Challenge studies with Listeria monocytogenes in a value-added seafood product stored under modified atmospheres

Challenge studies were carried out to evaluate the safety of value-added raw and cooked seafood nuggets (a(w) 0.98, pH 7.0) inoculated with 10(3) cfu g(-1) of Listeria monocytogenes. Nuggets were packaged in air, or 100% CO2, with and without an Ageless SS oxygen absorbent and stored at 4 or 12 degrees C. Headspace O-2 decreased to < 1% (v/v) in most packaged nuggets while headspace CO2 ranged between 1 and 100% depending on packaging conditions and storage temperature. Most products maintained acceptable appearance throughout storage, but nuggets stored at 12 degrees C developed sharp, acidic odors by day 28. Product pH decreased from approximately pH 7.0 at day 1 to approximately pH 4.2-5.2 in raw nuggets, and 5.5-6.7 in cooked nuggets, depending on the storage temperature. Bacillus spp. and lactic acid bacteria counts increased to 10(2) and 10(7) cfu g(-1) respectively in raw nuggets, while only Bacillus spp. reached 10(4) cfu g(-1) in cooked nuggets by 28 days. With the exception of nuggets packaged in 100% CO2, with or without an absorbent, counts of L. monocytogenes increased to approximately 10(7) cfu g(-1) in nuggets stored at both 4 and 12 degrees C after 28 days. (C) 1998 Academic Press.