## 1 Introduction  
Cellular metabolic processes and environmental factors, i.e., atmospheric pollutants, cigarette smoke, and radiation, generate free radicals categorised as either reactive oxygen species (ROS) or reactive nitrogen species (RNS). An excess of free radicals, inducing oxidative stress, is detrimental to cell structures by way of DNA strand damage as well as lipid and protein peroxidation [1]. Long-term oxidative stress can accelerate the aging process as well as contribute to the development of a range of chronic diseases which include cancer, diabetes, and cardiovascular disease. Lifestyle and diet play an important role in the regulation of oxidative stress and can be modified to promote cellular redox balance, thereby potentially preventing damage and disease. Protection against oxidative stress in the body is provided via intracellular enzymatic antioxidant defence systems namely superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), as well as non-enzymatic defence systems such as the glutathione system consisting of reduced (GSH) and oxidized (GSSG) forms of glutathione. The antioxidant enzyme, SOD, is the first line of defence against free radicals and converts the superoxide anion (O\({}_{2}\)\({}^{-}\)) to hydrogen peroxide (H\({}_{2}\)O\({}_{2}\)) and oxygen. Both CAT and GSH-PX then reduce H\({}_{2}\)O\({}_{2}\) to water and oxygen, thereby preventing the formation of free radicals. GSH, which is a substrate for antioxidant enzymes such as GSH-Px also directly scavenges free radicals, regenerates nutrient antioxidants (vitamins A and E) to their active forms and assists the transport of amino acids through the plasma membrane [2]. A number of antioxidative fish protein hydrolyses with potential to induce health benefits via promoting cellular redox balance have been identified [3; 4; 5; 6; 7; 8]. However, the generation of antioxidant protein hydrolyses is dependent on hydrolysis conditions (protease source, temperature, pH, and degree of hydrolysis (DH)), which ultimately influences the peptide profile and amino acid composition of the resulting fractions [9]. Small molecular weight (MW) fractions rich in hydrophobic amino acids and hydrophobic di- and tripeptides are generally reported to exhibit effective antioxidant activity owing to the proton donating or electron/lipid radical scavenging ability of hydrophobic amino acids. Fish protein hydrolyses have also demonstrated both anti-inflammatory activity [10; 11; 12; 13; 14; 15] and proinflammatory activity [16; 17] via modulation of nitric oxide (NO) and inflammatory cytokines such an interleukin (IL)-6 and tumour necrosis factor-alpha (TNF-\(\alpha\)) in macrophage cell lines. The use of macrophage cells has become an increasingly popular approach to investigate the antioxidant potential of natural bioactive compounds. Although macrophages are responsible for the recognition and elimination of microbial pathogens, some virulent bacteria have been reported to induce macrophage apoptosis via stimulating ROS production [18]. Due to the adverse effects associated with some immunomodulatory drugs, protein hydrolyses generated from underutilised fish species may offer a sustainable and safe alternative for therapeutic immunomodulation. Blue whiting (_Micromesitisus poutassou_) protein hydrolyses (BWPH) have previously been demonstrated to exhibit antioxidant activity as measured by DPPH radical scavenging activity, ferrous chelating activity and reducing power [19; 20]. In addition, BWPH have also displayed cardioprotective and antigenicity activity in vitro, antidiabetic activities in vitro and in vivo and antiobesity activities in vitro, in vivo, and in clinical trials [19; 21; 22; 23; 24]. Identification of bioactive fractions or peptides from blue whiting contributes to the sustainability ethos through reducing waste by converting an underutilised source of high-quality protein, harvested at high volumes into high-value functional food ingredients.