Fraunhofer Institute for Molecular Biology and Applied Ecology IMEShrimp are among the most popular and high-quality seafood products from aquaculture worldwide. However, after harvesting, their shells often turn black quickly. These so-called black spots are harmless to humans but appear unappetizing. The result: tons of high-quality food end up in the trash. To stop this waste, chemical agents are often used, but these are not in line with organic production principles. Our research therefore seeks natural solutions to maintain the shelf life of shrimp and avoid food waste.
Natural active ingredients to prevent black spots (melanosis) in organic shrimp
untreated White Tiger Shrimps
untreated Black Tiger Shrimps
Organic shrimp: Sustainable but sensitive
Organic shrimp farming protects both the environment and the animals. In contrast to conventional farming, the animals are raised at significantly lower stocking densities. This reduces stress and protects sensitive ecosystems such as mangrove forests, which often serve as natural filters and food sources. Furthermore, the use of antibiotics and chemical additives is strictly regulated or prohibited. However, this is precisely where the difficulty lies: after the catch, there is a lack of effective protection against the naturally occurring black spots on the animals (post-mortem melanosis).
In the conventional industry, the chemical agents sodium metabisulfite (E223) and 4-hexylresorcinol (E586) prevent this unsightly discoloration. In organic production, however, these substances are undesirable, leading to dark spots on the shell after a short time. Although the shrimp remain fresh and edible, retailers reject the goods.
But why do shrimp turn black at all?
The answer lies in two proteins: tyrosinase and haemocyanin. Tyrosinase is part of the shrimp's innate immune system and helps with wound healing. However, as soon as the animal dies and air reaches the body, tyrosinase starts a chain reaction: it converts colorless building blocks in the body into dark pigments – similar to how sliced fruit browns in the air. This process is supported by haemocyanin. In living shrimp, this substance performs the role that hemoglobin plays in our blood: it transports oxygen. The problem: in the post-harvest stage, haemocyanin can also behave like a tyrosinase under certain conditions and further accelerate the formation of black spots.
Our research aims to specifically slow down this enzymatic activity using natural active ingredients.
treated White Tiger Shrimps
treated Black Tiger Shrimps
From the computer simulation to the application test
To find the right active ingredients in nature's vast diversity, we utilized modern chemoinformatics as part of our MbioShrimp project. Instead of laboriously testing thousands of samples in the laboratory, we first simulated the search on a computer. Using digital models, we pre-tested which molecules fit into the binding pockets of the enzymes and thus held the potential to block them.
The most promising candidates from this simulation were then examined in the laboratory for their actual inhibitory effect. Through kinetic measurements, we precisely analyzed how quickly and firmly an active ingredient blocks the enzyme. After identifying the most effective substances, the step into practice followed. To this end, we investigated the effectiveness in completely suppressing melanosis in aquaculture operations using realistic storage experiments on the Whiteleg shrimp and the Black Tiger shrimp. These two species are the most economically relevant and together account for over 85 % of the global market.
The results confirmed our predictions: the natural active ingredients reliably prevented the discoloration over the entire storage period. These promising preliminary works are the starting point for the upcoming development toward market readiness.
Collaboration as an innovation motor: A precise profile for market success
Together with partners from the shrimp industry, we have defined a clear requirement profile to translate our research results into a market-ready product. A practical solution must not only be effective but, above all, economical and safe. Our investigations to date confirm this potential: the active ingredient is harmless to health and leaves almost no residue on the edible part of the shrimp. The sensory quality also appears to be preserved – taste, smell, and appearance do not change.
For industrial use, we have optimized the process so that it can be seamlessly integrated into existing workflows. As with established methods, the shrimp are simply dipped into an aqueous solution. We pay particular attention to ensuring that the active ingredients also function in salt and brackish water. This is crucial for the world's most important production areas in Africa, Southeast Asia, and Latin America.
With targeted costs of just a few cents per kilogram of shrimp, we are working on an economically viable solution. The additional costs of the treatment should ultimately pay off twice: through a significantly higher value of the shrimp and greater consumer acceptance of natural, chemical-free products.
This success is only made possible by the close interdisciplinary cooperation with our partners from Naturland, the Justus Liebig University Giessen, the Johannes Gutenberg University Mainz, the Fraunhofer CBP, and Damm Aquakultur GmbH. Together, we bundle the necessary expertise from applied natural product research, biology, certification, and industrial practice. We would like to thank the Federal Ministry of Education and Research (BMBF), the Hessian Ministry of Science and Research, Art and Culture (HMWK), as well as the DAAD and COLFUTURO for the financial support of our project team.