Water/protein ratio in farmed shrimp

Reference data provide insight into the significance of the water/protein ratio for the evaluation of food fraud

Food fraud in seafood is a relevant issue for importers and trading partners. For shrimp, the water/protein ratio is commonly used to assess extraneous water content in order to identify manipulated products. However, the currently available reference values vary considerably and there is uncertainty as to what is to be regarded as "natural", i.e. what may be expected in terms of a commercial perception.

On behalf of the German Seafood Association (Deutscher Seafood Verband e.V.), Eurofins therefore conducted a study in which reference data for the water/protein ratio were collected, taking into account important factors such as the raw protein content or the processing stage. In the following, we have summarised the main study results for you.

"Determination of reference data for the water/protein ratio in farmed shrimp of the species Litopenaeus vannamei in relevant countries of origin, taking into account the processing stages"
Published in "DLR - Deutsche Lebensmittel-Rundschau, Vol. 117 June 2021 Behr's Verlag | Hamburg | ZKZ 9982". Click here to download the publication free of charge.

Why shrimp of the same species may have different firmness to bite

As a relatively expensive foodstuff, shrimp is susceptible to food fraud. In particular, the undeclared addition of water plays an important role and influences the composition and thus the sensory properties of the product. For example, the addition of water changes the consistency in such a way that the shrimp becomes crunchy and juicy. Many consumers see this as a positive characteristic that they associate with good taste and high quality. Producers and importers are obliged to indicate if water has been added in excess of 5% according to European law. Trade laboratories and the official monitoring authorities check and evaluate the marketability of shrimp, e.g. on the basis of the water/protein ratio. Can manipulations and incorrect declarations be reliably identified in this way, or is more detailed analytical testing required?

For a valid database: sampling along the value chain

Sampling within the scope of the study was carried out by Eurofins or independent partners in the countries of Ecuador, Vietnam and India according to predefined instructions. All samples were sealed directly during sampling to prevent any subsequent manipulation. A total of six resp. seven technological processing stages were individually sampled according to a standardised test plan. Two size gradings and the living environment were taken into account. In order to obtain results that were as unbiased as possible, samples were analysed both on site and according to the usual procedure in Germany. For the collection of reference data, the parameters water, protein, sodium, chloride, potassium and phosphorus as well as pH were determined.

Crude protein loss due to technological processing increases the water/protein ratio

The absolute crude protein loss during the technological processing steps plays an essential role in the evaluation of the water/protein ratio and the associated extraneous water calculations. Raw protein is washed out by mechanical stress, the use of water and ice for cooling and rinsing, or transport in water basins. The duration of the respective process step must also be taken into account. An "increased" water/protein ratio therefore does not necessarily mean that extraneous water has been added - the loss of crude protein must also be considered.

Water uptake in farmed shrimp and its technological limits

Repeatedly, official German authorities calculate extraneous water contents in the mid-two-digit range, based chemical data currently available. However, there are technological limits to the water uptake of farmed shrimp. On the basis of technological experience, up to 25% water addition can be achieved by pH shift and/or water-binding additives (e.g. diphosphates).

Evaluation of traded goods

For the evaluation of products commercially traded (in retail or wholesale), the question arises whether the water/protein ratio should correctly be defined for each processing step. However, this can also vary greatly within a processing stage due to the origin and size of the animals. Consequently, the challenge arises to define a general average value.

The examination of a large number of samples subjected to comparable treatment and analysis shows the high variability in terms of shrimp composition, depending on provenance and living conditions.

Conclusion: "The one" assessment parameter for shrimp probably does not exist

The studies have shown that the analysed water/protein ratio does not necessarily reflect the sole water intake, since technological processing steps lead to an absolute raw protein loss. Thus, the water/protein ratio cannot be used as a valid and decisive criterion for the evaluation of food fraud in farmed shrimp of the species Litopenaeus vannamei. Rather, the composition of the shrimp in terms of crude protein content, pH, and elements such as chloride, sodium, and potassium must be evaluated in the overall context.

The exact analysis results, as well as further details and illustrations, can be found in the original publication, which we offer here as a whitepaper translated into English. If you have any questions, please contact our author Markus Paul.

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