_Article_  
**Evaluation of the Antioxidant and Antimicrobial Activities of Porcine Liver Protein Hydrolysates Obtained Using Alcalase, Bromelian, and Papain**  
**[PERSON] 1(c)**, **[PERSON] 1(c)**, **[PERSON] 2(c)**, **[PERSON] 1(c)**,  
**[PERSON] 3 and [PERSON] 1,**  
1 Centro Tecnologico de la Carne de Galicia, Rua Galicia No 4, Parque Tecnologico de Galicia, San Cibrao das Vinas, 32900 Ouresne, Spain; [EMAIL_ADDRESS] (P.B.); [EMAIL_ADDRESS] (M.P.); [EMAIL_ADDRESS] (D.F)
2 Food Quality and Sensory Science Department, Teagasc Ashtown Food Research Centre, Ashtown, D15 DY05 Dublin 15, Ireland; [EMAIL_ADDRESS]
3 Key Laboratory of Meat Processing and Quality Control, Ministry of Education China, Jiangsu Collaborative Innovation Center of Meat Production and Processing, Quality and Safety Control, College of Food Science and Technology, Nanjing Agricultural University, Nanjing 210095, China; [EMAIL_ADDRESS]
* Correspondence: [EMAIL_ADDRESS]; Tel.: +34-988-548-277  
Received: 29 February 2020; Accepted: 24 March 2020; Published: 27 March 2020  
**Featured Application: Bioactive peptides derived from meat by-products have generated increasing interest in the development of functional foods. This application promotes the principles of a sustainable circular economy, since it allows an efficient use of meat by-products. Therefore, the use of by-products generated from slaughterhouses, which are not appropriate for human consumption, would maximize the use of existing nutritional sources and avoid the contamination caused by these waste products. In addition, the antioxidant and antimicrobial activities associated with these bioactive compounds would allow them to replace the synthetic products used today, which are associated with adverse effects on human health.**  
**Abstract:** In order to make the by-products generated from the porcine industry more valuable, pig livers were used in this trial to obtain protein hydrolysates. Three proteases (alcalase, bromelin, and papain) were utilized for enzymatic hydrolysis with two different durations, 4 and 8 hours. Ultrafiltration process was used for the recovery of the extracts, employing three different membrane pore sizes (30, 10, and 5 kDa). The porcine livers contained considerable amounts of protein (19.0%), considering they are almost composed of water (74.1%). The antioxidant activity of the obtained hydrolysates was investigated using four antioxidant methods (2,2-Diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity, 2-2'-Azino-di-[3-ethylbenzthiaazoline sulfonate] (ABTS) radical scavenging activity, ferric reducing antioxidant power assay (FRAP), and oxygen radical absorbance capacity assay (ORAC)). Antibacterial properties were also measured against Gram-negative and Gram-positive bacteria. Results indicated that the three studied factors (type of enzyme, membrane pore size, and time) significantly affected the parameters evaluated. Hydrolysates obtained at 8 hours with alcalase had the best antioxidant properties. The 30 kDa alcalase extracts exhibited the highest DPPH (562 \(\upmu\)g Trolox/g), FRAP (82.9 \(\upmu\)mol Fe\({}^{2+}\)/100 g), and ORAC (53.2 mg Trolox/g) activities, while for ABTS the 10 kDa alcalase showed the higher values (1068 mg ascorbic acid/100 g). Concerning the antibacterial activity, 30 kDa hydrolysates obtained with bromelin for 4 hours exhibited the highest antimicrobial capacity, providing an inhibition of 91.7%.  
**Keywords:** meat by-products; enzymatic hydrolysis; antibacterial; radical scavenging activity