 13.42 ± 0.38b,c,d

SSD 160 �C + HP (66.7% d.b.) 41.97 ± 0.65b,c 2.18 ± 0.25a 13.63 ± 0.34c,d

SSD 160 �C + HP (42.8% d.b.) 45.67 ± 0.37d 2.16 ± 0.09a 13.33 ± 0.45b,c

a–e in the same column with different superscripts mean that the data are significantly different (p < 0.05).


moisture contents, however, had no effect on the change incolors of dried chicken samples.(see Table 2).

3.3. Shrinkage

When proteins of chicken muscle exposed to heat, myo-fibril collagen is physically shortened to about one-third ofits original length at temperature as low as 56 �C and tohalf or more at temperatures around 61–62 �C or higher(Forrest et al., 1975). As is seen in Table 3, chicken meatdried by SSD was therefore much more shortened whenthe drying temperature increased. Comparing this resultwith those of both combined drying techniques, it revealedthat chicken dried by SSD had the least shrinkage due toless drying time.

Table 3Percentage of shrinkage of dried chicken meat

Drying process % Shrinkage

SSD 120 �C 50.70 ± 0.70a

SSD 120 �C + AD (66.7% d.b.) 57.13 ± 0.55c

SSD 120 �C + AD (42.8% d.b.) 56.70 ± 0.30c

SSD 120 �C + HP (66.7% d.b.) 55.00 ± 0.90b

SSD 120 �C + HP (42.8% d.b.) 54.73 ± 0.21b

SSD 140 �C 62.30 ± 0.10d

SSD 140 �C + AD (66.7% d.b.) 67.87 ± 0.15g

SSD 140 �C + AD (42.8% d.b.) 67.67 ± 0.35g

SSD 140 �C + HP (66.7% d.b.) 66.73 ± 0.21f

SSD 140 �C + HP (42.8% d.b.) 66.47 ± 0.15f

SSD 160 �C 65.17 ± 0.25e

SSD 160 �C + AD (66.7% d.b.) 70.57 ± 0.15h

SSD 160 �C + AD (42.8% d.b.) 69.97 ± 0.21h

SSD 160 �C + HP (66.7% d.b.) 67.83 ± 0.15g

SSD 160 �C + HP (42.8% d.b.) 67.85 ± 0.50g

a–e in the same column with different superscripts mean that the data aresignificantly different (p < 0.05).

Chicken dried by SSD/HP had less shrinkage than thatdried by the SSD/AD because the drying time of the for-mer technique was less than the latter and hence the lowerdegree of thermal deformation. Nevertheless, the effect ofintermediate moisture content on the shrinkage of driedchicken in each combined technique was not obviousbecause the drying time was not much varying with differ-ent cases.

3.4. Rehydration behavior

As shown in Table 4 the percentage of rehydration ofchicken meat dried by SSD increased with the drying tem-perature. This could be explained by the fact that whenchicken was heated its myofibril protein coagulated and

Table 4Percentage of rehydration of dried chicken meat

Drying process Rehydration

SSD 120 �C 57.17 ± 0.28a

SSD 120 �C + AD (66.7% d.b.) 61.48 ± 0.44b

SSD 120 �C + AD (42.8% d.b.) 62.04 ± 0.31b

SSD 120 �C + HP (66.7% d.b.) 67.21 ± 0.60d

SSD 120 �C + HP (42.8% d.b.) 66.30 ± 0.62c,d

SSD 140 �C 65.13 ± 0.99c

SSD 140 �C + AD (66.7% d.b.) 70.69 ± 0.57e

SSD 140 �C + AD (42.8% d.b.) 70.52 ± 0.63e

SSD 140 �C + HP (66.7% d.b.) 73.76 ± 0.94f

SSD 140 �C + HP (42.8% d.b.) 73.17 ± 0.60f

SSD 160 �C 70.65 ± 0.72e

SSD 160 �C + AD (66.7% d.b.) 77.51 ± 1.13g

SSD 160 �C + AD (42.8% d.b.) 78.55 ± 1.42g

SSD 160 �C + HP (66.7% d.b.) 85.60 ± 1.02h

SSD 160 �C + HP (42.8% d.b.) 86.66 ± 1.58h

a–e in the same column with different superscripts mean that the data aresignificantly different (p < 0.05).

Fig. 13. SEM of longitudinal section of chicken dried by SSD at 120 �C.

Fig. 14. SEM of longitudinal section of chicken dried by SSD at 160 �C.

Fig. 12. SEM of longitudinal section of fresh chicken.


became more rigid. Further heating at higher temperaturesmade the vapor pressure inside the samples to increase andexpand to create larger voids, as is seen in Figs. 13 and 14.As a result, more water was able to be added to the chickenmeat samples dried at higher temperatures. This effect oftemperature on the rehydration behavior was also observedin the case of the two combined two-stage dryingtechniques.

Nevertheless, the percentage of rehydration of chickendried by purely SSD was less than those dried by bothtwo-stage combined drying techniques. This is becausechicken dried by SSD was exposed to high-temperatureenvironment for a long duration, making proteins of myo-fibrilar and collagenous connective tissue denature and losetheir water holding ability. Lower percentage of rehydra-tion of chicken dried by SSD/AD compared with that driedby SSD/HP was also due to longer exposure to heat duringthe second-stage air drying. However, the effect of interme-diate moisture content on the percentage of rehydrationwas not obvious.

3.5. Microstructure

The SEM image of fresh chicken breast is shown inFig. 12. This image clearly shows the muscle fibers andconnective tissues. When chicken was dried by SSD themuscle fibers were shorten and shrank and the collage-nous connective tissue was broken and completely hydro-lyzed into gelatin. In addition, voids were created asexplained in the previous section (see Fig. 13). On theother hand, chicken dried by both combined techniquesexposed to the high-temperature environment of SSDshorter than in the case of purely SSD. Therefore, somebroken collagenous connective tissues still remained asshown in Figs. 15 and 16.

Fig. 15. SEM of longitudinal section of chicken dried by SSD/AD (SSD120 �C, AD 55 �C and intermediate moisture content of 42.8% d.b.).

Fig. 16. SEM of longitudinal section of chicken dried by SSD/HP (SSD160 �C, HP 55 �C and intermediate moisture content of 42.8% d.b.).


4. Conclusion

The overall drying rates of chicken dried by two-stagedrying techniques viz. SSD/HP and SSD/AD dependedmuch on the temperature of superheated steam in the firststage and drying techniques in the second stage. The dryingrates in the second stage also increased with an intermedi-ate moisture content of chicken.

The changes in colors of the dried chicken were due tobrowning reaction occurred at higher drying temperature,leading to the reduction of the lightness of dried chicken;the redness, however increased with the drying temperaturewhile the yellowness was not affected by the drying temper-ature. The percentage of shrinkage of dried chickendepended on an amount of heat supplied to the chicken,which corresponded to the drying time. Thus, chicken driedby purely SSD, which required the shortest drying time,had the least percentage of shrinkage as compared to driedchicken obtained from both combined drying methods.Similarly, chicken dried by SSD/HP had less percentageof shrinkage than that dried by SSD/AD due to shorterdrying time. The percentage of rehydration of driedchicken depended on the superheated steam temperatureand duration of the first stage SSD. Chicken dried with

high superheated steam temperature had larger void, andthus adsorbed more water than that dried at lower temper-atures. However, it is believed that long exposed time tohigh-temperature superheated steam environment madeproteins inside the chicken samples denature and lose watersolubility. Therefore, chicken dried by purely SSD hadlower percentage of rehydration than those of the com-bined drying techniques. Long drying duration of SSD/AD made the percentage of rehydration of dried chickento be less than those of another combined techniques.

In terms of the percentage of rehydration, SSD/HP is asuitable technique to dry chicken meat for using as aningredient in ready-to-eat noodle.

Acknowledgements

The authors express their sincere appreciation to theThailand Research Fund (TRF) and the National ResearchCouncil of Thailand for financial support.

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super heated steam drying

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