A histaminic-forming population was determined using the
technique described by Niven Junior, Jeffrey and Corlett Junior
(1981). Ten grams of muscle were homogenized as previously
described for total viable count, and 1 mL of suitable dilutions
was inoculated in modified Niven’s agar containing 0.5%
triptone, 0.5% yeast extract, 2.0% L-histidine·2HCl, 0.5% NaCl,
0.1% Calcium carbonate, 3.0% bacteriologic agar (Bioxon),
and 0.006% bromocresol purple; pH was adjusted to 5.5 with
0.1 N HCl. Petri dishes were incubated at 5 °C for ten days to
determine the presence of psychrophilic microorganisms, and
the presence of mesophilic microorganisms were determined
by incubating at 37 °C for 48 h. Colonies showing a purple halo
were considered to be histamine-forming bacteria.