## 2 FPHs for Human Functional Benefits
### FPH with Antioxidant and Antimicrobial Activities  
Oxidative stress, a key contributor to the degradation of essential biomolecules in both biological systems and food matrices, is closely linked to cellular impairment, tissue damage, and the decline of food quality. Antioxidants serve as critical defenders against this process by neutralising free radicals and interrupting oxidative chain reactions [48]. Inrecent years, marine-derived proteins have gained significant attention as a rich source of natural antioxidant peptides, owing to their promising bioactivity and diverse structural profiles [49]. A growing body of research has focused on the enzymatic hydrolysis of proteins from various fish species to isolate and characterise peptides with strong antioxidative potential [50; 51; 52; 53]. These peptides, typically under 6000 Da in molecular weight, display activity influenced by several key factors, including peptide length, amino acid sequence, hydrophobicity, and overall composition [54]. [PERSON] et al. [50], in their review of FPHs, noted that short-chain peptides composed of 2 to 10 amino acid residues tend to exhibit superior antioxidant efficacy. This heightened activity is largely attributed to the presence of specific amino acids known for their redox potential. [PERSON] et al. [51], further supported this observation in a study utilising Indian mackerel waste hydrolys with Alcalase and Flavourzyme, revealing that residues such as valine, leucine, proline, histidine, and particularly tyrosine play pivotal roles. Tyrosine, for instance, acts as an effective electron donor, helping to stabilise reactive species and prevent oxidative damage. Peptides exert their antioxidant effects through various mechanisms. Firstly, they can donate hydrogen atoms or electrons to free radicals, effectively neutralising and stabilising these reactive species and thereby preventing oxidative damage to biological molecules [50; 55]. Secondly, peptides possess the ability to chelate transition metal ions such as iron and copper, which are key catalysts in the generation of reactive oxygen species; by binding these metals, peptides inhibit the redox reactions that fuel oxidative stress [56; 57]. A third mechanism involves the direct interaction of peptides with reactive oxygen species, through which they interrupt the lipid peroxidation chain reaction and halt the propagation of oxidative damage across cellular membranes or food lipids [58]. Lastly, peptides may function as physical barriers by forming protective layers around lipid droplets, thereby preventing the penetration of pro-oxidative initiators and safeguarding lipid molecules from degradation [59]. [PERSON] and colleagues [60] identified three potent antimicrobial peptides from the enzymatic breakdown of Turbot viscera. These peptides, generally comprising between 1 and 50 amino acids, had molecular weights under 10 kDa. Structurally, they exhibited amphipatible properties, were notably enriched in cysteine, and carried a net cationic charge in their active conformation--features that enabled them to effectively target and disrupt bacterial cell structures. In their study, [PERSON] and colleagues [52] enzymatically hydrolys the viscera of yellowfin tuna (_Thununus albacares_) and fractionated the hydrolysate into four distinct molecular weight fractions via membrane ultrafiltration (<3 kDa, 3-10 kDa, 10-30 kDa, and >30 kDa). They evaluated the antioxidant and antibacterial activities of both the unfractionated hydrolysate and its individual fractions. The findings revealed that the smallest molecular weight fraction (<3 kDa) exhibited the most potent antibacterial effects, significantly inhibiting both Gram-positive bacteria and Gram-negative strains. These results underscore the exceptional structural and functional traits of marine-derived antimicrobial peptides, which tend to show diverse structural motifs, broad-spectrum activity, limited sedimentation, and high bacterial target specificity. [PERSON] et al.