Journal of Food Engineering 66 (2005) 43–50
www.elsevier.com/locate/jfoodeng
Effect of osmotic dewatering on apple tissue structure
Piotr P. Lewicki *, Renata Porzecka-Pawlak
Department of Food Engineering and Process Management, Faculty of Food Technology, Warsaw Agricultural University (SGGW),
Nowoursynowska 159c, 02-776 Warszawa, Poland
Received 15 July 2003; accepted 23 February 2004
Abstract
Apple cubes were subjected to osmotic dehydration in 61.5% sucrose and changes in tissue structure were examined in light
microscope. Fixed and embedded in raisin 3 lm thick slices were analysed and indices characterising apple tissue structure were
calculated with computer image analysis. It was found that osmotic dehydration affects size and shape of cells, and in consequence
changes shape and dimension of intercellular spaces. No broken cell walls were found in osmosed tissue. Osmotic treatment increased the share of small cells in tissue and moved shape factor toward smaller values. There was a difference in response of cells to
osmotic stress dependent on the cell location. Cells, which are in contact with intercellular spaces reacted to osmotic stress in
different way than those surrounded by other cells. Shrinkage of cells and deformation of cell walls caused increase of circumference
of intercellular spaces. The increase was more than 30% until 120 min of osmosis. Moreover, intercellular spaces became more
irregular than those did in raw apple. Further osmotic treatment caused substantial increase of small intercellular spaces, which was
probably due to detachment of some cells and splitting of middle lamella. This observation suggested that prolonged osmotic
dehydration could disintegrate apple tissue and destroy its continuity.
2004 Elsevier Ltd. All rights reserved.
1. Introduction
Osmotic dewatering is an important process, which
enables water removal as well as modification of
chemical composition of the material. It is simultaneous
counter-current mass transfer process in which water
outflows to the surrounding solution and the solute infuse into the product (Lewicki & Lenart, 1995; Torreggiani, 1993). Besides the chemical changes osmotic
dehydration causes alteration of physical properties of
plant tissue. Shrinkage, decreased water holding capacity, changes in porosity and resistance to deformation is
usually observed during osmotic dehydration. Alteration of physical properties reflects deleterious influence
of osmotic dehydration on the structure of plant tissue
and morphology of the cell.
Texture of plant tissue is determined mainly by
properties of the cell wall and middle lamella and the
turgor pressure (Jackman & Stanley, 1995). Moreover,
cell size and shape, volume occupied by vacuole in the
*
Corresponding author. Tel./fax: +48-22-8434602.
E-mail address: [email protected] (P.P. Lewicki).
0260-8774/$ - see front matter 2004 Elsevier Ltd. All rights reserved.
doi:10.1016/j.jfoodeng.2004.02.032
cell, volume of intercellular spaces, presence of starch
granules and chemical composition of the cell sap are
all affecting plant tissue texture (Ilker & Szczesniak,
1990).
Water removal from the plant tissue causes numerous
processes going on simultaneously or in a sequence.
Plant tissue can be considered as a capillary-porous
body consisting in liquid and gas phases and solid matrix. The solid matrix forms continuum capable of
transporting water and small molecules known as
apoplast. On the other hand protoplasm of neighbouring cells is interconnected and another continuous network is formed known as symplast. Moreover,
interconnected intercellular spaces form channels, which
exhibit suction potential.
Barat, Fito, and Chiralt (2001) observed that apple
tissue subjected to osmotic dehydration sucked hipertonic solution into intercellular spaces. Cells surrounding intercellular spaces shrunk, the solid matrix was
deformed and the spaces increased in size. Decreased
pressure caused further suction of hipertonic solution. A
hydrodynamic mechanism for osmotic dehydration was
proposed (Fito & Pastor, 1994).
Cells on the surface of the material undergoing osmotic dehydration are fully plasmolysed in a short time
44
P.P. Lewicki, R. Porzecka-Pawlak / Journal of Food Engineering 66 (2005) 43–50
while those in the interior can be in full turgor. Hence,
during osmotic dehydration a gradient of turgor pressure is developed, which can deform structure. Le Maguer (1997) suggests that full plazmolysis of cells is
needed for expansion of intercellular spaces. The turgor
pressure gradient hinders increase of the spaces and
water flow is caused mainly by the difference in pressure.
Osmotic dewatering causes many macro- and microscopic changes in plant tissue. Marcotte, Le Maguer,
and Toupin (1991) showed that potato slices dehydrated
in 40% sucrose shrink by 5–40%. Softening of surface
layers, breaking of cells and detachment of one cell from
the other was observed in apple tissue subjected to
osmotic dehydration (Monsalve-Gonz
ales, BarbosaCanovas, & Cavalieri, 1993). Osmotic dehydration of
pears until initial mass was reduced by 20% caused
softening of the tissue while further dewatering lead to
increased firmness, which attained original value at 50%
reduction of mass (Bolin & Huxsoll, 1993).
In experiments carried out by Alzamora, Gerschenson, Vidales, and Nieto (1997) impregnation of strawberry tissue with glucose caused lysis of plasmalemma
and tonoplast and disorganisation of cytoplasm. No
breakage of cell walls was observed. Osmotic treatment
of kiwi fruit caused intensive plasmolysis and distortion of plasmalemma and middle lamella. Seldom
breakage of cell wall was observed. Size of cells was
reduced proportionally to the tissue shrinkage.
Ferrando and Spiess (2001) observed two types of
cell response to osmotic treatment. In one type of tissue (onion) middle lamella was degraded, cells were
separated and underwent shrinkage. The cross-sectional area of cells was reduced by 40–46%. In another
type of tissue (strawberries) there was no separation of
cells and typical plasmolysis was observed. Plasmalemma was detached from the cell wall and the crosssectional area of cells was reduced by 24–35%.
Protoplasts of onion survived osmotic dehydration
while only 25 ± 15% of strawberry cells osmosed for 30
min showed viability.
During osmotic dehydration changes in sample
volume and porosity promote the non-diffusional mass
transfer in the tissue. In osmotically treated apple
samples porosity increases in line with dehydration and
this is mainly due to changes in the volume of sample
gas phase. Sample pores are slowly filled with osmotic
solution, hence the higher the solute gain the smaller
change in sample volume is observed (Barat, Chiralt, &
Fito, 1998; Barat, Chiralt, & Fito, 2000).
Studies done on fully turgid cells showed that
hypertonic solution causes initial shrinkage which was
followed by a swelling period (Dainty, 1963). Mizrahi,
Eichler, and Ramon (2001) observed swelling of gels
during osmotic dehydration and the phenomena is driven by the difference in osmotic pressures of gel and the
polymer network. In experiments done on rye and
spinach protoplasts it was shown (Dowgert & Steponkus, 1984; Steponkus, Dowgert, & Gordon-Kamm,
1983; Wolfe & Steponkus, 1981) that dewatering leads
to plasmalemma shrinkage and formation of numerous
endocytotic vesicles. This phenomenon is accompanied
by the loss of viability. The most important is the ratio
between surface of hypertonically shrunken membrane
and surface of plasmalemma of untreated protoplast. At
some critical value of that ratio the loss of viability was
observed.
Osmotic dewatering of celery petioles caused changes
in cell structure dependent on water activity of the
material. Dewatering to aw ¼ 0:995 caused changes
which were completely reversible upon rehydration
(Willis & Teixeira, 1988). However at aw ¼ 0:987 regain
of weight upon rehydration was only 82%. Osmotic
dewatering to aw ¼ 0:920 caused extensive leaching of
solubles during rehydration. Microscopic examination
showed distortion of plasma membrane. In samples air
dried to aw ¼ 0:25 distortion of the cell wall and
detachment of middle lamella was observed. In osmotically treated celery petioles a decrease of elasticity
modulus was noted. Since almost 4-fold decrease was
not accompanied by distortion of the cell wall it was
concluded that the damage of plasmalemma and tonoplast is responsible for the observed changes (Willis &
Teixeira, 1988).
Treatment of apple tissue with 65% grape juice
concentrate under vacuum caused extensive changes in
the cell structure. Plasmolysis and membrane shrinkage
was observed, but liquid filled the cells and avoided
deformation of the cell walls (Martinez-Monz
o, Martinez-Navarrete, Chiralt, & Fito, 1998). Osmotic
dewatering under atmospheric pressure caused changes
in both intercellular spaces and cells. Intercellular
spaces were large in comparison to cells and more
cylindrical in shape. Cells were shrunken, with irregular
shape and bent walls (Barat et al., 1998). In osmosed
cells the detachment of plasma membrane from the cell
wall was not observed. On the other hand application
of vacuum caused separation of plasmalemma from the
cell wall and filling the empty space with hypertonic
solution (Barat, Albors, Chiralt, & Fito, 1999). Upon
rehydration intercellular spaces regain their shape but
changes in cells were partly irreversible.
Research done on mature and immature apples vs.
Jonagold showed that plasmalemma and tonoplast are
permeable to sugars. The permeability to sugars increases during maturation and the increase is much
greater in tonoplast than in plasmalemma. However
the permeability of plasmalemma is larger than that of
tonoplast regardless of the stage of maturation. Hence,
in mature apple about 90% of sugars are accumulated
in vacuole (Yamaki & Ino, 1992).
The aim of this work was to investigate the effect of
osmotic dehydration on microstructure of surface layers
P.P. Lewicki, R. Porzecka-Pawlak / Journal of Food Engineering 66 (2005) 43–50
45
of apple cubes including changes of size, shape and
diameter of cells and intercellular spaces.
Histograms of measured values were calculated using
Excel v.97 (Microsoft).
2. Material and methods
3. Results and discussion
Apple variety Idared was cut into 10-mm cubes and
dipped for 10 min into 0.5% citric acid in order to prevent enzymatic browning.
Apple cubes were dewatered by osmosis in 61.5%
sucrose solution at 30 C with continuous stirring of the
suspension. Material to solution ratio was 1:4 w/w. The
process was interrupted at 30, 60, 120 and 180 min.
Osmosed material was sprayed with water for 30 s and
blotted with filter paper.
Parallelepipeds 5 mm long and 3 · 3 mm in crosssection were cut from the centre of osmosed cubes and
subjected to fixation and dehydration. Cutting was
done in such a way that one surface 3 · 3 mm of the
parallelepiped was that which was in contact with osmotic solution. The opposite surface was that from the
centre of the apple sample. Samples were fixed in 0.45
molar solution of glutaraldehyde–paraformaldehyde in
a cacodylic buffer for 24 h. Washing was done in 0.2
molar cacodylic buffer for 30 min, repeating the process four times. Dehydration was done by dipping the
samples into a series of ethanol solutions with concentration increasing from 10% to 70% v/v in steps of
10%. Dehydration in each solution was done for 20
min and repeated twice. Partly dehydrated samples
were kept for four days in 70% ethanol in a refrigerator. Then the samples were dehydrated in 80%, 90%
and 100% ethanol in series as was described above.
The dehydration was finished with pure acetone and
repeated twice for 40 min. Dehydrated material
was saturated with Epon, polymerised for 24 h at 60
C and cut in microtome into 3 lm thick slices
beginning from the surface contacted with osmotic
solution. Slices were dyed with azur and methylene
blue, washed with water and examined under the
microscope.
Microscope AX-70 Provis (Olympus) interconnected
with computer was used in this experiment to examine
the structure of osmosed apple. Software Analysis v. 3.0
(Soft Imaging Software) and Mocha v. 1.2 (Jandel Scientific) was used to improve the image and to calculate
parameters characteristic for the tissue. Analysis was
done on 600 cells on the average.
Feret diameter, circumference and shape factor was
calculated for cells and intercellular spaces. Shape factor
was calculated as:
3.1. Osmotic dewatering
sf ¼
Osmotic dewatering resulted in an increased dry
matter content and reduced water concentration. The
largest increase in dry matter content was observed after
30 min of osmosis (Fig. 1). The increase was equal to
almost 70%. Further osmotic dewatering resulted in
slow increase in dry matter content. After 3 h of dewatering dry matter content was doubled.
Assuming that water and sucrose are the only substances which diffuse in the apple tissue it can be calculated that 30-min osmosis caused infusion of sucrose
which accounted for 36.5% of dry matter of osmosed
material. After 3 h of osmosis that value increased to
44%. Water content of raw apple was 5.71 g/g d.m. and
decreased to 2.34 g/g d.m. during 3 h of osmosis. Again,
the largest difference was noticed after 30 min of
osmosis, which amounted to more than 80%.
Above analysis shows that fluxes of sucrose and water
are large during the first 30 min of osmosis and the tissue
is subjected to large concentration gradients during that
time. Further osmotic dewatering causes decrease of
sucrose and water fluxes and stresses build up by concentration gradients should be much smaller than those
created at the beginning of the dewatering process.
3.2. Tissue structure
3.2.1. Raw apple
Microscopic analysis of raw apple shows nearly circular cells with well-defined cell walls (Fig. 2). The crosssectional area of cells shows some convexities, which
4p A
P2
where A––area, P ––perimeter of the cell.
Fig. 1. Changes of dry matter content during osmotic treatment of
apple cubes.
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P.P. Lewicki, R. Porzecka-Pawlak / Journal of Food Engineering 66 (2005) 43–50
Fig. 2. Microphotograph of raw apple tissue. Shaded areas are intercellular spaces. Bar is 300 lm.
suggest that the cells are rather polyhedrons and not
spheres. The regular shape of parenchyma cells is pronounced by the shape factor. The most frequent shape
factor is 0.82 and some 56% of cells have shape factor
between 0.5 and 0.8. Cells with shape factor lower than
0.5 account for about 12% of cells (Fig. 3).
The Feret diameter of cross-sectional area of cells
varies between 46 and 346 lm and the dominating value
is 130 lm. Cumulative frequency shows that cells with
the diameter smaller than 75 lm account for about 8%
of cells, and 72% of cells have the Feret diameter between 75 and 150 lm.
Circumference of cells varies from 190 to 2110 lm.
Dominating value is 425 lm. Some 22% of cells have
circumference smaller than 330 lm, and 26.5% of cells
have circumference larger than 530 lm. Hence, more
than 50% of cells have circumference between 330 and
530 lm. If cells with circumference larger than 1000 lm
are not taken into account then the frequency distribution is nearly normal.
Fig. 3. Effect of time of osmotic dehydration on shape factor of cells in
apple tissue.
Fig. 4. Frequency distribution of shape factor of intercellular spaces in
raw apple tissue.
Intercellular spaces are clearly visible on microphotographs as cavities of various shapes and sizes (Fig. 2).
The spaces are irregular, elongated objects with concave,
toward the centre, walls. The irregularity of shape is
expressed by the shape factor, which is in the range from
0.16 to 0.84, and practically shows no dominating values
(Fig. 4). Intercellular spaces with shape factor smaller
than 0.3 account for 15% of voids and with shape factor
larger than 0.6 for 11% of cavities. The remaining 74%
of intercellular spaces have shape factor between 0.3 and
0.6.
Circumference of intercellular spaces is between 172
and 2297 lm. There is no dominating circumference, but
most of intercellular spaces have circumference between
400 and 1000 lm. Intercellular spaces with circumference below 500 lm account for 32% of voids, and cavities with circumference larger than 1000 lm are 19%.
Hence, almost 50% of intercellular spaces have circumference between 500 and 1000 lm.
3.2.2. Osmosed apple tissue
Osmotic treatment of apple tissue causes changes in
its microscopic structure. There is a substantial difference in response to osmotic stress between cells surrounded by other cells and those being in contact with
intercellular spaces. Cells surrounded by other cells become more circular at the beginning of osmotic process.
With progressing osmosis their shape change to elliptical
with folded and wrinkled cell walls. Cells contacting
intercellular spaces are strongly affected by osmotic
dewatering. From the very beginning they are deformed,
elongated with cell walls, those contacting intercellular
space, concave toward the centre of the cell (Fig. 5). The
cells look like crescents and further osmosis causes
folding and wrinkling of cell walls.
Intercellular spaces become large elongated with
irregular shape. At the final stages of osmosis they are
more regular in shape but the circumference is composed of many concavities.
P.P. Lewicki, R. Porzecka-Pawlak / Journal of Food Engineering 66 (2005) 43–50
Fig. 5. Microphotograph of apple tissue osmosed for 30 min. Shaded
areas are intercellular spaces. Bar is 300 lm.
At any time of osmosis there was no broken or
damaged cell walls observed. At the final stages of
osmosis some separation of cells was noticed and individual cells suspended in the intercellular space were
observed.
Shape factor of cells. Shape factor of cells was affected
by osmotic process. Number of cells with shape factor
larger than 0.8 (circular cells) decreased substantially
(Fig. 3) from 31% for raw apple to 10% in apple osmosed for 120 min. Number of very irregular cells also
decreased, especially during the first 60 min of osmosis.
In consequence number of cells with shape factor between 0.5 and 0.8 increased from 57% in raw apple to
over 70% in osmosed tissue. The change occurs during
the first 30 min of osmosis and then the number of cells
with sf ¼ 0:5–0:8 stabilises on the level of 71–79%.
The osmotic process also influenced the range of
shape factors. The shape factor in raw apple was from
0.12 to 0.94 and was progressively narrowed during
osmotic treatment. In apple osmosed for 180 min it was
from 0.46 to 0.87.
Cell diameter. Changes in shape caused by osmotic
treatment are accompanied by changes in size of cells.
The dominating Feret diameter decreases from 130 lm
in raw apple to 105 lm in apple osmosed for 180 min.
Number of cells with the diameter larger than 150 lm is
independent on osmosis time and is between 18.4% and
22.5%. However, number of small cells increases progressively from 8.2% in raw apple to 23.0% in apple
osmosed for 180 min. (Fig. 6). In consequence number
of cells with the diameter from 75 to 150 lm decreased
from 72% in raw apple to 55% in apple osmosed for 180
min.
The distribution of cell sizes is affected by osmotic
process. In raw apple cells are characterised by the Feret
diameter ranging from 46 to 346 lm. Apple osmosed for
180 min shows cell diameters from 39 to 212 lm. The
spread of cell sizes in osmosed apple is much narrower
47
Fig. 6. Effect of time of osmotic dehydration on diameter of cells in
apple tissue.
than in raw apple, and the change concerns the side of
large diameters.
Cell circumference. Osmotic dewatering causes decrease of the number of cells with circumference between
330 and 530 lm in the product. After 180 min of
osmosis number of those cells is 39%, while in raw apple
that value was about 50%. The decrease is mainly due to
the increase of number of cells with circumference
smaller than 330 lm. (Fig. 7). The number of those cells
increases from 22% to 32.3%. These changes follow the
changes of cell diameter. Increase in number of small
cells must cause increase of share of cells with small
circumference in the analysed population.
Shape factor of intercellular spaces. Intercellular
spaces are less affected by osmotic dewatering than the
cells. There is no dominating shape factor, but most of
intercellular spaces are in the range from 0.3 to 0.6. In
raw apple those spaces account for 73.5% of all the
intercellular cavities. The share of those spaces in the
population does not change during osmotic dewatering
Fig. 7. Effect of time of osmotic dehydration on circumference of cells
in apple tissue.
48
P.P. Lewicki, R. Porzecka-Pawlak / Journal of Food Engineering 66 (2005) 43–50
spaces with circumference exceeding 1000 lm increase
from 18.5% to 43% after 120 min of osmosis (Fig. 9).
Osmotic treatment for 180 min causes increase of
number of intercellular spaces with small circumference
and decrease of number of large cavities.
Frequency distribution of circumference of intercellular spaces shows the same tendency. In raw apple 80%
of intercellular spaces have circumference below 960 lm,
while after 120 min of osmosis that circumference increases to 1285 lm.
4. Discussion
Fig. 8. Effect of time of osmotic dehydration on shape factor of
intercellular spaces in apple tissue.
until 120 min of osmosis. Then the share decreases to
65–67% (Fig. 8).
Intercellular spaces in raw apple are characterised by
a shape factor in the range from 0.16 to 0.84. During
osmotic treatment the shape of the very irregular intercellular spaces does not change much. Osmotic treatment causes changes of those intercellular spaces, which
are more regular in shape. The upper end of the shape
factor distribution curve is moved toward lower values,
and decreases from 0.84 to 0.73–0.75. Hence, osmotic
treatment moves intercellular spaces toward more
irregular shapes.
Circumference of intercellular spaces. Circumference
of intercellular spaces in raw apple varies between 172
and 2297 lm. However, the spaces with large circumference are just few, and most of the intercellular spaces
are with circumference smaller than 1500 lm. Osmotic
dewatering causes substantial changes in intercellular
spaces. Small spaces with circumference lower than 500
lm decrease from 32% in raw apple to about 6.5% after
60 min of osmosis. On the other hand number of large
Fig. 9. Effect of time of osmotic dehydration on circumference of
intercellular spaces in apple tissue.
Results presented above show the response of apple
parenchyma tissue to osmotic treatment. Most of
changes both weight and dry matter content occurs
during the first 30 min of processing, while microscopic
properties such as cell shape, cell size, and shape of
intercellular spaces change during the whole investigated
time of osmotic treatment.
In raw apple cells are in the turgor state and exert
pressure one on the other. Due to different sizes and
convexities of the contact surfaces the shape of cells is
distorted in respect to the ideal spherical form. The
shape factor has a log-normal distribution and a dominating value is typical for pentagons or hexagons. The
turgor pressure pushes cell walls toward the centre of
intercellular spaces. Hence, the intercellular spaces are
very irregular and look like an ellipse with wavy circumference (Fig. 2). Cell walls are under the stress and
are stretched.
Osmotic treatment, due to high osmotic pressure of
the solution, causes changes in spatial distribution of
pressure gradients in the tissue. Cells being in direct
contact with osmotic solution lose water and release
turgor pressure. Cells become smaller and the share of
those cells in osmosed tissue increases substantially (almost 3-fold). Some wrinkling of cell walls is observed
but the shape factor moves toward smaller values in
comparison to raw material. Hence, release of turgor
pressure does not lead to rounding off of the parenchyma cells. This is probably due to the fact that cells
are not separated from each other, and relaxing and
shrinking walls of cells are also subjected to stretching
forces exerted by neighbouring shrinking cells. This
mechanism is perfectly seen in cells, which are surrounding intercellular spaces. A part of cell wall, which
is in contact with intercellular space, is subjected to
shrinkage forces. The rest of cell wall is prevented from
extensive shrinkage by stretching forces. In consequence
cell wall on the intercellular space side collapses and
assumes shape similar to crescent (Fig. 5).
In tissue undergoing osmotic dewatering volume of
cells decreases, and the cell sizes move toward smaller
values. Small cells are less susceptible to deformation
P.P. Lewicki, R. Porzecka-Pawlak / Journal of Food Engineering 66 (2005) 43–50
than the large ones due to small radius and excess
pressures according to the Kelvin equation. Hence, osmotic dewatering causes less variability in cell shapes in
comparison with those in raw apple. An outcome of
these changes is a tissue with cells more deformed than
in raw apple but less variable in shape.
Changes in cell size and shape caused by osmotic
treatment affect intercellular spaces. Shrinkage of cells
and wrinkling and convexities of cell walls cause increase of circumference of intercellular spaces. The increase is more than 30% during 120 min of osmosis.
Moreover, the intercellular spaces become more irregular (Fig. 10) than those do in raw apple. Hence, the
shape factor moves toward smaller values.
Changes in shape factor and circumference of intercellular spaces are correlated with time of osmosis until
120 min of the process. At 180 min substantial increase
of small intercellular spaces is observed (Fig. 11), which
is accompanied by the decrease of number of large
intercellular spaces. This is probably due to detachment
49
of some cells and splitting of middle lamella. It is already
seen in tissue subjected to osmotic dewatering for 120
min (Fig. 10). Detached cells enter intercellular spaces
and make them smaller and new cavities are formed.
This observation suggests that prolonged osmotic
dewatering can disintegrate apple tissue and destroy its
continuity. It can be due to either chemical changes
which weaken middle lamella or build up of stretching
forces sufficient to split it.
5. Conclusions
Results collected in this work show that osmotic
dewatering causes changes in size and shape of parenchyma cells of apple, which in consequence affect
intercellular spaces.
Contact with osmotic solution releases turgor pressure and cells are subjected to shrinkage and stretching
forces. These forces are not strong enough to break cell
walls or to split middle lamella. Hence, integrity of the
tissue structure is preserved. However, prolonged osmotic dewatering (3 h) causes some detachment of cells
and formation new, small intercellular spaces. This
detachment and splitting of middle lamella causes discontinuities in tissue structure.
Shrinkage and stretching forces acting on cell walls in
the tissue undergoing osmotic dewatering result in
deformation, wrinkling and creasing of cell surface. This
also affects shape and circumference of intercellular
spaces. In consequence tissue structure of osmosed apple
is less regular than that of raw apple, but more
homogenous. The shape factor is moved toward smaller
values, but the frequency distribution is much narrower
than in raw apple.
Fig. 10. Microphotograph of apple tissue osmosed for 120 min. Shaded
areas are intercellular spaces. Bar is 300 lm.
References
Fig. 11. Microphotograph of apple tissue osmosed for 180 min. Shaded
areas are intercellular spaces. Bar is 300 lm.
Alzamora, S. M., Gerschenson, L. N., Vidales, S. L., & Nieto, A.
(1997). Structural changes in the minimal processing of fruits: some
effects of blanching and sugar impregnation. In P. Fito, E. OrtegaRodriguez, & G. V. Barbosa-Canovas (Eds.), Food engineering
2000 (pp. 117–139). New York: Chapman & Hall.
Barat, J. M., Albors, A., Chiralt, A., & Fito, P. (1999). Equilibration
of apple tissue in osmotic dehydration: microstructural changes.
Drying Technology, 17(7 & 8), 1375–1386.
Barat, J. M., Chiralt, A., & Fito, P. (1998). Equilibrium in cellular
food osmotic solution systems as related to structure. Journal of
Food Science, 63, 836–840.
Barat, J. M., Chiralt, A., & Fito, P. (2000). Structural change kinetics
in osmotic dehydration of apple tissue. In Proceedings of the
International Drying Symposium IDS 2000, CD paper no. 416.
Barat, J. M., Fito, P., & Chiralt, A. (2001). Modelling of simultaneous
mass transfer and structural changes in fruit tissue. Journal of Food
Engineering, 49, 77–85.
Bolin, H. R., & Huxsoll, C. C. (1993). Partial drying of cut pears to
improve freeze/thaw texture. Journal of Food Science, 58, 357–360.
50
P.P. Lewicki, R. Porzecka-Pawlak / Journal of Food Engineering 66 (2005) 43–50
Dainty, J. (1963). Water relations of plant cells. In R. D. Preston (Ed.),
Advances in botanical research (Vol. 1, pp. 279–326). New York:
Academic Press.
Dowgert, M. F., & Steponkus, P. L. (1984). Behavior of cytoplasmic
membrane of isolated protoplasts during a freeze/thaw cycle. Plant
Physiology, 75, 1139–1151.
Ferrando, M., & Spiess, W. E. L. (2001). Cellular response of plant
tissue during the osmotic treatment with sucrose, maltose, and
trehalose solutions. Journal of Food Engineering, 49, 115–127.
Fito, P., & Pastor, R. (1994). Non-diffusional mechanism occurring
during vacuum osmotic dehydration. Journal of Food Engineering,
21, 513–519.
Ilker, R., & Szczesniak, A. S. (1990). Structural and chemical bases for
texture of plant foods. Journal of Texture Studies, 21, 1–36.
Jackman, R. L., & Stanley, D. W. (1995). Perspectives in the textural
evaluation of plant food. Trends in Food Science and Technology, 6,
187–194.
Le Maguer, M. (1997). Mass transfer modelling in structured food. In
P. Fito, E. Ortega-Rodriguez, & G. V. Barbosa-Canovas (Eds.),
Food engineering 2000 (pp. 253–269). New York: Chapman & Hall.
Lewicki, P. P., & Lenart, A. (1995). Osmotic dehydration of fruits and
vegetables. In A. S. Mujumdar (Ed.), Handbook of industrial drying
(Vol. 1, pp. 691–713). New York: Marcel Dekker.
Marcotte, M., Le Maguer, M., & Toupin, C. J. (1991). Mass transfer in
cellular tissue. Part I. The mathematical model. Journal of Food
Engineering, 13, 199–220.
Martinez-Monz
o, J., Martinez-Navarrete, N., Chiralt, A., & Fito, P.
(1998). Mechanical and structural changes in apple (var. Granny
Smith) due to vacuum impregnation with cryoprotectants. Journal
of Food Science, 63, 499–503.
Mizrahi, S., Eichler, S., & Ramon, O. (2001). Osmotic dehydration
phenomena in gel systems. Journal of Food Engineering, 49, 87–96.
Monsalve-Gonzales, A., Barbosa-Canovas, G. V., & Cavalieri, R. P.
(1993). Mass transfer and textural changes during processing of
apples by combined methods. Journal of Food Science, 58, 1118–
1124.
Steponkus, P. L., Dowgert, M. F., & Gordon-Kamm, W. J. (1983).
Destabilization of the plasma membrane of isolated plant protoplasts during a freeze–thaw cycle. The influence of cold acclimation.
Cryobiology, 20, 448.
Torreggiani, D. (1993). Osmotic dehydration in fruit and vegetable
processing. Food Research International, 261, 59–68.
Willis, C. A., & Teixeira, A. A. (1988). Controlled reduction of water
activity in celery: effect on membrane integrity and biophysical
properties. Journal of Food Science, 53, 111–116.
Wolfe, J., & Steponkus, P. P. (1981). The stress–strain relation of the
plasma membrane of isolated protoplasts. Biochimica et Biophysica
Acta, 643, 663–668.
Yamaki, S., & Ino, M. (1992). Alteration of cellular compartmentation
and membrane permeability to sugar in immature and mature
apple fruit. Journal of the American Society for Horticultural
Science, 117, 951–954.