16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11975
Influence of cropping systems on the potential formation of
acrylamide in different cultivars of wheat
Stockmann, F.1,,Graeff, S.2, Weber, A.3 & Claupein, W.4
Key words: acrylamide, asparagine, production systems, cultivars, food products
Abstract
Acrylamide (AA) – probably carcinogen – is thermally created in carbohydrate-rich
food (e. g. cereals) within the Maillard-Reaction by the reaction of asparagine and
reducing sugars. First steps to decrease AA focused on changes in the technological
food production process. However, these possibilities are limited due to occurring
taste anomalies and consumer tolerance. Therefore, it might be an alternative to
influence the precursors of AA. Up to now, multiple studies considering the influence
of fertilisation, species, and cultivars on the content of asparagine (Asn) and reducing
sugars have been carried out. But there is still a lack of information about the influence
of the production system on the AA level. It can be expected that the amount of AA is
different and might be lower in organic production systems, because of the difference
in nitrogen management (amount and type). The aim of this study was to check
organically and conventionally grown wheat samples of different cultivars for the level
of the precursor Asn and the AA-formation-potential. The samples were obtained from
locations in Switzerland and Germany. Partial significant differences in the amount of
Asn and in the AA-formation-potential suggested an influence of the production
system and thus a further chance to intervene.
Introduction
The health and safety of foodstuff nowadays is a very important aim even in
industrialised countries (Nau et al. 2003). Normally the avoidance of food toxicants is
quite well manageable. But for substances, created through food processing, like
acrylamide (AA), it is problematical. Acrylamid, a so called “foodborne toxicant”, was
first reported in 2002 by the Swedish National Food Administration in connection with
food products. It is formed in carbohydrate-rich food stuffs like potatoes and cereals
within the Maillard-Reaction (Mottram et al. 2002), where the amino acid asparagine
(Asn) and reducing sugars (e. g. glucose) react by thermal processes to AA (Stadler et
al. 2002). In this context, Asn is the limiting factor of the formation of AA in cereals
(Weisshaar 2004). Furthermore, according to the IARC (International Agency for
Research on Cancer 1994) it is a probably carcinogen substance. Consequently many
efforts have been undertaken to understand the syntheses, the metabolism, the
toxicology, the formation and, in the end, what can be done to minimize the amount of
AA in foodstuffs. Up to now, a focal point was to find minimization strategies by
changing technological food production steps. It has been successfully shown, that the
1
Institute of Crop Production and Grassland Research, Universität Hohenheim, Fruwirthstr. 23,
70599 Stuttgart, Germany, E-Mail fastock@uni-hohenheim.de, Internet www.uni-hohenheim.de
2
As Above
3
As Above
4
As Above
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11975
amount of AA can be minimized by changing temperature, pH, time of heating,
backing agents and adding additives. However, the possibility to change technological
process steps is limited, because of negative impacts on the quality of produced
products. Modifications in technical food processing are linked to changes in taste,
smell and texture and thus consumers’ acceptance can be endangered. Therefore,
additional strategies are needed to minimize AA. An alternative to reduce AA might be
to limit the contents of precursors (e.g. free Asn) by using crop species and cultivars
with lower levels. Furthermore, different amounts of N-fertilization can also increase
the Asn level. Weber (2007) investigated different conventionally grown cereal species
and cultivars of wheat, spelt and rye and found different levels of Asn. Weber et al.
(2008) also found that conventional N-fertilization levels can increase the level of Asn.
As organic farming uses different N-fertilization strategies e.g. crop rotation,
enhancement of mineralization and organic N-fertilizer that lead to crude protein levels
below 13 %, it can be expected that the amount of Asn in organic grain samples is
lower. Thus it seems that organic products can contain a lower amount of AA and by
this might have an advantage for consumers’ health. Up to now only few studies have
investigated the impact of organic production systems on levels of AA in foodstuffs,
wherefore further research is necessary.
Hence the aim of these study was i) to evaluate differences in Asn content of
organically and conventionally grown wheat cultivars, ii) to compare the content of Asn
and AA-formation-potential between organically and conventionally grown wheat
cultivars and iii) to evaluate the correlation between Asn and AA-formation-potential of
organically and conventionally produced wheat cultivars.
Materials and methods
The organically produced 16 wheat samples (Wiwa, MAA 48, TEPP 117, Wenge,
Pollux, Ataro, Aszita, AIRA 28) were obtained from field trials of two different locations
(Vielbringen, Montezillon) in Switzerland from the seed breeder Peter Kunz in
2004/2005. The selected two locations were in the Regions Chaumont (Montezillon:
770 m above sea level) and Bern (Vielbringen: 560 m above sea level). The annual
precipitation ranged about 800 – 1030 mm. Annual average temperature ranged from
6.2 to 9.9 °C. The field trials were arranged in a block design (randomised), with two
replications on a sandy loamy soil. Liquid manure was applied as N-source, previous
crops at both locations were grass-clover ley.
The conventionally produced 16 wheat samples (Enorm, Altos, Monopol, Batis, Elvis,
Tiger, Cubus, Transit, Tommi, Natutastar, Magnus, Terrier, Dekan, Punch, Manhatten,
Wasmo) were collected from the experimental station Ihinger Hof of the University of
Hohenheim (south-west of Germany, 48° 44’ N; 8° 56’ E, mean annual precipitation
693 mm, mean temperature 8.1 °C). The samples were arranged in a block design
(randomised) with three replications. The soil texture was classified as loamy clay.
Sugar beet was cultivated as previous crop. N-fertilization was applied as KAS in
accordance to the quality levels of wheat (quality level E, A, B, K) from 170 kg N ha -1
to 200 kg N ha-1. The selected cultivars were used because of their relevance in the
applied production system.
The lab analyses of Asn and the AA-formation-potential in the grain samples were
done according to Weber et al. (2008). Asn- and AA-data were analyzed according to
the experimental design with a linear mixed model. Analyses of variance (ANOVA)
were performed using PROC GLM of the SAS 9.1 statistical software package (SAS
Institute Inc., Cary, NC, USA). Tukey-Tests were carried out for comparison of means
using the procedure PROC MIXED. All effects were set as fixed.
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11975
Results and discussion
16
14
f
12
abc
Montezillon A
def
cdef
bcde
10
f
def
abc
Vielbringen
abc
ab
ab
abcd
A
ef
bcde
abc
a
8
6
4
2
AIRA.28
Aszita
Wenga
Ataro
Pollux
TEP.117
MAA.48
Wiwa
AIRA.28
Aszita
Wenga
Ataro
Pollux
TEP.117
MAA.48
0
Wiwa
asparagine [mg 100g
-1
DM]
Figure 1 shows the results of Asn levels [mg 100 g-1 in DM] in organically produced
wheat. The content of Asn differed significantly between the chosen cultivars. Asn
levels ranged from 7.8 mg 100 g-1 DM as minimum to 13.8 mg 100 g-1 as maximum
with a mean of 10.7 mg 100 g-1 DM. Against this the conventionally produced wheat
cultivars (results not shown) had significant differences by a mean content of 15.2 mg
100 g-1 DM, with a minimum of 7 mg 100 g-1 DM and a maximum of 21.2 mg 100 g-1
DM. The higher Asn contents in grain samples of conventional production systems
might be the result of higher N-fertilization levels which can significantly enhance the
amount of Asn (Weber et al. 2008). Means over two organic locations did not indicate
significant differences in Asn level, but comparing the same cultivars a significant
difference was given wherefore it is concluded that the location could have an effect.
Figure 1: Asparagine levels [mg 100 g-1] of analysed organic wheat cultivars.
Cultivars with the same letters did not differ significantly (α<0.05).
asparagine [mg 100g-1 DM]
18
16
I
b
14
12
a
10
8
6
4
2
0
conventional
organic
formation potential of AA [ng g -1 DM]
In a further step, the content of Asn and AA-formation-potential were analysed and
compared between the two production systems (figure 2 I & 2 II). The results showed
a statistically significant difference in the amount of Asn (figure 2 I) as well as in AAformation-potential (figure 2 II) between the systems. Asn potential of organically
grown cultivars was significantly lower than in conventionally grown cultivars. Further,
the same effect was found for the amount of AA-formation-potential (Fig. 2 II). Wheat
cultivars of organic production systems had a significant lower level (almost four
times) than conventionally produced samples.
1800
1600
b
II
1400
1200
1000
800
600
400
a
200
0
conventional
organic
Figure 2: Comparison of means of (I) asparagine [mg 100 g-1] and (II) acrylamide (AA) formation potential levels [ng 100 g-1] of analysed wheat cultivars.
Production system with the same letters did not differ significantly (α<0.05).
16th IFOAM Organic World Congress, Modena, Italy, June 16-20, 2008
Archived at http://orgprints.org/11975
3500
350
3000
300
2500
250
R2=0,14n.s.; n=16
2000
200
1500
150
1000
100
R2=0,75***, n=16
500
50
0
0
0
5
10
15
20
25
formation potential of AA [ng g -1 DM]
formation potential of AA [ng g -1 DM]
The correlation between Asn and AA (figure 3) was only significant for the
conventional samples. Due to a narrow range of Asn in organic samples, no
correlation was obtained.
Figure 3: Correlation between asparagine (Asn)
and acrylamide (AA) formation potential of conventionally (R2=0.75***, black
dots, left y-axis) and organically (R2=0.14n.s., white triangles, right y-axis) grown
wheat.
asparagine [mg 100 g-1 DM]
Conclusions
The results of the study indicated significant differences in the content of Asn and the
final AA-formation-potential within organically produced wheat cultivars. A possible
strategy to minimize AA in foodstuffs seems to be the selection of wheat cultivars low
in free Asn. Further, the location might to have an impact on the content of free Asn
when comparing single cultivars. The production system seems also to have an
influence. However, no clear statement can be given because of different cultivars and
locations. Further research on the overall influence of the production system is
needed.
References
IARC (1994): Monographs on the Evaluation of Carcinogen Risk to Humans, vol. 60, International
Agency for Research on Cancer, Lyon, p. 389.
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