Natural Products: A Bio-Based Approach to Mitigate Post-Mortem Melanosis in Shrimp Aquaculture

The progression of aquaculture is crucial to satisfy the growing requirement for aquatic protein driven by the expanding global population and heightened market demands. Colombian aquaculture plays a significant role. As reported by the Colombian Federation of Aquaculture Producers (Fedeacua), there are approximately 36,000 producers in Colombia, collectively producing 204,000 tons of shrimp and fish annually. The sector experienced robust growth in 2022, with Colombian aquaculture exports exceeding 200,000 tons, marking an impressive growth rate of 193% since 2015. Furthermore, as recognized by the National Aquaculture and Fisheries Authority (AUNAP) on World Aquaculture Day, the industry provides a considerable number of employment opportunities in Colombia, supporting 57,756 direct and 173,269 indirect jobs.

Shrimp farmers face significant challenges that render their supply chains highly vulnerable. One key issue impacting the global shrimp industry, including markets in Colombia and Germany, is post-mortem melanosis3.

The formation of melanin is a biochemical process involving the enzymatic conversion of monophenols into o-diphenols, which are subsequently oxidized to form o-quinones that eventually when exposed to air, is oxidized forming black pigment called melanin. Polyphenol oxidase (PPO) is widely recognized as the main enzyme that kicks off the enzymatic blackening process. Normally, sulphites like sodium metabisulfite (E223) are used in high concentrations (between 1,5 and 3 g/L) in order to counteract this enzymatic action, but it has been recognized that these agents can trigger allergic reactions. A second marketed anti-melanotic chemical compound is 4-hexylresorcinol (E586). In contrast to the sulfites E586 is a specific PPO inhibitor and applied in significant lower concentrations at 50 mg/L. The absence of a natural alternative capable of inhibiting melanosis, or the black spot syndrome, in whole shrimps poses a significant threat to the market value and reach of end-products particularly affecting the organic sector. 

The aim of the project is the exploration of fungal- and plant-derived natural products in their potential to prevent melanosis in shrimp and to characterize shrimp polyphenol oxidase (PPO) in order to investigate the molecular interaction of the natural inhibitors with the PPO, providing deeper insights for the development of effective melanosis inhibition strategies.

The project sources the Fraunhofer strain collection to identify novel or repurpose known natural products from fungi. The application tests on shrimps necessitates bigger natural product quantities, requiring the development of optimized fermentation processes (Upstream Processing (USP)) and isolation strategies (Downstream Processing (DSP)) for each target compound. Initially, design of experiments (DOE) are performed in small scale to identify optimized media and condition that lead to increased titers of the target compounds in the fermentation broth of the producer fungi. This is followed by optimization of process parameters in parallelized 2-L bioreactors, eventually guiding scale-up in a 30-L bioreactor to produce the compound in required quantities.