Organic farming: possibilities and limitations of stable isotope testing

Transcription

1 Organic farming: possibilities and limitations of stable isotope testing Dr. Werner Nader Eurofins Global ontrol GmbH Februar

2 Eurofins pioneer in stable isotope analysis SNIF-NMR - developed by Profs. Maryvonne and Gérard Martin, University of Nantes, to measure the non-statistical deuterium distribution within a given molecule The method was the first service provided by Eurofins in 1987, which developed from a start-up company to the largest provider of food analysis worldwide

3 Stable Isotope Analyses Average isotopic composition of organic products HYDROGEN ARBON OXYGEN Atom 1 H 2 H 3 H O 17 O 18 O Atomic number (1) (2) (3) () (13) (14) (16) (17) (18) (and mass) Proportions % (a) (b)

4 General principles of Stable Isotope Ratio Analysis 13 Organic matter 13 Within a given molecule, isotope ratios of bio-elements depend on: - Precursors and synthesis pathway (natural / synthetic) - Metabolism and physiology (botanical origin) - Environment (geographical origin) 13 / Isotopic fingerprint 15 N/ 14 N Genesis of a bio-product 18 O/ 16 O 2 H/ 1 H 2

5 Stable Isotope Analyses H 2 O H 2 O H 2 O H 2 O DHO DHO DHO H 2 O H 2 O DHO DHO H 2 O DHO H 2 O DHO H 2 O H 2 O DHO

6 Stable Isotope Analyses October

7 Stable Isotope Analyses October

8 Stable Isotope Analyses Net effect on 2 H and 18 O abundance through the global hydrological cycle Decreasing Increasing latitude latitude Increasing 2 H and 18 O content Decreasing 2 H and 18 O content

9 How isotope ratios are measured (1/2) Isotopic Ratio Mass Spectrometry (IRMS) 1- ombustion or Pyrolysis of the organic product omb Product N 2 + O 2 + H 2 O + SO 2 Py Product + O + H 2 2- Gases (O 2, N 2, or O) are then measured by mass spectrometry 13 O 2 (MW=45) and O 2 (MW=44) are separated ratio 45/44 is calculated; 13 / is proportional to 45/44 13 /, 15 N/ 14 N, 18 O/ 16 O, 2 H/ 1 H, 34 S/ 32 S 3- Results are expressed using the Delta (δ) notation : δ 13 ( ) = (13 / ) spl - ( 13 / ) ref ( 13 / ) ref x

10 How isotope ratios are measured (2/2) Site-specific Natural Isotopic Fractionation studied by deuterium Nuclear Magnetic Resonance (SNIF-NMR ) Deuterium distribution within the molecule is non-statistical. This can be measured by SNIF-NMR. H 3 HDOH TMU=ref H 2 DH 2 OH H 3 H 2 OD δ ppm (D/H)i (ppm) = N ref * n ref Ni spl * n spl * purity spl (D/H) ref * * S spl S ref

11 Stable isotopes: a powerful authentication tool The content of... Is influenced by And can reveal Examples 13, 2 H, 15 N Metabolism of the product Addition of sugars from other plants Fruit juices 13, 15 N Diet Mislabeling Animal products 13, 2 H Synthetic pathway Addition of artificial substances Flavours : vanillin O, 2 H Origin of water Dilution with tap water Pure juices 13, 2 H, 18 O, 15 N Geographic origin Mislabeling Wine, All products

12 Isotopic methods recognition year Method Product Fraction Techniques Isotope ratios 1987 OIV, recueil des méthodes d'analyse wine Ethanol SNIF-NMR (D/H) I, (D/H) II,R 1990 E regulation 2676/90, annex 8 wine Ethanol SNIF-NMR (D/H) I, (D/H) II,R 1991 AOA method honey honey & proteins IRMS 13 / 1993 EN (T174 N108, ENV 140) fruit juice Sucre IRMS 13 / 1995 AOA Official method fruit juice Ethanol (from fermentation) SNIF-NMR (D/H) I, (D/H) II,R 1996 OIV resolution ENO 2/96 wine water IRMS 18 O/ 16 O 1997 E regulation 822/97 wine water IRMS 18 O/ 16 O 1997 EN (T174 N109, ENV 141) fruit juice water IRMS 18 O/ 16 O 2000 AOA Official method maple syrup Ethanol (from fermentation) SNIF-NMR (D/H) I, (D/H) II,R 2001 OIV resolution ENO 17/2001 wine Ethanol IRMS 13 / 2003 E regulation 440/ 2003, annex 2 wine Ethanol IRMS 13 / fruit juice & Ethanol (from 2004 AOA method IRMS 13 maple syrup fermentation) / 2006 AOA method Vanillin Vanillin SNIF-NMR (D/H) i

13 Isotopic methods to verify «organic» plants National and international standards exist for organic agricultural product Generally enforced through paper trail traceability Synthetic nitrogen fertilizers are not permitted Permitted fertilizers include: animal manure, compost, bloodmeal, fishmeal, seaweed-derived products Synthetic fertilizers have a stable nitrogen isotope ( 15 N/ 14 N) composition which is different to that of most «organic» fertilizers

14 hemical fertiliser production Expect dδ 15 N = 0 ENERGY + NITROGEN FROM AIR dδ 15 N = 0 + Hydrogen Ammonia Urea Ammonium nitrate alcium ammonium nitrate Nitrogen solutions Ammonium sulphate From Kelly et al., Eurofins International Seminar 2008

15 Origin of the nitrogen isotope signature δ 15 N =? Organic Nitrogen (effluent, manure) δ 15 N >10 Plant Nitrogen hemical Nitrogen δ 15 N ~0 Soil Nitrogen δ 15 N influenced by location and cultural practices

16 Favorable case: «intensive» crops (fertilizing influence is high) Nb of individuals Organic vs. onventional tomatoes Organic onventional Also works for greenhouse-grown grown pepper

17 Some cases are less favorable than others... δ 15 N (Mean - all data) Tomato Mushroom Lettuce arrot onv Org Low nitrogen requirement (From Bateman et al., JAF 55, 2007)

18 Limitations of the 15 N approach - Not applicable to N 2 -fixing plants (δ 15 N close to 0 ), which also tend to influence the soil δ 15 N of subsequent crops -Total soil δ 15 N value is not a fair indicator of the plant-available nitrogen, so soil cannot be used as a witness - Plant-available nitrogen pool has a fast turn-over and a high spatial variability due to complex processes like nitrification/denitrification, minerilization, volatilization, leaching, etc. - The discrimination also varies with plant nitrogen uptake and fertilizing regime (type, amount, growth stage, etc.) - Organic fertilizers can also be used by conventional growers 15 N must be used with care, and is only one piece of the puzzle

19 Authentication of animal products: «we are what we eat» Geographical origin, climate Feed: herb or maize silage Agricultural practices, Fertilizers, soil 18 O, D/H N

20 haracterisation of maize silage feeding the PAAV7 package (milk, meat) d13 ( ) milk casein % maize in the feed an be used when production rules exclude maize use

21 Milk from organic farming, 3-omega fatty acid Seasonal variation of the 18:3ω3 content in milk fat (RM, conventional retail milk; ORM, organic retail milk; OFM, organic farm milk). (source: J. Molkentin, J. Agric. Food hem., 2009)

22 Milk from organic farming, isotope analysis Seasonal variation of δ 13 in milk fat. (source: J. Molkentin, J. Agric. Food hem., 2009)

23 Milk from organic farming, combination of isotope and fatty acid analysis orrelation (r ) -0.93) between the 18:3ω3 content and δ13 of retail milk fat (source: J. Molkentin, J. Agric. Food hem., 2009) 2

24 Geographical origin of meat product: the PAAV6 package Fatt. 2: 29,02% ombines: Proteins extraction 13 15N 2H Measurements Fatt. 1: 52,46% arpentras (FR) Limousin (FR) halkidiki (GR) Ireland Allgau (GER) Franconia (GER) ornwall (UK) Orkney - pasture fed (UK) Orkney - barn fed (UK) Toscana - mixed fed (IT) Toscana - milk fed (IT) Trentino (IT) Sicily (IT) Muhlviertel (AU) Also available: 87Sr Applicable to beef, poultry, lamb Also available for HONEY

25 onclusion Stable isotopes can contribute to the analytical control of some organic production practices, especially regarding the fertilisation regime of plants and the use of maize silage for animal feeding One of the main interests is that this approach follows the legal definition of organic production, defining an obligation of means However a single isotope analysis alone is often not sufficient, and we recommend to use multi-element approaches in order to improve the reliability of traceability assesments Finally analytical control can support but not replace audit trails by organic certification bodies

26 Thank you. Dr. Werner Nader Eurofins Global ontrol GmbH Am Neuländer Gewerbepark 1 D Hamburg +49 (0) wernernader@eurofins.de