Proteinases from the Liver of Albacore Tuna (Thunnus Alalunga): Optimum Extractant and Biochemical Characteristics

Abstract

Proteolytic activity of the extract from albacore tuna (Thunnus alalunga) liver was studied. Optimum pH and temperature for casein hydrolysis were 8.5 and 55C, respectively. The enzyme was stable to heat treatment up to 50C and in the pH range of 7.0–10.0 for 30–120 min. The proteolytic activity was strongly inhibited by soybean trypsin inhibitor, N-p-tosyl-L-lysine chloromethyl ketone and phenylmethylsulfonyl fluoride. Activities of the liver extract continuously decreased with increasing NaCl concentration (0–30%), while activities increased as CaCl2 concentration increased. Based on activity staining, the molecular weights of the proteinases in albacore tuna liver were 21, 24, 30 and 34 kDa. Optimum extraction medium for proteinase recovery from albacore tuna liver was also investigated. Extraction of the liver powder with 50 mM Na phosphate buffer (pH 7.0) containing 0.2% (v/v) Brij 35 rendered a higher recovery of proteinase activity than other extractants tested (P < 0.05). The results suggested that major proteinases in albacore tuna liver were heat-activated alkaline proteinases, most likely trypsin-like serine proteinases. Practical Applications High amount of albacore tuna liver–containing proteinases is generated during canned tuna manufacturing. Major proteinases found in albacore tuna liver were trypsin-like serine proteinase that can be recovered and used mainly for hydrolysis purposes. Therefore, it is expected that albacore tuna liver can be used as a promising source of proteinase for further applications.