Effects of Selected Process Parameters on Physical and Sensorial Properties of Yellowfin Tuna (Thunnus albacares) Skin Gelatin

Four potential input variables, namely, acid concentration (0.01-0.1mol/L), pretreatment time (1-3h), extraction temperature (40-55C) and extraction time (1-6h) were investigated to identify the key factors that affect gelatin yield and the physical (gel strength, viscosity and melting point) and sensorial (color, odor and overall liking) properties of gelatin produced from yellowfin tuna (Thunnus albacares) skins. For all processes employed, a preliminary two-step alkaline pretreatment was applied using a 0.2mol/L sodium hydroxide solution for 30min for each step. Factorial analysis indicated that acid concentration, extraction temperature and time, as well as the interaction term extraction temperaturexextraction time were significant for gelatin yield, while acid concentration and the interaction term acid concentrationxextraction time were important for the physical properties of gelatin (P<0.05). Sensorial properties were affected by acid concentration only (P<0.05). Sum scores analysis revealed that the most suitable process for gelatin manufacture from yellowfin tuna skins comprises of the preliminary two-step alkaline pretreatment, followed by an acidic pretreatment using a 0.1mol/L acetic acid solution for 1h and subsequently extracting gelatin with water at 55C for 6h. Practical ApplicationsProcessing of yellowfin tuna (T.albacares) in the north central coastal region of Greece generates large amounts of byproducts (e.g., skins, bones, heads, scales and viscera), which can account for up to 50% of the total fish weight. Despite the presence of several valuable components, such as protein and lipid, yellowfin tuna processing byproducts are usually being dumped into landfills or end up as low commercial value products (e.g., animal feed). Utilization of the aforementioned byproducts, especially of collagen-rich fish skins, for the production of gelatin, will not only increase their commercial value, but will also satisfy the needs of the fish processing industries that face waste disposal problems.