3 July 2008

SPAIN - A new DNA detection method has been devised by Spanish scientists after they discovered that one in every four boxes or bags of langoustines is labelled incorrectly.

The scientists from the University of Santiago de Compostela (USC) and from the Instituto de Investigaciones Marinas del CSIC (Institute of Marine Research, Spanish Council for Scientific Research) analysed 41 commercial products, which include prawns or langoustines.

The results showed that 24.4 per cent of the labels display the wrong species name, and that information is incomplete in 39 per cent of cases.

The researchers have now patented a molecular method that enables this type of shellfish species to be distinguished by its mitochondrial DNA. The researcher and professor at the Laboratorio de Higiene, Inspección y Control de Alimentos (LHICA) (Laboratory for Hygiene, Inspection and Monitoring of Food), at the Spanish Council for Scientific Research (USC), Jorge Barros, who is managing the project, said that the morphological differentiation between crustaceans "is not easy, and is more or less impossible to achieve in the peeled product. This makes it difficult for both people working in the industry and consumers to be sure that the labelling is correct". In fact, some companies resort to a "generic" labelling system, simply naming them "langoustines" or "prawns" without specifying the marketed species, "probably because they do not have reliable methods available to identify the marketed species".

However, each species has its own organoleptic properties, which determine their price and commercial value, Barros explained.

"In Japan they will even pay 100 dollars per kilo for certain types of langoustines, for which reason if there is a methodology available that enables the species to be determined this could be very useful for both the industrial sector and the authorities too," he added.

In order to carry out the study, langoustines or prawns used as commercial ingredients and other pre-cooked products were analysed. In order to compare results, a collection of reference species was used as a reference marker and was set up with the co-operation of Julio Maroto, a researcher from the Centro Tecnológico del Mar (CETMAR) (Marine Technology Centre) in Vigo, and marine biologists from the CSIC (Spanish National Research Council).

New Molecular Method for Differentiating between Langoustines

The authentication method developed by the Galician scientists has been patented and published in the Electrophoresis journal and enables more than 20 species of langoustine to be differentiated by using DNA mitochondrial analysis.

To differentiate between them, the 16S gene sequence is analysed (this codifies the long mitochondrial ribosomal RNA) and the gene sequence that codifies the valine amino acid RNA transfer, although the scientists have already started studying the importance of other markers, such as mitochondrial cytochrome b and cytochrome-oxidase.

The results obtained confirm that in Spain, a large variety of whole or processed langoustine species is marketed under the format of two pre-cooked dishes ingredients".

Furthermore, this methodology enables the degree of relationship or phylogenetic relationships between this type of crustacean to be studied.

In addition, the researchers have developed a specific technique for determining the two species having the greatest commercial impact: the giant tiger prawn (Penaeus monodon) and the Pacific white shrimp (Litopenaeus vannamei).

Both species come from aquaculture farms in Central American countries or from South-East Asia, and represent almost 80% of the total volume of farmed langoustines marketed world-wide.

The researchers from the Institute of Marine Research, CSIC, headed by scientist José Manuel Gallardo, have made advances in the definition of species differentiation markers.

They are also studying certain allergenic proteins in langoustines, such as tropomyosine, with a view to designing immunological methods to make it possible to detect and identify these in foodstuffs.

Source: TheFishSite News Desk