Fish viscera are usually discarded as waste, causing environmental problems, or as low-value by-products. This study describes a self-sufficient and zero waste approach to obtain enzymes and protein hydrolysates from fish by-products. Firstly, recovery steps of viscera enzymatic extract were applied, and the resulting raw extract was stable at a pH range of 8–9 and at temperatures between 40 and 50 °C. The application of the extracted enzymes and alcalase on fish by-products hydrolysis was also determined. The selected conditions for the enzymatic hydrolysis were 10% (E/S) for 6 h using viscera enzymatic extract and 3% (E/S) for 2 h using alcalase. Fish protein hydrolysates (FPH) proved to have a notable antioxidant capacity with similar activity, ~11 mg ascorbic acid/g dry extract (ABTS assay) and ~150 mg Trolox/g dry extract (ORAC assay). FPH were also able to inhibit the angiotensin-converting enzyme, however, alcalase hydrolysates revealed a higher antihypertensive potential, IC₅₀ of 101 µg of protein/mL. In general, FPH obtained by both enzymes systems maintained these bioactivities after the passage throughout a simulated gastrointestinal tract. The hydrolysates also displayed important technological properties, namely oil absorption capacity (~1 g oil/g sample) and emulsifying property (~40%). Therefore, it will be conceivable to use fish by-products based on a circular economy approach to generate added value compounds for animal and human nutrition.

The apparent digestibility coefficients (ADCs) of differently processed okara meals were assessed in Nile tilapia diets: dried okara not autoclaved (FOK), dried okara autoclaved (AOK), okara hydrolyzed with Alcalase (ALOK) or Cynara cardunculus proteases (CYOK), and hydrolyzed okara fermented with lactic bacteria: Lactobacillus rhamnosus R11 (CYR11OK) or Bifidobacterium animalis ssp. lactis Bb12 (CYB12OK). Okara processing significantly affected nutrient digestibility: dry matter ADC was highest in CYR11OK (80%) and lowest in FOK (40%). The lowest protein digestibility was observed in CYR11OK (72%), and the highest in AOK (97%) and CYOK (91%), evidencing the effectiveness of the autoclave and the use of C. cardunculus proteases to increase okara protein bioavailability. The inclusion of up to 20% of AOK or CYOK did not affect fish growth, nutrient utilization, or whole body composition of Nile tilapia. The flesh quality (color, pH, water activity, cohesiveness, elasticity and resilience) was not affected by the dietary incorporation of AOK or CYOK. Fish fed with AOK diets stand out for their high density of muscle fibers, particularly in AOK20, which can explain their high muscle firmness and may result in further hypertrophic growth. Altogether, results suggest that hydrolyzed or autoclaved okara are valuable ingredients for Nile tilapia diets.

Porcine blood is a major slaughterhouse by-product and a sustainable source of high-quality proteins with potential food and nutraceutical applications. This study valorized porcine whole blood (WB, 6.7 ± 0.1% protein) and red cell fraction (CF, 50.4 ± 0.2% protein) through alcalase hydrolysis, generating hydrolysates (WBH and CFH) with bioactive and techno-functional properties. Optimal hydrolysis conditions, defined as enzyme-to-substrate (E/S) and incubation time yielding the highest degree of hydrolysis (DH) with cost-effective enzyme usage, were 1% E/S for 4 h (WBH) and 2.5% E/S for 4 h (CFH). WBH showed a higher DH (59.5 ± 2.6%) than CFH (30.8 ± 3.3%). Antioxidant assays revealed higher ABTS activity in CFH (14.1 vs. 11.1 mg ascorbic acid equivalents/g, p < 0.05), while both exhibited similar ORAC values (166.8–180.2 mg Trolox equivalents/g, p > 0.05). After simulated gastrointestinal digestion, ABTS activity was preserved, whereas ORAC decreased (~40%). ACE inhibitory activity was also pronounced, particularly in CFH (IC₅₀ = 59.5 µg protein/mL), but digestion converged values between hydrolysates (118–135 µg protein/mL). Techno-functional tests showed moderate emulsifying activity (~40%), with CFH displaying markedly higher oil absorption (4.79 vs. 1.31 g oil/g). Considering the limited information on porcine blood hydrolysates under gastrointestinal conditions, these findings provide new insights into their stability and support their potential as multifunctional ingredients for health-promoting foods and functional formulations.