Available via license: CC BY 4.0
Content may be subject to copyright.
Journal of Engineering Science Vol. XXX, no. 1 (2023), pp. 154 - 164
Fascicle Food Engineering ISSN 2587-3474
Topic Food Technologies and Food Processes eISSN 2587-3482
Journal of Engineering Science March, 2023, Vol. XXX (1)
https://doi.org/10.52326/jes.utm.2023.30(1).13
UDC 664.8:634.13
DRYING OF PEARS IN CO2 MODIFIED ATMOSPHERE
Mihail Melenciuc*, ORCID: 0000-0001-6575-8814
Technical University of Moldova, 168 Stefan cel Mare Blvd., Chisinau, Republic of Moldova
*Corresponding author: Mihail Melenciuc, mihail.melenciuc@pmai.utm.md
Received: 12. 26. 2022
Accepted: 02. 17. 2023
Abstract. One of the biggest problem encountered in drying area of food processing are the
losses in food quality. While drying process is held, there is an important damage done to
vitamins, polyphenols and other important nutriments. Being easily affected by high
temperature and oxygen exposure, our concern was to find out what will be the effect of
convective drying in air flow and CO2 modified atmosphere upon pears, “Conference” variety
quality. Testing took place with temperatures between 60 and 100°C for both drying
methods, one also used three different CO2 concentration regimes for the modified
atmosphere approach, namely 30, 60, and 80%. The usage of carbon dioxide instead of air
inside the drying chamber is expected to reduce oxygen exposure of the product during
drying process, thus reducing oxidative reactions. Using CO2 as air substituent for convective
drying showed good results from the organoleptic point of view by preserving a more natural
pear color closer to the row material one, reduced damage done to ascorbic acid and total
polyphenols concentration presumably thanks to reducing oxygen concentration and a slight
drying duration reduction. There was deducted and established a mathematical model for the
convective modified CO2 drying atmosphere as well as a pilot drying installation was
designed for combined dying methods equipped with a CO2 recycling system.
Keywords: pears, experimental drying plant, convection, drying kinetic curves, ascorbic acid,
polyphenols.
Rezumat. Una din cele mai grave probleme întâlnite la procesarea produselor alimentare și
anume în domeniul uscării, este pierderea calității. În funcție de durata procesului de uscare
pot fi grav denaturate vitaminele, polifenolii și alte nutrimente. Astfel cum, toate aceste
substanțe, sunt mult afectate de expunerea la temperaturi înalte și oxigen, noi am avut ca
scop să determinăm care va fi efectul uscării convective cu aer și în mediu modificat de CO2
asupra calității perelor de soi „Conferința”. Pentru ambele metode de uscare, testările au avut
loc la temperaturi cuprinse între 60 și 100°C, iar pentru metoda de uscare cu CO2 au fost
utilizate și trei regimuri de concentrații 30, 60 și 80%. Prin utilizarea dioxidului de carbon în
camera de uscare, ca substituent al aerului, se așteaptă o reducere considerabilă a proceselor
oxidative prin reducerea concentrației de oxigen. Folosirea CO2 ca substituent pentru uscarea
convectivă a arătat rezultate bune din punct de vedere organoleptic și anume prin păstrarea
unei culori a perelor aproape de cea a perelor proaspete, a redus nivelul de denaturare a
acidului ascorbic și a conținutului total de polifenoli, fapt care probabil se datorează reducerii
Drying of pears in CO2 modified atmosphere 155
Journal of Engineering Science March, 2023, Vol. XXX (1)
concentrației de oxigen și unei micșorării ușoare a duratei de uscare. A fost dedus și stabilit
modelul matematic pentru uscarea convectivă în atmosferă modificată de CO2 și proiectată
instalația experimentală pentru uscarea combinată cu sistem de reciclare a CO2.
Cuvinte cheie: pere, instalația de uscare experimentală, convecție, curbele vitezei de uscare, acid
ascorbic, polifenoli.
1. Introduction
The human diet consists in a high percentage of fruits and vegetables. Pears, bring us
a delicate taste and a sweet aroma as well as being characterized by a high digestibility,
making them very popular [1]. The popularity of pears is due to their composition, containing
polyphenols, minerals, vitamins, amino acids, sugars as well as an important quantity of water [2, 3].
Drying is the oldest method of food preservation and is used till our days as it brings
a large gamma of benefits as reducing storage and transportation space as well as energy
consumption. Through the time there were lots of scientist and researches that developed
this conservation method introducing new drying types and regimes, that were meant to
reduce food treatment time and assure an overall better final product quality. Such drying
methods as microwave, vacuum, freeze were introduced for the food industry. As each method
has its own advantages and disadvantages, there’s a good decision to combine those and use
their strong qualities to create new hybrid drying methods as convection with microwave,
vacuum with microwave drying, etc.
One of the recent drying methods that was highlighted by researchers is modified
atmosphere drying, in which the conventional drying agent – the air, is changed or mixed
with an inert gas (carbon dioxide, nitrogen, etc.).
Using the modified atmosphere drying method is a potential way to reduce oxidative
processes during drying course. Reducing oxygen concentration inside the drying chamber,
or even fully eliminating it, being replaced by another gas (carbon dioxide, nitrogen, etc.) has
already proved to be a promising drying method. Several studies [4-6] were conducted in this
context using as experimental material vegetal products (ginger, apples, strawberry, carrot,
etc.) for whom were determined some important submitted to oxidative reactions
components, such as gingerol, acid ascorbic, carotedoids, etc.
A group of scientists [4] experimented with different drying methods (freeze, vacuum,
conventional and modified atmosphere convection) on ginger, namely they analyzed the
effect of those specific drying methods upon 6-gingerol content preservation in dried ginger.
For this goal the researchers had designed a closed circuit heat pump drying installation,
adjusted for modified atmosphere drying. The results of the study represent the comparison
between different drying methods dried ginger 6-gingerol content. As such, the highest
content of gingerol was characteristic for vacuum (11 mg/g) drying method whilst modified
atmosphere (carbon dioxide and nitrogen) was close enough to the same result (9.5 mg/g).
The lowest 6-gingerol content was shown for conventional air drying (6 mg/g) [4].
The next study [5] was concentrated on analyzing the effect of freeze, conventional
and modified atmosphere convection drying on ascorbic acid content in dried strawberries.
The researchers have designed as well a close circuit drying installation, that allows the use
of modified atmosphere. Analyzing the results, we can conclude that the highest losses of
ascorbic acid were found to be in air dried strawberry samples (28 %), while the lowest were
in freeze dried one (4 %). In terms of ascorbic acid losses, good result had also shown the
modified atmosphere dried strawberry samples (6 %) [5].
156 M. Melenciuc
Journal of Engineering Science March, 2023, Vol. XXX (1)
The influence of drying atmosphere oxygen concentration on carotenoid and ascorbic
acid retention ratio in dried carrot samples was researched [6] using a designed closed circuit
experimental tunnel drier. The researchers experimented with different (5%, 10%, 15%,
20.9%) oxygen concentrations and established that retention ratio of ascorbic acid and
carotene in dried carrot samples (70°C conventional and modified atmosphere convection) is
inversely proportional to oxygen concentration, namely it increases 1.8 times for carotene
and 1.7 times for ascorbic acid retention ratio.
The most undesirable drying results are the effect of browning of vegetal food, that is
visible right away at the end of the process and important nutriments losses as a result of
oxidation effects in general that happens throughout the drying procedure. This effect has
been spotted and analyzed by diverse plants breeders, plants physiologists and food
scientists. Some browning reaction are useful but their majority is not, as they lead to food
quality diminution as result of organoleptic and nutritional properties alteration. The food
browning of enzymatic nature brought by polyphenol oxidases has a significant economic
effect on products like cereals, fruits and vegetables that should be well controlled [7-9].
The main goal of the study was to create a technology of drying vegetal food, namely
“Conference” pears, in CO2 modified atmosphere as well as designing a pilot drying
installation for the same purpose. To accomplish that goal one formed the following
objectives: optimizing the process of drying pears in CO2 modified atmosphere, by
mathematical modeling; elaboration of the experimental installation for drying pears in a CO2
modified atmosphere; analysis of the quality parameters of dried pear fruits in a CO2
controlled atmosphere in order to develop recommendations.
2. Materials and methods
2.1 Samples preparation
“Conference” variety pears belong to the family Rosaceae, genus Pyrus, species
Communis, were selected from Republic of Moldova marketplaces according to [10] and
prepared for the experiment.
The “Conference” pears were washed and cut in half circles (Figure 1) with a
0.005±0.0005 m thickness and a total pieces’ weight of 100 ± 0.2 g. The drying was performed
by two convective methods: in air flow and CO2 modified atmosphere.
Figure 1. Preparation of half circles sliced “Conference” pears for drying.
There were chosen several temperature regimes between 60°C and 100°C, drying agent
velocity of 1.5±0.13 m/s for both drying methods and three concentrations for modified CO2
atmosphere, namely 30%, 60% and 80% of CO2.
Drying of pears in CO2 modified atmosphere 157
Journal of Engineering Science March, 2023, Vol. XXX (1)
2.2 Experimental drying installation
For the experimental part, one has designed and elaborated an experimental
laboratory drying installation (Figure 2), that allows drying to take place through different
methods, including conventional convection – using air, microwave drying and their
combination, as well as the use of modified atmosphere by replacing air with different
concentrations of carbon dioxide.
Figure 2. Experimental laboratory drying installation.
1 – carcass; 2 – control panel; 3 – cooling installation; 4 – CO2 recipient;
5 – temperature controller; 6 – fan inverter; 7 – CO2 income hose; 8 – electrical motor;
9 – intermediate pipe; 10 – centrifugal fan; 11 – pipe fastening; 12 – condenser;
13 – heat source; 14 – magnetron; 15 – drying chamber; 16 – CO2 concentration
indicator; 17 – drying agent recycling pipe; 18 – receiver; 19 – electronic scale;
20 – electronic scale space; 21 – lid.
The installation presents a drying chamber 15 which is installed on a metallic carcass
1 along with the heat source 13 and a centrifugal fan 10 which is driven by the electrical
motor 8 and an inverter 6 which allows fan’s velocity control. The gas, from the drying
chamber may be recycled (Figure 3) through the recycling pipe 17, that is connected to the
condenser 12, from which the gas is transferred into the drying chamber using the centrifugal
fan 10 and the intermediate pipe 9. The installation allows drying using microwave energy.
For this purpose, the installation is equipped with a magnetron 14 on the top of the drying
chamber, that allows changing the height of the magnetron towards the product. For research
purposes and data collection there is an electronic scale 19 installed under the working
chamber 20. The drying chamber is hermetically closed using the lid 21 which holds the
carbon dioxide concentration indicator 16 and receiver 18.
2.3 Total polyphenol content
The total polyphenol content was expressed in milligram of gallic acid equivalent
(GAE) per 100 g of the researched product. Polyphenols content was established by optical
density measurement of an extract that, in presence of the Folin-Ciocalteu reagent, absorbs
at the wavelength of 765 nm. For the analysis 5 mL double distilled water, 1 mL of dried
pears sample and 0.5 mL Folin-Ciocalteu reagent in a 10 mL volumetric flask were mixed.
158 M. Melenciuc
Journal of Engineering Science March, 2023, Vol. XXX (1)
After 3 minutes, 1.5 mL of 10% sodium carbonate was added and brought up to the mark with
double-distilled water. The solutions are placed on the water bath at a temperature of 50°C
for 16 min, after which it cools down to room temperature. Afterwards the absorbance is
measured using a Hach Lange DR-5000 spectrophotometer [11].
Figure 3. Experimental drying installation gas recycling system.
2.4 Vitamin C content
Using a mortar, 10 g of each analyzed “Conference” pear samples: fresh, convection-
dried (air and CO2), were separately crushed in the presence of 1% oxalic acid and
quantitatively transferred to a 100 cm3 volumetric flask and brought up to the mark with
oxalic acid and mixed. The content of the flask was poured through filter material into a
conical flask adding. 6 cm3 of 2,6-dichlorophenolindophenol. The extinction is determined
transferring the obtained solution to the cuvette and subjected to photocolorimetry at the
wavelength 540 nm. For the second extinction: a few crystals of ascorbic acid are added to
the cuvette with the analyzed solution (the color of 2,6-dichlorophenolindophenol
disappears), the solution is stirred and photocolorimetry is performed again [12].
2.5 Mathematical modelling
For the drying process to be performed there was created a mathematical model which
takes in account the changes of drying atmosphere by establishing boundary conditions
adapted for carbon dioxide [13]:
(0,0008
+0.0149)(,)
+(0,0008 +0,0149)
[
(,)]
(1)[0,167 0,13 10(0,0004
+0,8252 +163,69)
.
.
.
](,)=0
(1)
(0,0008
+0.0149)(,)
+
(,)
+ [0,167
0,13 10(0,0004
+0,8252 +163,69)
. .
.
](,)=0
(2)
Drying of pears in CO2 modified atmosphere 159
Journal of Engineering Science March, 2023, Vol. XXX (1)
where t – moist body temperature, K; ta – drying atmosphere temperature, K; τ – drying
time, s; H – layer thickness, m; aq, am – temperature and potential diffusion coefficients, m2/s;
ε – phase transformation criterion; r’ – vaporization latent heat, kJ/kg; c’T, cq – specific mass,
kg/kg·M and specific heat, J/kg·K capacities; ρ – moist body dry part density, kg/m3;
δ – moist body Sore coefficient, 1/K; θ – mass transfer potential (moisture), M potential units;
λ
q,
λ
m – thermal conductivity, W/m·K and mass conductivity, kg/m·s·M;
Re – Reynolds criterion; Pr – Prandtl criterion; Nu – Nusselt criterion.
2.6 Statistical processing of the results
To determine the error of a series of successive measurements of experimental data
(ascorbic acid concentration, polyphenol concentration, etc.) standard deviations were
calculated [14]. All calculations were performed using Microsoft Office Excel 2007 (Microsoft,
Redmond, WA, USA). Data obtained in this study are presented as mean values ± standard
error of the mean calculated from three parallel experiments.
3. Results and discussions
The speed of the drying agent plays an important role in the process of diffusion of
moisture evaporated from the surface of the product into the surrounding environment. In
the given case, the mathematical description of this phenomenon is strictly necessary for
more efficient optimization of the drying process. The correct choice of the speed of the
heating agent leads to the reduction of the energy consumption of the fans that ensure the
parameters of the given flow and the consumption of thermal energy in the case of
convection drying. In order to determine the optimal drying speed, the mathematical model
of the speed of the drying agent at the mass transfer between the product and the
environment was built. After performing the calculus, the following product temperature and
humidity, for CO2 environment formulas were deducted:
=+
(3)
=+
(4)
A, B, C – deducted coefficients which take in account drying process conditions and
product characteristics
The mathematical model presented and the results of its verification for deviations,
allows it to be used both for drying pears in a CO2 modified environment and for air
convection, more than that, the given model, after introducing some modifications, which
would take into account thermophysical properties, would also find application in the
determination of temperature and humidity during drying for other vegetable food products
with a pear-like structure.
To carry out the experimental drying, the experimental drying installation with a
modified CO2 medium, with a closed cycle of the drying agent, with the possibility of changing
the concentration of carbon dioxide inside the drying chamber and automatically taking over
the experimental data during the drying process was designed and made (Figure 3).
In order to establish the influence of the environment modified by CO2 on the drying
process, experimental dryings of pears of the “Conferința” variety were carried out, both by
the conventional method - with air, and in a modified environment. Drying took place at
several thermal regimes and for CO2 at several gas concentrations in the working chamber
(30, 60 and 80%).
160 M. Melenciuc
Journal of Engineering Science March, 2023, Vol. XXX (1)
Based on the experiments drying process and drying kinetics curves were established
for convective air drying (Figure 4) and convective 80% CO2 modified atmosphere drying
(Figure 5), from 60 to 100°C and 1.5±0.13 m/s drying agent velocity.
Analyzing Figure 4a and Figure 5a, an intensification of the drying process can be
observed with the increase in the temperature of the drying agent. As a result of mass and
heat transfer phenomena, at 60°C (air, convective regime), the drying time is 525 min, while
at 100°C – 260 min, showing a 2.02 times diminution in drying duration. The same effect was
reported by other researches [15-18].
a)
b)
Figure 4. Drying process (a) and drying kinetics process (b) curves for dried “Conference”
pears, by air flow method; drying agent air: 60, 70, 80, 90 and 100°C, drying agent
velocity 1.5±0.13 m/s.
The drying kinetic curves for both methods (Figure 4b and Figure 5b) highlight all
three stages of drying, in which the heating stage takes place up to 73-75% humidity, the
constant drying stage – from 73-75% to 34 -38% and the speed reduction step – from 34-
38% until equilibrium humidity is reached.
a) b)
Figure 5. Drying process (a) and drying kinetics process (b) curves for dried “Conference”
pears, by CO2 modified atmosphere method; drying agent CO2: 60, 70, 80, 90 and 100°C;
carbone dioxide concentration: 80%; drying agent velocity 1.5±0.13 m/s.
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400 500 600
Humidity, %
Drying duration, min
Temperature 60°C Temperature 70°C Temperature 80°C
Temperature 90°C Temperature 100°C
0
0.1
0.2
0.3
0.4
0.5
10 30 50 70 90
Drying kinetics, %/min
Humidity, %
Temperature 60°C Temperature 70°C Temperature 80°C
Temperature 90°C Temperature 100°C
0
10
20
30
40
50
60
70
80
90
0 100 200 300 400 500
Humidity, %
Drying duration, min
Temperature 60°C Temperature 70°C Temperature 80°C
Temperature 90°C Temperature 100°C
0
0.1
0.2
0.3
0.4
0.5
0.6
10 30 50 70 90
Drying kinetics, %/min
Drying duration, min
Temperature 60°C Temperature 70°C Temperature 80°C
Temperature 90°C Temperature 100°C
Drying of pears in CO2 modified atmosphere 161
Journal of Engineering Science March, 2023, Vol. XXX (1)
One can notice that temperature growth also shows an augmentation of drying process
velocity, for example air drying constant drying stage velocity, for 60°C, 0.21±0.01 %/min, at
70°C – dU/dτ ≈ 0.26±0.01 %/min, at 80°C – dU/dτ ≈ 0.31±0.02 %/min, at 90°C – dU/dτ ≈
0.36±0.02 %/min and at 100°C – dU/dτ ≈ 0.43±0.02 %/min, meaning an increase of 2.04 times
from 60°C to 100°C. the same effect was mentioned by other authors [20, 21].
Drying kinetics curves for 80% CO2 modified atmosphere (Figure 5 b.) has the same
patterns as air drying one (Figure 4 b.) except higher values for the constant drying stage:
60°C, 0.25±0.01 %/min, at 70°C – dU/dτ ≈ 0.32±0.02 %/min, at 80°C – dU/dτ ≈ 0.38±0.02 %/min,
at 90°C – dU/dτ ≈ 0.43±0.02 %/min and at 100°C – dU/dτ ≈ 0.54±0.03 %/min, showing an
increase of 1.19 times for 60°C and 1.26 times for 100°C, that confirms the drying process
acceleration namely while humidity is evaporated from the product surface.
The small reduction in drying time for the CO2 modified atmosphere compared to air
drying, which is most likely explained by an intensification of mass transfer from the product
to the medium, and less by mass transfer within the product. This phenomenon can also be
related to the reduction of the vapor pressure of the drying product while the CO2 is washed,
a fact noted by other researchers [6].
After performing the experiments there was determined the total polyphenols content
and ascorbic acid concentration for dried “Conference” pears samples. Basing on the Figure
6. One can identify the effect of drying upon total content of polyphenol in dried “Conference”
pears by both methods of air and CO2 convection.
Analyzing the diagram from Figure 6., one can observe an augmentation of total
polyphenols content with temperature increase. The same effect was mentioned by other
scientists [15, 19, 22], and is presumably caused by shorter exposer of polyphenols to
temperature action, as a result of reduced drying time at higher temperatures. identify an
evolution of the polyphenol content as CO2 concentration augments, if taking the same
temperature of 60°C, we’ll have 28.03±1.45 mg GAE/100 g of plant for air drying; 36.77±1.90
mg GAE/100 g of plant for 30% CO2 drying; 40.73±2.11 mg GAE/100 g of plant for 60% CO2
drying and 42.34±2.19 mg GAE/100 g of plant for 80% CO2 drying respectively.
Figure 6. Total polyphenol content in dried pears, “Conference” variety, by air flow and
CO2 modified atmosphere methods. Drying agent temperature (air and CO2): 60 and 80°C;
Carbone dioxide concentration: 30, 60 and 80%.
22
32
42
52
62
72
82
92
60 70 80
Total polyphenols content,
mg GAE/100 g
Temperature, °C
Air CO2-30% CO2-60% CO2-80%
162 M. Melenciuc
Journal of Engineering Science March, 2023, Vol. XXX (1)
If compared, the same CO2 concentrations will show a boost for the temperature of
80°C: 35.79±1.85 mg GAE/100 g for air drying; 47.59±2.46 mg GAE/100 g for 30% CO2 drying;
65.25±3.38 mg GAE/100 for 60% and 81.90±4.24 mg GAE/100 g for 80% CO2 drying which
shows an increase of total polyphenols preserved of 1.27 times for air drying environment
and 1.93 times for 80% CO2 drying atmosphere. The increase in total polyphenols content in
CO2 modified atmosphere, as noticed by other researchers [5], is due to the even more
reduced drying time, as such decreased product temperature exposure, as well as the reduced
concentration in oxygen, that presumably reduce the probability that oxidative reactions will
occur.
From Figure 7 one can observe the degradation process of vitamin C which is easily
affected by high temperature exposure, as well as oxygen presence. Researches also noticed
that diminution in ascorbic acid is closely connected to moisture content of the product to be
dried [15, 23], so lower temperatures are not recommended, for a rich vitamin C dried product.
Beginning with a fresh “Conference” pear concentration in ascorbic acid of 44.05±2.47
mg/100 g DW (dried weight), for air convective drying, versus 43.86±2.41 mg/100 g DW, for
CO2 modified atmosphere drying, one can notice the deterioration process intensifying with
drying process length.
Figure 7. Ascorbic acid concentration for dried pears, “Conference” variety by air flow and
CO
2
modified atmosphere methods (Carbone dioxide concentration: 80%; t= 70°C).
As such at 390 min the losses in Vitamin C represents 77 %, or 11.45±0.63 mg/100 g
DW for air dried pears and 50%, or 22.74±1.24 mg/100 g DW for modified atmosphere one.
There is a boost of 27%, or 1.98 times to preserved ascorbic acid. As mentioned by other
sources [5, 15] that effect can be explained by the reduction of oxidative processes of ascorbic
acid during drying process, that is possible to achieve with oxygen concertation reduction in
the drying chamber when using CO2 modified atmosphere.
4. Conclusions
This study was meant to investigate the effect of different types of drying agents,
namely air and carbon dioxide for half-circle sliced pieces of “Conference” pears convective
drying, with a temperature range of 60 – 100°C, and three CO2 concentration: 30%, 60%, 80%.
0
5
10
15
20
25
30
35
40
45
50
030 60 90 120 150 180 210 240 270 300 330 360 390
Vitamin C content,
mg/100 g DW
Drying duration, min
Vit. C, mg/100 g DP, 70°C, air Vit. C, mg/100 g DP, 70°C, CO2, 80%
Drying of pears in CO2 modified atmosphere 163
Journal of Engineering Science March, 2023, Vol. XXX (1)
The resulting data allowed to conclude that the above mentioned boost to
polyphenols and ascorbic acid content can be explained as an effect of CO2 modified
atmosphere, as it allows to diminish oxygen presence thus reducing the oxidative action
inside the drying chamber during heat treatment. There is as well a correlation between the
augmentation of drying temperature and lower levels of damage to nutriments in dried
products which is presumably due to the fact that drying temperature elevation means shorter
drying duration which reduce polyphenols and Vitamin C temperature and oxygen exposure
thus preserving them better.
In conclusion, one can recommend to maintain the quality of dried vegetable products,
it is recommended to apply the drying method in a CO2 modified environment, with the speed
of the drying agent of 1.5 ± 0.13 m/s; temperature of the thermal agent of 70°C; concentration
of carbon dioxide in the working chamber of 80%.
Acknowledgments. This work was funded by the Moldova State Project no.
20.80009.5107.09, “Improvement of food quality and safety by biotechnology and food
engineering”, running at the Technical University of Moldova.
Conflicts of Interest: The author declares no conflict of interest.
References
1. Guiné, R.P.F.; Barroca, M.J.; Gonçalves, F.J.; Alves, M.; Oliveira, S.; Correia, P.M.R. Effect of drying on total
phenolic compounds, antioxidant activity, and kinetics decay in pears. International Journal of Fruit Science
2015, 15, pp. 173-186. https://www.tandfonline.com/doi/full/10.1080/15538362.2015.1017073.
2. Al Juhaimi, F.; Uslu, N.; Özcan M.M.; EL Babiker, El F.; Ghafoor, K. Effect of drying on antioxidant activity, total
phenol and mineral contents of pear fruits. Journal of Food Safety and Food Quality 2016, 67, pp. 113-148.
3. Jukanti, A. Polyphenol Oxidases (PPOs) in Plants. Singapore: Springer 2017, 137 p. ISBN 978-981-10-5746-5
4. Hawlader, M.N.A.; Perera, C.O.; Tian, M. Comparison of the Retention of 6-Gingerol in Drying of Ginger Under
Modified Atmosphere Heat Pump Drying and other Drying Methods. Drying Technology 2006, 24, pp. 51-56.
https://doi.org/10.1080/07373930500538675
5. Cam, I. B.; Basunal Gulmez, H.; Eroglu, E.; Topuz, A. Strawberry drying: Development of a closed-cycle
modified atmosphere drying system for food products and the performance evaluation of a case study. Drying
Technology 2018, 36, pp. 1460-1473. https://www.tandfonline.-
com/doi/abs/10.1080/07373937.2017.1409233
6. Liu, Y.; Wu, J.; Miao, S.; Chong, C.; Sun, Y. Effect of a Modified Atmosphere on Drying and Quality
Characteristics of Carrots. Food Bioprocess Technol 2014, 7, pp. 2549-2559. https://agris.fao.org/agris-
search/search.do?recordID=US201400125568
7. Jangam, S.V.; Law, C.L.; Mujumdar, A. S. Drying of Foods, Vegetables and Fruits. Singapore, 2010, 1, 282 p. ISBN:
978-981-08-6759-1. https://arunmujumdar.com/wp-content/uploads/2020/03/Drying-of-Foods-
Vegetables-and-Fruits-Volume-1.pdf
8. Hui, Y.H. Food Biochemistry and Food Processing. Blackwell Publishing, USA, Ames, Iowa, 2006, 760 p. doi:
10.1002/9780470277577
9. Osuna-Garcia, J.A.; Wall, M.M. Prestorage moisture content affects color loss of ground paprika (Capsicum
annuum L.) under storage, Journal of Food Quality 1998, 21, pp. 251-259. https://doi.org/10.1111/j.1745-
4557.1998.tb00520.x.
10. Government Decision no. 929, regarding the approval of the Quality and marketing requirements for fresh
fruits and vegetables. Published: 19-01-2010, Monitorul Oficial 5-7 art. 26, 2009.
https://www.legis.md/cautare/getResults?doc_id=110404&lang=ro# 1 [In Romanian]
11. Kupina, S.; Fields, Ch.; Roman, M.C.; Brunelle, Sh.L. Determination of total phenolic content using the Folin-
C assay: Single-laboratory validation, First action 2017.13. Journal of AOAC International 2018, 101, pp. 1466-
1472. https://doi.org/10.5740/jaoacint.18-0031
12. Tarrago-Trani, M.T.; Phillips, K.M.; Cotty, M. Matrix-specific method validation for quantitative analysis of
vitamin C in diverse foods. Journal of Food Composition and Analysis 2012, 26, pp 12-25
https://doi.org/10.1016/j.jfca.2012.03.004
164 M. Melenciuc
Journal of Engineering Science March, 2023, Vol. XXX (1)
13. Țislinscaia, N.; Lupașco, A.; Bernic, M. Mathematical modeling of transfer phenomena in drying processes. ITA,
Chisinau, 2008, 108 p. http://repository.utm.md/bitstream/handle/5014/14943/Monografie-ModelMatemat
FenomenTransferProceseUscare.pdf?sequence=1 [In Romanian].
14. Kalinin, A.G. Data processing by methods of mathematical statistics. Transbaikal Institute of Entrepreneurship,
Siberian University of Consumer Cooperatives, Chita, 2015, 107 p. ISBN 978-5-89807-182-0.
http://zip.sibupk.su/upload/medialibrary/monografii/2014/% [in Russian].
15. Djendoubi Mrad, N.; Boudhrioua, N.; Kechaou, N.; Courtois, F.; Bonazzi, C. Influence of air drying temperature
on kinetics, physicochemical properties, total phenolic content and ascorbic acid of pears. Food and
Bioproducts Processing 2012, 90, pp. 433-441. https://doi.org/10.1016/j.fbp.2011.11.009
16. Guiné, R.P.F.; Ferreira, D.M.S.; Barroca, M.J.; Goncalves, F.M. Study of the drying kinetics of solar-dried pears.
Biosystems Engineering 2007, 98, pp. 422-429. https://doi.org/10.1016/j.biosystemseng.2007.09.010
17. Guiné, R.P.F.; Almiro, J.; Castro, A.M. Analysis of Moisture Content and Density of Pears During Drying. Drying
technology 2003, 21, pp. 581-591. http://dx.doi.org/10.1081/DRT-120018464
18. Marzec, A.; Kowalska, H.; Kowalska, J.; Domian, E.; Lenart, A. Influence of pear variety and drying methods on
the quality of dried fruit, Molecules 2020, 25, 17 p. https://doi.org/10.3390/molecules25215146
19. Garau, M.C.; Simal, S.; Rosselló, C.; Femenia, A. Effect of air-drying temperature on physico-chemical
properties of dietary fibre and antioxidant capacity of orange (Citrus aurantium v. Canoneta) by-products,
Food Chemistry 2007, 104, pp. 1014-1024. https://doi.org/10.1016/j.foodchem.2007.01.009
20. Bernic, M. Contributions to the study of the hot pepper drying process kinetics. UTM., Chisinau, 2005, 160 p.
ISBN 9975-9853-1-9 [In Romanian].
21. Malejik, I.F.; Tarlev, V.P.; Lupashko A.S. Convective high frequency drying of stone fruits. UTM, Chisinau 2005,
460 p. ISBN 9975-9888-8-1
22. Devic, E.; Guyot, S.; Daudin, J.-D.; Bonazzi, C. Kinetics of polyphenol losses during soaking and drying of cider
apples, Food and Bioprocess Technology 2010, 3, pp 867-877. https://doi.org/10.1007/s11947-010-0361-1.
23. Mc Laughlin, C.P.; Magee, T. R.A. The determination of sorption isotherm and the isosteric heats of sorption
for potatoes, Journal of Food Engineering 1998, 35, pp. 267-280. https://doi.org/10.1016/S0260-
8774(98)00025-9.
Citation: Melenciuc, M. Drying of pears in CO2 modified atmosphere. Journal of Engineering Science 2023, 30 (1),
pp. 154-164. https://doi.org/10.52326/jes.utm.2023.30(1).13.
Publisher’s Note: JES stays neutral with regard to jurisdictional claims in published maps and
institutional affiliations.
Copyright:© 2023 by the authors. Submitted for possible open access publication under the terms
and conditions of the Creative Commons Attribution (CC BY) license
(https://creativecommons.org/licenses/by/4.0/).
Submission of manuscripts: jes@meridian.utm.md
