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Optimal Conditions for Popping Amaranth SeedsT. Inouea; H. Iyotaa; T. Uemuraa; J. Yamagataa; Y. Konishib; Y. Tatemotoc

a Department of Mechanical and Physical Engineering, Osaka City University, Osaka, Japan b

Department of Food Science and Nutrition, Osaka City University, Osaka, Japan c Department ofMaterials Science and Chemical Engineering, Shizuoka University, Hamamatsu, Japan

To cite this Article Inoue, T. , Iyota, H. , Uemura, T. , Yamagata, J. , Konishi, Y. and Tatemoto, Y.(2009) 'OptimalConditions for Popping Amaranth Seeds', Drying Technology, 27: 7, 918 — 926To link to this Article: DOI: 10.1080/07373930902988254URL: http://dx.doi.org/10.1080/07373930902988254

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Optimal Conditions for Popping Amaranth Seeds

T. Inoue,1 H. Iyota,1 T. Uemura,1 J. Yamagata,1 Y. Konishi,2 and Y. Tatemoto31Department of Mechanical and Physical Engineering, Osaka City University, Osaka, Japan2Department of Food Science and Nutrition, Osaka City University, Osaka, Japan3Department of Materials Science and Chemical Engineering, Shizuoka University,Hamamatsu, Japan

Amaranth seeds can be popped under suitable heating conditions.On the basis of experimental results obtained in our laboratory, wehave developed a prototype of a continuous processing system forcommercial application. In addition, the effects of gas temperature,flow rate, and feed speed on the popping quality of seeds, such astheir volume expansion ratio and yield, were examined.

The experimental results showed that the undersized yield ratioincreased with the flow speed, whereas it decreased with an increasein the gas temperature. In addition, to achieve a high expansionratio and maximum output, the feed speed was increased with thegas temperature. Furthermore, measuring the differential pressurein the test section of the experimental apparatus enabled the estima-tion of the quantity of seeds therein during the popping experiment.

Keywords Amaranthus hypochondriacus; Drying; Feed speed;Gas temperature; Popping; Volume expansion; Yield

INTRODUCTION

Puff drying methods are beneficial in terms of shortdrying time and improved texture of the dried food mate-rial. Hence, this drying method is used for drying foodmaterials such as rice, chestnut, potato, and carrot. Thisdrying is generally carried out in a pressurized container.The material is fed into this container and heated underhigh pressure. The pressure is then abruptly reduced tothe atmospheric pressure. This causes flash evaporation ofthe moisture contained within the material, accompaniedby volume expansion.

This drying can be carried out by employing suitableoperating conditions without using a pressurized container.For example, low permeability materials can be dried byhot air drying, whose gas temperature is higher than a boil-ing point temperature under atmospheric pressure. Thisdrying induces internal evaporation in these materials and,thus, the internal pressure is easily increased; this also leads

to an increase in the boiling point temperature of themoisture content of the materials.

Tatemoto et al. indicated the temperature in the sampleincreased because of the increment of pressure when themass transfer in a sample was low for fluidized bed dryingwith superheated steam and hot air.[1] Johanasson et al.examined the variations in the internal pressure of woodchips during hot air drying and superheated steamdrying.[2] Rattanadecho et al. investigated the effect of theinitial moisture content of the material on its total internalpressure duringhot air drying.[3] In addition,Perre et al.mea-sured the internal pressure during drying in superheatedsteam and moist air using light concrete and softwood assample materials.[4] Further, Asaeda et al. investigatedthe effect of the total pressure gradient in the dried regionof materials during the falling drying rate period on thedrying rate in the case of drying techniques such as hotair drying and superheated steam drying.[5] Iyota et al.reported that isobaric approximations are effective in esti-mating the vapor diffusion rate in the dried region of mate-rials with microsized pores, and vapor flow approximationsare effective in estimating the vapor flow rate in the driedregion of materials with pores that are filled almost withvapor only.[6]

Seeds of amaranth, which is one of the most promisingfood crops with high protein and mineral content,[7,8] canbe popped by rapidly evaporating the moisture containedwithin the seeds, accompanied by starch gelatinization inthe seeds, when it is heated and dried rapidly. The poppedseeds are soft in texture and taste like nutty-flavoredpopcorn; therefore, popping is a simple method to renderamaranth seeds edible. In order to process seeds andimprove their texture, measuring their yield and expansionvolume after popping is important; a high expansionvolume improves texture and edibility and, therefore, thequality of the food product is improved.[9]

Hot plates have been traditionally used for poppingseeds. However, the resulting products have certain draw-backs: (1) they have a low expansion volume, (2) they areprone to browning or carbonization due to overheating,

Correspondence: H. Iyota, Department of Mechanical andPhysical Engineering, Osaka City University, 3-3-138, Sugimoto,Sumiyoshi-ku, Osaka City 558-8585, Japan; E-mail: iyota@mech.eng.osaka-cu.ac.jp

Drying Technology, 27: 918–926, 2009

Copyright # 2009 Taylor & Francis Group, LLC

ISSN: 0737-3937 print=1532-2300 online

DOI: 10.1080/07373930902988254

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and (3) the recovery of popped seeds due to inhomogeneityis low. These demerits also lead to low nutritional value;e.g., a decrease in the amino acid score due to the occur-rence of an amino-carbonyl reaction.[10] Therefore, a fluidi-zed bed system is favorable for popping amaranth seeds,because the operating conditions of such a poppingmethod, such as the temperature or flow rate of hot air,can be controlled, thus resolving the above-mentionedproblems.[11]

Nelly and Jenny used a household corn popper to popamaranth seeds under certain operating conditions andassessed their quality in terms of their yield, expansionvolume, swelling power, water solubility, and proteincontent.[12] In addition, Marek et al. reported that dryingat high puffing temperature made seeds more rigid and lessviscous.[13]

However, popping treatment of amaranth seeds hasnot been done under optimum operational conditions inconsideration for product quality, such as expansion ratioand yield. This is because only a few popping apparatushave been specially designed for popping amaranth seeds,and control techniques to maintain the optimal operatingconditions have not yet been established.

In the previous study, we examined the effects of heatingtime, gas temperature, and initial moisture content of seedson the volume expansion ratio during hot air and super-heated steam drying using a fluidized bed system speciallydesigned in our laboratory. In addition, the mechanismof popping was studied by conducting a numerical studyusing a simple calculation model of popping.[14]

In the present study, the effects of gas temperature onthe popping quality of seeds, such as their volume

expansion ratio, were examined on the basis of the resultsof the previous study conducted in our laboratory.

Next, on the basis of experimental results obtained inour laboratory, we developed a prototype of a continuousprocessing system for commercial application. In addition,to determine the optimal operating conditions such as thefeed speed, volume expansion ratio, and undersized yieldratio, a continuous-type experiment was carried out. In thisexperiment, the effects of gas temperature, flow rate, andfeed speed on the popping quality of the seeds, such as theirexpansion ratio and yield, were examined.

Furthermore, measuring the differential pressure in thetest section was considered, as a method of monitoringthe progress of seeds treatment therein.

POPPING AMARANTH SEEDS

First, the effect of gas temperature on the popping qual-ity of the seeds, such as their volume expansion ratio, wasexamined, and the mechanism of popping was studied.

Material and Experimental Method

Amaranthus hypochondriacus seeds having a size ofapproximately 1.0mm were used (product of the UnitedStates). A schematic of the experimental apparatus(Shinkyo Sangyo Co., Ltd., Japan) is shown in Fig. 1. Itcomprises the following: (1) an electric boiler, (2) a hotair blower, (3) super heater 1, (4) a flow meter, (5) superheater 2, (6) a strainer section, (7) a removable cylindricaltest section (56.6mm in diameter and 110mm in length,made of Pyrex glass) equipped with a 24-mesh screen,and (8) an exhaust blower. We show the experimentalresults using hot air for the drying medium here.

FIG. 1. Experimental apparatus for popping amaranth seeds.

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Sample seeds (1 g) were fed into the test section forcarrying out the popping experiment. After heating, thecylindrical test section with the popped seeds was removedfrom the strainer section at an arbitrary time. The volumeexpansion ratio of the seeds, g (volume of popped seeds=volume of raw seeds), was evaluated from the apparentvolume of the popped seeds measured using a 20-mLgraduated cylinder. The popped seeds were observed usinga high-speed camera, and their condition was monitored.We conducted experiments at least twice in some experi-mental conditions to confirm the reproducibility.

Changes in Moisture Content and VolumeExpansion Ratio

Figure 2 shows the high-speed camera images obtainedduring the popping of the amaranth seeds. The shape ofthe seeds changed during the experiment, as shown inFigs. 2a–c. The breaking of the seed coat during the experi-ment is shown in Fig. 2b.

Figures 3a and 3b show the effects of heating time onthe moisture content and volume expansion ratio of theseeds, respectively. The initial moisture content of theamaranth seeds was 0.13 kg=kg. The flow rate of gas inthe test section was 1.6m=s—slightly higher than theincipient fluidization velocity of raw amaranth seeds.

The moisture content of the seeds dropped rapidly ata temperature above 200�C during the experiment, asshown in Fig. 3a; g increased because of the inherentpopping, as shown in Fig. 3b. At 170�C, the moisture con-tent decreased slowly without an increase in g, indicatingthat the amaranth seeds dried without popping. Asshown in Fig. 3b, popping occurred at 200�C for 5 s;only 10% of the seeds popped (determined by countingthe number of popped seeds). Above 230�C, the seedsstarted popping rapidly (5 s), and all the seeds had poppedwithin 15 s.

In addition, g at gas temperature above 260�C washigher than that at 230�C after heating for 15 s. This isbecause the internal pressure of seed increased drasticallyin a short time and the popping occurred more extremelyas the gas temperature increased. In the following experi-ments, heating was carried out for 15 s.

Effect of Gas Temperature on Volume Expansion Ratio

Figure 4 shows the effects of gas temperature on thevolume expansion ratio and quality of the popped seeds.The gas temperature was 170–320�C. The heating timewas constant at 15 s.

Figure 4a shows a seed that was incompletely poppedafter heating; its g was approximately 1.2 at 200�C. g atgas temperatures of 230�C–290�C (Figs. 4b–d) was higherthan that at 200�C, and it reached 8.4 at 260�C, as shownin Fig. 3b; this implies that the seeds were successfullypopped.

A decrease in g and higher degree of browning occurredat gas temperature above 290�C. The degree of browningabove 320�C was higher than that at 290�C, as shown inFIG. 2. High-speed camera images showing popping of amaranth seeds.

FIG. 3. Effect of heating time on moisture content and volume expan-

sion ratio (initial moisture content: 0.13 kg=kg).

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Figs. 4d and 4e. These results suggest that the operatingtemperature of 290�C is inappropriate for carrying outthe popping experiment.

Here, the effects of gas temperature on the poppingquality of amaranth seeds are summarized. The amaranthseeds popped when their internal pressure exceeded the ten-sile strength of their coat as a result of water evaporationoccurring during heating. Further, their seed coat has avery low permeability for steam generated during heating.This implies that the seeds should be heated quickly so thatthe internal pressure increases before the moisture in theseeds evaporates completely.

In particular, at low gas temperature, the seeds did notpop or they popped partially, because their internal pres-sure did not increase up to a sufficient level. On the otherhand, at very high gas temperature, the seeds poppedincompletely because the tensile strength of their coatreduced due to thermal denaturation.

It is very important to optimize the operating conditionssuch as the gas temperature, flow rate, and initial moisturecontent during popping. Among these factors, gas tem-perature affects not only the heat flux in the seeds but alsothe tensile strength of the seed coat. Hence, the gas tem-perature should be optimized for enhancing the poppingquality of amaranth seeds.

DEVELOPMENT OF CONTINUOUS PROCESSINGSYSTEM

On the basis of the results presented above, a prototypeof a continuous processing system was developed for com-mercial application. In addition, to determine the optimaloperating conditions such as the feed speed, volume expan-sion ratio, and undersized yield ratio, a continuous-typeexperiment was carried out.

Continuous Processing System for PoppingAmaranth Seeds

The specifications of the continuous processing systemare as follows: the popping process is continuous-type,seeds are heated in a fluidized bed, exhaust gas is circulatedto achieve high energy efficiency, maximum electric poweris less than 1500W (100V) for domestic use, and the size ofthe system is as small as possible.

Experimental Method

A schematic of a prototype of the above-mentioned con-tinuous processing system is shown in Fig. 5. It comprisesthe following: (1) blower 3, (2) a heater, (3) a strainer sec-tion, (4) a cylindrical test section (55mm in diameter and220mm in length, made of Pyrex glass) equipped with a24-mesh screen, (5) a cyclone, (6) blower 4, (7) a feeder,and (8) a paddle.

The effects of gas temperature, flow rate, and feed speedon the popping quality of the seeds, such as their volumeexpansion ratio and yield, were examined. For this experi-ment, we have arranged a configuration of continuousprocessing system in Fig. 5 to measure the flow rate usinga flow meter; we have used experimental apparatus in ourlaboratory subsidiary as shown in Fig. 1. The valve (11in Fig. 1) and blower 3 (1 in Fig. 5) were connected andblower 4 (6 in Fig. 5) was removed.

The experimental conditions are shown in Table 1. Theflow rate U (m=s) was estimated by using a flow meter (4 inFig. 1) and by measuring the differential pressure in theheater section (2 in Fig. 5). The gas temperature Tgas (

�C)was measured using a thermocouple attached to the endof the strainer section.

For the batch popping experiment, 3 g of sample wasinserted from the top side of the test section, all at once.For the continuous popping experiment, the seeds were

FIG. 4. Images of amaranth seeds after treatment at various gas temperatures (initial moisture content: 0.13 kg=kg).

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inserted at different feed speeds F (g=s) using the feeder.The total sample quantity for each experimental conditionwas 100 g.

In addition, the differential pressure DP (Pa) wasmeasured using a pressure gauge (9 in Fig. 5), and thetemperature in the test section (20mm above the entranceof the test section; 10 in Fig. 5) was measured to monitorthe condition of the seeds during the experiment.

The popped and the raw seeds were separated in the testsection, and the popped seeds were carried by air flow fromthe test section to the cyclone, because the air resistance of

the popped seeds was higher than that of the raw seeds.This implies that the flow rate of the gas and the lengthof the test section (220mm) are important factors to beconsidered for successful separation of raw and poppedseeds.

The apparent volume of raw seeds and product—seedscollected after the popping process by cyclone and theremaining seeds in the test section—was measured with a200-mL graduated cylinder and expressed as the expansionratio g (the volume of seeds collected after the poppingprocess=the volume of raw seeds). Next, the product wasclassified into two groups by size using a sieve (aperturesize: 1.18mm). The undesirable yield ratio was calculatedfrom the undersized yield ratio / (mass of seeds having sizeless than 1.18mm=mass of total yield). In this experiment,the initial moisture content of the seeds was 0.15 kgwater=kg dry weight.

Estimating Quantity of Seeds by MeasuringDifferential Pressure

First, measuring the differential pressure in the testsection was considered, as a method of monitoring theprogress of seeds treatment therein.

Figure 6 shows the relationship between the differentialpressure and the quantity of seeds in the test section (gastemperature: 20�C). The differential pressure in a fluidizedbed is given by Eq. (1) when all the seeds are floating.[15]

Under this condition, the gravitational force is equal tothe frictional force. The values estimated using Eq. (1)are indicated by a dotted line in this figure.

DPt ¼mg

Atð1Þ

where m, g, and At are the quantity of seeds in the fluidizedbed, gravitational acceleration, and cross-sectional area ofthe fluidized bed, respectively.

It can be observed in Fig. 6 that at m¼ 1 g, DPt wasalmost constant regardless of the flow rate (1.5–4.0m=s).In addition, DPt increased with the quantity of seeds

FIG. 5. Prototype of continuous processing system for popping

amaranth seeds.

TABLE 1Experimental conditions for batch-type and

continuous-type processing

Operation Batch-type Continuous-Type

Drying medium Hot Air Hot AirGas temperatureTgas (

�C)180, 220, 260, 300 220, 260, 300, 340

Flow rate U (m=s) 3.5 2.8, 3.5, 4.1, 4.7Sample quantitym (g)

3 100

Feed speed F (g=s) 0.18,0.33, 0.47, 0.58

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(3–5 g). The errors between the measured and the estimatedvalues of DPt were below 15% at U¼ 3.5m=s and m¼ 1, 3,and 5 g. These errors occurred because the seeds weredispersed in the test section during the experiment andsome seeds were not floating at a certain moment.

Results of Batch-Type Popping Experiment

Next, batch-type experiments were carried out to studythe basic characteristics of amaranth seeds popped usingthis system.

Figure 7 shows the effects of gas temperature on DPt

in the test section during a batch-type experiment. Theheating time required for the popping was decided bymeasuring DPt in the test section. For the batch-typeexperiment, 3 g of sample seeds was fed into the test sectionfrom the top, without using the feeder.

It can be observed in Fig. 7 that at 180�C and 3.5m=s,when the gas temperature was the minimum, DPt increasedfor 3 s as the seeds were fed, and then it remained constant,indicating that popping never occurred. In addition, this

value of DPt was almost equal to that at m¼ 3 g, as shownin Fig. 6 (Tgas¼ 20�C). This implies that the relationshipbetween the quantity of seeds and differential pressure isindependent of the gas temperature.

At 220�C, DPt decreased after 10 s as the popped seedswere carried away from the test section. This time isreferred to as the popping time tp (s) in this study. At highgas temperatures (260 and 300�C), the popping timereduced (6 and 4 s, respectively).

Results of Continuous-Type Popping Experiment

Variations in Differential Pressure

Figure 8 show the variations in DPt in the test sectionduring the continuous-type experiment.

At 260�C and 0.18 g=s, when the gas temperature wasthe minimum in this figure, DPt increased rapidly for 10 sand then continued to increase slowly until the end of theexperiment (t¼ 500 s), as shown in Fig. 8. At 300�C,0.18 g=s, DPt remained constant (4–5 Pa) after 10 s. Underthese conditions, more than 1–1.2 g of seeds was presentin the test section during the popping experiment, whichwas estimated from DPt calculated using Eq. (1).

At 300�C and 0.58 g=s, when the feed speed was the maxi-mum,DPt increased rapidly after 60 s as the quantity of seedsin the test section increased, and the seeds ceased to pop.Under this condition, continuous operation could not be car-ried out, because the feed speed was higher than the poppingcapacity of the system. On the other hand, at 340�C and0.58 g=s, continuous operation could be carried out.

Next, the limit of continuous operation and the pro-duct quality, such as g and /, were estimated. Table 2the experimental results obtained under each operatingcondition employed in this study.

At 220�C, 0.18 g=s, and 3.5m=s, when the gastemperature was the minimum, continuous operationcould not be carried out successfully, because the seeds

FIG. 7. Effect of gas temperature on differential pressure in test section

(sample seeds quantity: 3 g, flow rate: 3.5m=s).

FIG. 8. Differential pressure in test section during continuous-type

experiment (flow rate: 3.5m=s).

FIG. 6. Relationship between quantity of seeds and differential pressure

in test section (gas temperature: 20�C).

OPTIMAL CONDITIONS FOR POPPING AMARANTH SEEDS 923

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accumulated in the test section with time. At 260�C,0.18 g=s, and 3.5m=s, continuous operation was carriedout successfully. However, at 260�C, 0.33 g=s, and3.5m=s, the seeds accumulated in the test section withtime and continuous operation could not be carried out.

At 300�C, continuous operation was carried out both atU¼ 2.8–4.1m=s and F¼ 0.18 g=s and at U¼ 3.5m=s andF¼ 0.33–0.47 g=s.

At 340�C and 0.58 g=s, the maximum output wasachieved. On the other hand, at 0.18 g=s, continuous opera-tion could not be carried out successfully, because the seedswere carbonized easily due to overheating.

The optimal operating conditions for achieving opti-mum product quality, such as high volume expansionand undersized yield ratio, were then established usingthe values shown in Table 2.

Effect of Flow Rate on Undersized Yield Ratio

Figure 9 shows the effects of flow rate and gas temperatureon g and /.

At 260�C, 3.5m=s, and 0.18 g=s, the maximum volumeexpansion ratio was realized in this continuous-type pop-ping experiment (g¼ 6.9). At U¼ 4.1–4.7m=s, g decreased

as / increased rapidly. This is because not only the poppedseeds but also the raw seeds were carried away by air flowdue to increased air resistance at high flow rates. / at300�C and 3.5m=s was less than that at 260�Cand 3.5m=s because the popping time tp was shorter.

FIG. 9. Effect of flow rate and gas temperature on volume expansion

ratio and undersized yield ratio (feed speed: 0.18 g=s).

TABLE 2Mass and volume measurements of popped amaranth seeds

Total seedsUnder-sized yieldratio (1.18mm)

g (mass%)Gas temp.Tgas (

�C)Feed speedF (g=s)

Flow rate U(m=s)

Volume V(ml)

Mass m(g)

Expantion ratio g(m3=m3)

220 0.18 3.5 �

260 0.18 2.8 �

3.5 807 83.1 6.9 44.1 769 83.5 6.6 94.7 704 83.7 6.0 17

0.33 3.5 �

300 0.18 2.8 734 83.0 6.3 33.5 677 83.4 5.8 24.1 670 82.9 5.7 6

0.33 3.5 754 83.3 6.4 30.47 785 82.8 6.7 40.58 �

340 0.18 3.5 �

0.33 648 82.2 5.5 20.47 692 83.0 5.9 20.58 742 83.2 6.3 3

Raw seeds 117 100.0 1.0 100

�Outside the range of operating conditions.

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In addition, the value of undersized yield ratio (/¼ 2) wasless or equal to that reported before.[9,12]

In the following experiments, the flow rate was heldconstant at 3.5m=s, and the undersized yield ratio wasthe minimum.

Effect of Feed Speed on Volume Expansion Ratio

Figure 10 shows the effects of feed speed and gastemperature on g and /.

The maximum volume expansion ratio was realized(g¼ 6.9) at 260�C, 3.5m=s, and 0.18 g=s, as shown inFig. 9. In addition, g at 300�C and 3.5m=s was less thanthat at 260�C and 3.5m=s, because the seeds were carboni-zed easily due to overheating. Furthermore, at Tgas¼ 300–340�C, g increased with the feed speed (0.47–0.58 g=s).

Here, the reason why g was high at high feed speed andhigh gas temperature (300–340�C) is clarified.

Figure 11 shows the relationship between thetemperature of the fluidized bed and the quantity ofseeds in the test section under the same conditions asthose shown in Fig. 10.

The quantity of seeds was estimated from the differen-tial pressure in the fluidized bed calculated using Eq. (1).In addition, because the seeds were dispersed in the testsection during the experiment, the temperature of the flui-dized bed, Tt (�C), was assumed to vary between thetemperature at the entrance of the test section (¼Tgas)and the temperature within the test section measured usingthe thermocouple 20mm above the entrance of the testsection (10 in Fig. 5).

At 260�C and 0.18 g=s, the temperature of the fluidizedbed was the minimum, approximately 230�C, as shown inFig. 11. Under these conditions, there was approximately2.2 g of seeds present in the test section (at 500 s). At300�C and 0.18 g=s, the temperature of the fluidized bedwas the minimum (285�C), and it remained constant duringthe experiment. At F¼ 0.33–0.47 g=s, the temperature ofthe fluidized bed decreased as the quantity of seeds in thetest section increased.

In addition, at 340�C and 0.58 g=s, the temperature ofthe fluidized bed remained constant at 260�C, which wasless than that at 300�C and 0.18 g=s. This difference inthe temperature of the fluidized bed may have stronglyaffected the volume expansion ratio, as shown in Fig. 10;g at 340�C and 0.58 g=s was higher than that at 300�Cand 0.18 g=s.

From these results, it was found that not only the gastemperature but also the feed speed affected the tempera-ture of the fluidized bed. In addition, we could preventoverheating of the seeds to increase the feed speed. Inshort, to achieve maximum output and a high volumeexpansion ratio, the feed speed should be increased withthe gas temperature. These results indicated that we shouldconsider the effect of feed speed on the product qualityespecially when using a small-sized test section for heating(low heating capacity of the heating medium).

In addition, measuring and regulating the differentialpressure in the test section are important to maintain theoptimal operating conditions of the continuous processingsystem. This will constitute a topic of study for the future.

CONCLUSIONS

In this study, on the basis of experimental resultsobtained in our laboratory, we developed a prototype ofa continuous processing system for commercial applica-tion. In addition, the effects of gas temperature, flow rate,and feed speed on the popping quality of seeds, such astheir volume expansion ratio and yield, were examined.

The results of a continuous-type popping experimentsuggested that the undersized yield ratio increased withthe flow rate, and it decreased at high gas temperature.

FIG. 11. Relationship between temperature of fluidized bed and quan-

tity of seeds in test section (flow rate: 3.5m=s).

FIG. 10. Effect of feed speed and gas temperature on volume expansion

ratio and undersized yield ratio (flow rate: 3.5m=s).

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In addition, the results suggested that the feed speedshould be increased with the gas temperature to achievemaximum output and a high volume expansion ratio.Furthermore, the quantity of seeds was estimated by mea-suring the differential pressure in the test section during thecontinuous-type popping experiment.

NOMENCLATURE

F Feed speed (g=s)mt Quantity of seeds in test section (g)DP Differential pressure (Pa)DPt Differential pressure in fluidized bed (Pa)Tgas Gas temperature (�C)Tt Temperature of fluidized bed (�C)t Heating time (s)U Flow rate (m=s)X Dry basis moisture content (kg=kg)

Greek Letters

g Expansion ratio (m3=m3)/ Undersized yield ratio (mass %)

Subscripts

0 Initial

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