2.4.6. Protein solubility
Protein solubility was determined as described by Benjakul and
Bauer (2000) with some modifications. To a 2 g sample, 18 ml of
0.6 M KCl was added and the mixture was homogenized for 30 s at
a speed of 13,000 rpm. The homogenate was stirred at room
temperature (25–27 C) for 4 h using a magnetic stirrer (IKAWERKE,
Staufen, Germany), followed by centrifuging at 12,000 g
for 20 min at 4 C using a Sorvall RC 26 Plus refrigerated centrifuge
(Sorvall, Norwalk, CT, USA). To 10 ml of the supernatant, cold 50%
(w/v) TCA was added to obtain the final concentration of 10%. The
precipitate was washed with 10% TCA and solubilized in 10 ml of
0.5 M NaOH. The muscle was also solubilized using 0.5 M NaOH to obtain total protein amount. Protein content was determined using
the Biuret method (Robinson & Hodgen, 1940). Protein solubility
was expressed as percentage of soluble protein relative to total
proteins in the muscle excluding connective tissues.