Commercial fish sauce from squid liver was purchased from a
local market in Japan. Fish sauce samples were exposed to air for
1 month and were treated with the commercial chelate resins DIAION
CR11 and CR20 (Mitsubishi Chemical Co., Tokyo, Japan), which
are approved as food additives in Japan. Chelating groups on CR11
and CR20 include iminodiacetic acid and ethylene diamine, respectively.
Prior to experiments, resins were conditioned using the
standard procedures described in associated operation manuals.
Briefly, chelate resins (7 g) were washed with 2-M hydrochloric
acid (30 mL), water (30 mL, 2 times), 2-M sodium hydroxide
(30 mL), and then water (30 mL, 3 times) in sequence.