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<p>Global aquaculture confronts twin sustainability imperatives: dwindling fishmeal supplies due to overfishing and the annual generation of over 20&#xa0;million tonnes of processing by-products. Addressing these interconnected challenges, we developed an integrated bio-valorization strategy that transforms rainbow trout (Oncorhynchus mykiss) viscera—a ubiquitous aquaculture waste stream—into fish protein hydrolysate (FPH) serving as a nitrogen-rich substrate for purple sulfur bacteria (PSB)-initiated biofloc technology (BFT). Through systematic optimization of carbon-to-nitrogen ratios and microbial harvest intervals, we generated functional single-cell protein (SCP) capable of replacing 30–50% of conventional fishmeal in larviculture diets while advancing circular bioeconomy principles in aquatic food systems. Trout viscera were enzymatically hydrolyzed using Alcalase® under controlled conditions (pH 8.0, 55&#xa0;°C, 3&#xa0;h, enzyme-to-substrate ratio 1:100 w/w). The resulting FPH was characterized for proximate composition, degree of hydrolysis, antioxidant capacity (DPPH, FRAP, H₂O₂ scavenging), and peptide molecular weight distribution. FPH then served as the nitrogen source in PSB-inoculated biofloc systems operated at three carbon-to-nitrogen ratios (10:1, 20:1, 30:1) with harvest intervals spanning 3 to 12&#xa0;h. Harvested SCP biomass underwent comprehensive analysis: proximate composition, amino acid and fatty acid profiling, antioxidant activity, peptide fractionation, microbial enumeration (total heterotrophs and PSB), and safety assessments (heavy metals, histamine, Salmonella spp., Vibrio spp.). Water quality parameters (total ammonia nitrogen, total suspended solids, dissolved oxygen, pH) were monitored throughout cultivation. A preliminary feeding trial using <i>Daphnia magna</i> evaluated SCP bioavailability and growth promotion relative to commercial fishmeal and yeast-based SCP. Economic feasibility was estimated through ingredient cost analysis and projected market positioning. Alcalase® hydrolysis yielded FPH containing 78.85 ± 1.20% protein (dry weight) with a degree of hydrolysis of 17.65 ± 0.85%, demonstrating robust antioxidant properties (FRAP: 153.20 ± 4.10 µmol Trolox equivalents g⁻¹; DPPH scavenging: 79.55 ± 2.30% at 20&#xa0;mg mL⁻¹). Two-way ANOVA revealed highly significant effects of both C/N ratio and harvest time on all measured SCP quality parameters (P &lt; 0.001). The optimal treatment—30:1&#xa0;C/N ratio with 12-hour harvest—produced SCP with 42.55 ± 1.35% crude protein, a balanced lipid profile (total lipids: 15.85 ± 0.95%; MUFA: 30.27 ± 1.20%; PUFA: 22.42 ± 1.10%; n-3/n-6 ratio: 1.18), and superior antioxidant activity (H₂O₂ scavenging: 78.90 ± 2.15%; FRAP: 168.50 ± 5.20 µmol TE g⁻¹). Lipid oxidation remained minimal (TBARS: 0.22 ± 0.03&#xa0;mg malondialdehyde kg⁻¹). Microbial loads were high (total heterotrophs: 8.95 ± 0.35 × 10⁹ CFU g⁻¹; PSB: 6.45 ± 0.25 × 10⁹ CFU g⁻¹), contributing to an enriched amino acid profile with essential amino acids meeting FAO/WHO reference patterns (lysine: 8.34 ± 0.40&#xa0;g 100&#xa0;g⁻¹ protein; methionine + cysteine: 4.12 ± 0.25&#xa0;g; threonine: 5.24 ± 0.30&#xa0;g). Peptide fractionation revealed 27.75 ± 1.50% of protein as low-molecular-weight peptides (&lt; 3&#xa0;kDa), enhancing digestibility. Safety screening confirmed compliance with regulatory thresholds: heavy metals (Pb: 0.12&#xa0;mg kg⁻¹; Cd: 0.05&#xa0;mg kg⁻¹; Hg: 0.02&#xa0;mg kg⁻¹), histamine (18.5&#xa0;mg kg⁻¹), and absence of *Salmonella* and pathogenic *Vibrio* species. Water quality in biofloc systems was stabilized (total ammonia nitrogen: 0.01 ± 0.00&#xa0;mg L⁻¹; total suspended solids: 645 ± 35&#xa0;mg L⁻¹), achieving a 70% reduction in effluent discharge compared to conventional flow-through controls (*P* &lt; 0.05). The <i>D. magna</i> bioassay demonstrated that 40% dietary inclusion of PSB-FPH SCP supported growth performance and survivability comparable to high-grade fishmeal, significantly outperforming yeast-based SCP (P &lt; 0.01). Economic analysis projected a 25% reduction in protein ingredient costs at commercial scales. Integrated PSB-FPH biofloc technology effectively valorizes aquaculture processing waste into safe, bioactive, and nutritionally dense functional SCP. This system enables substantial fishmeal substitution, significantly improves water quality through effluent reduction, and demonstrates both biological efficacy and economic viability. These findings support the scalability of this circular technology as a cornerstone for sustainable larviculture nutrition under the global Blue Transformation framework.</p>

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

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年8月2日

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  • Saeid Vahdat,
  • Manizheh Biabani Asrami,
  • Reza Safari

摘要

Global aquaculture confronts twin sustainability imperatives: dwindling fishmeal supplies due to overfishing and the annual generation of over 20 million tonnes of processing by-products. Addressing these interconnected challenges, we developed an integrated bio-valorization strategy that transforms rainbow trout (Oncorhynchus mykiss) viscera—a ubiquitous aquaculture waste stream—into fish protein hydrolysate (FPH) serving as a nitrogen-rich substrate for purple sulfur bacteria (PSB)-initiated biofloc technology (BFT). Through systematic optimization of carbon-to-nitrogen ratios and microbial harvest intervals, we generated functional single-cell protein (SCP) capable of replacing 30–50% of conventional fishmeal in larviculture diets while advancing circular bioeconomy principles in aquatic food systems. Trout viscera were enzymatically hydrolyzed using Alcalase® under controlled conditions (pH 8.0, 55 °C, 3 h, enzyme-to-substrate ratio 1:100 w/w). The resulting FPH was characterized for proximate composition, degree of hydrolysis, antioxidant capacity (DPPH, FRAP, H₂O₂ scavenging), and peptide molecular weight distribution. FPH then served as the nitrogen source in PSB-inoculated biofloc systems operated at three carbon-to-nitrogen ratios (10:1, 20:1, 30:1) with harvest intervals spanning 3 to 12 h. Harvested SCP biomass underwent comprehensive analysis: proximate composition, amino acid and fatty acid profiling, antioxidant activity, peptide fractionation, microbial enumeration (total heterotrophs and PSB), and safety assessments (heavy metals, histamine, Salmonella spp., Vibrio spp.). Water quality parameters (total ammonia nitrogen, total suspended solids, dissolved oxygen, pH) were monitored throughout cultivation. A preliminary feeding trial using Daphnia magna evaluated SCP bioavailability and growth promotion relative to commercial fishmeal and yeast-based SCP. Economic feasibility was estimated through ingredient cost analysis and projected market positioning. Alcalase® hydrolysis yielded FPH containing 78.85 ± 1.20% protein (dry weight) with a degree of hydrolysis of 17.65 ± 0.85%, demonstrating robust antioxidant properties (FRAP: 153.20 ± 4.10 µmol Trolox equivalents g⁻¹; DPPH scavenging: 79.55 ± 2.30% at 20 mg mL⁻¹). Two-way ANOVA revealed highly significant effects of both C/N ratio and harvest time on all measured SCP quality parameters (P < 0.001). The optimal treatment—30:1 C/N ratio with 12-hour harvest—produced SCP with 42.55 ± 1.35% crude protein, a balanced lipid profile (total lipids: 15.85 ± 0.95%; MUFA: 30.27 ± 1.20%; PUFA: 22.42 ± 1.10%; n-3/n-6 ratio: 1.18), and superior antioxidant activity (H₂O₂ scavenging: 78.90 ± 2.15%; FRAP: 168.50 ± 5.20 µmol TE g⁻¹). Lipid oxidation remained minimal (TBARS: 0.22 ± 0.03 mg malondialdehyde kg⁻¹). Microbial loads were high (total heterotrophs: 8.95 ± 0.35 × 10⁹ CFU g⁻¹; PSB: 6.45 ± 0.25 × 10⁹ CFU g⁻¹), contributing to an enriched amino acid profile with essential amino acids meeting FAO/WHO reference patterns (lysine: 8.34 ± 0.40 g 100 g⁻¹ protein; methionine + cysteine: 4.12 ± 0.25 g; threonine: 5.24 ± 0.30 g). Peptide fractionation revealed 27.75 ± 1.50% of protein as low-molecular-weight peptides (< 3 kDa), enhancing digestibility. Safety screening confirmed compliance with regulatory thresholds: heavy metals (Pb: 0.12 mg kg⁻¹; Cd: 0.05 mg kg⁻¹; Hg: 0.02 mg kg⁻¹), histamine (18.5 mg kg⁻¹), and absence of *Salmonella* and pathogenic *Vibrio* species. Water quality in biofloc systems was stabilized (total ammonia nitrogen: 0.01 ± 0.00 mg L⁻¹; total suspended solids: 645 ± 35 mg L⁻¹), achieving a 70% reduction in effluent discharge compared to conventional flow-through controls (*P* < 0.05). The D. magna bioassay demonstrated that 40% dietary inclusion of PSB-FPH SCP supported growth performance and survivability comparable to high-grade fishmeal, significantly outperforming yeast-based SCP (P < 0.01). Economic analysis projected a 25% reduction in protein ingredient costs at commercial scales. Integrated PSB-FPH biofloc technology effectively valorizes aquaculture processing waste into safe, bioactive, and nutritionally dense functional SCP. This system enables substantial fishmeal substitution, significantly improves water quality through effluent reduction, and demonstrates both biological efficacy and economic viability. These findings support the scalability of this circular technology as a cornerstone for sustainable larviculture nutrition under the global Blue Transformation framework.