Agronomic strategies to reduce potential precursors of acrylamide formation in cereals

Paracelsus postulierte Alle Dinge sind Gift, und nichts ist ohne Gift. Allein die Dosis macht, daß ein Ding kein Gift ist. Dies ist für Acrylamid (AA) in Frage zu stellen, da es hier keine Dosis gibt, unter der eine Gesundheitsgefährdung auszuschließen ist. Daher sollte AA in Nahrungsmitteln (NM) so niedrig wie möglich sein. Das AA in NM vorkommt, wurde erstmals im Jahr 2002 bewiesen. Am stärksten betroffen sind erhitzte, stärkereiche NM auf Getreide- oder Kartoffelbasis. Es reagieren reduzierende Zucker und die Aminosäure Asparagin (Asn) innerhalb der Maillard Reaktion und bilden AA. Bei der NM Produktion gibt es viele Eingriffsmöglichkeiten, AA zu senken (u.a. Höhe & Dauer der Hitzeeinwirkung, Austausch von Backtriebmitteln, Verlängerung der Teigstandzeit, Einsatz von Zusatzstoffen & Enzymen). Solche Maßnahmen sind aber teilweise begrenzt, da unerwünschte Auswirkungen auf die Qualität der NM auftreten können oder sie sind schlicht zu teuer zur Umsetzung im Großindustriellen Maßstab. Außerdem schwanken die AA-Gehalte in NM seit 2011 jahresbedingt. Dies zeigt, dass vor allem der Rohstoff (z. B. Mehl) die AA Gehalte beeinflusst. Somit wäre ein wichtiger Schritt, schon vor der NM Herstellung, auf dem Feld, Rohstoffe zu produzieren, die geringe Gehalte an AA-Vorstufen aufweisen. Die Hauptvorstufe von AA ist bei Getreide das freie Asn. Die Reduktion der Aminosäure erfordert jedoch geeignete ackerbauliche Anbaumaßnahmen, um Getreide mit wenig Asn zu produzieren. Somit war das Hauptziel der Arbeit den Einfluss folgender Maßnahmen auf den Gehalt an freiem Asn bei Getreide zu untersuchen. 1. Welche Rolle spielt das Produktionssystem (ökologisch vs. konventionell)? 2. Welche Stickstoff Düngestrategie ist beim Getreideanbau zu wählen, im Vergleich der Produktionssysteme? 3. Welchen Einfluss hat die Schwefeldüngung, bzgl. der Schwefelmenge und der Art des Düngers? 4. Können weitere Reihenabstände und eine reduzierte Saatmenge in Low Input Systemen die Backqualität von Mehlen verbessern ohne den Asn-Gehalt zu erhöhen? 5. Welche Rolle spielen Getreidearten und Sorten inkl. der Urgetreide Einkorn & Emmer im ökologischen Landbau? 6. Sollte Asn als Züchtungsziel eingeführt werden, wenn eine hohe genetische Fixierung vorliegt, also der Asn-Gehalt stark sortengebunden ist? 7. Hat der Erntezeitpunkt einen signifikanten Einfluss? Ergebnisse von Feldversuchen: Das Produktionssystem hatte einen signifikanten Einfluss auf den Asn-Gehalt. Im Mittel über die Getreidearten lag der Asn-Gehalt bei den ökologisch erzeugten Proben 26 % niedriger vgl. zu den Konventionellen. Bei Weizen war im ökologischen Sortiment bis zu 50 % weniger Asn. Bei Dinkel und Roggen war der Effekt mit max. 33 % geringer und nur in einzelnen Jahren gegeben. Die Stickstoffdüngung wirkte sich signifikant auf den Kornertrag und die Backqualität in beiden Produktionssystemen aus. Im Gegensatz dazu zeigten sich bis zu einer Stickstoffdüngung von 180 kg N ha-1 keine signifikanten Unterschiede im Asn-Gehalt zur ungedüngten Variante. Die Weizensorte hatte einen signifikanten Einfluss. Die Sorte Capo zeigte die geringsten Asn-Gehalte bei 180 kg N ha-1 jedoch hohe Rohproteingehalte von > 15 % (konventionell) und > 12 % (ökologisch). Somit scheint die Reduzierung von Asn über die Stickstoffdüngung nicht auf Kosten der Backqualität zu gehen. Die Schwefeldüngung hatte, unabhängig von Menge und Düngerform, keinen signifikanten Effekt auf den Asn-Gehalt. Weite Reihenabstände können bei Winterweizen die Backqualität unter ökologischen Anbaubedingungen positiv beeinflussen. Die Saatdichte war signifikant verknüpft mit höheren Kornerträgen und Hektolitergewichten. Der Effekt beider Maßnahmen auf den Asn-Gehalt war gering. Der Asn-Gehalt scheint mit der Anzahl der Getreidekörner pro Ähre zusammenzuhängen (R2=0.72). Das eröffnet neue Einblicke in die Asn-Synthese, während der Kornreifung und ermöglicht eine einfache Vorhersage von Asn ohne aufwendige Laboranalysen. Zwischen dem Asn-Gehalt und dem Rohprotein wurde keine Beziehung gefunden. Ein deutlicher Zusammenhang lag zwischen dem AA-Gehalt und dem Rohproteingehalt vor. Wenn der Rohproteingehalt stieg sank die AA-Bildung in erhitzen Mehlen. Der Gehalt an Asn variierte signifikant zwischen ökologisch erzeugten Getreidearten und Sorten bei sehr marginaler Stickstoffversorgung. Wird Roggen mit Dinkel ersetzt ergibt sich eine Reduktion im Asn-Gehalt von 85 %. Die Urgetreidearten Einkorn und Emmer erreichten sehr hohe Asn-Mengen. Vor allem Einkorn lag in Höhen, die sonst nur bei Roggen gemessen wurden. Das freie Asn kann auch in ökologischen Produktionssystemen als Indikator für die AA-Bildung dienen (R2=0,69). Die Heritabilität war im Vergleich der Standorte sehr hoch für Weizen und Dinkel. Im Jahreseinfluss war die Heritabilität niedrig für Weizen aber hoch für Dinkel und Roggen. Der Erntezeitpunkt hatte einen signifikanten Einfluss auf die Asn-Bildung. Eine Vorverlegung der Kornernte um ein bis zwei Wochen führte, abhängig von Produktionssystem und Getreideart, zu einer Abnahme im Asn-Gehalt von bis zu 60 %. Zusammenfassend können agronomische Strategien einen wesentlichen Beitrag leisten, um die AA-Vorstufe freies Asn deutlich zu minimieren. Ableitungen für die landwirtschaftliche Praxis und die Entwicklung eines pflanzenbauliches Vorhersage-models können den Asn-Gehalt nachhaltig zu senken. Die Zukunft der agronomischen Minimierungsstrategien liegt in der Lösung der Frage: Warum unterscheiden sich Getreidearten und Sorten im Asn-Bildungs- und Akkumulierungspotenzial im Korn? Wird diese Frage gelöst sind weitaus effizientere Maßnahmen möglich Asn im Getreidekorn zu senken. In der vorliegenden Arbeit wurden Erklärungen angedeutet und weitere Puzzleteile zur Senkung von Asn bei Getreide beigetragen.Food safety is of great importance as harmful substances formed during food processing can negatively affect human health. When the carcinogenic food ingredient acrylamide (AA) accidentally appeared in 2002, it was not expected that AA would take this much attention during the next years. Yet, after around 15 years of research, AA has finally been recognized as being harmful. In a first step, research focussed on food processing implications on AA formation. The impact of heat treatment, time of heating, baking agents, fermentation time, additives and enzymes were reported in several studies. Nevertheless, since 2011 food AA levels seem to stagnate or even increase in some years. Thus, the food industry did not show sufficient progress in reducing AA. Reducing sugars and amino acid free asparagine (Asn) are the main AA precursors. They can fluctuate in their content for instance in grain flour or potatoes shifting the focus of AA origin to the raw material. Thus, the production of raw material low in AA precursors seems important. However, lowering precursors of AA in the raw material necessitates suitable agronomic strategies to grow cereal species and cultivars low, especially in free Asn. Hence, the major goal of this thesis was to investigate the following questions concerning their impact on free Asn formation in cereals: 1. Which role does the management system plays, as organic vs. conventional farming systems highly differ in their cropping strategies? 2. What is the best nitrogen fertilization strategy when comparing organic vs. conventionally cropping systems? 3. Is there an impact of sulphur fertilization concerning sulphur amount and sulphur type? 4. Can expanding row distance and lowering seed density in low-input farming systems positively influence baking quality while keeping free Asn amounts low? 5. For organically grown cereals no level of free Asn was available. Thus, the question came up to which extent organically grown cereal species and cultivars including ancient grains like einkorn and emmer differ in free Asn. 6. Should free Asn be implemented in breeding programs if heritability is high? 7. Is there an impact of harvest timing on free Asn formation? Out of several field trials the following results were obtained: The cropping system had a significant impact on grain yield, the level of free Asn and quality traits. Across all species, free Asn contents in flour were 26% lower under organic conditions compared to conventional farming. For wheat a maximum reduction of 50% in free Asn content was possible if organically produced. Spelt and rye were affected to a minor extend as only in single years organically grown cultivars showed up to 33% lower Asn contents. Nitrogen (N) fertilization significantly influenced grain yield and baking quality in both cropping systems. In contrast, up to a certain amount of N free Asn was only affected to a minor extend. In particular, within the organic farming samples no significantly higher free Asn amounts were determined even if N fertilizer was raised or the N form was changed. A late N fertilization within the conventional cropping system increased crude protein content, while no clear effect was found on free Asn. Also, cultivars affected free Asn level significantly. Wheat cultivar Capo exhibited the lowest AA formation potential at a N supply of 180 kg N ha−1 while simultaneously reaching a crude protein content > 15% (conventional) and > 12% (organic). Thus, lowering free Asn by adjusting N treatments should not necessarily affect baking quality. In general, free Asn amounts in wheat varied widely both within cultivars and between cropping systems. Besides N, neither type nor amount of sulphur fertilization influenced free Asn significantly. Extending row distance can increase quality traits protein and sedimentation value. Seed density was highly related to grain yield and test weight. Most importantly, free Asn was only minor affected by both treatments. Thus, larger row distances can be recommended to raise baking quality in organic farming systems without simultaneously affecting free Asn. Number of grains spike-1 seems to be related to free Asn (R2=0.72). This provides new insights on Asn synthesis during grain development and offers the opportunity to predict free Asn formation without expensive chemical analyzes. In contrast Asn and protein content did not show any relation while high protein contents in grain seem to lower AA amount in heated flour samples. The impact of organically grown cereal species and cultivars in combination with marginal N supply on free Asn was clearly shown. A reduction potential of 85% was reached if rye was replaced by spelt. Surprisingly, the ancient species einkorn and emmer reached a very high free Asn content similar to rye. Heritability was high for wheat and spelt concerning locations, while regarding years, heritability was low for wheat but high for spelt and rye. For organically grown cereals, the relation between free Asn and AA formation was proven. Across species and years free Asn can serve as an indicator for AA formation (R2 of 0.69). Harvest timing affects free Asn levels. In this context a delayed harvest can increase Asn significantly while shifting harvest 1-2 weeks earlier decreased Asn by up to 60% depending on cereal species and cropping system. After summarizing and stating the most promising steps in the frame of agronomic strategies to lower free Asn, a prediction tool for free Asn should be implemented that classifies the impact of agronomic strategies and leads to recommendations to farmers. Finally, the main riddle, that should be solved during the next studies is the question, why cereal species and cultivars differ in their Asn formation. This thesis gives some preliminary ideas but a much deeper insight is essential to establish long-term strategies to lower free Asn content

Acrylamid-Bildungspotenzial ökologisch erzeugter Getreidearten und Sorten

By heating up carbohydrate-rich food, like cereals and potatoes, Acrylamide (AA), a probably carcinogen food ingredient, will be created due to a reaction of free Asparagine (Asn) and reducing sugar within the Maillard-Reaction. Up to now two opportunities to decrease AA are discussed. Firstly by changing technological food processing steps e.g. receipt modifications and secondly by plant production e.g. finding species and cultivars low in the content of precursors of AA. For cereals, free Asn is the limiting factor for formation of AA. By investigations of conventionally produced wheat-, spelt- and rye samples differences were found in the amount of Asn both in species and cultivars. It was assumed that these differences could also be found in organically produced cereals. However, up to now no study has investigated the AA content of organically produced cereals. Therefore, the objectives of this study were to investigate i) are there species and cultivars low in free Asn And, ii) is there a correlation between the content of free Asn and the formed AA? To clarify these aspects, organically produced grain samples (mainly wheat, spelt and rye) of a 2-yr field trial were analysed of free Asn and the AA-Formation Potential (AA-FP). The results showed differences in the content of free Asn within species and cultivars, indicated by a strong correlation between Asn and the AA-FP. In conclusion, an option for reducing AA in organic products could be the selection of species and cultivars low in free Asn

Influence of cropping systems on the potential formation of acrylamide in different cultivars of wheat

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

Impact of Nitrogen and Sulfur Supply on the Potential of Acrylamide Formation in Organically and Conventionally Grown Winter Wheat

In a two-year field trial, the effect of nitrogen (N) and sulfur (S) fertilization was investigated on grain yield, grain quality parameters, formation of acrylamide (AA), and the precursor free asparagine (Asn) in organically and conventionally produced winter wheat cultivars. In both production systems, different types, amounts, and temporal distributions of N were tested. The the effect of S fertilizer types and amounts on free Asn was only tested in the conventional farming system. Within both cropping systems, grain yield and baking quality were significantly influenced by N treatment while the effect on free Asn was only minor. Especially within the organic farming system, increasing N fertilization levels did not increase free Asn significantly. A slight trend of increasing free Asn levels with an intensified N supply was observed, especially in the presence of crude protein contents of 14% or higher. However, only N amounts of 180 kg N ha−1 or higher increased the probability of high free Asn contents considerably, while N supply below that amount led to free Asn values similar to the unfertilized controls. The results indicated that good baking quality can be achieved without significantly increasing free Asn levels. In addition, cultivars affected the levels of free Asn significantly. Compared to cv. Bussard and Naturastar, cv. Capo exhibited the lowest AA formation potential at an N supply of 180 kg N ha−1 while simultaneously reaching a crude protein content > 15% (conventional) and > 12% (organic). Thus, it seems that cultivars differ in their ability to store and incorporate free Asn into proteins. Over all trials, a relation of free Asn and AA was shown by R2 = 0.77, while a relation of free Asn and protein was only R2 = 0.36. Thus, lowering free Asn by adjusting N treatments should not necessarily affect baking quality. S fertilization within conventional farming did not change the free Asn amount or crude protein significantly, probably due to the fact that soil was not sulfate-deficient. In summary, it was evident that free Asn amounts in wheat varied widely both within cultivars and between cropping systems. In order to clearly unravel genotypic differences and their interaction with environmental factors and especially N fertilization, further research is needed

Impact of Row Distance and Seed Density on Grain Yield, Quality Traits, and Free Asparagine of Organically Grown Wheat

Organic farming faces challenges providing sufficient nutrient supply as manure and crop rotations are often the major nutrient inputs. Larger row distances and fewer seed densities can support nitrogen availability by giving more space to the single plant. As free asparagine (Asn) the main precursor of acrylamide (AA) in plants is closely related to nitrogen uptake and storage, the question arose whether free Asn will be affected by row distance and seed densities in organic farming. This study investigated the effect of row distance and seed density on yield, yield components, baking quality, and free Asn in organic farming. A two-year field trial was carried out including two winter wheat cultivars, two row distances, and two seed densities. Year and cultivar highly influenced all traits. The impact of both treatments was mainly caused by interaction. Nevertheless, enlarged row distances raised baking quality, while free Asn was changed to a minor extent. Thus, we recommend larger row distances for raising baking quality without increasing free Asn. Seed density is of minor relevance. The close relation found between free Asn and grains per spike (R2 = 0.72) indicates that smaller grains contain more Asn than bigger grains. This opens new insights into Asn synthesis during grain development and offers a potential prediction of Asn amounts

Acrylamide-Formation Potential of Cereals: What Role Does the Agronomic Management System Play?

As bakery products contribute considerably to the daily intake of the carcinogen acting substance acrylamide (AA), the aim of this study was to evaluate the impact of the management system (conventional vs. organic farming) on AA precursor levels of free asparagine (Asn) across different cultivars of the cereal species, namely winter wheat (Triticum aestivum), winter spelt (Triticum aestivum ssp. spelta) and winter rye (Secale cereale) with simultaneous consideration of gained grain yields and flour qualities. For this purpose, orthogonal field trials were established at two sites in Southwest Germany over two growing seasons (2006–2007 and 2007–2008). The results indicated a significant impact of the management system on free Asn contents in white flour. Across all species, free Asn contents in the white flour was 26% lower under organic compared to conventional farming. The impact of the management system on individual cultivars was obvious with a maximum reduction in free Asn contents of 50% in wheat cultivars if organically produced (e.g., for cultivars Ludwig, Privileg, Capo). For spelt, a significant impact of the management system was only found in 2008 with a reduction in free Asn of up to 25% if organically produced. Across both cropping systems, cultivar Franckenkorn reached the lowest levels of free Asn. For rye, a significant impact of the management system was observed only in 2007 with 33% higher Asn amounts in the conventional management system. Independent of the cropping system, rye reached the highest levels of free Asn followed by wheat and spelt. Depending on species, there was also an impact of the two systems on crude protein. The organically cropped wheat had a significantly lower level, but this was not observed for spelt and for rye only in 2007. The possible reason for the low free Asn content in the organically produced wheat flour could partially be the lower crude protein amount. Furthermore, the results indicated that lower AA contents in bakery products can be achieved by proper selection of species (e.g., 66% lower if rye is replaced by wheat) and cultivars. With an appropriate choice of the cultivar, a reduction of up to 65% was possible within wheat, along with a reduction of 44% within spelt and 12.5% within rye. In summary, the results indicated that organically produced wheat especially offers the opportunity to significantly lower the AA potential of bread and bread rolls by the choice of raw materials low in free Asn

Evaluation of Asparagine Concentration as an Indicator of the Acrylamide Formation in Cereals Grown under Organic Farming Conditions

This study investigated the impact of organically grown cereals on the level of free asparagine (Asn) with simultaneous consideration of grain yields and flour qualities over three growing seasons in Germany. Additionally, the relation of free Asn and acrylamide (AA) was investigated. By including free Asn results of a second trial site, heritability of the trait free Asn was calculated. Free Asn was significantly influenced by species and within species by cultivars. Rye showed the highest free Asn amount, followed by einkorn, emmer, wheat, and spelt. Replacing rye with spelt would reduce free Asn by 85%. Cultivars differed in free Asn by up to 67% (wheat), 55% (spelt), and 33% (rye). Year significantly influenced free Asn levels. Heritability was high for wheat and spelt concerning locations, but regarding years, heritability was low for wheat but high for spelt and rye. For organically grown cereals, the relation between free Asn and AA formation has never been investigated. Across species and years, a correlation of R2 = 0.69 *** was found. Thus, free Asn can serve as an indicator for AA formation. In conclusion, the level of free Asn can be highly influenced by proper selection of species and cultivars