## 1 Introduction  
The practical and value-added utilization of animal by-products is crucial to sustainable livestock production goals, particularly considering the significant socio-economic losses and environmental pollution associated with their disposal [1]. Generally, animal by-products are categorized as edible, non-edible, and waste materials [2]. Edible by-products include the blood and organs (e.g., liver, kidney, heart, lung, and intestine), which are both nutritious and protein-rich and are traditionally consumed as delicacies or used as valuable feed ingredients [1]. Meanwhile, despite their low cost, non-edible animal by-products are industrially rendered to produce carbonaceous and nitrogenous compounds without a value-adding process [2; 3]. Industrial efforts have mainly focused on identifying novel ways to commercialize these underutilized by-products and developing advanced technologies to enhance their value. Protein hydrolysate from animal by-products has been identified as a potential animal feed resource due to its nutritional benefits (such by-products are high in protein, with a balanced amino acid profile), high digestibility, growth-promoting effects, immune support, palatability, and competitive cost [3]. Traditionally, protein hydrolysis has primarily been used to improve the solubility and digestibility of low-value by-products such as bone, skin, and feathers [2]. Recently, however, enzymatic hydrolysis has been utilized to generate bioactive peptides, enhancing the physiological benefits of edible by-products. In particular, the application of enzymatic hydrolyzates derived from edible by-products has markedly increased in sectors that place greater emphasis on anti-allergenic and functional properties, such as in pet food production, whereas such processes are not considered when creating traditional animal feed for livestock [3]. Moreover, protein hydrolyzates derived from animal by-products containing antioxidant peptides enhance the antioxidant content in animal feed [3]. Previous studies have reported that incorporating antioxidant protein hydrolyzates could delay lipid oxidation in feed or produce antioxidant effects in vivo in animals [4; 5]. Previous studies have indicated that porcine liver is a promising edible by-product which produces protein hydrolyzates rich in antioxidative peptides; this can be attributed to its high protein content and balanced amino acids [6; 7; 8; 9]. [PERSON] et al. [6] reported that trypsin outperformed Alcalase and papain in terms of enhancing the antioxidant and antimicrobial activities of porcine liver hydrolyzates. Meanwhile, [PERSON] et al. [7] observed that Alcalase-hydrolyzed porcine liver had a better antioxidant capacity compared to hydrolyzates treated with bromelain or papain. According to [PERSON] et al. [8], ferritin and trypsinogen in porcine liver are parent proteins that play major roles in the generation of antioxidative peptides. Moreover, previous research found that whole trypsin-mediated porcine hydrolyzate exhibited higher antioxidant capacity than specific molecular weight fractions [9]. Given that peptide fractionation involves additional costs associated with the separation and purification processes, the applicability of whole protein hydrolyzates could be highly encouraging from an industrial perspective. Moreover, previous reports suggest that Alcalase and trypsin are industrially applicable proteases capable of ensuring effective protein hydrolysis [8; 9]. Animal by-products collected from slaughterhouses are often gathered and distributed in bulk without undergoing any form of sorting or categorization. In Korea, it is common practice to separate edible pork by-products into red offal (thoracic organs, such as liver, heart, and lung) and white offal (abdominal organs, such as stomach, pancreas, spleen, kidney, and intestines) to prevent cross-contamination.