Innovative Freeze-Dried Snacks with Sodium Alginate and Fruit Pomace (Only Apple or Only Chokeberry) Obtained within the Framework of Sustainable Production

Abstract

The aim of the work has been to develop freeze-dried fruit snacks in the form of bars with the use of by-products derived from fruit processing. In effect 14 product designs of fruit gels based on: apple pulp, apple juice, water, sodium alginate and only apple or only chokeberry pomace were prepared. The snacks were freeze-dried. The dry matter content, water activity, structure, colour, mechanical properties, as well as organoleptic evaluation were determined. Freeze-dried bares were obtained according to sustainability production which in this case was relied on application of fruit pomace. The freeze-drying process ensures the microbiological safety of the product without the need to use chemical preservatives. Freeze-dried samples obtained low water activity in the range of 0.099–0.159. The increase in pomace concentration (3–9%) boosted the dry matter content to above 98%, and decreased the brightness of the freeze-dried bars about 6 to 10 units. Mechanical properties varied depending on the product design. With the increase in the amount of pomace, the shear force increased at 23% to 41%. Based on the results, the best variant, that has the most delicate structure and the best organoleptic properties, has proven to contain 1% sodium alginate and 2% pomace.

Full text

Citation: Ciurzy´nska, A.; Popkowicz,
P.; Galus, S.; Janowicz, M. Innovative
Freeze-Dried Snacks with Sodium
Alginate and Fruit Pomace (Only
Apple or Only Chokeberry) Obtained
within the Framework of Sustainable
Production. Molecules 2022,27, 3095.
https://doi.org/10.3390/
molecules27103095
Academic Editor: Adele Papetti
Received: 14 March 2022
Accepted: 6 May 2022
Published: 11 May 2022
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molecules
Article
Innovative Freeze-Dried Snacks with Sodium Alginate and
Fruit Pomace (Only Apple or Only Chokeberry) Obtained
within the Framework of Sustainable Production
Agnieszka Ciurzy ´nska, Paulina Popkowicz, Sabina Galus and Monika Janowicz *
Department of Food Engineering and Process Management, Warsaw University of Life Sciences (WULS-SGGW),
159c Nowoursynowska St., 02-776 Warsaw, Poland; agnieszka_ciurzynska@sggw.edu.pl (A.C.);
s186435@sggw.edu.pl (P.P.); sabina_galus@sggw.edu.pl (S.G.)
*Correspondence: monika_janowicz@sggw.edu.pl; Tel.: +48-2259-37566
Abstract:
The aim of the work has been to develop freeze-dried fruit snacks in the form of bars with
the use of by-products derived from fruit processing. In effect 14 product designs of fruit gels based
on: apple pulp, apple juice, water, sodium alginate and only apple or only chokeberry pomace were
prepared. The snacks were freeze-dried. The dry matter content, water activity, structure, colour,
mechanical properties, as well as organoleptic evaluation were determined. Freeze-dried bares were
obtained according to sustainability production which in this case was relied on application of fruit
pomace. The freeze-drying process ensures the microbiological safety of the product without the
need to use chemical preservatives. Freeze-dried samples obtained low water activity in the range of
0.099–0.159. The increase in pomace concentration (3–9%) boosted the dry matter content to above
98%, and decreased the brightness of the freeze-dried bars about 6 to 10 units. Mechanical properties
varied depending on the product design. With the increase in the amount of pomace, the shear force
increased at 23% to 41%. Based on the results, the best variant, that has the most delicate structure
and the best organoleptic properties, has proven to contain 1% sodium alginate and 2% pomace.
Keywords: freeze-drying; snack; fruit pomace; hydrocolloids; structure
1. Introduction
The sustainable development is a conceptual framework that provides for the quality
of life at the level of the current civilisational development. The idea of the sustainable
development was created as part of the activities of the United Nations World Commission
for Environment and Development, the so-called Brundtland Commission established
in 1983. Since then, it has addressed the problems of the contemporary world [
1
]. The
production of food in a traditional way may be inefficient, therefore it is important to use
raw materials, means of production that do not have such an adverse impact on the natural
environment, society and the national economy. In addition, the sustainable development
refers to the lack of dependence on energy sources that may run out over time, and the
marketing of products that have a positive impact on human health [2].
The fruit and vegetable industry in Poland in 2018/2019 processed approx. 1.3 million
tons of vegetables and 0.97 million tons of fruit [
3
]. As a result of processing fruit into juice,
drink, cider or wine, by-products are obtained to be the so-called pomace that consists of
seeds, remains of pulp and skins [
4
]. Their composition depends mainly on the processing
conditions and the fruit variety. After the production process, about 20% of residual waste
remains from the raw material. Since the pomace contains a lot of water (often over 80%),
it is easily microbiologically contaminated. This makes the pomace a perishable product
and entails various storage difficulties, mainly due to limited storage space in processing
plants and inadequate preservation of the pomace, which may have a negative impact on
the natural environment. The storage problems are even greater due to the structural and
Molecules 2022,27, 3095. https://doi.org/10.3390/molecules27103095 https://www.mdpi.com/journal/molecules

Molecules 2022,27, 3095 2 of 17
chemical diversity and the differences in the intended use of the pomace. Preserved (by
drying or ensiling) or pre-treated waste would be suitable for further use [5].
Pomace, especially apple pomace, accounts for the largest percentage share in the
fruit and vegetable industry (over 90%) [
6
,
7
]. Apple pomace is a by-product of the fruit
processing [
8
]. One of the ways to manage apple pomace is to add dried pomace to dietary
food [
8
–
10
]. In the course of chokeberry fruits pressing most of the colour compounds
remain in the pomace, which is why they constitute a valuable secondary raw material and
are used, among others, for producing dark anthocyanin dyes [11,12].
With the development of a healthy and balanced diet as well as consumers’ better
understanding of the relationship between diet, health and the environment, innovative,
healthy and environmentally friendly food products are being developed more and more,
which perfectly fits into the sustainable development policy. New sources of dietary fibre,
such as fruit and vegetable by-products, may be added to food products as cheap and low-
calorie substances to partially replace flour, fat or sugar [
13
]. Most fruit and vegetable by-
products account for high nutritional value, which is useful when designing new products.
One option is to dry them and eat as snacks. On the other hand, a more unconventional
solution is to obtain dried gels or foams which, after freeze-drying, may become one of the
meals or supplement a meal by taking the form of a snack [
14
]. The addition of pomace also
enhances the colour of food products, making them look more attractive and tastier, e.g.,
juice or wine is less tart or has a deeper and more distinct flavour than the counterparts
without pomace. The pomace also improves the rheological properties (for example it
is the case with bakery products or snacks) and may also replace ingredients harmful to
people with celiac disease or gluten intolerance. Supplementing food products available in
the market with natural sources of nutrients is a way to minimise the content of artificial
ingredients and improve the health-promoting properties of those products. The pomace is
also used in medicine, in cancer therapy or in the production of antidiabetic drugs [
15
,
16
].
The growing demand for healthy snacks combined with product innovation is a major
driver to increase consumer interest in dried fruit. Sustainable and ethical production is
also becoming an important aspect for European traders and consumers. Freeze-dried
food, that is characterised by high quality, easy storage, universal application and a long
shelf life, is an example of innovative food. The dry product is usually very porous, brittle,
hygroscopic, and has excellent rehydration capacity. Freeze-dried food products may be
produced by means of freeze-drying gels consisting of fruit concentrate or puree. Those
products are dry and crunchy, with a high content of nutrients [17].
The aim of the work has been to develop a product design and technology for the
production of food products in the form of bars, with the use of by-products derived
from fruit processing. The bars were preserved in the freeze-drying process and tested for
selected physical and organoleptic properties.
2. Results and Discussion
2.1. The Dry Matter Content and Water Activity of Freeze-Dried Bars with Fruit Pomace
In Table 1samples symbol and formulations were presented.
The water content in food products is one of the main criteria determining their
nutritional value, quality and storage stability. Gronowska-Senger et al. [
18
] explain that
the higher the percentage of water in a product, the greater the risk of microbial growth. It
has been shown that sodium alginate increase has no effect on water content of samples
before freeze-drying whereas apple or chokeberry pomace addition increase in most cases
cause significant decrease in water content (Table 2). For freeze-dried fruit snacks with
apple or chokeberry pomace the dry matter content is high. Given the samples with the
same apple pomace content, the increase in sodium alginate addition from 1.5 to 2% in most
cases causes the dry matter content to reduce statistically significantly. Taking into account
the effect of the amount of added apple pomace on the dry matter content of bars with the
same sodium alginate content, in most cases differences are statistically insignificant. In the
case of bars with the addition of chokeberry pomace it has been shown that the increase in

Molecules 2022,27, 3095 3 of 17
the amount of added hydrocolloid and pomace causes the statistically significant increase
in the dry matter content in the case freeze-dried products.
Table 1.
Formulation of individual bar variants. Index (A) next to the sample symbol—bars with the
apple pomace, Index (C) next to the sample symbol—bars with the chokeberry pomace.
Sample
Symbol
Apple
Pomace
Chokeberry
Pomace Apple Pulp Apple
Juice Water Calcium
Lactate
Sodium
Alginate
2_3A 3% - 50% 22.5% 22.4% 0.1% 2%
2_3C - 3%
2_6A 6% - 50% 21% 20.9% 0.1% 2%
2_6C - 6%
2_9A 9% - 50% 19.5% 19.4% 0.1% 2%
2_9C - 9%
1.5_3A 3% - 50% 22.7% 22.7% 0.1% 2%
1.5_3C - 3%
1.5_6A 6% - 50% 1.2% 21.2% 0.1% 2%
1.5_6C - 6%
1.5_9A 9% - 50% 19.7% 19.7% 0.1% 2%
1.5_9C - 9%
1_2A 2% - 50% 23.6% 23.4% 0.1% 2%
1_2C - 2%
Table 2.
The effect of hydrocolloid and pomace addition amount on the dry matter content and water
activity of freeze-dried fruit bars with apple or chokeberry pomace and water content of samples
before freeze-drying. Denotations in Table 1include. Index (A) next to the sample symbol—bars with
the apple pomace, Index (C) next to the sample symbol—bars with the chokeberry pomace. Mean
values marked with the same index letter (a–e, A–F) do not differ statistically significantly at the level
of p= 0.05. The small index letter (a–e) indicates the statistical analysis results for samples with apple
pomace whereas the big index letter (A–F) indicates the statistical analysis results for samples with
chokeberry pomace.
Freeze-Dried Samples Samples before
Freeze-Drying
Sample Average Dry Matter
Content
Average Water
Activity Average Water Content
1.5_3A 98.23% ±0.013 a,b 0.14 ±0.002 d77.12% ±0.086 c,d
1.5_6A 98.40% ±0.055 b,c 0.12 ±0.001 b74.74% ±0.036 b,c
1.5_9A 98.56% ±0.013 c0.099 ±0.001 a71.92% ±0.006 a
2_3A 97.99% ±0.009 a0.148 ±0.003 e77.26% ±0.057 c,d
2_6A 98.07% ±0.01 a0.126 ±0.002 b75.00% ±0.03 a,b
2_9A 98.17% ±0.087 a,b 0.102 ±0.003 a71.31% ±0.314 a
1_2A 99.46% ±0.28 d0.132 ±0.001 c81.07% ±1.078 d
1.5_3C 97.11% ±0.00 A0.15 ±0.001 E79.572% ±0.411 C
1.5_6C 97.90% ±0.014 C0.116 ±0.002 C73.178% ±0.317 B
1.5_9C 98.04% ±0.034 D0.106 ±0.001 A70.98% ±0.192 A
2_3C 97.28% ±0.038 B0.159 ±0.001 F76.90% ±0.063 C
2_6C 98.00% ±0.022 D0.126 ±0.000 D71.65% ±0.526 B
2_9C 98.11% ±0.046 E0.112 ±0.001 B70.32% ±1.298 A
1_2C 98.29% ±0.000 F0.116 ±0.001 B,C 78.087% ±0.376 C
The sample with the addition of 1% sodium alginate and 2% pomace (apple or choke-
berry) (1_2) proves high water content before freeze-drying but the highest dry matter
content after freeze-drying may be connected with the structure of the samples that are
characterised by high porosity and fragile walls separating empty spaces (Figure 1). Cell
walls are much thinner; thus, water is removed easily. Marciniak-Łukasiak [
19
] investigated
the water content in cereal bars with the constant concentration of apple and chokeberry

Molecules 2022,27, 3095 4 of 17
pomace, while the proportions of instant flakes to expanded seeds were changed. With
the increase in the percentage share of processed seeds, the dry matter content increased,
ranging from 94% to 96%, which is consistent with the results for the freeze-dried bars un-
der consideration, where the dry matter content increases with the increase in the pomace
addition. Karwacka et al. [
20
] obtained similar dry matter content values for freeze-dried
vegetable bars with 2% apple pomace. Ciurzy ´nska et al. [
21
] obtained similar dry matter
content for freeze-dried vegetable snacks with 1.5% sodium alginate (96.72–97.67%). In
dried products, and particularly in freeze-dried ones, the dry matter content is at the level
of 95–99.5% [
22
]. Therefore, it is plausible to confirm that the freeze-drying is effective in
the area of water removal from the product and ensures long-term shelf life.
Figure 1.
The effect of the amount of hydrocolloid and pomace addition on the structure of freeze-
dried fruit bars with apple and chokeberry pomace at 100
×
Magnification. Denotations in Table 1
include Index (A) next to the sample symbol—bars with the apple pomace, Index (C) next to the
sample symbol—bars with the chokeberry pomace.

Molecules 2022,27, 3095 5 of 17
The state of water in food changes continuously from the most orderly, with low water
content, to that of pure water. The description of this state is expressed in terms of water
activity [
23
], which is an important parameter for the stability of properly prepared dried
fruit. Its low value guarantees the inhibition of the course of chemical and enzymatic
reactions. Microbiological safety is considered to be achieved when the water activity
is below 0.6. Under such conditions, microbes cannot grow. This parameter also has a
significant impact on the sensory evaluation, and in particular largely contributes to shaping
the sensory perception of some texture features [
24
–
26
]. Water activity of freeze-dried fruit
snacks ranges between 0.099–0.148 for samples with the addition of apple pomace and
0.106–0.159 for samples with the addition of chokeberry pomace (Table 2). For snacks
with apple pomace it has been shown that the increase in pomace addition significantly
causes the freeze-dried bars water activity to decrease, while the increase in hydrocolloid
centration in most cases has not caused any significant changes in the tested parameter.
In the case of bars obtained with the addition of chokeberry pomace, it has been shown
that increasing the addition of pomace by 3–9% and sodium alginate from 1.5% to 2%
statistically significantly reduces the water activity. Marciniak-Łukasiak et al. [
19
] studied
cereal bars with the addition of apple and chokeberry pomace. For all cereal bars, the water
activity value decreased with the increase in the percentage share of expanded seeds. The
water activity in which most microbes were able to grow ranged from 0.990 to 0.995. All the
tested samples had the water activity below 0.6, which ensured their microbio-logical safety
and may have indicated their stability during storage, provided that a sealed package was
used, protecting against air penetration. Similar conclusions were also drawn by Karwacka
et al. [
27
] for freeze-dried vegetable bars with apple pomace. On the basis of the obtained
results of water activity, it is plausible to state that the tested freeze-dried bars are not
susceptible to any colour change because the water activity at the value below 0.2 does not
cause any non-enzymatic browning reactions to occur.
2.2. The Structure of Freeze-Dried Bars with Fruit Pomace
Karwacka et al. [
27
] indicate that the texture of food is an important factor influencing
its attractiveness to consumers. It has been shown that the structure of freeze-dried fruit
bars is porous (Figure 1). With the increase in pomace concentration the structure is more
irregular and compact. In the case of samples with chokeberry pomace, the structure
is more closed than the samples with apple pomace. The structure of samples with the
lowest value of sodium alginate and pomace 1_2 is the most delicate. As far as freeze-dried
vegetable bars with apple pomace are concerned, Karwacka et al. [
27
], also observed the
heterogeneous structure of the samples and indicated that the method of their preparation
(mixing or grinding) resulted in the fact that the pores were disordered and irregular.
They found that the internal structure of the obtained freeze-dried bars differed from the
microstructure of freeze-dried plant tissue, where, after sublimation of water, cell walls
built a porous skeleton of dried products. Comparing the internal structure of vegetable
bars with pomace without the of hydrocolloids [
27
] and fruit bars with apple or chokeberry
pomace with the addition of sodium alginate as a skeleton-forming component, it was found
that the addition of sodium alginate allowed to obtain blended products characterised
by a porous structure similar to the structure of plant tissue, which was observed in the
previous studies conducted by Ciurzy´nska et al. [
21
,
28
]. The presence of the hydrocolloid
also protects the product structure against breakdown during freeze-drying process by
increasing the phase transition temperature [27,29].
2.3. The Colour of Freeze-Dried Bars with Fruit Pomace
In the case of fruit bars with the addition of apple pomace, the lightness coefficient
[L*] ranges from 70.4–61.3 units, the percentage share of red colour coefficient [a*] 7.8–3.8
units, and the yellow colour coefficient [b*] 28.8–26.2 units (Figure 2). The highest value
of the parameter [L*], that is responsible for the brightness, is ensured by samples 2_3A,
and 1_2A, while the lowest by sample 1.5_9A. Increasing the addition of apple pomace

Molecules 2022,27, 3095 6 of 17
significantly decreases the value of the [L*] parameter, thus the samples are darker. In the
case of varied addition of hydrocolloid, the samples with its 2% addition are brighter than
those with 1.5% addition. The highest value of the red colour coefficient [a*] is proven by
sample 1.5_9A, while the lowest by sample 2_3A. Increasing the addition of pomace and
hydrocolloid in most cases results in the increase in the colour index [a*] and no significant
changes in the colour parameter [b*].
Figure 2.
The effect of the amount of hydrocolloid and pomace addition on the colour in freeze-dried
fruit bars with apple pomace. Mean values marked with the same index letter (a–e) do not differ
statistically significantly at the level of p= 0.05. Denotations in Table 1include Index (A) next to the
sample symbol—bars with the apple pomace.
In the case of fruit bars with the addition of chokeberry pomace, the lightness coef-
ficient [L*] ranges from 43.7–28.9 units, the percentage share of the red colour [a*] 20.6–
14.4 units, and the yellow colour coefficient [b*] 8.6–5.3 units (Figure 3). The highest value
of the parameter [L*] is characteristic for sample 1_2C, while the lowest for sample 1.5_9C.
Increasing the addition of chokeberry pomace significantly decreases the lightness fac-
tor [L*]. It has been found that the samples with 2% sodium alginate are brighter than
those with 1.5% additive. The highest value of the red [a*] and yellow [b*] colour index is
obtained for sample 1.5_3C and 1_2C. Increasing the addition of chokeberry pomace signif-
icantly decreases the value of [a*] and [b*] coefficient, while the increase in the addition
of hydrocolloid in most cases does not cause any significant changes in the index [a*] but
decreases [b*] coefficient. The lowest value of the colour parameter [a*] and [b*] is proven
by the samples with 9% addition of pomace.
Figure 3.
The effect of the amount of hydrocolloid and pomace addition on the colour in freeze-dried
fruit bars with the addition of chokeberry pomace. Mean values marked with the same index letter
(a–g) do not differ statistically significantly at the level of p= 0.05. Denotations in Table 1include
Index (C) next to the sample symbol—bars with the chokeberry pomace.

Molecules 2022,27, 3095 7 of 17
With the amount of water removed, some raw materials become lighter and others
darken depending on the form in which they are present. The decrease in the values of the
yellow colour coefficient [b*] and the red colour coefficient [a*] may indicate the degradation
of some naturally occurring dyes, while their increase indicates the occurrence of non-
enzymatic browning reactions [
30
]. Ciurzy´nska and Lenart [
31
] investigated the freeze-
dried strawberry gels, and showed that the aeration time and the type of hydrocolloid
significantly affected their brightness [L*], so the values of respective colour parameters
were influenced by the product design, sample form, the degree of aeration and the method
of drying. Ciurzy ´nska and Lenart [
32
], examining the colour of freeze-dried strawberry
jellies, found that the addition of chokeberry juice concentrate significantly decreased the
brightness factor of strawberry jelly by about 50 units. Increasing the percentage share
of chokeberry juice concentrate from 5% to 10% resulted in obtaining a brightness factor
lower by 2 units. The red colour index was 26 units, and the addition of chokeberry
juice concentrate also reduced the value of this index. It was similar in the case of freeze-
dried fruit bars with the addition of pomace, the brightness of which decreased with
the addition of pomace. The highest values of lightness coefficient for samples with the
lowest concentration of hydrocolloid and pomace (1_2) may have been connected with the
structure of those samples, that was more delicate and reflected light to a varied degree as
compared to the samples with higher concentration of solid ingredients.
To evaluate the effect of the addition of pomace and hydrocolloid on the colour change
of the surface of fruit bars, the colour saturation index has been calculated (Table 3). In
the case of the variants with the addition of apple pomace, the lowest saturation index (SI)
value is proven for sample 1_2A, which is statistically significantly different from the rest.
Increasing the addition of apple pomace and hydrocolloid in most cases does not cause
significant changes in the examined parameter. In the case of samples with the addition
of chokeberry pomace, the highest SI value is proven for variants 1.5_3C and 1_2C, while
the lowest for variants with 9% of pomace. Increase in the addition of chokeberry pomace
significantly decreases the colour saturation index, while the increase in the hydrocolloid
concentration in most cases does not cause significant changes in this parameter.
Table 3.
Colour saturation index [SI] of freeze-dried fruit bars. Mean values marked with the same
index letter (a–d) do not differ statistically significantly at the level of p= 0.05. Denotations in Table 1
include Index (A) next to the sample symbol—bars with the apple pomace, Index (C) next to the
sample symbol—bars with the chokeberry pomace.
Sample Symbol Samples with Chokeberry
Pomace [C]
Samples with Apple Pomace
[A]
1.5_3 21.9 ±0.33 d29.6 ±0.37 c
1.5_6 18.2 ±0.78 b,c 29.0 ±1.38 b,c
1.5_9 15.3 ±0.18 a29.5 ±0.77 c
2_3 18.8 ±0.35 c28.2 ±0.49 b
2_6 17.8 ±0.43 b28.9 ±0.26 b,c
2_9 15.6 ±0.63 a28.6 ±1.54 b,c
1_2 22.3 ±0.81 d26.6 ±0.24 a
2.4. The Mechanical Properties of Freeze-Dried Bars with Fruit Pomace
The mechanical properties of the fruit bars have been tested by means of a cutting
test. Based on the obtained data, the maximum cutting force has been determined. The test
means cutting the bar until it is cut to a depth of 10 mm, in 10 replications for each variant to
serve the purpose of drawing representative curves. During the drying process, water loss
and material shrinkage occur, which affects the mechanical properties and changes in tissue
hardness [
31
]. The course of the cutting curves is similar for freeze-dried fruit bars with
the addition of apple (Figure 4) and chokeberry pomace (Figure 5). With the increase in
pomace concentration, the hardness of samples increases, and the higher cutting force value
is necessary to destroy samples. It has been found that both the cutting curves of the bars

Molecules 2022,27, 3095 8 of 17
with the addition of apple pomace and the bars with the addition of chokeberry pomace
are characteristic of an irregular course. At the beginning of the process, the increase in
the cutting force is observed, which is related to overcoming the resistance of the surface
layers (Figures 4and 5). The applied blade destroys the cellular structures. The degree of
damage depends on the structure and strength of the tissue. For all variants, after reaching
the maximum force, a period of constant force is shown. This means that the structure is
more homogeneous under the surface layer. Differences in force values result from diverse
textures of individual variants. In the case of variants with the addition of apple pomace,
the curves are flat, while samples with the addition of chokeberry pomace are characterised
by a dynamic course of curves, which indicates a compact structure and higher hardness of
the samples (Figure 5). Variants 2_9A (Figure 4) and 2_9C (Figure 5) are characterised by
the highest hardness. Konrade et al. [
33
] also showed that the increase in apple pomace
flour from 5 to 15% addition of pomace in cereal crispbreads increased the hardness of
products. Only freeze-dried bars with the lowest concentration of hydrocolloid and pomace
(1_2A and 1_2C) were characterised by the most delicate structure and required the lowest
maximum cutting force, which indicated thinner walls separating the pores and easier
destruction of the structure under the influence of the applied force.
Figure 4.
The cutting curves of freeze-dried fruit bars with apple pomace. Denotations in Table 1
include Index (A) next to the sample symbol—bars with the apple pomace.
Figure 5.
The cutting curves of freeze-dried fruit bars with chokeberry pomace. Denotations in
Table 1include Index (C) next to the sample symbol—bars with the chokeberry pomace.

Molecules 2022,27, 3095 9 of 17
The maximum cutting force of freeze-dried fruit snacks is 30–82 N for bars with apple
pomace (Figure 6) and 23–68 N (Figure 7) for bars with chokeberry pomace. In both cases,
sample 1_2 proves the lowest shear force, while the sample with 9% pomace is characterised
by the highest cutting force. The amount of added hydrocolloid in most cases is statistically
insignificant, while the amount of pomace is significant, and the larger the amount of
pomace is, the stronger the cutting force is. Karwacka et al. [
20
] showed that freeze-dried
vegetable bars with apple pomace obtained lower hardness than samples without pomace.
Ciurzy´nska et al. [
21
], using a deformation test to investigate the mechanical properties
of vegetable snacks based on sodium alginate, obtained the maximum cutting force in the
range from 13.16 to 13.29 N, which accounted for lower results than those obtained for fruit
bars with the addition of fruit pomace. The differences in the results may be related to
structure. Pomace addition probably strengthened the structure that had more resistance
to cutting. Karwacka et al. [
20
] indicated that the addition of fruit pomace as a structure
and texture forming carrier agent in dairy, meat, bakery and pastry products raised much
interest among researchers whereas there was no research available on using pomace as a
carrier agent in freeze-dried products.
Figure 6.
The maximum cutting force [N] of freeze-dried fruit bars with apple pomace. Mean values
marked with the same index letter (a–e) do not differ statistically significantly at the level of p= 0.05.
Denotations in Table 1include Index (A) next to the sample symbol—bars with the apple pomace.
Figure 7.
The maximum cutting force [N] of freeze-dried fruit bars with chokeberry pomace. Mean
values marked with the same index letter (a–d) do not differ statistically significantly at the level
of
p= 0.05
. Denotations in Table 1include Index (C) next to the sample symbol—bars with the
chokeberry pomace.

Molecules 2022,27, 3095 10 of 17
2.5. The Organoleptic Evaluation of Freeze-Dried Bars with Fruit Pomace
The 6 variants of fruit snacks that have proven to be the best ones have been subjected
to organoleptic evaluation, namely 3 of them with the addition of apple pomace and the
other 3 with the addition of chokeberry pomace, the composition of which is presented
in Table 1. Such features as general impression, crispness, taste, aroma and colour have
been distinguished. A five-point rating scale has been applied, with 5 being the best
one and 1 representing the worst one [
34
]. The results of the organoleptic evaluation of
respective features of the snacks with the addition of apple and chokeberry pomace are
high (Figure 8). The colour of the snacks depends on the addition of pomace because the
samples containing 2% addition of pomace characterised by higher brightness (L*) have
ensured more effective evaluation. Due to the composition of the bars and the freeze-drying
process, their aroma is mild and may have become less perceptible, which may explain the
scores that do not exceed the value of 3 points. The taste is very highly rated, especially in
the case of the samples with 2% addition of pomace. The samples with the 3% of pomace
are more compact, less fragile and more durable in the cutting test than those with the 2%
additive, that have a softer structure, which contributes to better crispness scores. Taking
into account the general impression, the best rated variants are those with the addition of
2% pomace.
Figure 8.
The average results for the organoleptic discriminants of fruit snack. Denotations in Table 1
include Index (A) next to the sample symbol—bars with the apple pomace, Index (C) next to the
sample symbol—bars with the chokeberry pomace.
The statistical analysis shows no differences between the ratings of bars with 3%
addition of pomace. The variant with 2% addition of pomace, both in the case of bars with
apple or chokeberry pomace, differs statistically significant from the others and proves to
be the best one (Table 4).
Silva-Espinoza et al. [
35
] indicated that the attractiveness of dried snacks was con-
nected with their textural and sensory properties. Consumers are interested in products
that are the source of pleasure when being eaten, have rich flavour and aroma, crispness
whereas many of them are also interested in the nutritional values of food. Parra et al. [
36
]
showed that sugar snap cookies with apple pomace raised much interest among consumers,
which indicated that samples with apple pomace obtained higher sensory assessment than
the samples without it. In general, bars with fruit pomace are of interest to potential cus-
tomers. The obtained results of organoleptic evaluation were influenced by the addition of
pomace, external appearance, crispness, as well as individual preferences of the evaluators.
There was no correlation between gender and education and the way the samples were
assessed. The pomace concentration increases decreased crispness and general impression,
which was connected with harder structure of samples in comparison to bars with the
lowest hydrocolloid and pomace addition. Summarising the above results in terms of

Molecules 2022,27, 3095 11 of 17
physical and organoleptic properties, the best option was the one with the addition of 1%
sodium alginate and 2% pomace (1_2), both in the case of adding apple and chokeberry
pomace. It was characterised by the best product design that was the most optimal due to
the properties of the bar.
Table 4. The average results of organoleptic evaluation for freeze-dried bars. Denotations in Table 1
include Index (A) next to the sample symbol—bars with the apple pomace, Index (C) next to the
sample symbol—bars with the chokeberry pomace. Mean values marked with the same index letter
(a,b) do not differ statistically significantly at the level of p= 0.05. The small index letter (a,b) indicates
the statistical analysis results for samples with apple pomace whereas the big index letter (A,B)
indicates the statistical analysis results for samples with chokeberry pomace.
Sample Symbol
1_2A 1.5_3A 2_3A 1_2C 1.5_3C 2_3C
Color 4.5 ±0.5 a4.7 ±0.5 a4.8 ±0.4 a4.8 ±0.4 B4.1 ±0.3 A4±0.7 A
Aroma 2.8 ±0.4 a3±0.7 a2.9 ±0.7 a2.7 ±0.5 A3.1 ±0.7 A3±0.7 A
Taste 5±0.0 b4±0.5 a3.8 ±0.6 a4.9 ±0.3 B4.1 ±0.3 A3.9 ±0.7 A
Crisspness 4.9 ±0.3 b3.6 ±0.5 a3.5 ±0.5 a4.7 ±0.7 B3.7 ±0.5 A3.6 ±0.7 A
General
impression 4.8 ±0.4 b3.9 ±0.6 a3.6 ±0.7 a4.7 ±0.5 B4±0.5 A3.8 ±0.8 A
Average 4.4 3.84 3.72 4.36 3.8 3.66
3. Materials and Methods
3.1. Material
Characteristics of Ingredients
The raw material used for the research purposes included fruit bars obtained with the
use of the following ingredients:
•
Golden Delicious apples from one production batch purchased in November 2020
constituted the basic raw material for obtaining freeze-dried food products. The fruits
had been stored at the temperature of about 4
◦
C until the tests were carried out.
Apple pulp served as the basic ingredient of the bars. Some of the apples were used
for obtaining apple juice.
•
In order to enrich the taste of snacks and to use by-products from fruit and vegetable
processing, dried chokeberry or apple pomace were used after having been purchased
from Greenherb Company (Wysoka, Poland) in 2021.
•
Sodium alginate (Agnex, Białystok, Poland) and calcium lactate (Hortimex, Konin,
Poland) were used as binders to initiate gelation.
3.2. Methodology
3.2.1. Technological Methods
Preparation of Bars
The first step in the technological process of obtaining fruit snacks in the form of
bars was to peel the apples, remove the seed chamber and chop them. Next the apples
were ground into a smooth mass in a Thermomix TM31-1 made by Vorwek (Wuppertal,
Germany) at the temperature of 70
◦
C, at the average speed of the stirrer, for about 15 min.
In each of the variants, apple pulp constituted 50% of all ingredients. Some of the apples
had their cores removed and chopped, and then pressed in a GOTIEGSJ-620 Evergreen
(Gliwice, Poland) slow juicer to obtain juice. The rest of the ingredients included water,
hydrocolloid (sodium alginate), calcium lactate and pomace (apple or chokeberry) (Table 1).
The next step was to heat the apple pulp, juice and water up to the temperature of 70
◦
C.
After reaching the appropriate temperature, juice, water, pomace and sodium alginate were
successively added to the pulp. The level of the addition of the texturising substance was
determined experimentally. The goal was to obtain a compact gel that would retain its
shape once removed from the mould (Figure 9) [21].

Molecules 2022,27, 3095 12 of 17
Figure 9.
Photos of bars with apple pomace (A) and chokeberry pomace (C) after gelation and after
freeze-drying. Denotations in Table 1include Index (A) next to the sample symbol—bars with the
apple pomace, Index (C) next to the sample symbol—bars with the chokeberry pomace.
The percentage share of sodium alginate was 2%, 1.5% and 1%. The whole of it was
subsequently blended by means of a BOSH MaxoMixx 750 W blender for about 2 min. After
that, 0.1% addition of calcium lactate was applied after having been previously dissolved in
a small amount of water before being added to the other ingredients. It was then blended
for about 2 min.
Freeze-Drying
The obtained gels were poured into silicone moulds of 14
×
10
×
2.5 cm in dimensions,
manufactured by Tescoma (Poland). The semi-finished product was cooled down to reach
the ambient temperature, removed from the moulds to be subsequently frozen in an Irinox
freezer (Treviso, Italy) at −40 ◦C for 2 h.
After freezing, the fruit bars were placed on the shelves of a Christ ALPHA 1–4 freeze
dryer (Osterode am Harz, Germany). In the course of drying, the pressure in the freeze
dryer chamber was 63 Pa, and the temperature of the heating plates of the freeze dryer was
30
◦
C. The drying process lasted 48 h, while the pressure was 63 Pa. After freeze-drying,
the bars kept their shape of a rectangle showing the dimensions of 14
×
10
×
2.5 cm. The
photos of the bars are included in Table 1.

Molecules 2022,27, 3095 13 of 17
The technological scheme of obtaining freeze-dried food products is shown in
Figure 10
,
while the designs of respective snack variants are presented in Table 1.
Figure 10. Process diagram for obtaining freeze-dried food products.
3.2.2. Analytical Methods
Determination of Physical Properties of Obtained Snacks
Water activity was determined by means of a Rotronic HygroLab C1 apparatus
(Bassersdorf, Switzerland) in accordance with the manufacturer’s instructions. The snacks
were chopped and placed in a dish that was an integral part of the device. Samples of
approximately
3
4
of the volume occupied the cell. Three repetitions of the measurement
were performed for each variant. The measurement time was approximately 4–5 min.
Dry matter content. The dry substance content was measured by means of the drying
method. About 1 g of bars—before and after freeze-drying—were weighed into weighing
vessels of pre-set weight, and then placed in a convection dryer WAMED SUP 65 W/G
(Warsaw, Poland) to be treated at the temperature of 70
◦
C. The determination process took
24 h, after which the sample vessels were placed in a desiccator to cool down, and subse-

Molecules 2022,27, 3095 14 of 17
quently reweighed to calculate the dry matter content [
37
]. Measurement was repeated
three times for each product design.
s.s =(w3−w1)
(w2−w1)×100 (1)
The water content [%] for samples before freeze-drying was calculated on the basis of
equation
H2O=100 −s.s. (2)
where:
s.s—dry matter content [%],
w1—the mass of the empty vessel [g],
w2—weight of the sample dish before drying [g],
w3—weight of the sample dish after drying [g].
Microscopy. The changes in structure in terms of the effect of the composition were
determined by means of a scanning electron microscope TM-3000 HITACHI (Fichtenhain,
Germany) [
34
]. Out of the freeze-dried gel cubes, a piece of about 1–2 mm was cut out
across the cube. Structural changes were determined at 100×magnification.
Colour. The colour change was assessed using a Chroma-Meter CR-300 made by
Minolta (Tokyo, Japan). The material was tested in the CIE L*, a*, b* system with the
following parameters: observer 2
◦
, measuring diameter 8 mm and the light source D65 [
38
].
In the CIE L*, a*, b* system, the L* parameter means the brightness of the sample, the
higher the value of the L* parameter, the closer the colour of the sample to white (range
0–100 units). The a* and b* coordinates, on the other hand, take positive and negative
values. The a* coordinate indicates the proportion of red in the case of positive values and
the proportion of green in the case of negative values. Correspondingly, the b* parameter
relates to the percentage share of yellow and blue colours. Ten measurements were made
in various places on the surface of the obtained bars. Based on the L*, a*, b* parameters, the
colour saturation (SI) was calculated.
SI—color saturation indicator [39]
SI =q(a∗)2+(b∗)2(3)
where:
a*—red colour coefficient [dimensionless value]
b*—yellow colour coefficient [dimensionless value]
Mechanical properties. The study of mechanical properties was checked using a
TA.HD plus Texture Analyzer (Stable Micro Systems, Surrey, UK) at an ambient temperature.
The cutting test was performed using a knife 62 mm long, 24 mm wide and 0.5 mm thick.
The test was carried out until the bar was cut to the depth of 10 mm, with a head travel
speed of 1.0 mm/s. The test results, that is strength, distance and time, were recorded by
the computer software program Texture Export [
31
]. The determination was performed in
10 replications for each variant. Based on the obtained data, the maximum drought cutting
force was determined and the curves of mechanical properties were drawn.
Organoleptic evaluation. The organoleptic evaluation of the obtained food products
was carried out using a 5-point rating scale, where 1 meant the least favourable impression,
and 5 the most favourable one [
36
]. The following features were distinguished: general
appearance, colour, taste, smell, crispness and general impression [
40
]. The group of
evaluators consisted of 10 students from the Warsaw University of Life Sciences (SGGW).
Six samples, that had been appropriately coded, were subjected to evaluation.

Molecules 2022,27, 3095 15 of 17
Statistical Analysis
The results were statistically analysed by means of the Statistica Statgraphics XVII
software program. For this purpose, the one-way analysis of variance (ANOVA) was used
and homogeneous groups were determined using the F test.
4. Conclusions
The increase of apple or chokeberry pomace concentration decreased the water activity
and brightness, whereas in most cases the dry matter content of freeze-dried bars increased.
Mechanical properties vary depending on the product design. With the increase in the
amount of pomace, the shear force increases, which is influenced by the structure of the
samples. The variant with the 2% addition of pomace is characterised by the most delicate
structure that influences mechanical properties. Organoleptic evaluations confirm the high
quality of freeze-dried bars with the addition of fruit pomace. Taking into account the
results of determinations and organoleptic evaluation, the variant with 1% addition of
sodium alginate and 2% addition of pomace has proven to be the best variant in terms of
physical and organoleptic properties.
Author Contributions:
Conceptualisation, A.C. and P.P.; methodology, A.C. and P.P.; software, A.C.;
validation, A.C., M.J. and S.G.; formal analysis, A.C., M.J. and S.G., investigation, A.C. and P.P.;
resources, A.C. and P.P.; data curation, A.C. and P.P.; writing—original draft preparation, A.C., M.J.,
S.G. and P.P.; writing—review and editing, A.C., M.J., S.G. and P.P.; visualisation, A.C. and P.P.;
supervision, A.C., M.J.; project administration, M.J. All authors have read and agreed to the published
version of the manuscript.
Funding: This research received no external funding.
Institutional Review Board Statement: Not applicable.
Informed Consent Statement: Not applicable.
Acknowledgments:
This research was carried out as part of the III BIOSTRATEG “The develop-
ment of an innovative carbon footprint calculation method for the basic basket of food products”—
task in the project “Development of healthy food production technologies taking into consider-
ation nutritious food waste management and carbon footprint calculation methodology” BIOS-
TRATEG3/343817/17/NCBR/2018 of the National Centre for Research and Development. Some of
the research was performed with the use of Research equipment was purchased as part of the “Food
and Nutrition Centre—modernisation of the WULS campus to create a Food and Nutrition Research
and Development Centre (C ˙
Zi ˙
Z)” co-financed by the European Union from the European Regional
Development Fund under the Regional Operational Programme of the Mazowieckie Voivodeship for
2014–2020 (Project No. RPMA.01.01.00-14-8276/17).
Conflicts of Interest: The authors declare no conflict of interest.
Sample Availability: Samples of the compounds are available from the authors.
References
1. Płachciak, A. The idea of sustainable development—A principle of justice. Annales 2009,12, 197–204.
2.
Tiwari, B.K.; Norton, T.; Holden, N.M. Introduction. In Sustainable Food Processing; Tiwari, B.K., Norton, T., Holden, N.M., Eds.;
John Wiley & Sons: Hoboken, NJ, USA, 2014; pp. 1–7.
3.
Fruit and Vegetables Market—Production, Processing (IERiG ˙
Z Analysis). Available online: www.sadyogrody.pl (accessed on 20
January 2020).
4. Wichrowska, D.; ˙
Zary-Sikorska, E. Health-promoting properties of apple press cake. In˙
zynieria Apar. Chem. 2015,54, 286–287.
5.
Tarko, T.; Duda-Chodak, A.; Bebak, A. Biological activity of selected fruit and vegetable pomaces. ˙
Zywno´s´c Nauka Technol. Jako´s´c
2012,4, 55–65. [CrossRef]
6.
Krishnaswamy, K.; Vali, H.; Orsat, V. Value-adding to grape waste: Green synthesis of gold nanoparticles. J. Food Eng.
2014
,142,
210–220. [CrossRef]
7.
Kowalska, H.; Lenart, A.; Marzec, A.; Ciurzy ´nska, A.; Cichowska, J.; Czajkowska, K.; Wojnowski, M.; Hankus, M. Development of
sustainable processing technologies for converting by-products into healthy, added value ingredients and food products. Post˛epy
Tech. Przetwórstwa Spo˙
zywczego 2015,2, 119–125.

Molecules 2022,27, 3095 16 of 17
8.
Rana, S.; Gupta, S.; Rana, A.; Bhushan, S. Functional properties, phenolic constituents and antioxidant potential of industrial
apple pomace for utilization as active food ingredient. Food Sci. Hum. Wellness 2015,4, 180–187. [CrossRef]
9.
Skinner, R.C.; Gigliotti, J.C.; Ku, K.; Tou, J.C. A comprehensive analysis of the composition, health benefits, and safety of apple
pomace. Nutr. Rev. 2018,76, 893–909. [CrossRef] [PubMed]
10.
Lyu, F.; Luiz, S.F.; Azeredo, D.R.P.; Cruz, A.G.; Ajlouni, S.; Ranadheera, C.S. Apple pomace as a functional and healthy ingredient
in food products: A review. Processes 2020,8, 319. [CrossRef]
11.
Pawlak, S.; Sielicka, M. Wpływ Rozpuszczalnika Zastosowanego do Ekstrakcji na Oznaczon ˛a Zawarto´s´c Zwi ˛azków Fenolowych i Aktywno´s´c
Przeciwutleniaj ˛ac ˛a Wytłoków z Aronii. Zagospodarowanie Ubocznych Produktów Przemysłu Spo˙
zywczego; Górecka, W.D., Pospiech, E.,
Eds.; Uniwersytet Przyrodniczy w Poznaniu: Pozna ´n, Poland, 2016; pp. 25–35.
12. Fronc, A.; Nawirska, A. The waste from vegetable and fruit processing—Possibilities of using. Ochr. Sr. 1994,2, 31–32.
13. Grasso, S. Extruded snacks from industrial by-products: A review. Trends Food Sci. Technol. 2020,99, 284–294. [CrossRef]
14.
Ciurzy´nska, A.; Cie´sluk, P.; Barwi´nska, M.; Marczak, W.; Ordyniak, A.; Lenart, A.; Janowicz, M. Eating Habits and Sustainable
Food Production in the development of innovative “healthy” snacks. Sustainability 2019,11, 2800. [CrossRef]
15.
Kowalska, H.; Czajkowska, K.; Cichowska, J.; Lenart, A. What’s new in biopotential of fruit and vegetable by-products applied in
the food processing industry. Trends Food Sci. Technol. 2017,67, 150–159. [CrossRef]
16.
Majerska, J.; Michalska, A.; Fiegiel, A. A review of new directions in managing fruit and vegetable processing byproducts. Trends
Food Sci. Technol. 2019,88, 207–219. [CrossRef]
17.
Orrego, C.E.; Salgado, N.; Botero, C.A. Developments and trends in fruit bar production and characterization. Crit. Rev. Food Sci.
Nutr. 2013,54, 84–97. [CrossRef] [PubMed]
18.
Gronowska-Senger, A.; Drywie ´n, M.; Hamułka, J.; Wawrzyniak, A. Oznaczanie zawarto´sci wody i suchej masy w wybranych
produktach spo˙
zywczych. In Analiza ˙
Zywno´sci Zbiór´
Cwicze´n; Gronowska-Senger, A., Ed.; Wydawnictwo SGGW: Warszawa,
Poland, 2018; pp. 13–20.
19.
Marciniak-Łukasiak, K.; ˙
Zbikowska, A.; Kaˇcániová, M. Ocena jako´sci batonów zbo ˙
zowych z dodatkiem wybranych surowców
odpadowych przemysłu owocowego. In Proceedings of the Surowce Pochodzenia Zwierz˛ecego Jako ´
Zródło Składników
Bioaktywnych: XIII Konferencja Naukowa z Cyklu ˙
Zywno´s´c XXI Wieku, ˙
Zywno´s´c a Składniki Bioaktywne”, Kraków, Poland,
24–25 September 2018; Słupski, J., Tarko, T., Dro ˙
zd ˙
z, I., Eds.; Oddział Małopolski Polskiego Towarzystwa Technologów˙
Zywno´sci:
Kraków, Poland, 2018; pp. 143–153.
20.
Karwacka, M.; Gumkowska, M.; Rybak, K.; Ciurzy´nska, A.; Janowicz, M. Impact of sodium alginate and dried apple pomace
powder as a carrier agent on the properties of freeze-dried vegetable snacks. Pol. J. Food Nutr. Sci. 2021,71, 451–461. [CrossRef]
21.
Ciurzy´nska, A.; Marczak, W.; Lenart, A.; Janowicz, M. Production of innovative freeze-dried vegetable snack with hydrocolloids
in terms of technological process and carbon footprint calculation. Food Hydrocoll. 2020,108, 105993. [CrossRef]
22.
Gaidhani, K.A.; Harwalkar, M.; Bhambere, D.; Nirgude, P.S. Lyophilization/freeze drying—A review. World J. Pharm. Res.
2015
,8,
516–543.
23. Pałacha, Z.; Markiewicz, M. Water activity of choosen food-stuff groups. Post˛epy Tech. Przetwórstwa Spo˙
zywczego 2011,2, 24–29.
24.
Grzegory, P.; Piotrowski, D. Effect of drying method on selected properties of dried fruits and vegetables. Przemysł Ferment.
Owocowo-Warzywny 2013,57, 5–6.
25.
Gondek, E.; Gauze, J.; Jakubczyk, E.; Janczar-Smuga, M.; Nowak, D.; Stasiak, M.; Kami´nska-Dwórznicka, A.; Samborska, K. The
high-fibre vegetable and cereal based snacks—Analysis of selected physical and functional properties. Zesz. Probl. Post˛epów Nauk.
Rol. 2017,590, 15–27.
26.
Tapia, M.S.; Alzamora, S.M.; Chirife, J. Effects of water activity (aw) on microbial stability as a hurdle in food preservation. In
Water Activity in Foods: Fundamentals and Applications; Wiley-Blackwell: Hoboken, NJ, USA, 2020; Chapter 14; pp. 323–355.
27.
Karwacka, M.; Ciurzy ´nska, A.; Galus, S.; Janowicz, M. Freeze-dried snacks obtained from frozen vegetable by-products and
apple pomace—Selected properties, energy consumption and carbon footprint. Innov. Food Sci. Emerg. Technol.
2022
,77, 102949.
[CrossRef]
28.
Ciurzy ´nska, A.; Mieszkowska, A.; Olsi ´nski, I.; Lenart, A. The effect of composition and aeration on selected physical and sensory
properties of freeze-dried hydrocolloid gels. Food Hydrocoll. 2017,67, 94–103. [CrossRef]
29.
Silva-Espinoza, M.A.; Camacho, M.M.; Martínez-Navarrete, N. Use of different biopolymers as carriers for purposes of obtaining
a freeze-dried orange snack. LWT 2020,127, 109415. [CrossRef]
30.
Valentina, V.; Pratiwi, A.R.; Hsiao, P.Y.; Tseng, H.T.; Hsieh, J.F.; Chen, C.C. Sensorial characterization of foods before and after
freeze-drying. Austin J. Nutr. Food Sci. 2016,1, 1–5.
31.
Ciurzy´nska, A.; Lenart, A. Effect of aerated structure on selected properties of freeze-dried hydrocolloids gels. Int. Agrophys.
2016,30, 9–17. [CrossRef]
32.
Ciurzy´nska, A.; Lenart, A. Wybrane wła´sciwo´sci fizyczne liofilizowanych galaretek truskawkowych. Zesz. Probl. Post˛epów Nauk.
Rol. 2010,553, 31–39.
33. Konrade, D.; Klava, D.; Gramatina, I. Cereal crispbread improvement with dietary fibre from apple by-products. CBU Int. Conf.
Proc. 2017,5, 1143–1148. [CrossRef]
34.
PN-ISO 4121:1998; Analiza Sensoryczna. Metodologia. Ocena Produktów˙
Zywno´sciowych Przy U ˙
zyciu Metod Skalowania.
Polish Committee for Standardization: Warsaw, Poland, 2013.

Molecules 2022,27, 3095 17 of 17
35.
Silva-Espinoza, M.A.; Salvador, A.; Camacho, M.D.M.; Martínez-Navarrete, N. Impact of freeze-drying conditions on the sensory
perception of a freeze-dried orange snack. J. Sci. Food Agric. 2011,101, 4585–4590. [CrossRef]
36.
Parra, A.F.R.; Sahagún, M.; Ribotta, P.D.; Ferrero, C.; Gómez, M. Particle size and hydration properties of dried apple pomace:
Effect on dough viscoelasticity and quality of sugar-snap cookies. Food Bioprocess Technol. 2019,12, 1083–1092. [CrossRef]
37.
Ciurzy´nska, A.; Lenart, A.; Traczyk, W. Influence of chemical composition and structure of strawberry gels on the choosen
physical properties of freeze–dried final product. Ital. J. Food Sci. 2013,2, 149–159. [CrossRef]
38.
Zalewska, M.; Otreszko-Arski, A.; Zalewski, M. Wpływ suszenia konwekcyjnego i liofilizacji na barw˛e wybranych owoców. Apar.
Badaw. Dydakt. 2016,3, 141–145.
39.
Kowalska, H.; Marzec, A.; Domian, E.; Masiarz, E.; Ciurzy´nska, A.; Galus, S.; Małkiewicz, A.; Lenart, A.; Kowalska, J. Physical
and sensory properties of japanese quince chips obtained by osmotic dehydration in fruit juice concentrates and hybrid drying.
Molecules 2020,25, 5504. [CrossRef] [PubMed]
40.
Kita, A.; Górnicka, E.; Wojdyło, A.; Dro˙
zd˙
z, W. Wpływ dodatku wytłoków rzepakowych na wła´sciwo´sci sma ˙
zonych chrupek
ziemniaczanych. Ro´sliny Oleiste Oilseed Crops 2012,33, 285–294. [CrossRef]