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Cereal Chemistry. 2019;96:994–1003.
wileyonlinelibrary.com/journal/cche
1
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INTRODUCTION
During the past years, many food products containing
sprouted grains appeared on the market. Consequently, the
use of sprouted grain to produce bread, pasta, breakfast cere-
als, biscuits, and porridge was studied and discussed (Richter,
Christiansen, & Guo, 2014; Singkhornart, Gu, & Ryu, 2013).
In order to achieve this desired incorporation in a controlled
manner, it is important to understand how the raw material
changes during the sprouting process. This is necessary to
understand the possible consequences of the incorporation of
sprouted grains for final product properties.
The term sprouted grains is used to refer to germinated
grains with radicles and coleoptile with a length greater than
that of the most important reference product, the green malt
in malting for brewing purpose. The coleoptile of green malt
is only allowed to grow to a maximum of two‐thirds of the
grain length under controlled conditions. In contrast, during
sprouting of grains further growth of the seedling is toler-
ated up to the onset of the photosynthetic metabolic activity.
Received: 21 December 2018
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Revised: 19 July 2019
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Accepted: 30 July 2019
DOI: 10.1002/cche.10203
RESEARCH ARTICLE
Sprouting of oats: A new approach to quantify compositional
changes
JuliaKrapf1
|
FranziskaKandzia1
|
JulianeBrühan1
|
GoeranWalther2
|
EckhardFlöter1
This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original
work is properly cited.
© 2019 The Authors. Cereal Chemistry published by Wiley Periodicals, Inc. on behalf of AACC International, Inc.
1Department of Food Process
Engineering,Technische Universität Berlin,
Berlin, Germany
2General Mills, Cereal Platform, James
Ford Bell Technical Center,R&D, Cereal
Technology, Golden Valley, MN, USA
Correspondence
Julia Krapf, Department of Food Process
Engineering, Technische Universität Berlin,
Seestr. 13, 13353 Berlin, Germany.
Email: [email protected]
Abstract
Background and objectives: The aim of this research was to gain a deeper insight
into the effect caused by the addition of sprouted oat to food products. The effect
of temperature and duration of the sprouting process was systematically studied by
sprouting oat grains between 10 and 30°C for up to 3days.
Findings: Overall, it was found that temperatures between 20 and 25°C yield the
most dramatic changes in the properties of sprouted oats. Based on the data, a simple
system to characterize the sprouting progress by a visual inspection of the lengths of
the coleoptile and radicles was developed. This degree of sprouting (DoS) was cor-
related with further grain properties.
Conclusions: It was found that an exponential relationship between the DoS and
grain properties existed. Furthermore, the observed increase in the reducing sugar
content (up to 14.6g/100g) with increasing DoS was closely related to the increase
in α‐amylase activity (up to 25U/g).
Significance and novelty: The good predictive power found indicates that the ap-
plication of the concept degree of sprouting could develop into a reliable characteri-
zation method for sprouted grains usable for product development and specification.
KEYWORDS
degree of sprouting, oat, sprouting, sprouting effects
|
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KRAPF et Al.
Sprouting, hence further progressed germination, gives rise
to significant metabolic changes. This offers the opportunity
to produce sprouted grains according to desired objectives,
such as improved nutritional profiles.
Basically, during sprouting the embryo generates a new
plant by metabolizing carbohydrates, allowing the growth
of the radicles and coleoptile (Kunze, 2011). Therefore, hy-
drolases, for example, amylases and proteinases, are secreted
from the aleurone layer into the endosperm of the grain. As
a consequence, starch and proteins are degraded in the endo-
sperm into transportable sugars, for example, glucose, pep-
tides, and amino acids. In the embryo, these substances are
transported into the growing regions for the synthesis of a
first leaf and radicles (Bewley, 2001). Sprouting only takes
place at a sufficiently high moisture content (>30%), at bene-
ficial temperatures, and under aerobic conditions. Controlling
these conditions, the biological processes in the grain can be
directly affected (Narziss & Back, 2012).
It is well established that the sprouting process pos-
itively affects the nutritional value of the grains. This fact
is used in different technical applications, for example, the
hydrothermal activation of grains for the bread production
(DE3038463A1, 1980). The activation of the grain results in
an enhancement of the vitamin and mineral content in the
bread. Moreover, the taste of the bread is improved.
A significant increase in the vitamin content in grains
due to sprouting was also reported in many other studies
(Harmuth‐Hoene, Bognar, Kornemann, & Diehl, 1987; Yang,
Basu, & Ooraikul, 2001; Žilić et al., 2014). Tian et al. (2010)
found that, next to vitamins, also the total polyphenol content
in oat increased by 100% after 3days of sprouting at 16°C.
Xu et al. (2009) also studied the changes in the phenolic acids
after different steeping and sprouting times of huskless oat.
They found a 60% increase in the total phenol content after
2days of sprouting at 16°C. Due to physiological changes
during sprouting, stress is exerted on the grain and the redox
equilibrium is disturbed. This way, the formation of second-
ary metabolites like antioxidants such as phenolics and vita-
mins is stimulated to protect the seedling (Swieca & Dziki,
2015). It was stated that sprouted grains with increased levels
of antioxidants can be applied in products to suppress rancid-
ity and color changes (Xu et al., 2009).
An additional benefit of the sprouting process is the reduc-
tion of the phytic acid content (Tian et al., 2010). Since phytic
acid hampers the bioavailability of minerals, its content in
bread is typically reduced during the sourdough leavening
process (Schuchmann & Schuchmann, 2012). In product con-
cepts not suited for sourdough processing, the usage of flour
from sprouted grains could be a means to reduce the level of
phytic acid.
The sprouting process has, however, not only positive
effects. During the sprouting process, cell wall material,
especially β‐glucan, a soluble fiber with health benefits, is
degraded as well. β‐glucan increases the viscosity in the in-
testine and causes a retarded absorption of glucose and hence
reduced surges of the blood sugar level (Anttila, Sontag‐
Strohm, & Salovaara, 2004).
Wood et al. (1994) studied the acid hydrolysis of oat gum
drinks for 15 and 60min. The acid‐hydrolyzed drinks and
the reference had the same β‐glucan concentration but dif-
fered in viscosities and showed different glucose responses.
The strong correlation between glucose response and reduced
viscosities found indicates that not only the total β‐glucan
concentration but also the molecular weight distribution of
β‐glucan is important.
Wilhelmson et al. (2001) studied degradation of β‐glucan
during sprouting of oat grains as a function of temperature
and time depending. The β‐glucan content was most reduced,
by 75%, after 3days of sprouting at 25°C. Under the same
conditions, the average molecular weight reduced by 38%
compared to the initial value.
Another problem arising during sprouting is microbio-
logical activity. The usual sprouting conditions, such as long
steeping stages, high moisture contents, and possible tempera-
tures of 25–30°C, benefit the growth of microorganisms and
can result in unwanted fermentation processes. Consequently,
bacteria, mold, and yeast growths were observed during
sprouting and dormant spores might be activated as well
(Helland, Wicklund, & Narvhus, 2002; Wilhelmson et al.,
2001).
Tian et al. (2010) studied the length of the coleoptile and
radicles of 30 sprouted oat kernels by ruler and did not find
any correlation with other grain characteristics except for
color changes. The work presented here documents an at-
tempt to systematically relate the changes in the composition
of sprouted grains to the progression of the sprouting pro-
cess. Grains were analyzed after sprouting for defined time–
temperature combinations. In order to quantify the degree of
sprouting, a new method based on the length of the coleoptile
was developed and employed in an effort to correlate prog-
ress of the sprouting process and composition. The targeted
simple approach to categorize the sprouted material would
have the advantage to define and standardize specifications
for sprouted material, which are directly verifiable and yet
ensure a successful product application.
2
|
MATERIALS AND METHODS
The huskless oat “Gehl,” cultivated in 2016 in Canada, was
used throughout the study. The grains were stored in sealable
containers at 10°C.
During preliminary studies, different methods to evaluate
the sprouting progress were tested. Finally, the grains were
sprouted at different temperatures (10, 14, 20, 25, and 30°C)
and for different times (1, 2, and 3days). A temperature of
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KRAPF et Al.
14°C is applied because this setting is usually used in the
malting step for brewery purposes (Jacob, 2016). During the
sprouting process, the changes in the content of respectively
vitamin C, β‐glucan, and reducing sugar were monitored.
Additionally, the α‐amylase activity was studied as a marker
for the total enzyme activity.
2.1
|
Standard sprouting process at
laboratory scale
For the steeping and sprouting process, 500g of oat grains
was washed for 30min under running tap water in order to
clean the grain surface from microorganism to minimize mi-
crobiological growth. Afterward, the grains were steeped in
closed containers filled with water (so that all grains were
covered with water): 4.5‐hr wet steeping, 19‐hr air rest, and
4‐hr steeping, all at 20°C (Jacob, 2016). After the steep-
ing step, the grains were drained and put on a metal sheet.
The steeped grains were covered with cling film and put in
a climate cabinet (Lovibond 220P‐02) in the dark. During
the sprouting step, the grains were washed once a day using
a sieve. Due to the washing process, the water content was
kept constant and checked by using the moisture analyzer
MA35 (Sartorius).
At the end of the different sprouting periods, the grains
were deep‐frozen (Siemens Comfort Plus, −20°C) and sub-
sequently freeze‐dried (Beta 1‐16—Christ) for approximately
60hr until a final moisture content between 4% and 8% was
reached.
Prior to analysis, the oat grains were ground in a speed
rotor mill (Pulverisette 14—Fritsch) with a sieve ring of
0.5mm at 3220 g.
2.2
|
Study of different methods to
characterize grain growth progress
By use of visual and gravimetric measurements using dif-
ferent sprouted oat material, an attempt was made to find an
easy systematic characterization method for the quantifica-
tion of the progression of the sprouting process.
For the different samples, the 1,000 kernel weight was
determined gravimetrically by counting 100 kernels and mul-
tiplying the result by 10. The dry matter was analyzed using
the moisture analyzer MA35 (Sartorius). Determinations
were done in duplicate.
The mass percentage of the radicles and coleoptile of the
total grain was determined by cutting off radicles and coleop-
tile with a dissecting needle and weighing the undried grain
with and without the radicles and coleoptile. The determina-
tion was performed in duplicate.
The degree of sprouting was determined by visually clas-
sifying the length of the coleoptile and radicles of 100 kernels
by dividing them into the six categories shown in Figure 1. The
determination was done in triplicate. On each day of sprouting,
an average degree of sprouting was calculated as the sum of
relative occurrence of the different classes (DoSi) multiplied by
its respective degree of sprouting (i):
2.3
|
Determination of the α‐ and β‐
amylase activity
The α‐ and β‐amylase activities were determined by using
the Megazyme (2012) Malt‐Amylase assay procedure K‐
MALTA 05/15. Determinations were done in duplicate.
2.4
|
Determination of the ascorbic
acid content
The vitamin C content was determined according to the
Indophenol Method (Nielsen, 2003). For the determination
of the vitamin C content in flour, a modified dilution factor
of eight had to be applied. The sprouted flour sample was
dispersed in a mixture of 30g/L metaphosphoric acid and
8% (v/v) acetic acid and centrifuged at 3,000g. A volumet-
ric sample of the resulting supernatant was diluted and used
for titration according to the method. The procedure was ex-
ecuted in duplicate per specimen.
2.5
|
Determination of the reducing
sugar content
The reducing sugar content was determined using DNS (3,5
dinitrosalicylic acid) in combination with a colorimetric
(1)
Average DoS
=
5
∑
i=0
i⋅relative occurrunce (DoSi
)
FIGURE 1 Definition of the degree
of sprouting of oat grains by the lengths of
their coleoptile and radicles
|
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KRAPF et Al.
analysis. Determinations were done in duplicate. In detail,
the sprouted flour samples (1g) were mixed with 5ml of
a mixture of 40% (v/v) ethanol and 60% (v/v) of a 10mM
copper chloride solution to extract the reducing sugars.
After shaking the mixture for 10min, the suspension was
centrifuged for 15min at 3,000g (Heraues, Labofuge 200).
This procedure was repeated twice. The collective super-
natant, three subsequent extractions of the same material,
were diluted and filled to 25ml with the above‐mentioned
ethanol/copper chloride solution mixture. By addition of
0.625g polyvinylpolypyrrolidone to the solution, all phe-
nols present were precipitated. The precipitate was filtered
off (Tian et al., 2010), and 1ml of the filtrate was mixed
with 1ml of an aqueous solution containing 10g/L DNS,
16g/L sodium bicarbonate, and 300g/L potassium sodium
tartrate. After shaking this mixture for 10min at 100°C, the
solution was diluted with 5ml distilled water. The reduc-
ing sugar content was determined spectrophotometrically
(Spekol 1300—Analytik jena) at 545 nm. For the cali-
bration, different concentrations of maltose monohydrate
were used. The reducing sugar content determination is
thus related to the reducing potential of maltose. However,
glucose exhibits a reducing potential, which is identical to
maltose per molecule.
2.6
|
Determination of β‐glucan content
The β‐glucan contents of the differently sprouted oat sam-
ples were determined by using the Megazyme (2017)
Mixed‐Linkage Beta‐Glucan assay procedure (McCleary
Method—K‐BGLU 02/17; AACC Method 32‐23.01).
Determinations were done in duplicate.
2.7
|
Statistical evaluation (ANOVA)
The statistical evaluation of the methods tested to evaluate
the sprouting process, the temperature and time effect on se-
lected grain properties, and the dependence of selected grain
properties and the degree of sprouting was performed using
Microsoft Excel 2016. The p‐value (probability of error) was
calculated by analyzing the experimental data by means of
ANOVA (analysis of variance) using a single‐factor variance
analysis. A level of significance (α) of .05 was chosen.
The significance of the temperature effect was analyzed
by using the data of the 3‐day sprouted samples, and the sig-
nificance of the temperature effect was analyzed by compar-
ing the data of the samples sprouted at 20°C.
3
|
RESULTS AND DISCUSSION
3.1
|
Statistical evaluation of experimental
data
Table 1 presents the p‐values of all properties considered.
These were calculated as part of the ANOVA. Since all p‐
values are lower than the level of significance, the found dif-
ference can be considered significant.
3.2
|
Evaluation of different methods to
characterize the sprouting progress
Different properties of the grains were evaluated for their us-
ability to characterize the progress of the sprouting process.
This evaluation of the different approaches was done based
on the β‐glucan content as an output property. This marker
was chosen because of its importance due to health‐promot-
ing and functional property effects (Choi et al., 2012). A first
approach to characterize the progress of the sprouting pro-
cess is based on the visual inspection of the lengths of the
coleoptile and radicles.
In Figure 1, the definition of the degree of sprouting as
used in this study to identify the sprouting progress is shown
and the different development stages of the oat grains during
the sprouting process can be seen. The length of the coleop-
tile was selected as a criterion of the categorization of the
degree of sprouting.
TABLE 1 p‐Values from statistical analysis (ANOVA) of all studied properties
β‐glucan content
(Figure 1)
Properties in dependence on the
degree of sprouting
Time effect (1–3days,
20°C)
Temperature effect
(10–30°C, 3days)
Degree of sprouting 8.46E−06 4.64E−05 7.78E−10
Coleoptile and radicle
percentage
3.52E−09
1,000 kernel weight 7.36E−03
α‐amylase 5.26E−11 1.84E−05 1.27E−08
Reducing sugar content 4.67E−10 4.31E−05 9.45E−08
Vitamin C content 4.85E−04 5.00E−02 3.07E−04
β‐glucan 8.46E−06 3.27E−03 1.19E−03
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KRAPF et Al.
Grains of degree 0 do not show any radicle or coleoptile
growth. Degree 1 characterizes grains with visible embryos
(small white point), while the radicles and coleoptile are not
visible. Degree 2 describes grains already showing a devel-
oped embryo emerging from the seed coat. The grains of de-
gree 3 reveal coleoptile lengths of at least half the oat grain
length. Degree 4 represents coleoptile lengths between half
and a full grain length. Under degree 5, grains with a coleop-
tile longer than a full grain length are summed up.
Alternatively, to the degree of sprouting it is conceivable
to determine the 1,000 kernel weight (dry matter based) to
characterize differently sprouted grains. Another alternative
to describe the progress of the sprouting process is the deter-
mination of the weight fraction of both the radicle and cole-
optile of the full grain.
In Figure 2, the β‐glucan content is shown as a function
of three possible properties to characterize the progression of
the sprouting process, respectively.
From the properties evaluated, the 1,000 kernel weight
corresponds to the least with the β‐glucan content (R2=.63).
Both other methods show a high degree of correlation: degree
of sprouting (R2=.98) and weight fraction of coleoptile and
radicles (R2=.90). Even though both correlations with the β‐
glucan content were found to be very good, only the degree of
sprouting was considered for further consideration. Reason to
do so is the simplicity of the procedure, which renders it less
prone to errors. An obvious downside is the integer nature of
this parameter. However, the “degree of sprouting” method
was used as lead parameter to correlate with changes in grain
properties due to sprouting.
3.3
|
Influence of sprouting
temperature and time
The degree of sprouting as defined above for subsets of oats
in a single sprouting process was used to quantify the oat
sprouting process at different temperatures and for different
periods of time. For each time–temperature combination for
the sprouting process the grain population exhibited a spe-
cific distribution of the degree of sprouting.
The number fractions of the grains with different degrees
of sprouting are shown in Figure 3. Here, the results obtained
for the five different sprouting temperatures after 3days of
sprouting are depicted. From the distribution of degrees of
sprouting within a sample, the average degree of sprouting
can be derived according to Equation 1. These values are rep-
resented in Figure 3 by diamonds. The error bars are based
on counting three independent samples from one sprouting
experiment. For the 3‐day sprouting period, the longest cole-
optile was observed for sprouting at 25°C. Sprouting at a tem-
perature of 20°C resulted in less vigorous sprouting. At 30°C,
the oat grains did practically not show any radicle growth.
The data gathered also allowed to determine the germin-
ability. The germinability is defined as the percentage of
grains reaching a degree of sprouting above 0. For all tem-
peratures investigated, the germinability after 3 days was
about 99%.
Figure 3 also reveals that around 20% of the grains which
were sprouted at 20 and 25°C have a coleoptile longer than
a full grain length (degree of sprouting 5). Less long coleop-
tiles developed at the other sprouting temperatures studied.
No standard deviation of the average degree of sprouting
is given in Figure 3, because the chart already illustrates the
contribution of different degree of sprouting within the sam-
ple to the average degree of sprouting. This illustrates how
homogeneously a sample had been sprouted. The consider-
ation of the homogeneity is an important point with respect
to a large‐scale sprouting operation. A narrow distribution of
the degree of sprouting within a production run would allow
for better control of product properties.
The data gathered reveal that a high average degree of
sprouting (e.g., 20 & 25°C) corresponds to a high standard
deviation and thus a low homogeneity. Vice versa, processes
with a low average degree of sprouting (e.g., sprouting at
30°C—average degree of sprouting 1.4) do not show a high
variation and are rather homogeneous. This was also found
for the standard malting temperature of 14°C. The choice for
this temperature is probably motivated by low risk for micro-
biological spoilage, homogeneous radicle growth and limited
losses due to radicle and coleoptile growth.
In Figure 4, the effect of the sprouting time and tempera-
ture on the average degree of sprouting is shown. One can see
that the sprouting started fastest for the oat which sprouted
at 20°C. The data indicate linear increase in the degree of
FIGURE 2 Correlation of degree of sprouting (●), coleoptile
and radicle percentage (■), and 1,000 kernel weight (dry matter based)
(▲) with the β‐glucan content; oat was sprouted for 3days at 20°C
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KRAPF et Al.
sprouting with time for the samples sprouted at 10, 20 and
25°C.
3.3.1
|
Effect of sprouting time and
temperature on oat properties
In Figure 5a–d, the effect of the sprouting temperature and
time on the different quality parameters of the sprouted
grains is illustrated.
In Figure 5a, the results of the α‐amylase analysis are
shown. The data reveal that after 1day, the α‐amylase ac-
tivities between the different temperatures did not differ
too much. After 3days however, the α‐amylase activities
at 20 and 25°C increased significantly to values one order
of magnitude larger than those for the other temperatures
(10, 14, and 30°C).
In contrast to the increase in α‐amylase activity during the
sprouting process, the analysis of β‐amylase activity revealed
no changes (data not shown) and the enzyme was apparently
not synthesized de novo.
In line with the data for the α‐amylase activities, the con-
tent of reducing sugars in oat increased most at sprouting tem-
peratures of 20 and 25°C (Figure 5b). Expectedly, the limited
α‐amylase activity at 10, 14, and 30°C corresponded to only
subtle increases in the reducing sugar contents. The limited data
available suggest a linear relation between the levels of reduc-
ing sugars and the duration of sprouting.
As can be seen in Figure 5c, the β‐glucan content is also a
function of the temperature and duration of the sprouting pro-
cess. At all sprouting temperatures studied, the β‐glucan con-
tent was decreased after 3days of sprouting. For a sprouting
temperature of 20°C, the degradation is most pronounced, al-
most halving the initial β‐glucan content to 3.9%. At sprout-
ing temperatures of 10 and 14°C, the β‐glucan content only
slightly decreased, confirming the findings by Wilhelmson
et al. (2001) that the β‐glucan content decreases less at low
sprouting temperatures.
In line with Lintschinger et al. (1997), vitaminC was cho-
sen as a marker for the general vitamin content because of
its high reactivity. No ascorbic acid was present in the native
grain. Upon sprouting, a significant increase in the ascorbic
acid content was found (Figure 5d). The highest levels were
found when sprouting at 20°C. Except for the sprouting tem-
perature of 30°C, all other sprouting temperatures also re-
sulted in increased levels of ascorbic acid.
3.3.2
|
Discussion of the effect of sprouting
time and temperature on property changes in
oat grains
The results gathered reveal a rather consistent picture, re-
vealing relations between the different grain properties. It
was shown that the different properties changed systemati-
cally with temperature and duration of the sprouting process.
During the sprouting process, a de novo synthesis
of α‐amylase in the oat grain was observed. This is most
FIGURE 3 Effect of the sprouting
temperature on the degree of sprouting after
3days
FIGURE 4 Effect of sprouting time and temperature on the
average degree of sprouting
1000
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KRAPF et Al.
pronounced at a sprouting temperature of 20°C. Since
the starch degradation relates to the α‐amylase activity,
the increase in the amount of reducing sugars followed a
corresponding pattern. The relationship of certain proper-
ties appears more complicated considering that sugars are
transported into the growth regions of the grain for further
development of the coleoptile and radicles. This suggests
that the coleoptile and radicle growth (input parameters for
the degree of sprouting) and the reducing sugars and α‐am-
ylase activity are interdependent.
The acceleration of the sprouting process on increas-
ing sprouting temperatures was also found for barley by
Müller (2015). Varying the sprouting temperature from 16
to 24°C resulted in a reduction of the sprouting time of
about 24hr per 4°C. It was further found that sprouting at
20°C yielded best results, which is in line with the results
presented here.
Progression of the sprouting process also resulted
in changes of the ascorbic acid levels. Ascorbic acid is
needed as protective antioxidant in the growing grain. The
increase in the vitamin C contents of oat during sprouting
(see Figure 5) is a function of several processes. In order
to terminate the dormancy and start the sprouting process,
reactive oxygen species have to be released. However, the
presence of these species results in an oxidative stress in
the cells. Moreover, the exposure to light also causes stress
in the grain inducing the synthesis of antioxidants, for
example, ascorbic acid (Pitzschke, Fraundorfer, Guggemos,
& Fuchs, 2015).
With respect to improve the nutritional value of sprouted
oats, the increase in vitamins is desired while the degradation
of beta‐glucan is considered a downside (El Khoury, Cuda,
Luhovyy, & Anderson, 2012). Consequently, optimizing the
sprouting process for best nutritional values would involve
balancing the levels of these two nutrients.
3.4
|
Study of oat having different
degrees of sprouting
Oat samples of varying degrees of sprouting were studied.
These grains were sprouted at 20°C for 3days and sorted
according to their degree of sprouting. In Figure 6, the data
on reducing sugar content, ascorbic acid content, β‐glucan
content, and α‐amylase activity in oat samples with each a
homogeneous different degree of sprouting (1–5) are shown.
In this context, a homogeneous sample means that it com-
promises only grains with the respective degree of sprouting.
The data reveal a systematic evolution of the α‐amylase
activity, ascorbic acid, β‐glucan, and reducing sugar contents
with increasing degree of sprouting. One could argue about
the correct choice of the mathematical function to be fitted to
the experimental data. It appears to be beyond the scope of
this work to formulate a model to describe the changes. The
choice of the function to be fitted to the data remains thus
FIGURE 5 Effect of time and
temperature during oat sprouting on the
changes in α‐amylase activity (a), in
reducing sugar content (b), in β‐glucan
content (c), and in vitamin C content (d)
|
1001
KRAPF et Al.
arbitrary. Even though linear regressions would also allow
to describe the data quite well, it was chosen to use simple
exponential functions. This choice was motivated by the na-
ture of the properties of the described reaction products. The
exponential fits show a quite strong correlation between the
response parameters as a function of the degree of sprouting.
It has to be noted though that the degree sprouting is not a
transformed reaction time.
Increased amounts of reducing sugars and ascorbic acid
were found particularly in the radicles and coleoptile (data
not shown). The ascorbic acid content in the radicles and co-
leoptile was four times higher than that in the grain without
the radicles and coleoptile. Hence, for the production of oat
flour having a high nutritional value it is of special interest
to leave radicles and coleoptile at the grains. The oat grains
which were sprouted for 3days at 20°C had an average de-
gree of sprouting of 3 (Figure 3); hence, the radicles and co-
leoptile contribute about 8% of mass.
These findings indicate that a fast visual determination of
the degree of sprouting allows to estimate, for example, the
ascorbic acid content without doing expensive experiments.
Moreover, the sweetness of the product can be estimated
based on the correlation between the degree of sprouting and
the reducing sugar content.
FIGURE 6 Changes in oat kernel
properties in dependence on the degree of
sprouting: 3‐day sprouting, 20°C
FIGURE 7 Parity plots for the
calculated and measured values of the
contents of reducing sugars, β‐glucan, and
ascorbic acid and α‐amylase activity of
samples of various sprouting conditions
1002
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KRAPF et Al.
3.5
|
Evaluation of the suitability of the
degree of sprouting
In order to evaluate whether or not the degree of sprouting
could be of any practical value in estimating characteristic
data of sprouted material, calculated data were compared to
experimental data (see Figure 7).
A set of 15 samples (five different sprouting temperatures,
three different sprouting durations) was used for the evaluation.
It has to be pointed out that the correlations between proper-
ties of samples and degree of sprouting, as displayed in Figure
6, were based on homogeneous subsamples of the sprouting
process at 20°C. The 15 samples differing due to variation of
the process conditions are each inhomogeneous (see Figures 3
and 4). Consequently, the training set for the correlations and
the evaluation set are not only independent from one another,
but also differ with respect to homogeneity. The content of
ascorbic acid, β‐glucan, and reducing sugars and α‐amylase
activity were calculated as function of the respective degree of
sprouting based on the functions displayed in Figure 6. It goes
without saying that for an exponential function averaging the
argument of the function yields a different result than averag-
ing the values. Hence, good predictions are only possible by
averaging the properties over the different homogeneous frac-
tions constituting an inhomogeneous sample. The use of the
average degree of sprouting would systematically yield over-
predictions as a function of the homogeneity of the samples.
The parity plots depicted in Figure 7 show that the func-
tions derived from the data shown in Figure 6 yield reasonably
good predictions for the different properties of the inhomoge-
neous samples. Each data point represents the grain popula-
tion generated by a specific process setting. For each sample,
the distribution of sprouted grains over the different degrees
of sprouting was determined (Figure 3). Per degree of sprout-
ing, the respective property was computed. The property per
sample was subsequently derived by pro rata contribution
from the different degrees of sprouting within a sample.
In detail, the α‐amylase activities and contents of reducing
sugars were predicted quite well by the approach outlined.
The level of ascorbic acid appears to be underpredicted sys-
tematically. This is also true for the prediction of the β‐glucan
levels. In this case, it has to be noted that the experimental
values did only vary in a limited range between the different
samples. However, it appears fair to summarize that Figure 7
documents that the concept of the degree of sprouting can be
used to predict the properties of a sprouted sample, taken that
averaging is done in an adequate way.
4
|
CONCLUSIONS
The effect of temperature and duration of the sprouting pro-
cess was systematically studied for oats. Process temperatures
between 10 and 30°C were studied for a duration of up to 3days.
The resulting samples of sprouted oats were studied for their
concentrations of β‐glucan, ascorbic acid, and reducing sugars.
Additionally, the α‐amylase activity was determined. It was
found that the composition of oat changed in a rather systematic
pattern. The obvious interdependency of reducing sugar content
and α‐amylase activity was verified. The degradation process
of β‐glucan seemed to correlate with the degree of sprouting
as well. This is only true for a lesser extent for the presence
of ascorbic acid. This might be due to complex processes in
the growth process during which ascorbic acid is formed and
later consumed. Overall, it is found that for a process duration
of 3days, temperatures between 20 and 25°C yield the most
significant changes in the properties of sprouted grains.
In order to simplify the categorization of samples of
sprouted materials, a correlation of the compositional prop-
erties mentioned above to an easy applicable descriptor of a
sprouted grain sample was sought. Initial assessment revealed
that the 1,000 grain weight is insufficiently linked to quality
parameters. The mass fraction of radicle and coleoptile in the
grain correlated very well with the β‐glucan level. A similarly
good correlation was found for the much easier applicable de-
gree of sprouting. This DoS is derived based on the visual as-
sessment of coleoptile length set into relation to the grain size.
The degree of sprouting was assessed for various sam-
ples, and it was found that for different process settings,
a typical distribution of the degree of sprouting within a
sample existed. Correlations between the measured com-
positional properties and the degree of sprouting were
derived from subsets of grains for a single process condi-
tion (20°C, 3days). The sample of grains was subdivided
into homogeneous subsamples with identical degree of
sprouting. Based on these homogeneous samples, func-
tions to calculate the grain properties as a function of the
DoS were derived. These functions were used to predict
the properties of inhomogeneous samples originating from
different sprouting process settings. The surprisingly good
predictive power found indicates that the application of the
concept of degree of sprouting could develop into a reli-
able characterization method for sprouted grains usable for
predicting compositional and nutritional changes of oats
during sprouting and ultimately leveraging this information
for product development and specification.
ORCID
Julia Krapf https://orcid.org/0000-0002-1056-3603
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How to cite this article: Krapf J, Kandzia F, Brühan
J, Walther G, Flöter E. Sprouting of oats: A new
approach to quantify compositional changes. Cereal
Chem. 2019;96:994–1003. https ://doi.org/10.1002/
cche.10203
