Value-added utilization of undersized Paralichthys olivaceus through enzymatic hydrolysis: Fish protein supports recovery of muscle strength in age-related muscle loss!

Globally, rising sea temperatures and intensive aquaculture practices are leading to an increase in small Paralichthys olivaceus (< 500 g; sPO) that are not utilized in standard markets. Despite their high nutritional density, their small size and lower fillet yields (50 % in large vs. 40 % in small fish) reduce marketability, and they are primarily used in low-value applications such as feed and fishmeal. This study aimed to develop a high-value protein hydrolysate (sPOppH) with muscle-enhancing properties using a combined enzymatic hydrolysis process utilizing these low-marketability small P. olivaceus. sPOppH, produced through a two-step hydrolysis using Protamex®-pepsin, showed a protein yield of approximately 55 %. The results of the physicochemical property analysis showed that 80 % of the molecular weight was below 500 Da, with an average particle size of 1345 nm indicating high bioavailability, and stable viscosity under various temperature and shear conditions. Functional evaluation demonstrated that sPOppH significantly increased leg muscle weight and gastrocnemius fiber cross-sectional area in an aging-induced sarcopenia mouse model, while suppressing inflammation and oxidative stress. Furthermore, it restored myotube diameter and fusion index in C2C12 cells induced with dexamethasone, and lipidomic analysis confirmed its role in restoring of major membrane phospholipids. Therefore, this study highlights the potential of converting low-value small P. olivaceus into a functional protein source to improve muscle function, supporting the development of high-value marine products and health-oriented foods.