Purple sulfur bacteria convert aquaculture waste into antioxidant-rich single-cell protein through biofloc technology

Aquaculture faces the dual sustainability challenges of dwindling fishmeal supplies due to overfishing and the massive generation of processing waste. To tackle this, researchers have developed an innovative bio-valorization technique that converts rainbow trout viscera waste into high-quality fish protein hydrolysate (FPH). This FPH is then used as a nitrogen source in biofloc systems with purple sulfur bacteria (PSB), creating single-cell protein (SCP) that can replace up to 50% of conventional fishmeal in larval fish diets.

In this system, the trout viscera are enzymatically hydrolyzed using Alcalase® under specific conditions, resulting in FPH that boasts excellent antioxidant properties and a balanced amino acid and fatty acid profile. The SCP generated through this process meets nutritional requirements, including optimal levels of essential amino acids like lysine, methionine, and threonine. Antioxidant activity is also notable, with the SCP exhibiting high scavenging capacity for reactive oxygen species.

The optimal conditions for SCP production involve a 30:1 carbon-to-nitrogen ratio and a 12-hour harvest interval. This combination yields SCP with an impressive 42.55% crude protein content, a favorable lipid profile, and superior antioxidant capacity. Crucially, the SCP is free from heavy metals, histamine, and pathogenic bacteria, ensuring food safety.

Water quality in the biofloc systems is well-maintained, with total ammonia nitrogen levels reduced by 70% compared to traditional systems. This improvement in water quality reduces the environmental impact of aquaculture operations. Furthermore, feeding trials with Daphnia magna confirm that the SCP is highly digestible and supports robust growth in fish, outperforming both fishmeal and yeast-based SCP alternatives.

Economically, adopting this SCP production method can lead to a 25% reduction in protein ingredient costs, making it a cost-effective solution for sustainable aquaculture. This integrated approach not only addresses the critical issue of fishmeal scarcity but also promotes a circular economy by transforming waste into valuable resources.

This research, supported by various institutions and funding bodies, demonstrates the potential of this technology to contribute to sustainable larviculture while aligning with global blue transformation goals for a more sustainable aquaculture industry.