Co esponding au ho : Aboubaka Compao e
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Ho ai -d ying cha ac e is ics o pale- leshed, whi e-skinned swee po a o sphe es
(Ipomoea ba a as)
Aboubaka Compao e 1, 2, 3, *, Sali ou Oued aogo 3, Hono é Kondia Ouoba 3, Fayçal Ilboudo 3 and Bé aboalé
Naon 3
1 Lédéa Be na d OUEDRAOGO Uni e si y ( o me ly Uni e si y o Ouahigouya), 01 BP 346 Ouahigouya 01, No h Region,
Bu kina Faso.
2 Labo a o y o En i onmen al Physics and Chemis y (LPCE), Doc o al School o Science and Technology (ED-ST), Joseph
KI-ZERBO Uni e si y, Ouagadougou, Bu kina Faso.
3 Labo a o y o Ma e ials, Heliophysics and he En i onmen (La.M.H.E.), T aining and Resea ch Uni in Exac and Applied
Sciences (UFR/SEA), Nazi BONI Uni e si y o Bobo Dioulasso, PO Box 1091, Bu kina Faso.
Wo ld Jou nal o Ad anced Resea ch and Re iews, 2025, 26(02), 798-813
Publica ion his o y: Recei ed on 28 Ma ch 2025; e ised on 03 May 2025; accep ed on 06 May 2025
A icle DOI: h ps://doi.o g/10.30574/wja .2025.26.2.1707
Abs ac
D ying o pale- leshed, whi e-skinned sphe ical swee po a o (Ipomoea ba a as) (a newly in oduced a ie y g own in
Bu kina Faso) was ca ied ou a ai empe a u es o 50°C, 60°C, 70°C, and 80°C using 2 and 3 cm diame e samples o
de e mine i s d ying cha ac e is ics. The esul s o he analysed d ying da a indica ed ha d ying occu ed du ing he
dec easing a e pe iod. The mois u e con en o he sample and he d ying a e o swee po a o we e in luenced by he
ai -d ying empe a u e and he sphe ical diame e o he samples. The d ying ime o swee po a o dec eased and i s
d ying a e inc eased wi h he dec ease in he diame e o sphe ical samples and he inc ease in ai d ying empe a u e.
The a e age e ec i e mois u e di usi i y alues we e ob ained in he ange o 1.4086 × 10-9 o 3.7214 × 10-9 m2/s
and 2.6715 × 10-9 o 6.8775 × 10-9 m2/s o 2 cm diame e samples and 3 cm diame e samples espec i ely as
empe a u es inc eased om 50 °C o 80 °C. This dependence allowed he de e mina ion o he ac i a ion ene gy alues
o 2 and 3 cm diame e swee po a o samples which we e ound o be 30.50 and 27.71 kJ/mol, espec i ely.
Keywo ds: Swee po a o sphe es; Con ec i e d ying; Mois u e di usi i y; Ac i a ion ene gy
1 In oduc ion
Food secu i y is one o he majo global challenges acing he wo ld oday. The e a e an es ima ed 795 million people
who a e ood insecu e and unde nou ished. One o he ac o s leading o ood insecu i y is he loss o ood and
ag icul u al p oduc s due o hei de e io a ion h oughou he ood and ag icul u al chain and/o du ing he pos -
p oduc ion pe iod. A majo me hod o enhance ood secu i y is o educe losses due o pos -ha es spoilage o hese
ag icul u al p oduc s. To imp o e shel li e and educe spoilage o ag icul u al p oduc s, d ying is he mos commonly
used me hod [1]. D ying is an elemen a y p ocess aimed a emo ing liquid/ apo wa e om a ma e ial and he e o e
educing i s wa e ac i i y. D ying ood has many ad an ages, such as: blocking he de elopmen and mul iplica ion o
mic oo ganisms and ood spoilage eac ions by educing wa e ac i i y as well as educing anspo cos s, s o age and
p ese a ion h ough educ ion o ood weigh / olume [2].
Ho ai con ec ion d ying is he p ocess o emo ing wa e wi h ai ia simul aneous ans e o hea , mass and
momen um. The ood's need o hea is achie ed by con ac o he ood wi h a low o ho ai . The ene gy ansmi ed o
he su ace o he ood by con ec ion o ho ai is ans e ed inside he ood by di usion and/o con ec ion, depending
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on he physical and biological s uc u e o he ood o be d ied. This hea low causes an inc ease in p oduc empe a u e
and e apo a ion o su ace wa e . Mois u e is ans e ed om he su ace o he p oduc o he ai by con ec ion in he
o m o wa e apo and om he in e io o he p oduc by di usion, con ec ion o capilla i y. The d ying a e and
cha ac e is ics o d ied oods depend on he condi ions o he ai -d ying p ocess such as ai empe a u e, ela i e
humidi y o he ai , ai eloci y, o ien a ion/ di ec ion o ai low and apo p essu e in ai . The d ying a e also depends
on he cha ac e is ics o he oods o be d ied such as geome y, hickness/size, shape and physical/biological
con igu a ions o he oods. The complexi y o he physic-biological con igu a ions o we oods, he a ie y o anspo
phenomena and biological di e si y make ood d ying a challenge. To mee his challenge, ma hema ical modelling and
simula ion can be a use ul ool o examine he d ying o oods and he quali y o oods ob ained a e d ying. This ool
can make i possible o achie e accep able p ocess condi ions o e en be e han he usual a e age h ough a p ocedu e
o op imizing he ope a ional a iables o d ying. Ma hema ical modelling o ood d ying in ol es he use o
ma hema ical equa ions o p edic /cap u e he physics and/o beha io o d ying [3]. Many ma hema ical models o
d ying p ocesses a e used o design new d ying sys ems o o imp o e exis ing d ying sys ems, o e en o con ol he
d ying p ocess. Among hese mul iple ma hema ical models p oposed o desc ibe he d ying p ocess, hin-laye d ying
models ha e been widely used. The e m “ hin laye ” is applied o a single ke nel eely suspended in he d ying ai o
one laye o g ain ke nels. I is also applied o a poly-laye o many g ain hicknesses i he empe a u e and he ela i e
humidi y o he d ying ai can be conside ed o he pu pose o he d ying p ocess calcula ions, as being in he same
he modynamic s a e a any ime o d ying [4]. Thin-laye models can be classi ied as heo e ical, semi- heo e ical and
empi ical [5]. Recen ly, many esea che s ha e ocused on he ma hema ical modelling and expe imen al d ying
p ocesses o a ious ube ous oo s such as swee po a o.
Swee po a o called scien i ic name Ipomoea ba a as is a plan cul i a ed mainly o i s edible ube s ( ube ose oo s),
ich in s a ch. These ube s p oduced a e designa ed by he same name as his plan . Swee po a oes p oduce mo e
edible ene gy on ma ginal lands han any o he majo ood c op. In addi ion o his use ul p ope y, hese ube s can
esis unwan ed abio ic and bio ic s esses and do no equi e in ensi e ca e. They he e o e play an impo an ole in
he economy o poo households whe e hey cons i u e a majo sou ce o subsis ence and a e conside ed a ood o
comba amine and child malnu i ion. Besides his impo an unc ion, swee po a o cul i a ion has immense semi-
indus ial/indus ial alue o s a ch ex ac ion and animal eed p oduc ion. Fo all hese explana ions, swee po a o
o e s g ea possibili ies o achie ing ood and nu i ional secu i y in de eloping and unde de eloped coun ies whe e
mos ag icul u al ields belong o ulne able popula ion ca ego ies [6]. Swee po a oes a e impo an ube s ich in
ibe , s a ch, i amins, mine als and bioac i e compounds. They con ain essen ial ca o enoid, phy ochemical, an icance
and an imic obial p ope ies use ul o human and animal heal h. Swee po a o aw o in i s p ocessed o m can be
consumed by humans as a s aple ood, snack o baked goods. Howe e , swee po a o is suscep ible o mic obial ac i i ies
which can lead o deg ada ion and spoilage due o i s high mois u e con en . Fu he mo e, swee po a o is seasonal and
canno main ain op imal quali y le el o a long pe iod a e ha es . Thus, i is o en used sho ly a e ha es o
p ese ed using he ho ai con ec ion d ying me hod [7]. In he li e a u e, se e al d ying p ocesses ha e been applied
o di e en swee po a o a ie ies, namely, in a ed and luidized bed d ying [8], con ec i e ho ai d ying [9],
mic owa e d ying [10], hyb id mic owa e and ho ai d ying [11], spou ed bed d ying [12], sun and d um d ying [13],
sp ay d ying [14], eeze-d ying [15] and sola d ying [16]. P e ea men s be o e d ying ha e been applied o swee
po a oes including s eaming [17], blanching wi h ho wa e and s eam [13], soaking in sodium me abisul i e solu ion
[18], osmo ic dehyd a ion wi h suc ose and so bi ol [10], imme sion in ci ic acid solu ion [15], lemon juice and saline
solu ion [19] and soaking in sodium me abisul i e solu ion [20]. These d ying and p e ea men echniques we e
applied on swee po a o samples wi h se e al sliced shapes, a ie ies, skin and lesh colo s including swee po a o cubes
[21], whi e skin and yellow- ed lesh swee po a o slices o K a ai cul i a [8], s ips [22], chips [23], Nige ian a ie y
slices [24] and Chinese local a ie y slices [25].
I was ound ha he e a e ew a icles on ai d ying o sphe ical swee po a o in his li e a u e. The objec i e o his
pape is o in es iga e he d ying cha ac e is ics e.g. mois u e a io, d ying a e, mois u e di usi i y, ac i a ion ene gy
o whi e skinned and pale leshed sphe ical swee po a o, a newly in oduced a ie y cul i a ed in Bu kina Faso.
2 Ma e ials and Me hods
2.1 Raw Ma e ial and P ocessing
Swee po a o (Ipomoea ba a as) was used as d ying ma e ial in his s udy. Samples o he local a ie y o swee po a o
wi h pale lesh and whi e-skinned, hea ily consumed in low-income households, we e pu chased du ing he pe iod o
July 2023 a he ui and ege able ma ke in he own o Bobo Dioulasso (Con ac de ails: 11 ° 11′ 00″ No h, 4° 17′
00″ Wes ), loca ed in he Hau Bassin egion o Bu kina Faso. Swee po a o samples we e anspo ed and s o ed in
e ige a ed condi ions (4 ± 0.5 °C) be o e he d ying p ocess a he GERME & TI labo a o y (S udy and Resea ch G oup
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in Ene gy Mechanics and Indus ial Techniques) om Nazi Boni Uni e si y. Be o e d ying, swee po a o samples we e
placed in labo a o y o each oom empe a u e (25 ± 1 °C). Swee po a o samples we e selec ed, washed, peeled, cu
in o sphe es wi h diame e s om 1 ± 0.002 cm o 3 ± 0.002 cm, measu ed manually using a digi al calipe . Sphe ical
samples a e imme sed in dis illed wa e o emo e excess su ace s a ch ilm. Excess wa e on he sphe ical samples
was emo ed using blo ing pape and hese swee po a o sphe es we e a anged in a single laye on a d ying ay. The
ini ial mois u e con en on a d y basis (d.b.) o swee po a o was de e mined using con ec i e o en me hod a 105 ± 5
°C o 24 h [26]. T iplica e samples we e used o de e mina ion o mois u e con en and he a e age alues we e
(3.0174±0.01) kgwa e /kgd y ma e .
2.2 D ying Equipmen
D ying expe imen s we e ca ied ou in an Ai Pe o mance labo a o y o en (F oilabo, Model AC S anda d Ve sion,
F ance, ange 10–250°C wi h an accu acy o ±0.5°C) ins alled a GERME & TI labo a o y (S udy and Resea ch G oup in
Ene gy Mechanics and Indus ial Techniques) om he Nazi Boni Uni e si y, Bobo-Dioulasso, Bu kina Faso, p e iously
desc ibed by Ouoba e al. [27]. Leng h, heigh and wid h o o en we e 0.579 m, 0.640 m and 0.526 m espec i ely. O en
essen ially consis ed o a cen i ugal an o p o ide he desi ed d ying ai low, a 1,000-Wa elec ic hea e con olling
he empe a u e o he d ying ai , an ai il e and a p opo ional-in eg al-de i a i e con olle (PID con olle ). Ai
empe a u e in con ec i e o en was egula ed o ±1∘C using a empe a u e con olle . The o en ope a ed a d y bulb
empe a u es o 10°C o 250°C. The desi ed d ying ai empe a u e was eached by an elec ic esis ance and con olled
by he hea ing con ol uni . The ai speed was egula ed by he cen i ugal an and a an speed con ol uni . The ai came
ou o he hea ing uni and was hea ed o he desi ed empe a u e, hen channeled o he d ying chambe h ough
en ila ion slo s loca ed in he ea side wall o he d ying chambe . Fan loca ed a he ea o chambe wall p oduced
g ea e ai low and mo e in ensi e ho izon al o ced ai ci cula ion o d y he p oduc samples. The samples we e d ied
on a squa e pe o a ed s ainless-s eel ay, ha ing a low c oss sec ion o 0.3 m x 0.3 m. The o en was adjus ed o he
selec ed ai empe a u e o app oxima ely 0.5 h be o e he s a o he expe imen s in o de o each i s s eady s a e.
2.3 D ying P ocedu e
Ai d ying empe a u es we e 50, 60, 70 and 80°C and ai ela i e humidi y was in ange om 5 o 20%. Ai eloci y
was kep a a cons an alue o 2.0 m/s wi h an accu acy o ±0.03 m/s o all d ying expe imen s. D ying p ocess began
when d ying condi ions eached cons an ai empe a u es. Once he o en eached s able condi ions o se poin s,
swee po a o samples we e placed on a ay in a single laye and measu emen s a ed om ha poin . Expe imen s
we e ca ied ou wi h 125 ± 0.3 g o swee po a o o all es s. T ay was emo ed om con ec i e d ye egula ly, a 20-
minu e in e als, and weighed wi h a digi al elec onic balance, hen placed back in o en. The ay was emo ed om
he d ye egula ly, a 20-minu e in e als, and weighed wi h a digi al elec onic balance, hen placed back in o he o en.
The elec onic digi al balance (model 2102, SARTORIUS, F ance, ange 0–2,100 g wi h an accu acy o ±0.001 g) was kep
less han 1 m om he d ye [28]. Con ec i e ho ai d ying was con inued un il he e was no longe any signi ican
a ia ion in he e olu ion o he masses o he sphe ical swee po a o samples. D ying es s we e e mina ed when
masses o samples we e s abilized, which assumed ha he modynamic equilib ium was eached. The d ied samples
we e cooled unde labo a o y condi ions a e each d ying expe imen and s o ed in ai igh ja s. The mass loss o he
samples du ing d ying was con e ed o mois u e con en on a d y basis and exp essed as kgwa e /kgd y ma e acco ding
o equa ion (1). Fo each d ying condi ion, a e ages o h ee eplica es we e aken as d ying da a. A end o each
expe imen , sample was hea ed in an o en a 105 °C o 24 h o d ying o ob ain he d y ma e mass o his sample [29].
𝑋(𝑡)=𝑚(𝑡)−𝑚𝑠
𝑚𝑠 ……….. (1)
Whe e X( ) is he mois u e con en on a d y basis (d.b.) exp essed in kg wa e /kg d y ma e ; m ( ), mass o sphe ical swee
po a o samples, exp essed in kg a ime in seconds and ms, mass o d y ma e o sphe ical samples (kg).
3 D ying Theo y
3.1 Mois u e Ra io
Mois u e a io (MR) was calcula ed om mois u e con en da a o sphe ical swee po a o samples du ing d ying.
Equa ion (2) was used o calcula e he mois u e a io [30]:
𝑀𝑅=𝑋−𝑋𝑒
𝑋0−𝑋𝑒 ……… (2)
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Whe e X, X0 and Xe a e espec i ely he a e age mois u e con en a any ime o d ying (kg wa e /kg d y ma e ), he ini ial
a e age mois u e con en (kg wa e /kg d y ma e ) and he equilib ium mois u e con en (kg wa e /kg d y ma e ).
As Xe is much smalle han X0 and X, i is negligible in his s udy. The mois u e a io hen becomes:
𝑀𝑅=𝑋
𝑋0 ………… (3)
3.2 D ying Ra e
The d ying a e (DR) o he sphe ical swee po a o samples is calcula ed using equa ion (4) [31]:
𝐷𝑅=𝑋𝑡+𝑑𝑡−𝑋𝑡
𝑑𝑡 ……….(4)
Whe e X and X +d a e mois u e con en s a and + d (kgwa e /kgd y ma e ), espec i ely, DR, d ying a e (kgwa e /(kgd y
ma e . s)) and is he ime (s).
3.3 E ec i e Mois u e Di usi i y
D ying o mos ood ma e ials akes place du ing he alling a e pe iod, and mois u e ans e du ing d ying p ocess is
con olled by in e nal di usion. Fick's second di usion equa ion (equa ion (5)) was widely used o desc ibe d ying
p ocess du ing alling a e pe iod o ag icul u al ma e ials [28]:
∂X
∂ =De ∇2X ……….. (5)
Di usion equa ion (equa ion (5)) is sol ed o a sphe e, assuming one-dimensional olume change o mois u e
mo emen , uni o m empe a u e and cons an mass di usi i y, and negligible ex e nal esis ance [32]:
𝑀R= 6
π2∑1
(2n−1)2
∞
n=1 exp[−(2𝑛−1)2π2De
4 2 ] …………. (6)
Whe e De is he e ec i e mois u e di usi i y (m2/s), is he adius o he sphe ical sample (m), and n is he posi i e
in ege . Fo long d ying imes, equa ion (6) simpli ies o a limi ing o m o he di usion equa ion as ollows:
MR=6
π2exp(−π2De
4 2 ) ……………. (7)
Plo ing o ln (MR) e sus d ying ime is exp essed wi h he dimensionless Fou ie numbe F0 acco ding o equa ion
(8).
ln𝑀𝑅=−lnπ2
6−π2
4F0 wi h F0 =De
2 …….. (8)
O
F0 =0.4053ln(𝑀𝑅)+0.2017 ……. (9)
3.4 Ac i a ion Ene gy
E ec i e di usi i y can be linked o ai empe a u e by A henius ype exp ession [30], such as:
De =D0exp[− Ea
R(T+273.15)] ……. (10)
Whe e D0 is he cons an o he A henius ype equa ion (m2/s), Ea is he ac i a ion ene gy (J/mol), T is he uni o m
empe a u e o he swee po a o (°C) and R=8, 3145 is he uni e sal gas cons an (J/mol K). Equa ion (10) can be
ea anged in o he o m:
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ln(De )=ln(D0)− Ea
R(T+273.15) ……….. (11)
3.5 S a is ical Analysis
Fo he adjus men o he d ying da a o he sphe ical swee po a o samples, a eg ession analysis by he leas squa es
me hod was ca ied ou using MATLAB 8.0 so wa e. Fou s a is ical pa ame e s we e used o de e mine he abili y o
he es ed model o ep esen he expe imen al da a, namely: he coe icien o de e mina ion (R2), he oo mean squa e
e o (RMSE), he educed chi-squa e (χ2) and he sum o squa ed e o s (SSE).
• The coe icien o de e mina ion(R2)
The main goal o using R2 in he con ex o s a is ical models is o p edic u u e ou comes based on associa ed
expe imen al da a. R2 helps cap u e he amoun o dispe sion in a d ying da a se which is accoun ed o by a
ma hema ical model. I measu es how likely u u e ou comes a e o be p edic ed by his ma hema ical model. R2 is
a ely equal o 0 o 1, bu a he somewhe e be ween hese limi ing alues. The close i is o 1, he mo e he
expe imen al and p edic ed alues ag ee. This alue is used o he compa ison ule and shows he le el o good i
be ween he measu ed and p edic ed alues. This was one o he i s coe icien s used o selec he app op ia e d ying
model o desc ibe ood d ying beha io [4].
𝑅2=1−∑(𝑃𝑒𝑥𝑝,𝑖−𝑃𝑝𝑟𝑒,𝑖)2
𝑁
𝑖=1
∑(𝑃
𝑒𝑥𝑝−𝑃𝑒𝑥𝑝,𝑖)2
𝑁
𝑖=1 …………….. (12)
• Roo Mean Squa e E o (RMSE)
The oo mean squa e de ia ion, RMSD, o oo mean squa e e o , RMSE, is a ool o measu ing he di e ences
be ween he alues p edic ed by a ma hema ical model and he alues ac ually obse ed om d ying expe imen s.
RMSD measu es he accu acy o his model well and is used o g oup he esiduals in o a single measu emen o he
p edic i e ool. I mus e ol e owa ds a ze o alue o a good adjus men o he d ying model and can be exp essed as
ollows [29]:
𝑅𝑀𝑆𝐸=[∑(𝑃𝑒𝑥𝑝,𝑖−𝑃𝑝𝑟𝑒,𝑖)2
𝑁
𝑖=1 𝑁]12
⁄ …………… (13)
• Chi-squa e educed (χ2)
This s a is ical coe icien o chi-squa e educed (χ2) is a ool o measu e he mean squa e o he di e ences be ween
he expe imen al alues and hose p edic ed om ma hema ical models. This makes i possible o e alua e he adequacy
o his model wi h he expe imen al da a. The smalle he alues o χ2, he be e he quali y o he i and could be
exp essed as ollows [4]:
𝜒2=∑(𝑃𝑒𝑥𝑝,𝑖−𝑝𝑝𝑟𝑒,𝑖)2
𝑁
𝑖=1 𝑁−𝑧 …………… (14)
• Sum o Squa ed E o s, SSE
The sum o squa ed e o s (SSE) gi es he measu e o he de ia ion o he da a o an expe imen al sample om i s
heo e ical alues p edic ed by a ma hema ical model. This pa ame e is explained as he di e ence be ween he
expe imen al da a and hose p edic ed by he d ying model and exp essed as [29]:
𝑆𝑆𝐸=∑(𝑃𝑒𝑥𝑝,𝑖−𝑃𝑝𝑟𝑒,𝑖)2
𝑁
𝑖=1 …………… (15)
Whe e P is he ho ai -d ying pa ame e , Pexp,i is he expe imen al alue o he pa ame e , Pp e,i is he alue o he
pa ame e P p edic ed by he s a is ical model, P exp,i is he a e age alue o he pa ame e P, N is he numbe o
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expe imen al obse a ions and z is he numbe o cons an coe icien s in he model eg ession. A good i o he d ying
model is ound o he highes alues o R2 and o he lowes alues o RMSE, χ2 and SSE [29].
4 Resul s and Discussion
4.1 Mois u e Ra io
F om he mois u e a io e olu ions in
(a)
(b)
Figu e 1a, i can be deduced ha he swee po a oes we e comple ely d ied o 2000, 1376, 840 and 580 minu es a 50
°C, 60 °C, 70 °C and 80 °C espec i ely o he sphe ical samples o 2 cm in diame e . Fo he 3 cm diame e samples, he
d ying du a ions we e ound o be 2080, 1600, 1419, and 915 minu es a 50 °C, 60 °C, 70 °C and 80 °C espec i ely (
(a)
(b)
Figu e 1b). The e o e, he mois u e con en o he sphe ical swee po a o samples dec eased o a cons an poin in a
ime ha depended on he ai -d ying empe a u e and he diame e o he sphe ical samples, wi h he lowes ime being
a 80 °C (i.e. 580 minu es) and he highes ime a 50°C (i.e. 2000 minu es) du ing he d ying o sphe ical samples o 2
cm in diame e . Fo he 3 cm diame e sphe ical samples, he lowes ime a 80°C was 915 minu es and he highes ime
a 50°C was 2080 minu es. Thus, an inc ease in d ying ai empe a u e esul s in a educ ion in d ying ime. Fo
sphe ical samples o a gi en diame e , o en empe a u e le els had a signi ican in luence on he mois u e con en o
swee po a oes.
(a)
(b)
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Figu e 1 D ying kine ics o sphe ical swee po a o samples d ied wi h ho ai a empe a u e le els (50, 60, 70 and
80°C) wi h sphe ical samples o (a) d=2 cm and (b) d= 3 cm in diame e
The lowe mois u e con en o d ied sphe ical swee po a o samples showed a dec ease in he olume and
anspo abili y o hese d ied samples du ing p ocessing, p ese a ion, and s o age. The educ ion in mois u e con en
educed hei wa e ac i i ies, which also minimized he mic obial de e io a ion and spoilage eac ion du ing hei
s o age. Ou d ying esul s o sphe ical swee po a oes we e in ag eemen wi h hose o o he esea che s o a ious
oods such as onion [29], Kiwi [33], ok a [34], cassa a [35], apple [36], ca o [37] and oma o [38]. In
(a)
(b)
Figu e 1, ega ding he physical mechanism o d ying, con ec i e d ying o sphe ical swee po a o samples did no show
a cons an a e pe iod. Mois u e con en dec eased wi h inc easing d ying ime o he sphe ical samples du ing he
dec easing a e pe iod a he ou empe a u e le els o bo h 2 and 3 cm diame e sphe ical swee po a o samples. This
showed ha mois u e di usion was he dominan physical mechanism o wa e mo emen in he sphe ical swee po a o
samples du ing he d ying p ocess [39]. Wa e di usion du ing he d ying p ocess could induce a dec ease in abso p ion
due o he educ ion in he wa e con en o ou p oduc o be d ied [40]. Some esea ch has been conduc ed on he
in luence o ai empe a u e on d ying kine ics. Fo d ying pea slices in a con ec i e d ye , Doymaz [41] in es iga ed
he in luence o d ying ai empe a u e. He no ed ha he educ ion in o al d ying ime wi h inc easing empe a u e
may be due o he inc ease in apo p essu e inside he p oduc wi h inc easing empe a u e, which esul ed in as e
mig a ion o mois u e o he p oduc su ace.
4.2 D ying Ra e
D ying a e is de ined as mass o wa e emo ed pe mass o d y ma e and ime [kg wa e / (kg d y solid s)] unde he
expe imen al condi ions. We es ima ed i based on equa ion (4) and i s a ia ions as a unc ion o d ying ime a ai
empe a u es o 50, 60, 70 and 80°C o sphe ical swee po a o samples o 2 cm in diame e we e as shown in Figu e 2.
I could be obse ed on he d ying kine ics a signi ican in luence o he ai -d ying empe a u e on he d ying a e o he
sphe ical swee po a o samples. This could show ha he d ying a e con inuously dec eased wi h inc easing d ying
ime, excep o he d ying a e cu e a 60°C ai empe a u e which showed a small ini ial hea ing o he swee po a oes.
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The e was no cons an a e d ying pe iod in hese cu es and mos o he d ying p ocess ook place du ing he
dec easing a e pe iod. These esul s we e in good ag eemen wi h p e ious obse a ions o a ious p oduc s such as
onion slices [29], g ape lea es [42], pomeg ana e a ils [43] and pomeg ana e peels [44]. Mois u e emo al inside he
sphe ical swee po a o samples a an ai empe a u e o 80 °C was g ea e and as e han a o he d ying empe a u es
s udied due o he apid mo emen o he mois u e o he su ace o he swee po a o and he high e apo a ion a e
om he su ace o he su ounding wa m ai . The high le el o ai empe a u e could acili a e hese wo physical
phenomena by apid ac i a ion o molecula di usion o wa e om he swee po a o solid ma ix. The bond o wa e
molecules wi h he solid ma ix was easily b oken, allowing wa e molecules o exi he swee po a o samples. The
emo al o mois u e inside he swee po a o dec eased wi h dec easing humidi y le el and hence he d ying a e also
dec eased. Addi ionally, sho e d ying ime was obse ed in Figu e 2 a highe empe a u es due o inc easing d ying
a e. This inc ease in d ying a e was due o he inc eased hea ans e po en ial be ween he d ying ai and he
sphe ical swee po a o samples, which accele a ed he e apo a ion o wa e om he sphe ical swee po a o samples.
Since he ela i e humidi y o ho ai a a highe empe a u e was lowe han ha a a lowe empe a u e, he di e ence
in pa ial apo p essu e be ween hin-laye swee po a o sphe es and hei su oundings was g ea e o he case o
d ying swee po a o a high ai empe a u e. Simila esul s had ea lie been epo ed in he o he s wo ks suck as he
con ec i e d ying o oma o slices [45], con ec i e ai d ying o swee po a o cube [21] and he ho ai d ying o pea
slices [46]. To ki-Ha chegani e al. [47] epo ed ha ood d ying occu ed in he pe iod o declining a e. Du ing he
pe iod o dec easing a e, wa e mig a ed om a eas o he ood o be d ied wi h a highe mois u e con en o a eas o
he same ood whe e he mois u e con en was lowe . The induced mo emen o wa e om he in e io o he ood o
i s su ace was con olled by molecula di usion o mois u e. This physical phenomenon could be explained by Fick’s
second law. The in es iga ion by Jiang e al. [48] explained ou indings ha he a e age mois u e mig a ion a e inside
whea g ains was lowe han he a e age e apo a ion a e ou side he whea g ains. He e al. [49] also explained his
mig a ion by he ac ha p omo ing he mois u e ans e mo emen o sea cucumbe s du ing he d ying p ocess a
dec easing a e could sho en he d ying ime o hei cucumbe samples.
Figu e 2 D ying a e cu es e sus ime (min) o di e en empe a u e a diame e 2 cm o swee po a o sphe es
The kine ics o he d ying a e o sphe ical swee po a o samples 2 cm in diame e as a unc ion o mois u e a io was
p esen ed in Figu e 3. A cons an a e pe iod was no obse ed in all cases o ai -d ying empe a u e. Examina ion o
Figu e 3 e ealed ha , in gene al, wo dis inc d ying pe iods we e iden i iable, namely he pe iod o wa ming o 60 °C
and he alling- a e pe iod a all ai -d ying empe a u es. The sho ini ial wa ming pe iod co esponding o sphe ical
samples hea ed o 60 °C was due o non-iso he mal d ying condi ions o he swee po a oes a he s a o he p ocess.
The p esence o dec easing d ying beha io was indica i e o a p og essi e inc ease in in e nal esis ance o mass and
hea ans e [29]. A con inuous dec eased in d ying a e as he mois u e a io dec eased could be obse ed in Figu e 3
. A he same ime, he inc ease in d ying a e was obse ed as he ai empe a u e inc eased, as shown Figu e 2. D ying
a es we e highe a he beginning o he p ocess and hen dec eased wi h dec easing mois u e con en in he sphe ical
swee po a o samples du ing he d ying p ocess. The educ ion in d ying a e could be due o he educed po osi y o
he sphe ical samples. This educed po osi y o igina ed om ma ix emo al om he sphe ical samples as he d ying
p ocess p og essed. This esul ed in an inc ease in massi e esis ance o wa e mig a ion, leading o a u he decline
in swee po a o d ying a es [50]. The esul s we e consis en wi h obse a ions made by o he esea che s on d ying
oods such as bay lea es [51], pu slane [52], by-p oduc s o pomeg ana e [53] and apple pomace [54]. M ad e al. [55]
epo ed ha , upon he pea s d ying, he alling d ying a e pe iod esul ed om he p edominance o in e nal di usion
mechanism due o bound wa e a he su ace and sh inkage o he p oduc .
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Figu e 3 D ying a e cu es e sus mois u e a io o di e en empe a u e a diame e 2 cm o swee po a o sphe es
The e olu ions o d ying a es as a unc ion o humidi y le el o wo sphe ical swee po a o samples wi h diame e s (2
cm and 3 cm) a an ai -d ying empe a u e o 50 °C, a e illus a ed in Figu e 4. The esul s o o he s ai empe a u es
(60, 70, 80°C) obse ed simila ly. D ying a e a 2 cm diame e was highe and as e han he 3 cm diame e . Sho e
d ying ime was ob ained o sphe ical swee po a o samples wi h smalle diame e , which inc eased hei d ying a e.
Thus, he d ying a e inc eased wi h dec ease in sample diame e s. The sphe ical diame e s o he samples could
in luence he a e o con ec i e d ying o he same mois u e con en o he swee po a o: he smalle he diame e o
he sample, he highe he d ying a e o he swee po a o. This inc ease is due o he dec eased mass ans e esis ance
o he sphe ical swee po a o samples, which acili a es he mo emen o wa e om he in e io o he sphe ical swee
po a o samples o hei su aces. Simila esul s we e epo ed by o he s esea ches on oods. Jiang e al. [56] ound
when ho ai -d ying c abapple slices ha he hickness o c abapple slices in luenced he ho ai -d ying ime. Wi h he
same mois u e con en , he hinne he hickness o he p oduc slices, he highe he d ying a e and he sho e he
d ying ime o c abapple slices. Jongyingcha oen e al. [57] explained ha he hinne he hickness o coconu d egs,
he sho e he d ying ime o he p ocess o 70 minu es. Ndisya e al. [58] ound ha as he hickness o hei sample
slices o be d ied inc eased, he d ying ime o he pu ple-speckled coconu slices also inc eased. In hin laye d ying o
onion a ie ies, Sobowale e al. [59] no iced ha he d ying a e o whi e and ed onion slices wi h inc easing hickness
illus a ed he a e a which liquid is mig a ed inside-ou o he bulb scales, simply h ough mass- ans e bound o e
ime. Simila esul s on he in luence o he hickness ha e been epo ed o ho ai d ying o banana [60], con ec i e
d ying o apple slices [61], hyb id con ec i e d ying o oma o slices [62], ho ai d ying o “Viole de Galmi” onion slices
[29], ho ai con ec i e d ying o oma o slices [63] and con ec i e ho ai d ying o po a o, ga lic and can aloupe [64].
Compao e e al. [29] was ound ha he d ying a e leek slices was highe a hin slices, and he o al d ying ime educed
subs an ially wi h he dec ease in slices hickness. Sadin e al. [65] epo ed ha in a ed d ying a e o oma o slices
was inc eased wi h inc easing empe a u e and educ ion hickness so ha maximum d ying ime o empe a u e and
hickness 60°C, 7 mm espec i ely and ha minimum d ying ime o empe a u e and hickness 80 °C, 3 mm
espec i ely. Ouoba e al. [66] indica ed ha , du ing con ec i e d ying o di e en sizes o swee po a o, he smalle he
sample size was, he as e he d ying a e was. The d ying was ound mo e e icien o small samples.
Wo ld Jou nal o Ad anced Resea ch and Re iews, 2025, 26(02), 798-813
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