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 American Journal of  
Food Science and Technology (AJFST)

Moisture Adsorption Characteristics of  Spray-Dried Composite Tropical Fruit Purees 
and Application to Shelf  Life Prediction in Flexible Packages

Jack Amedu Ankeli1, Ogbene Gillian Igbum3, Friday Godwin Okibe4, Charles Chukwuma Ariahu2, Ndi Betrand Bongjo3*

Volume 4 Issue 2, Year 2025
ISSN: 2834-0086 (Online)

DOI: https://doi.org/10.54536/ajfst.v4i2.4189
https://journals.e-palli.com/home/index.php/ajfst

Article Information ABSTRACT

Received: December 01, 2024

Accepted: January 08, 2025

Published: July 03, 2025

The moisture adsorption behavior of  spray-dried watermelon, orange, and mango 
composite puree was examined at temperatures of  20°C, 25°C, 30°C, 40°C, and 50°C across 
a water activity range of  0.11–0.95 by gravimetric static method and data obtained analyzed 
using the BET, GAB, and Oswin models. The sorption data and water vapor permeability 
of  commercial aluminum pouches, low density polyethylene (LDPE), Melinex 813, and 
Propafilm C were utilized to predict product shelf  lives under ambient storage conditions. 
The experimental data exhibited the type III isotherms, characteristic of  foods rich in soluble 
components. The GAB model provided the best fit to the adsorption data. BET monolayer 
moisture contents decreased with increasing temperature, suggesting fewer available water-
binding sites at higher temperatures. Aluminum pouches demonstrated superior moisture 
protection compared to the other packaging options. This study offers valuable insights for 
optimizing storage strategies and selecting packaging materials for spray-dried composite 
fruit products with practical applications in the food industry.

Keywords

Flexible Packages, Moisture 
Sorption Isotherms, Monolayer 
Moisture Content, Optimal 
Storage, Spray-Drying, Tropical 
Fruit Purees, Water Activity

1 Department of  Food Science &Technology, University of  Mkar, Mkar,Benue State, Nigeria
2 Department of  Chemistry, Benue State University, Makurdi, Nigeria
3 Centre for Food Technology and Research, Benue State University, Makurdi, Nigeria
4 Department of  Biochemistry, Federal University of  Health Sciences, Otukpo. Benue State, Nigeria
* Corresponding author’s e-mail: betrandbongjo@gmail.com

INTRODUCTION
The preservation and storage stability of  fruit products 
remain critical challenges in the food industry, particularly 
for tropical fruits which are often characterized by high 
moisture content and seasonal availability. Tropical fruits 
such as watermelon (Citrullus lanatus), orange (Citrus 
sinensis), and mango (Mangifera indica) are highly valued 
for their unique flavors, nutritional properties, and 
bioactive compounds. Watermelon, with its high water 
content (>90%) and rich lycopene composition, provides 
antioxidant properties and potential health benefits. 
Oranges are renowned for their high vitamin C content, 
flavonoids, and essential minerals, while mangoes are 
excellent sources of  provitamin A carotenoids, vitamin 
C, and polyphenols (Vicente et al., 2022). However, these 
fruits’ high moisture content (80-92%), coupled with 
their rich nutrient profile that supports microbial growth 
and seasonal nature, necessitate effective preservation 
methods to ensure year-round availability and reduced 
post-harvest losses. 
Spray drying has emerged as an effective method for 
extending the shelf  life of  fruit products while maintaining 
their nutritional and sensory qualities (Shishir & Chen, 
2017). This technology involves the transformation of  
liquid feed into dried particles through rapid atomization 
in a hot drying medium, typically air(Seth et al., 2018). The 
process offers several advantages including operational 
flexibility, rapid drying rates, and the production of  free-
flowing powders with controlled particle size. For tropical 
fruit purees, spray drying provides an efficient means 

of  moisture removal while preserving heat-sensitive 
components and minimizing thermal degradation of  
bioactive compounds (Santos et al., 2018).
Understanding moisture sorption characteristics is 
fundamental to predicting and controlling product 
stability during storage, especially when considering the 
hygroscopic nature of  fruit powders (Barbosa-Cánovas 
et al., 2020). These characteristics, typically represented 
through moisture sorption isotherms, provide essential 
information about water-solid interactions and help 
determine optimal storage conditions. Moreover, 
thermodynamic parameters derived from moisture 
sorption data offer valuable insights into the molecular 
mechanisms governing moisture binding and product 
stability.
Flexible packaging materials, varying in their moisture 
and oxygen barrier properties, can significantly influence 
product stability. The interaction between product 
moisture sorption characteristics and packaging material 
properties determines the moisture transfer rates and 
ultimately affects the product’s shelf  life. Understanding 
these relationships is essential for selecting packaging 
materials that can effectively protect spray-dried products 
from environmental factors while maintaining their 
quality attributes (Lechevalier, 2016; Wu et al., 2021).
While extensive research exists on individual fruit 
powders, there is limited comprehensive data on the 
moisture sorption behavior of  composite tropical fruit 
purees in their spray-dried form. Additionally, the practical 
application of  such data in predicting shelf  life stability 



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Am. J. Food. Sci. Technol. 4(2) 1-8, 2025

across different packaging materials remains relatively 
unexplored. This gap is particularly significant given the 
growing market demand for tropical fruit products and 
the need for efficient preservation methods.
This study investigated the moisture sorption 
characteristics of  spray-dried composite tropical fruit 
purees (watermelon, orange, and mango) and examined 
their implications for shelf  life prediction in various 
flexible packaging materials. Through the analysis of  
sorption isotherms, modelling of  sorption behavior, and 
evaluation of  thermodynamic properties, this research 
aimed to provide crucial insights for optimizing storage 
conditions and packaging selection in the food industry.

MATERIALS AND METHODS
Sources of  Raw Materials and Preliminary Handling
Watermelon, oranges, and mangoes were obtained from 
the “Railway market” in Makurdi, Benue State, Nigeria. 
They were thoroughly washed, cleaned and kept in the 
refrigerator for 12 hours prior to product development.

Fruit Purees Production
Watermelon Fruit Puree Production 
After washing and sorting, the fruits were peeled manually 
using stainless steel knives, followed by slicing, removal of  
the seeds, and blending of  pulps in a household electric 
blender (Kenwood Electricals, UK) at speed number 3 
for 15 s into smooth pastes, which were pasteurised at 
70 oC for 15s in 250 ml glass beakers with aluminum foil 
coverings. After cooling, the watermelon purees were 
kept in a refrigerator before use for composite puree 
formulation (Maurice, 2018).

Production of  Orange Fruits Puree
Orange fruit puree was produced with slight modifications 
as described by Obasi et al. (2017). Essentially, the fruits 
were sorted, washed, peeled and sliced using stainless 
steel knives. After the removal of  the seeds, the slices 
were blended into a smooth paste using the house hold 
electric blender. The orange puree was then pasteurized 
at 70 oC for 15s in 250 mL glass beakers with aluminium 
foil covers. The pasteurized orange puree was rapidly 
cooled in an ice bath and promptly stored in a refrigerator 
prior to use for mixed puree formulation.

Production of  Mango Fruits Puree
This was done by the method of  Labaky et al. (2020). 

The mango fruits were sorted, washed and blanched by 
immersion in a boiling hot water bath maintained at 98 oC 
for 5 min.  The blanched mango fruits were then cooled 
in running tap water, peeled using stainless steel knives 
and the fleshy mesocarp sliced to obtain pieces which 
were blended in the  Kenwood mixer in the presence of  
0.2 M citric acid buffer (pH 5.2) into a smooth slurry.  
The slurry was then stored in the freezer compartment 
of  a household refrigerator prior to use for composite 
puree formulation.

Composite Fruit Purees Formulation
The composite fruit puree compositions are shown in 
Table 1 Each puree type was treated with commercial 
maltodextrin as a carrier agent respectively to obtain a 
dextrose equivalent (DE) of  30 for each group.  The 
composite purees together with the malodextrins were 
each blended into smoothies and subjected to preliminary 
sensory evaluation which indicated that the composite 
puree sample comprising 50% watermelon, 30% orange 
and 20% mango composite puree (code: 618)  was the 
most acceptable smoothie and hence was used for the 
spray drying experiment.

Spray Drying Operations
Spray drying of  the composite fruits puree containing 50 
% watermelon, 30 % orange and 20 % mango was as 
described by Sabhadinde (2014) using a pilot plant spray-
dryer (Simon Dryers Ltd, Cheshire, England.) with a co-
current airflow. The speed of  the blower was set at 2400 
rpm for all the drying. Distilled water was pumped into the 
dryer at a set flow rate at 10 rpm (10 rpm ~ 30 mL/min) 
to achieve inlet and outlet temperatures of  200 °C and 120 
°C, respectively. The dryer was run at this condition for 
about 10 min prior to the introduction of  the feed. The 
feed puree was passed through the spray-dryer chamber 
(500 mm x 21 mm) with the aid of  a centrifugal pump. 
The speed of  rotation of  the pump controls the feed flow 
rate, which passes from the atomizer nozzle with an inner 
diameter of  0.5 mm. The inner temperature and feed 
rate were maintained at 160°C and 400 ml/h respectively.  
After the spray-drying operation, the powder obtained 
was collected in a pre-weighed, insulated glass bottle 
connected at the end of  cyclone collector and packed 
in aluminium pouches which were stored at 25°C in a 
desiccator containing activated silica gel prior to prompt 
use for analyses.

Table 1: Composite purees formulation
Sample Code Puree composition (%)

Watermelon Orange Mango
573 30 50 20
618 50 30 20*
335 20 50 30
804 50 20 30
732 20 30 50
408 30 20 50

*Most acceptable sample upon which quality analyses was carried out



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Measurement of  Equilibrium Moisture Content and 
Water Activity
Equilibrium moisture content was determined 
gravimetrically by exposing the samples to atmospheres 
of  known relative humidities following the method 
described by (Ariahu et al., 2005). Sulphuric acid (H2SO4) 
solutions of  10, 20, 30, 40, 50 and 60 % were used to 
provide water activities ranging from 0.15 to 0.96. A 
thermostatically controlled biochemistry incubator 
(Model: SPX-80-II, Searchtech Instruments) and 500 mL 
plastic containers were used for temperature and humidity 
controls respectively. The solutions made from the acid 
(200mL each) were carefully introduced into the plastic 
containers. A screen made of  wire gauze was arranged in 
the plastic containers above the acid solutions to provide 
a platform for the samples to rest. The experiment was 
carried out at four temperatures (20, 25, 30, 40 and 50 
oC). The equivalent moisture contents were determined 
by material balance from the initial moisture contents 1.
EMC: MW1+100(W3-W2)/(W1+(W3-W2)             (1)
where; M=initial moisture content of  the sample, W1=weight 
of  sample during sorption, W2=initial weight of  the sample and 
crown cork, W3=final weight of  the sample and crown cork at 
equilibrium, EMC= Equilibrium Moisture Content
Moisture Sorption Models 
The equilibrium moisture data was fitted using the 
Brunauer–Emmett–Teller (BET), GAB and Oswin 
models. These models were chosen for their reported fit 
for starchy foods. They are the most widely used model 
that gives a good fit to data for a variety of  foods over the 
aw region of  0.05 to 0.45 (Chirife & Iglesias, 1978; Rizvi, 
1995) in (Ocheme et al., 2013). The models are; 
BET Model: aw/(1-aw )M=1/(M0 C)+((C-1)aw)/(M0 C) (2)
GAB Model: M=(Mo Gkaw)/((1-kaw)(1-kaw+Gkaw))    (3)
Oswin Model: M=A[aw/(1-aw )]B                  (4)
where; M= equilibrium moisture content, Mo = 
monolayer moisture content and A, B, G, K and C are 
constants related to heat of  sorption, aw = water activity
The isotherm model parameters were obtained using 
OriginLab 2024 through linear and polynomial regression 
methods as the case may be. The goodness of  fit of  
different models used was evaluated using correlation 
coefficient (r2)
The net isosteric heat of  sorption was calculated by 
applying Clausius-Clapeyron equation to the isosteres 
obtained at constant moisture content following the 
procedure reported by Ariahu et al. (2005). By plotting 
ln (aw) versus 1/T for a specific moisture content, ∆Hst 
was evaluated from the slope (-∆Hst/R). The differential 
entropy of  sorption (∆So) was also obtained from the 
intercept, C, coefficient (∆So/R) of  the same plot. 
Applying this at different moisture contents allowed 
the dependence of  ∆Hst and ∆So with moisture to be 
determined as follows:
ln aw=Cst- ∆Hst/R  1/T                (5) 

Application of  Moisture Sorption to Shelf  Life 
Prediction
The relationship between effective diffusivity and 

storage temperature at 85 % RH was evaluated. From 
the parameters obtained from the packaging films 
(Aluminum Pouch, LDPE, Melinex 813 and Propafilm C) 
and sorption data, the shelf  life of  the instant fufu flour 
samples can be predicted following the expression for 
shelf  life predictions by Karel (1975) as cited in Offiah 
et al., (2016)
ln (Me-Mi)/(Me-Mc )=(B/x)(A/Ws )(P0/b)ts                 (6)
where; Me=equilibrium moisture content at outside relative 
humidity (obtained from sorption isotherm), Mi=Initial 
moisture content of  packaged food, Mc=Critical 
moisture content of  packaged food (from sorption 
isotherm), B=moisture permeability of  packaging 
materials, b=slope of  sorption isotherm, Ws=weight of  
solid food, A=package surface area, x=thickness of  the 
packaging material, Po=vapor pressure of  pure water at 
ambient temperature, ts=shelf  life.
A working isotherm straight line equation derived from a 
given sorption isotherm is given as;
M=Y+baw                (7)
where b=slope, Y=intercept at aw=0 (representing initial 
moisture content, Mi), M=moisture content (gH2O/100 
g solids) at given aw. The water vapour permeability of  
the different packaging films at 85 % RH are given as 
follows; Aluminum pouch (0.098 gH2O/m2.day.mmHg), 
Low-density polyethylene (0.8169 gH2O/m2.day.mmHg), 
Melinex 813 (0.88 gH2O/m2.day.mmHg), Propafilm C 
(0.122 gH2O/m2.day.mmHg). The surface area of  the 
packaging material was taken as 0.25 m2 with the weight 
of  the sample to be packaged being 500 g.

RESULTS AND DISCUSSION
Effect of  Temperature and Water Activity on 
Moisture Sorption Isotherms
As presented in Figure 1, the equilibrium moisture 
content was observed to be increasing as the water activity 
increased; but decreased with an increase in temperature. 
Also known as the Flory-Huggins Isotherms, the 
isotherms observed in this study were of  J-shaped (Type 
III). This type of  isotherm is common in foods with 
soluble components like sugars. Authors have reported 
similar types of  isotherm types in literature (Domínguez-
Chávez et al., 2023). This shape implies that with the 
presence of  the sugars, the food material sorbs small 
amounts of  water at low water activity and large amounts 
of  water at high relative humidity. Pedro et al. (2010) 
observed similar results for spray-dried passion fruit. The 
observed differences in moisture sorption capacity can 
be explained by the differences in bulk porosity and the 
pore size of  the dried materials. Such drying techniques 
such as Freeze-drying and spray drying, resulted in a 
highly porous product with small pores, which sorbed 
more water (Tsami et al., 1998). The behavior of  
the isotherms can be attributed to physical sorption 
occurring on highly active sites at low water activities, as 
water molecules primarily interact with surface hydroxyl 
groups of  crystalline sugar. The observed decrease in 
equilibrium moisture content with rising temperature 
aligns with findings from other researchers (Ocheme et 



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al., 2013; Pedro et al., 2010; Sengev et al., 2016). This trend 
may result from the reduced affinity of  water molecules 
for the product at higher temperatures. This trend is 
related to the excitation state of  molecules reported by 
Diosady et al in (Ariahu et al., 2005). The attractive forces 
between molecules are lower at high temperatures due 
to an increase in the kinetic energy of  water molecules, 
allowing the connection between moisture and sorption 
sites to be broken, which reduces the moisture content 
of  the product (Yadav & Mishra, 2023). Dalgıç et al. 
(2012) have also reported similar results for freeze-dried 
mint leaves. The effect of  spray drying on the moisture 
sorption isotherm of  coffee extract has also been studied 
and it aligns with the results in this study (Villegas-
Santiago et al., 2020). Similar results were also observed 
for spray-dried sweetened yoghurt powder (Seth et al., 
2018). An increase in moisture content with rising water 
activity was observed, with a more pronounced increase 
occurring in the water activity range of  0.5 to 1.0. This 
suggests that at water activity levels above 0.5, microbial 
growth, enzymatic reactions, and lipid oxidation are likely 
to accelerate, leading to faster spoilage of  the spray-dried 
fruit puree composites.

Model Regression Parameters and Derivative 
The regression parameters for the GAB, BET, and Oswin 
models are presented in Tables 2, 3, and 4, respectively. It 
was observed that the monolayer moisture content (Mo) 
decreased with increasing temperature. The Mo values are 
critical for identifying storage and preservation conditions, 
as exceeding these values could lead to deteriorative 
changes. It represents the minimum amount of  water 
bound to active sites to give a monolayer coverage and 
maximum stability of  storage foods (Yang et al., 2016). The 
monolayer moisture contents determined using the BET 
and GAB models were found to range from 6.60 to 15.50 
g H2O/100 g solids and 9.98 to 30.87 g H2O/100 g solids, 
respectively. Notably, the BET monolayer values were 
significantly lower than those obtained from the GAB 
model. Authors reported lower BET and GAB monolayer 
moisture contents ranging from 1.18-6.89 g H2O/100 g 
solids and 4.52-6.59 g H2O/100 g solids respectively; for 
spray-dried coffee extract (Villegas-Santiago et al., 2020). 
This reduction in monolayer values could be explained by 
the reduction in the total number of  active sites for water 
binding as a result of  physical and/or chemical changes in 

the product induced by temperature during the freezing 
process. Several researchers have observed similar 
scenarios  (Domínguez-Chávez et al., 2023). Though 
there was a general reduction in the monolayer moisture 
content, the decreasing trend was not clear as there was 
an initial decrease in Mo and then a subtle increase. This 
could be due to several factors which affect sorption in 
foods which can be complex (Harini, 2023).

Figure 1: Moisture sorption isotherms of  spray-dried 
tropical fruit composite purees

Fitting of  Sorption Models
Sorption experimental data for five temperatures (20 
°C, 25 °C, 30 °C, 40 °C, and 50 °C) were fitted to three 
models: BET, GAB, and Oswin, within their theoretically 
appropriate ranges. The quality of  the fit for each model 
was assessed using the correlation coefficient (r²), with the 
values presented in Tables 2, 3, and 4 for the BET, GAB, and 
Oswin models, respectively. The r² value, which indicates 
how well a model explains the variability of  the predicted 
values, suggests that models with r² values closer to 1 are 
more suitable (Gichau et al., 2020). The r² values ranged as 
follows: GAB (0.81–0.96), BET (0.50–0.87), and Oswin 
(0.49–0.62). Among the models, the GAB model had the 
lowest %RMS (5.8 – 7.6) and hence provided the best fit, 
as evidenced by its r² values being closer to 1 compared to 
the Oswin and BET models. This finding agrees with results 
reported by Pedro et al. (2010), who studied the sorption 
isotherms of  passion fruit pulp and Villegas-Santiago et al. 
(2020), who analyzed the drying process of  coffee extract.

Table 2: GAB Adsorption Regression Parameters for spray-dried composite tropical fruit puree
Sample Temperature K C Mo r2

20 0.67 1.84 30.87 0.96
25 0.70 6.13 9.98 0.88
30 0.87 8.75 11.89 0.80
40 0.82 4.11 13.40 0.84
50 0.80 2.35 13.97 0.81

r2=correlation coefficient, Mo=monolayer moisture content, G and K are GAB constants



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Thermodynamic Properties of  Spray-Dried 
Composite Tropical Fruit Purees
Net Isosteric Heat Of  Sorption
The net isosteric heat of  sorption exhibited strong 
dependency on EMC of  spray-dried composite tropical 
fruit purees (Figure 2). The net isosteric heat was 
maximum (3.3×10−4 kJ/mol) at the lowest EMC (2 % 
db) which decreased with the increase in EMC. This 
finding is also corroborated by several workers (Edrisi 
Sormoli & Langrish, 2015; Yogendrarajah et al., 2015). 
This could be attributed to the availability of  highly active 
polar sites that initially require greater interaction energy. 
Once the available polar sites become less, binding energy 
also diminishes (Seth et al., 2018). The isosteric heat of  
sorption decreased swiftly up to 6 % moisture content 
(db) followed by a gradual decrease with increasing 
moisture content. This implied that the water bound in the 
‘monolayer region’ is difficult to remove compared to the 
‘condensed water region’ of  isotherm (Seth et al., 2018). 
The high correlation coefficients (r2≥0.869) confirm 
the validity and effectiveness of  the Clausius-Clapeyron 
equation in describing the sorption energetics of  the 
spray-dried tropical fruit puree composites, as shown in 

Table 5. As the moisture content increases, the heat of  
sorption approaches that of  pure water, indicating that 
the moisture exists predominantly in a free form. This 
underscores the strong dependence of  isosteric heat on 
moisture content, with the energy required for sorption 
(beyond the latent heat) being significantly higher at low 
moisture content (Yazdani et al., 2006). Additionally, this 
suggests that the heat of  adsorption for the initial layers 
of  water molecules exceeds the heat of  condensation 
of  pure water. The heat of  sorption values at specific 
moisture contents offer valuable insights into the state 
of  the sorbed water, serving as an indicator of  the 
physical, chemical, and microbiological stability of  food 
materials under specific storage conditions. The variation 
in sorption heat with moisture content is particularly useful 
for calculating energy consumption and designing efficient 
drying equipment. Additionally, it aids in understanding the 
balance between water-water and water-solid interactions. 
Water sorption in foods is inherently complex, as the main 
water-sorbing constituents—such as proteins, starch, 
cellulose, and sugars—each contain distinct polar groups 
that create energetically preferential sites for water binding 
(Labuza & Altunakar, 2020).

Table 3: BET Adsorption Regression Parameters for spray-dried composite tropical fruit purees
Sample Temperature C Mo So r2

20 2.64 15.50 544.65 0.74
25 7.86 6.60 232.65 0.72
30 10.19 9.91 348.17 0.87
40 4.77 10.12 355.57 0.73
50 2.59 10.14 356.29 0.50

r2=correlation coefficient, Mo=monolayer moisture content ( g H2O/100g solids), So=surface area of  sorption (m2/100g solids), C= 
BET constant

Table 4: Oswin Adsorption Regression Parameters for spray-dried composite tropical fruit purees
Sample Temperature n C r2

20 0.28 8.96 0.49
25 0.21 6.11 0.50
30 0.23 11.12 0.62
40 0.26 7.88 0.56
50 0.29 5.92 0.52

A and B are Oswin constanst, r2=correlation coefficient

Table 5: Regression parameters for Clausius–Clapeyron equation relationship between lnaw  and 1/T for adsorption isotherms
Regression 
parameter

Moisture content (gH2O/100 g solids)
2 3 4 5 6 8 10 12

N 5 5 5 5 5 5 5 5
A -0.039 -0.049 -0.028 -0.027 -0.026 -0.023 -0.021 -0.019
B 8.96 12.32 6.43 6.29 6.13 5.64 5.23 4.76
r2 0.933 0.985 0.896 0.920 0.944 0.948 0.940 0.869
ΔHst 0.00033 0.00041 0.00024 0.00023 0.00022 0.00019 0.00017 0.00016
ΔSo -0.0745 -0.1024 -0.0535 -0.0523 -0.0510 -0.0469 -0.0435 -0.0395

n = no. of  entries; r2=correlation coefficient; b= intercept coefficient; a= slope; ΔHst=net isosteric heat (kJ/mol); ΔSo=net entropy of  
sorption (kJ/mol.oC).



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Entropy of  Sorption
Like isosteric heat of  sorption, sorption entropy exhibited 
strong dependency on EMC (Figure 2). The sorption 
entropy gives the status of  the available sorption sites for 
water binding on the surface (Yogendrarajah et al., 2015). 
The entropy of  sorption (ΔSo) values were determined 
from the intercept coefficients obtained through least-
square linear regression of  the relationship between 
lnaw and 1/T at constant moisture contents. Using 
the Clausius-Clapeyron equation, ΔSo was calculated 
as Cst=∆So/R. Negative ΔSo values were observed, 
increasing as moisture content increased. This reflects 
the thermodynamic compensation between the heat and 
entropy of  moisture sorption. At lower moisture contents, 
water molecules are tightly bound to the sorbent surfaces, 
exhibiting a low degree of  freedom and low entropy 
of  sorption. In contrast, at higher moisture contents, 
water molecules form multilayers over the tightly bound 
first layer, possessing greater degrees of  freedom and, 
consequently, higher entropy of  sorption (Li et al., 2011; 
Yang et al., 2016). For the spray-dried tropical fruit purees, 
the entropy of  sorption increased up to approximately 
6 % moisture content and then became asymptotic with 
further increases in moisture content. This behavior 
may be attributed to a balance between the increasing 
moisture content and the availability of  hydrophilic 
sites, which prevents significant fluctuations in entropy. 
Similar asymptotic tendencies in various products have 
been reported in the literature (Ariahu et al., 2005; Li et al., 
2011; Sengev et al., 2018).

(0.122 g H2O/m2.day.mmHg). For instance, at 20 °C, 
aluminum pouches were estimated to achieve a shelf  
life of  73.08 months, the longest among the tested 
packaging materials. In contrast, the shelf  life for the 
same packaging decreased significantly to 9.31 months 
at 50 °C, highlighting the influence of  temperature on 
product stability (Figure 3). These shelf-life estimations 
focused on the water vapor permeability of  the packaging 
materials. However, further investigations are necessary 
to understand the impact of  gas permeability, particularly 
to oxygen and carbon dioxide, which could contribute to 
lipid oxidation and affect product quality (Gichau et al., 
2020; Seth et al., 2018).

Figure 2: Net isosteric heat and net entropy of  sorption 
of  spray-dried composite tropical fruit purees

Shelf  life Prediction of  Spray-Dried Composite 
Tropical Fruit Purees
As anticipated, the shelf  life of  the product decreased 
with increasing initial storage moisture content and 
storage temperature across all packaging types. Storage 
conditions, particularly high ambient temperature and 
relative humidity, pose significant challenges for the 
stability of  dried products (Anandito et al., 2017). Higher 
storage temperatures are predicted to shorten shelf  
life due to the increased transmission rate of  water 
vapor (Gichau et al., 2020). Regardless of  temperature, 
aluminum pouches were predicted to offer the longest 
shelf  life due to their low water vapor transmission rate 

Figure 3: Shelf  life Prediction of  Spray-dried composite 
tropical fruit purees

CONCLUSION
This study provides comprehensive insights into the 
moisture sorption behavior and storage stability of  spray-
dried composite tropical fruit purees. The investigation 
revealed that the spray-dried products exhibited Type III 
isotherms, characteristic of  high-sugar materials, with the 
BET model providing the best fit for the experimental 
moisture sorption data. This finding is particularly 
significant for predicting moisture content under various 
storage conditions.The thermodynamic analysis revealed 
important relationships between moisture content and 
binding energy, as demonstrated by the increase in net 
isosteric heat of  sorption with increasing moisture 
content, indicating the presence of  thermodynamic 
compensation. The negative values of  net entropy of  
sorption, which approached zero with increasing moisture 
content, suggest reduced molecular mobility and increased 
order in the system at lower moisture content. These 
thermodynamic parameters provide valuable insights into 
the water-solid interactions that govern product stability. 
The comparative analysis of  different flexible packaging 
materials demonstrated that aluminum pouches offered 
superior protection and predicted longer shelf  life (73.08 
months at 20 oC) compared to other packaging options. 
This finding has significant practical implications for the 
food industry, particularly in the selection of  appropriate 
packaging materials for spray-dried fruit products. These 
results contribute to the fundamental understanding 
of  moisture sorption phenomena in composite fruit 



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systems and provide practical guidelines for the storage 
and packaging of  spray-dried tropical fruit products. The 
findings can be applied to optimize storage conditions 
and packaging selections, ultimately leading to improved 
product stability and extended shelf  life.

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