Protein dispersibility index (PDI), which measures the percent
of water-dispersible protein over the percent of total protein, was
determined by a slightly modified method of the AACC (1994) (that
is, the sample amount was scaled down 6 times). A 3.33-g sample
was dispersed and homogenized in 50 mL of water with a Waring
blender (Waring Laboratory and Science, New Hartford, Conn.,
U.S.A.) at 8400 rpm for 10 min (revolutions per min were measured
using a tachometer). After the slurry had separated, the supernatant
was centrifuged 10 min at 1730 × g, using a Beckman CS-6 centrifuge
(Missisauga, Ont., Canada). The supernatant was analyzed
for protein content using the method of Bradford (1976) with BSA
as standard. The % water-dispersible protein was calculated using
the following equation: PDI (%) = 100 × (soluble protein/total protein),
where the total protein was determined by Leco. Protein solubility
index (PSI), was determined by the method of Betschart
(1974) with minor modifications. A 1% protein suspension was prepared
in deionized water, stirred continuously for 30 min, and centrifuged
for 30 min at 2060 × g (Beckman CS-6 centrifuge). The supernatant
was measured for protein content using the method of
Bradford (1976). Protein solubility index was calculated as follows:
PSI (%) = 100 × (soluble protein/total protein).