Chiang Mai Journal of Science

Influence of extractants on acid proteases recovery from threadfin bream (Nemipterus hexodon) and lizardfish (Saurida micropectoralis) stomachs using a conventional method was investigated. Extraction using Tris-HCl (50 mM, pH 7.0) comprising Tween 20 (0.2% v/v) from both fish species exhibited a higher acid protease activity recovery than other extractants investigated (P<0.05). Ultrasound-assisted extraction (UAE) of acid proteases from both species was also studied. The results showed that optimal extraction parameters were as follows: an extraction time of 10 and 30 min (lizardfish and threadfin bream), an ultrasonic frequency of 24 kHz and an extraction temperature of 4°C. The optimal yield with UAE was slightly higher than that of conventional extraction. The stomach extract from threadfin bream and lizardfish exhibited maximal activities at 45 and 40°C, respectively, and had the same optimal pH at pH 2.0. Protease activities from both fish species were strongly inhibited by pepstatin A. ATP exhibited no change on activity and was activated by divalent cations (CaCl2, CoCl2, CuCl2 and MgCl2), indicating pepsin characteristics. The enzyme was tested as highly stable versus surfactants (Tween 80 and Triton X-100). The results suggested that major proteases in stomach of both fish species were pepsin-like aspartic proteases.