Suitability of instrumental analysis for the discrimination between wild-caught and conventionally and organically farmed shrimps

Abstract

Shrimps, primarily Penaeus monodon and Litopenaeus vannamei, from organic and conventional farms and free-living stocks were purchased from the German market over 1 year. This study examined the applicability of established analytical methods for the confirmation of the correct labelling of shrimp products. After species identification of 77 shrimp products, the proximate composition, carotenoid pattern, fatty acid profile and stable isotopes of carbon and nitrogen in the lipids and/or the defatted dry matter (DDM) were determined. To differentiate between the three types of production (wild, organically farmed or conventionally farmed), parameters alone or in combination, partly derived by multivariate tests, were considered. Stable isotope ratio mass spectrometry allowed the differentiation between organically and conventionally farmed Litopenaeus vannamei using the combination of ∆δ13C and δ15NDDM values. The gas chromatographic analysis of fatty acids also distinguished between organically and conventionally farmed shrimp of this species. The ratio of the free astaxanthin configurational isomers in shrimp flesh, analysed by high-performance liquid chromatography (HPLC), was inadequate for any assignment, because of the apparent ability to alter the structure of the ingested carotenoids. Thus, a general differentiation of the three production types, irrespective of individual species, could not be achieved by any single method.