American Journal of Applied Science and Technology
41
https://theusajournals.com/index.php/ajast
VOLUME
Vol.05 Issue 04 2025
PAGE NO.
41-43
10.37547/ajast/Volume05Issue04-10
Analysis of Raspberry Freeze-Drying Processes
S.N. Obloberdiyev
Assistant Teacher, Yangiyer Branch of the Tashkent Chemical-Technological Institute, Yangiyer, Uzbekistan
O.I. Boboyeva
Student, Yangiyer Branch of the Tashkent Chemical-Technological Institute, Yangiyer, Uzbekistan
G.N. Po
ʻ
latova
Student, Yangiyer Branch of the Tashkent Chemical-Technological Institute, Yangiyer, Uzbekistan
H.B. Nazarova
Student, Yangiyer Branch of the Tashkent Chemical-Technological Institute, Yangiyer, Uzbekistan
S.A. Xalikova
Student, Yangiyer Branch of the Tashkent Chemical-Technological Institute, Yangiyer, Uzbekistan
Received:
25 February 2025;
Accepted:
21 March 2025;
Published:
24 April 2025
Abstract:
The objective of this study was to comprehensively investigate the technological and physicochemical
aspects of freeze-drying (lyophilization) as applied to raspberries. Due to the delicate cellular structure and high
moisture content of raspberries, they are particularly sensitive to conventional drying methods, which often result
in significant degradation of organoleptic and nutritional qualities. Freeze-drying, by contrast, offers a promising
solution by preserving the original morphology, flavor, and bioactive compounds through sublimation of ice under
low-pressure conditions. This work aimed to optimize the key parameters of the freeze-drying process
—
specifically
the duration of the sublimation phase and the final drying temperature
—
to achieve maximal retention of quality
indicators while minimizing processing time. The findings can contribute to improving the industrial-scale
production of high-value, shelf-stable berry products for functional food applications.
Keywords:
Raspberry, freeze-drying, sublimation, low temperature dehydration, organoleptic quality.
Introduction:
Fruits and berries represent a rich and diverse source
of essential micronutrients, including vitamins,
minerals, antioxidants, and phytochemicals, which play
a crucial role in maintaining human health and
preventing various chronic diseases [1]. Their regular
consumption becomes particularly vital under adverse
environmental conditions and in populations affected
by micronutrient deficiencies. However, the inherent
seasonality, high perishability, and moisture content of
such products pose significant challenges for year-
round availability and long-term storage.
To address these limitations, various preservation
techniques have been developed, among which drying
is one of the most widely used. Dehydration effectively
reduces water activity, thereby inhibiting the growth of
spoilage and pathogenic microorganisms, enzymatic
activity, and oxidative processes, ultimately extending
the shelf life of the product without the use of chemical
preservatives.
Among all known drying technologies, freeze-drying
—
or lyophilization
—
emerges as one of the most
advanced and promising methods, especially for heat-
sensitive and structurally delicate products such as
raspberries. The core principle of freeze-drying is based
American Journal of Applied Science and Technology
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American Journal of Applied Science and Technology (ISSN: 2771-2745)
on the removal of frozen water from the product
through sublimation, which occurs under pressures
below the triple point of water (611 Pa). In this process,
water transitions directly from the solid (ice) phase to
the vapor phase, bypassing the liquid state entirely.
This mechanism enables the preservation of the
product’s structural integrity, nutritional profile, and
organoleptic qualities, including color, aroma, taste,
and texture [2].
Importantly, after the primary sublimation phase, a
secondary drying phase at mild temperatures
—
typically below +40°C
—
is applied to remove residual
moisture. This two-step process allows for minimal
thermal degradation and a high degree of retention of
the original (native) characteristics of the product,
which is particularly advantageous when processing
soft-textured fruits like raspberries. As a result, freeze-
drying has garnered increasing attention in the food
and nutraceutical industries for producing high-quality,
shelf-stable fruit ingredients suitable for functional
foods and specialized diets.
MЕTHОDS
Fresh raspberries of uniform size, color, and ripeness
were selected for the experiment. Prior to freeze-
drying, the fruits were carefully inspected to remove
any damaged or overripe specimens to ensure
consistency in the drying process and quality
assessment.
The selected raspberries were evenly distributed on
stainless steel trays and placed into the freeze-drying
chambers. Each chamber was hermetically sealed with
an airtight lid to maintain controlled pressure and
temperature conditions throughout the process. Once
sealed, vacuum pumps were activated to reduce the
internal pressure of the chambers to below the triple
point of water (611 Pa), thereby initiating the
sublimation phase of the drying process.
During this phase, the moisture within the product,
having been frozen beforehand, sublimated directly
from solid ice to vapor without transitioning through
the liquid phase. The vaporized moisture was
subsequently desublimated
—
converted back into solid
form
—
on the cold surfaces of the refrigeration
system's evaporator coils. This step prevented re-
condensation within the chamber and facilitated the
continuous removal of moisture from the system.
Following the primary drying phase (sublimation), the
product underwent a secondary drying stage to
eliminate residual bound moisture. This was achieved
using infrared (IR) heating lamps, with four lamps
installed in each chamber to provide uniform low-
intensity heat. The temperature during this stage did
not exceed +40°C, preserving the thermolabile
components of the raspberries while ensuring
complete dehydration and product stability.
Fresh raspberries of uniform size, color, and ripeness
were selected for the experiment. Prior to freeze-
drying, the fruits were carefully inspected to remove
any damaged or overripe specimens to ensure
consistency in the drying process and quality
assessment.
The selected raspberries were evenly distributed on
stainless steel trays and placed into the freeze-drying
chambers. Each chamber was hermetically sealed with
an airtight lid to maintain controlled pressure and
temperature conditions throughout the process. Once
sealed, vacuum pumps were activated to reduce the
internal pressure of the chambers to below the triple
point of water (611 Pa), thereby initiating the
sublimation phase of the drying process.
During this phase, the moisture within the product,
having been frozen beforehand, sublimated directly
from solid ice to vapor without transitioning through
the liquid phase. The vaporized moisture was
subsequently desublimated
—
converted back into solid
form
—
on the cold surfaces of the refrigeration
system's evaporator coils. This step prevented re-
condensation within the chamber and facilitated the
continuous removal of moisture from the system.
Following the primary drying phase (sublimation), the
product underwent a secondary drying stage to
eliminate residual bound moisture. This was achieved
using infrared (IR) heating lamps, with four lamps
installed in each chamber to provide uniform low-
intensity heat. The temperature during this stage did
not exceed +40°C, preserving the thermolabile
components of the raspberries while ensuring
complete dehydration and product stability.
RЕSULTS АND DISСUSSIОN
At first, the drying process was investigated by
selecting the duration of the sublimation and final
drying stages. The residual pressure was 400 Pa, the
temperature at the final drying stage was +40°C. The
duration of the first stage (sublimation stage) in
different experiments was 5, 6, 7 and 8 hours, after
which the infrared heating lamps were switched on and
the residual moisture in the product was removed.
It was found that the time by which the total duration
of lyophilization increases almost corresponds to the
time of increase in the sublimation stage. To assess the
quality characteristics of the obtained product, an
organoleptic assessment of dried raspberries was
carried out according to the following indicators: taste,
color, smell and consistency, each of which was
assessed on a 5-point scale. The results are summarized
in Table 1. According to the results of the organoleptic
assessment, the highest score was obtained with a
sublimation stage duration of 7-8 hours and,
accordingly, the least effect of temperature at the final
drying stage. Based on the data obtained, the optimal
American Journal of Applied Science and Technology
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American Journal of Applied Science and Technology (ISSN: 2771-2745)
duration of the sublimation stage is 7 hours.
Table 1
Results of organoleptic evaluation of dried raspberries
Indicator
Duration of the sublimation stage, h
5
6
7
8
Taste
4
5
5
5
Color
4
4
4
4
Smell
4
5
5
5
Consistency
4
4
5
5
Score
16
18
19
19
Further experiments were conducted to select the final
drying temperature. The values of this parameter
varied within the range from +30 to +60°C. The
duration of sublimation was 7 hours. Table 2 shows the
indicators of sublimation drying of raspberries at
different final drying temperatures.
Table 2
Indicators of sublimation drying of raspberries
Indicator
Final drying temperature, °С
30
40
50
60
Drying time, h
10,5
9
8
7,5
Organoleptic assessment, points
20
19
17
15
As expected, with an increase in the final drying
temperature, the duration of the drying process is
reduced, but at the same time, the quality
characteristics of the product also decrease, which is
confirmed by the results of the organoleptic
assessment, which is due to the more intense
temperature effect of the infrared heating lamps.
СОNСLUSIОN
Thus, as a result of the work carried out, the most
favorable modes of sublimation drying of raspberries
were established: the duration of the sublimation stage
is 7 hours, the final drying temperature is +40°C. With
the specified modes, the total dehydration time is 9
hours, and the organoleptic assessment is 19 points out
of 20. The above data can be useful for engineers-
technologists, food industry workers and researchers
engaged in research in this area. Lyophilized berries can
be used in the production of functional drinks, bakery
products [3, 4, 5].
RЕFЕRЕNСЕS
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vitamin C in fresh fruits, berries and in their processed
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freeze-drying) [Text] / A.G. Myakinkov // Food and
processing industry. Abstract journal. - 2003. - No. 3. -
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