Principles and Limitations of Stable Isotopes in Differentiating Organic and Conventional Foodstuffs: 1. Plant Products

Abstract

Among the lighter elements having two or more stable isotopes (H, C, N, O, S), δ(15)N appears to be the most promising isotopic marker to differentiate plant products from conventional and organic farms. Organic plant products vary within a range of δ(15)N values of +0.3 to +14.6%, while conventional plant products range from negative to positive values, i.e. -4.0 to +8.7%. The main factors affecting δ(15)N signatures of plants are N fertilizers, biological N2 fixation, plant organs and plant age. Correlations between mode of production and δ(13)C (except greenhouse tomatoes warmed with natural gas) or δ(34)S signatures have not been established, and δ(2)H and δ(18)O are unsuitable markers due to the overriding effect of climate on the isotopic composition of plant-available water. Because there is potential overlap between the δ(15)N signatures of organic and conventionally produced plant products, δ(15)N has seldom been used successfully as the sole criterion for differentiation, but when combined with complementary analytical techniques and appropriate statistical tools, the probability of a correct identification increases. The use of organic fertilizers by conventional farmers or the marketing of organic produce as conventional due to market pressures are additional factors confounding correct identification. The robustness of using δ(15)N to differentiate mode of production will depend on the establishment of databases that have been verified for individual plant products.

Multi‐isotopic signatures of organic and conventional Italian pasta along the production chain

“…multi‐elemental analysis and/or stable isotope analysis of several light or heavy mass elements including H, C, N, O, S and Sr, 1 H‐NMR profiling and near‐infrared reflectance spectroscopy. Only a limited number of studies have focused on discriminating organic and conventional wheat (both bread and durum) and cereals in general …”

“…In addition, the use of δ 15 N for organic authentication is challenged by the fact that N 2 ‐fixing plants (the Leguminosae family ) have δ 15 N values overlapping with the range of synthetic fertilizers and are frequently used as cover crops or green manures in organic crop rotations. Several studies have thus demonstrated that δ 15 N as a single parameter does not enable authenticity testing of organic plant products in all real‐life situations . To eliminate this problem, oxygen isotope analysis of nitrate has been utilized in a few studies .…”

Geographical Origin Characterization of Slovenian Organic Garlic Using Stable Isotope and Elemental Composition Analyses

“…After that, transpiration through the leaf stomata occurs, leading to enrichment of δ 18 O in the leaf water. 29 The distribution trends of δ 18 O values in garlic samples is similar to that observed in Slovenian groundwater, 30 when considering the δ 18 O content of groundwater in the Mediterranean re- Mean ± SD -26.9 ± 0.7 6.5 ± 2.6 1. gion and in garlic samples from this region (Fig. 2).…”

From production to consumption: tracing C, N, and S dynamics in Brazilian agroecosystems using stable isotopes

“…The use of stable isotopes to differentiate organic vs. conventional plant and animal products was reviewed by Inácio & Chalk (2015) and Inácio et al (2015a), respectively. In a study of conventionally and organically produced lettuce (Lactuca sativa L.) in the state of Rio de Janeiro, Inácio et al (2015b) concluded that the δ 15 N signatures of lettuce were an indicator of the principal N inputs (BNF, organic or manufactured fertilizer) instead of a definitive indicator of the production regime.…”