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polish journal of food and nutrition sciences
www.pan.olsztyn.pl/journal/
e-mail: joan@pan.olsztyn.pl
© Copyright by Institute of Animal Reproduction and Food Research of the Polish Academy of Sciences
Pol. J. Food Nutr. Sci.
2008, Vol. 58, No. 1, pp. 45-51
INTRODUCTION
Wholegrain foods such as whole meal or wholegrain
breads, crisp breads, breakfast cereals and puffed whole
grains are important sources of nutrients and photoprotective
substances that are in a short supply in our diet, including
dietary fibre, resistant starch, trace minerals, certain vita-
mins, and other components [Slavin et al., 1997; Richardson,
2000]. Wholegrain fibre is considered to be a significant fac-
tor contributing to reducing the risk of diseases such as dia-
betes, cardiovascular disease and certain cancers [Heiniö et
al., 2003]. Despite the growing interest in the health aspects
of wholegrain food, texture as the most important sensory at-
tribute, remains a priority consumer choice criterion.
Texture is mostly related to physical, and especially me-
chanical properties of food products. Most of dry crispy/
crunchy food products have a porous structure consisting of
beams and films of solid material surrounding air cells [Luyten
et al., 2004]. The mechanical and ultimate properties of these
cellular solids depend on the composition and homogeneity of
materials and also on the amount and structure of pores [Gib-
son & Ashby, 1997]. Non-uniformity in internal structure and
surface characteristics of brittle and crunchy foods result in
a very complex failure mechanism that involves repetitive de-
formation and fracturing of subsequent layers in a cell struc-
ture. The mechanical behaviour and structure of cellular solid
foods give an irregular and irreproducible force-deformation
relationship [Luyten et al., 2004]. Stokes & Donald [2000] re-
ported that fracture in dry bread started at voids in the smallest
beams between the open air cells. When the bread was moister,
buckling and large deformation of these beams occurring be-
fore fracturing was clearly visible. Dry cereal-based baked and
extruded products, such as crisp breads, wafers, crackers, and
snacks, are hygroscopic due to their chemical composition,
porosity and presence of starch in the amorphous state [Col-
onna et al., 1984; Marzec & Lewicki, 2006]. If the moisture of
these crispy products increases, due to water sorption from the
atmosphere or by mass transport from neighbouring compo-
nents, it results in a soggy, soft texture [Nicholls et al., 1995].
Crispness is associated with pleasing textural contact and with
freshness and good quality of low moisture cereal product; its
loss caused by increased moistness of the material is a major
cause of consumer rejection.
Water is a constituent of food which affects food stability,
quality and physical properties. In solid foods water affects
their response to force. Increasing water content can lead to
plasticizing or antiplasticizing effects [Lewicki, 2004]. The
plasticization of polymer chains facilitates deformation and
brittle material becomes ductile and losses crispness.
The effect of water activity on crispness of cellular prod-
ucts has been studied by many authors. Katz & Labuza [1981]
have described the texture of snack foods, such as crackers
and chips, as a function of water activity. They demonstrated
that baked saltine crackers, popcorn, and fried potato chips
lost crispness when their water activity exceeded 0.35 to 0.50
depending on the product. A slight decrease in crispness of
breakfast cereals occurred at aw <0.5. Thereafter a rapid de-
crease of crispness was observed until aw=0.8, at which the
product lost its brittleness completely [Sauvageot & Blond,
1991]. A similar behaviour was observed when hardness
RELATIONSHIP BETWEEN WATER ACTIVITY OF CRISP BREAD AND ITS MECHANICAL
PROPERTIES AND STRUCTURE
Ewa Jakubczyk, Agata Marzec, Piotr P. Lewicki
Department of Food Engineering and Process Management, Warsaw University of Life Sciences, Warsaw
Key words: crisp bread, mechanical properties, water activity, structure
The aim of this work was to determine the effect of water activity on structure and mechanical properties of rye crisp bread and fibre crisp bread
containing wholegrain rye flour, wheat bran, oat meal and sesame seeds. Breads were stored at water activities in the range of 0-0.75. Their mechanical
properties (deformability modulus, fracture stress and strain, fracture work) were measured by three-point bending tests. The microstructure of the
crisp breads was studied at two water activities by scanning microscopy. Water activity significantly influenced mechanical properties of crisp bread.
Increasing water activity caused an increase of the fracture stress at water activities ranging from 0.030 to 0.255 for rye bread and at aw 0.039-0.319 for
fibre bread. An increase of water activity above these values caused softening and a sharp decrease of the deformability modulus and fracture stress.
Microscopic photographs showed that water activity had an influence on the structure of crisp bread. The rye bread had lower resistance to deforma-
tion than the fibre bread, probably due to differences in composition, and the added grain ingredients gave a more heterogeneous structure.
Author’s address for correspondence: Ewa Jakubczyk, Department of Food Engineering and Process Management, Warsaw University of Life Sciences,
Nowoursynowska Str. 159C, 02-776 Warsaw, Poland; tel.: (48 22) 593 75 63; e-mail: ewa_jakubczyk@sggw.pl
46 E. Jakubczyk et al.
was considered. Force-deformation curves for an uniaxial
compression test were recorded for crackers at various water
activity (aw =0.14-0.80) [Kohyama et al., 1997]. The curves
became smoother and the maximum force decreased with the
increase in water activity. Roudaut et al. [1998] studied texture
properties of crispy bread as a function of water content using
a compression test. They observed plasticizing effects of water
in a range of water content between 3 and 9%; then up to 11%,
there was an apparent hardening of the material. Beyond wa-
ter content of 11%, the apparent modulus decreased and the
softening effect of water became dominant. In some cases, the
antiplasticizing effect is observed. Adsorbed water causes an
increase in mechanical resistance of the material and reduces
its brittleness. Marzec [2002] reported that failure stress of
flat wheat and rye bread increased as moisture was adsorbed
and reached a peak at an aw between 0.5-0.6. Baked and ex-
truded cereal products are generally in the glassy state, since
cooking is accompanied by the disappearance of most crystal-
line structures of native starch. Cereal products stored above
their glass transition temperature undergo changes which are
manifested, among others, by alterations of their mechanical
properties. Cellular products may thicken and their mechani-
cal strength can increase [Roudaut et al., 1998].
The mechanical properties and fracture behaviour of the
crispy food products are strongly affected by their structure.
Microscopy can provide information about structure of cellu-
lar material. The most commonly used technique to determine
bread structure is based on the light microscopy. The shape
and size of gas cells is an important quality indicator of cellu-
lar structures of bread crumb [Scanlon & Zghal, 2001]. Agu-
ilera et al. [2000] used hot stage light microscopy to elucidate
changes in starch and simultaneous development in cellular-
ity during frying potato chips. Electron microscopy is often
used to study the morphology of cell walls and their thickness.
SEM pictures of apple chips showed that the samples with
thicker cell walls and larger internal voids were judged crispier
[Sham et al., 2001]. Katz & Labuza [1981] studied the ef-
fect of water activity on the structural characteristics of crispy
snacks. Micrographs of popcorn showed cellular collapse at
a water activity as high as 0.75.
As demonstrated above many factors affect the texture of
cellular food products. Moreover, the knowledge of those pa-
rameters is important in determining real material properties
and also in predicting behaviour of products during storage.
Extruded and baked cereal products are very popular. Their
major attraction to consumers, apart from their nutritional
advantages, is their crispy texture. The loss of crispness in
foods can be caused by an increase of moisture due to water
sorption during storage of dry crisp bread. The aim of this
work was to obtain better understanding of the relationship
between water activity of crisp bread and its mechanical prop-
erties and structure. The characteristics of the effect of water
activity on mechanical parameters and structure can be used
to predict shelf life and quality of crisp bread.
MATERIALS AND METHODS
Wholegrain rye crisp bread and fibre crisp bread (Barilla
Wasa, Germany) made of wholegrain rye flour, wheat bran,
oat meal and sesame seeds were purchased in a local mar-
ket. Typical rectangular-shaped crisp bread had a size of
111 × 60 mm and was 4 mm thick. Samples were equilibrated
over saturated salt solutions in desiccators to water activity in
the range from 0 to 0.75 at 25oC. Water activity was measured
with the use of a Hygroskop DT (Rotronic, Switzerland) with
accuracy of ±0.001 after 49 days of storage, while water con-
tent of the samples was measured by drying according to the
Polish Standard [PN-84/A-8636].
Mechanical properties of the breads examined were mea-
sured by a three-point loading bending test. Samples were
placed on two supporting parallel bars situated 50 mm apart.
The loading bar connected to a crosshead of a Zwick Ma-
chine 1445 (ZWICK GmbH, Germany) was used to deform
the samples to the moment of their break. The bending test
for crisp bread was done at a deformation rate of 20 mm/min
with at least 9 replicates on the whole slice of crisp bread.
Force versus deformation data was recorded, analysed and
some mechanical indices were calculated.
Fracture stress σf was calculated from the equation [Kim
& Okos, 1999]:
2
3
2
f
FL
bt
s=
where: L – distance between the supports (m); F – fracture
force (N); b – width of the sample (m); and t-thickness of the
sample (m).
Deformability modulus EB was calculated as follows:
3
3
4
B
dF L
Edbt
d
æö
æö
÷
ç
÷
ç÷
=×
֍
ç÷
֍
ç÷
ç
èø
èø
where: dF/dδ- – initial slope of force – deformation curve.
Fracture strain εf was calculated from the following equa-
tion:
ma x
2
6
f
t
L
d
e=
where: δmax – deformation at fracture (m).
The fracture work (mJ) was calculated as the area under
the bending curve: force (N)- deformation (mm).
Environmental scanning electron microscopy was used to
investigate the microstructure of each commercial crisp bread
type at water activities of aw~0.28 and 0.56. The microstruc-
ture of the samples was observed in a scanning electron mi-
croscope Philips XL30ESEM TMP at accelerating voltage of
25 kV in high-vacuum mode (0.7 mm Hg). The microscopy
study was done at the Laboratory of Electron Microscopy of
Warsaw Agricultural University.
RESULTS AND DISCUSSION
In most literature references describing the effect of wa-
ter activity on textural properties [Sauvageot & Blond, 1991;
47
Water activity, mechanical properties and structure of crisp bread
Roudaut et al., 1998] it has been noticed that samples stored
over salts solutions, which assure relative humidity of the at-
mosphere, achieved moisture equilibration within a particular
period of time, usually between 1 and 3 weeks [Heidenreich et
al., 2004]. Rye and fibre crisp breads placed in the desiccators
had water activities in the range of 0.030 to 0.612 (Table 1).
However, the samples did not reach their particular assumed
water activity after 49 days of storage. A significant difference
in water activities between values obtained by the product
and of the environment in the desiccators was very evident at
high relative humidity. Research conducted by Marzec [2006]
demonstrated that rye extruded bread achieved water activity
moisture equilibration after 21 days of storage. The sorption
isotherms of wheat extruded bread have shown that 77 days
of storage were enough for moisture equilibration. The pres-
ence of one ingredient affects the capacity of water adsorption
by others ingredients. Water activity and moisture content of
the purchased samples were measured immediately after re-
moving them form packaging. As reported in Table 2, the aw
of rye and fibre breads was very similar but the samples ex-
hibited differences in water content. This was probably due
to the chemical composition of the breads. The fibre bread
contained whole sesame seeds and oat meal, especially on the
surface layer of the bread. A more heterogenous structure of
fibre crisp bread, than that of the rye crisp bread, could influ-
ence its mechanical properties (Table 2). The higher values of
the fracture stress and deformability modulus were observed
for fibre crisp bread but the differences were not statistically
significant (coefficient of variance 10-28%).
The influence of water activity on the bending-breaking
behaviour of rye crisp bread is demonstrated in Figure 1. It
shows the force versus deformation for aw of 0.030, 0.255,
0.453 and 0.612. For clarity, only one of the replicates at a wa-
ter activity has been selected for the figure. It can be seen from
the curves that brittle behaviour observed for crisp bread at
low water activities was characterised by multiple peaks. Sal-
eem [2005] observed that curves obtained from three-point
bending tests of biscuits gave more than one peak, which
could be attributed to progressive breakdown of the cellular
structure of the material. The low aw resulted in jaggedness of
the force-time curves. This phenomenon was strongly evident
for extruded corn-rye bread at an aw range 0.283-0.458 [Le-
wicki et al., 2004] and for extruded flat bread with 5.3 and 9%
moisture [Fontanet et al., 1997]. In rye crisp bread increasing
water activity from 0.030 to 0.453 resulted in a 2-fold increase
of the deformation at which the sample broke. Increasing wa-
ter activity smoothed out the bending curves, which indicated
that less micro-breaking events occurred. Above aw of ~0.4
increase of water activity decreased the breaking force and ex-
tended the deformation at fracture.
The mechanical properties of fibre crisp bread were similar
to those observed for rye crisp bread. The increase in force and
deformation at which breaking occurred was the result of in-
creasing water activity. Although, the shape of the curves and
the general tendency to smoothing the curves were similar to the
previously described for rye bread, the plastic behaviour of fibre
crisp bread occurred at higher water activity than for rye bread.
Decreasing the breaking force with increasing water activity was
observed above water activity of ~0.3 for fibre bread.
TABLE 1. Characteristics of crisp bread equilibrated to different water
activity.
Type
of bread
Water activity
in desiccator
Water activity
of crisp bread
Water content
in crisp bread
(%)
Fracture
work of crisp
bread (mJ)
Rye
00.030 (0.008)* 1.62 (0.36) 3.54 (0.85)
0.225 0.255 (0.011) 5.69 (0.09) 5.54 (1.74)
0.328 0.312 (0.015) 6.03 (0.34) 5.78 (1.32)
0.432 0.380 (0.012) 7.32 (0.03) 6.01 (0.75)
0.529 0.453 (0.011) 8.53 (0.10) 5.51 (0.76)
0.648 0.531 (0.006) 10.44 (0.18) 5.44 (1.09)
0.753 0.612 (0.002) 11.94 (0.09) 5.60 (0.91)
Fibre
0 0.039 (0.002) 2.14 (0.23) 4.04 (1.17)
0.225 0.237 (0.003) 5.22 (0.03) 4.67 (0.91)
0.328 0.319 (0.011) 6.16 (0.08) 8.50 (1.31)
0.432 0.399 (0.008) 6.70 (0.14) 6.48 (1.13)
0.529 0.389 (0.001) 8.03 (0.09) 5.80 (0.83)
0.648 0.525 (0.011) 10.05 (0.01) 6.11 (1.54)
0.753 0.560 (0.003) 10.85 (0.18) 8.00 (1.25)
*Standard deviations for average values of parameters are presented in
brackets.
TABLE 2. Mechanical properties of crisp bread determined directly for purchased sample.
Type
of bread
Water
activity
aw
Water content (%)
Fracture
stress
(kPa)
Fracture work
(mJ)
Deformability
modulus (MPa)
Fracture strain
(%)
Rye 0.274 (0.008)* 6.36 (0.01) 1032.8 (106.0) 7.51 (1.89) 95.5 (27.1) 1.04 (0.27)
Fibre 0.280 (0.002) 8.03 (2.29) 1069.5 (155.1) 7.21 (0.90) 100.6 (31.5) 0.92 (0.25)
*Standard deviations for average values of parameters are presented in brackets.
FIGURE 1. Breaking curves of rye crisp bread at different water activity.
48 E. Jakubczyk et al.
The fracture stress as a function of crisp bread water activ-
ity for rye and fibre crisp breads is shown in Figure 2. The frac-
ture stress of fibre and rye crisp bread was strongly related to
water activity. At low water activities, increasing the water ac-
tivity yielded a higher fracture stress. The fracture stress gen-
erally describes the fracture strength of products. Hence, the
fracture strength was the largest at critical water activity, i.e.
0.255±0.011 for rye bread and at aw = 0.319±0.011 for fibre
bread. After these values, the samples became more deform-
able and pliable and the higher the water content, the lower
values of the fracture stress were observed.
Adsorption of water resulted in strengthening of the inves-
tigated materials and reduced their brittleness. An increase in
strength along with an increase in water activity was explained
by Harris & Peleg [1996] as a result of partial plasticization of
air cell wall material, which increases the structure’s cohesion,
hence, hardness. The hardening of extruded crisp bread in
the range of water contents from 9 to 11% was also observed
by Fontanet et al. [1997] and Marzec & Lewicki [2006]. These
authors suggested that the mechanical behaviour of extruded
bread depended on the short range structural reorganization
caused by the increased molecular mobility. The changes of
starch and the mechanical behaviour of flat crisp bread were
a result of the extrusion process. In our work, the investigated
crisp breads were produced by baking a dough consisting of
a mixture of flour and water, with small amounts of salt and
some other ingredients (e.g. wheat bran). Therefore, the level
of critical water activity after which products lose toughness
was stipulated as 0.255 for rye and 0.319 for fibre crisp breads.
Water activity above these values affected the texture of crisp
breads by softening the starch/protein matrix. The fibre bread
was also made of rye flour, but the added sesame seeds and
oat meal altered the strength of the material. The fracture
stress at critical water activity for fibre crisp bread was about
12% higher than that for the rye product.
The effect of water activity on the deformability modu-
lus and fracture strain of rye and fibre bread is presented in
Figures 3 and 4. Figure 3 shows that for rye bread the rela-
tionships between deformability modulus, fracture strain and
water activity were linear. The deformability modulus of rye
bread decreased as water activity increased. The adsorbed
water affected the loss of stiffness and brittleness of the sam-
ples. A similar effect of water activity on Young’ modulus and
fracture strain was observed for biscuits [Saleem et al., 2005]
and wafers [Martinez-Navarette et al., 2004]. The decrease
of Young’s modulus was explained by increasing moisture in-
duced by structural degradation. The small fracture strains
of the samples at low water activities were characterised by
an initial elastic behaviour at fracture. The increase in frac-
ture strain reflected the plasticization of crisp bread by water.
The higher the water activity the more plastic the material
was. From a water activity of 0.039 the deformability modu-
lus and fracture strain of fibre bread remained constant until
a water activity of 0.237 (Figure 4). Above this water activ-
ity a decrease in deformability modulus values and a gradual
increase in fracture strain were observed as a result of in-
creasing water activity. Gondek & Marzec [2006] observed a
similar effect of water activity on sensory attributes of rye crisp
bread. The material having water activity in the range from
0 to 0.65 was subjected to Quantitative Descriptive Analysis
(QDA). A relationship between the majority of kinesthetic at-
tributes (overall quality and plasticity) and water activity re-
mained constant in the water activity range of 0.198–0.308.
The increase of water activity above ~0.31 caused a gradually
decrease of total quality and an increase in plasticity which
described the level of plasticity perceived at the first bite.
The average and standard deviation in the values for frac-
ture work at different water activities are presented in Table 1. FIGURE 2. Fracture stress as a function of crisp bread water activity.
FIGURE 3. Effect of water activity on deformability modulus and frac-
ture strain of rye bread.
FIGURE 4. Effect of water activity on deformability modulus and frac-
ture strain of bre bread.
49
Water activity, mechanical properties and structure of crisp bread
The general trend of a change of work with a change in water
activity was not consistent. An increase of water activity of
crisp breads caused an increase of the fracture work, and the
work reached a maximum value at aw = 0.432 for rye crisp
breads and at 0.328 for fibre bread, and after that the values
of work varied.
Water activity is an important factor influencing mechani-
cal behaviour of brittle food. Adsorbed water is supposed to
behave as a lubricant at high water activities and reduce the
friction between surfaces, which results in low strength. This
can be explained by differences in the microstructure of the
investigated products and composition of breads. Figures
5, 6, 7 and 8 demonstrate the effect of water activity on the
structure of rye and fibre crisp breads, respectively. The en-
vironmental scanning microscopy was used to analyse struc-
ture of bread samples. This microscopic method is suitable
for moist samples due to nondestructive preparation tech-
nique. A photograph of a typical cross section of commercial
rye bread, which was taken directly from a package at an aw of
0.274, is shown on Figure 5. In rye crisp bread the pores were
irregular, but most of them had characteristic sharp edges.
The structure of bread equilibrated to water activity of 0.560
(Figure 6) contained more smooth structures. In the moist
rye bread the pores became rounded, and thickness of cell
walls increased significantly. Crisp bread adsorbed about 6 g
of water per 100 g of solids in the range of activities between
0.274 and 0.560. This amount of water was sufficient to tran-
sition from a crisp to a non-crisp state. Katz & Labuza [1981]
observed that only 3 g of water per 100 g d.m. were needed to
be absorbed to lose the crispness of cellular snacks. Adsorbed
water softened the structure, which was shown by the loss of
mechanical resistance of rye bread.
The inner structure of commercial fibre bread (Figure 7)
was similar to that observed for rye bread, both breads were
very porous but fibre bread seemed to contain more irregu-
lar and larger cells. The composition of fibre bread was more
complex, some ingredients as wheat bran, oat meal, sesame
seeds, fragmented and whole grain of rye could play an im-
portant role in the formation of a harder structure. The mi-
crostructure of fibre bread at aw=0.280 differed form that
observed at water activity of 0.560. As expected, moist fibre
bread showed more round cells and thicker cell walls than
those observed for the material at low water activity (Figure
8). Moreover, the moist fibre bread was visibly collapsed in
the outer layer of the sample. The fibre bread was plasticized
by the adsorbed water, which resulted in decreasing crispness
of the material. Katz & Labuza [1981] postulated that water
adsorbed by popcorn dissolved some of intercellular glue-like
FIGURE 5. Scanning electron micrograph of rye crisp bread at
aw=0.274.
FIGURE 6. Scanning electron micrograph of rye crisp bread at
aw=0.560.
FIGURE 7. Scanning electron micrograph of bre crisp bread at
aw=0.280.
FIGURE 8. Scanning electron micrograph of bre crisp bread at
aw=0.560.
50 E. Jakubczyk et al.
material and gelatinised starch on the cell walls. At higher wa-
ter activity the starch granules were probably more swollen
and more amylose leached out.
CONCLUSIONS
The changes of water activity were responsible for the me-
chanical properties of rye and fibre crisp breads. Increasing
water activity caused an increase of the fracture stress at water
activities in the range form 0.030 to 0.255 for rye bread and
from 0.039 to 0.319 for fibre bread. The hardening of samples
was probably connected with structural rearrangements of
biopolymers and adsorbed water seemed to induce the new
matrix of proteins and carbohydrates. It seems that differ-
ences in the structure of crisp bread could play an important
role in the formation of more harder texture. An increase in
water activity above these critical values caused softening
and flowability of crisp breads. The decrease of deformability
modulus accompanied by an increase of the fracture strain
were explained by increasing moisture inducing structural
degradation. The high water activity affected the more plastic
behaviour of samples and loss of brittleness. At high water
content, texture became soft and rubbery. Moreover, at a mac-
roscopic level water had a plasticizing effect which resulted in
smoothing cell structures and increasing thickness of the cell
walls. The rye bread had a lower resistance to deformation
than the fibre bread, probably due to differences in composi-
tion, for the added grain ingredients yielded a more heteroge-
neous structure.
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51
Water activity, mechanical properties and structure of crisp bread
ZALEŻNOŚĆ MIĘDZY AKTYWNOŚCIĄ WODY A WŁAŚCIWOŚCIAMI MECHANICZNYMI I STRUKTURĄ
PIECZYWA CHRUPKIEGO
Ewa Jakubczyk, Agata Marzec, Piotr P. Lewicki
Katedra Inżynierii Żywności i Organizacji Produkcji, Szkoła Główna Gospodarstwa Wiejskiego w Warszawie
Celem pracy było określenie wpływu aktywności wody na strukturę i właściwości mechaniczne pieczywa chrupkiego: żytniego i pieczywa
żytniego wysokobłonnikowego z mąki pełnoziarnistej, z dodatkiem otrąb pszennych, płatków owsianych i ziaren sezamu. Pieczywo było prze-
chowywane w środowisku o aktywności wody w zakresie 0-0,75. Właściwości mechaniczne (moduł odkształcalności, naprężenie i odkształcenie
łamiące oraz pracę łamania) przeprowadzono przy wykorzystaniu trójpunktowego testu zginania. Mikrostrukturę pieczywa chrupkiego dla dwóch
aktywności wody zbadano za pomocą mikroskopii skaningowej. Aktywność istotnie wpływała na właściwości mechaniczne pieczywa chrupkiego
(rys. 1). Wzrost aktywności wody w zakresie od 0,030 do 0,255 dla pieczywa żytniego i dla pieczywa wzbogaconego w błonnik 0,039-0,319 wpły-
wał na wzrost wartości naprężeń łamiących (rys. 2). Wzrost aktywności wody powyżej tych wartości powodował mięknięcie pieczywa i gwałtowny
spadek wartości modułu i naprężenia łamiącego (rys. 3, 4). Zdjęcia mikroskopowe wskazują istotny wpływ aktywności wody na strukturę pieczywa
chrupkiego (rys. 5-8). Pieczywo żytnie charakteryzowało się mniejszą odpornością na odkształcenie niż pieczywo o wyższej zawartości błonnika,
które zawierało w swoim składzie otręby i ziarna, to wpływało na uzyskanie pieczywa o niejednorodnej strukturze.
