Survival and thermal resistance of Listeria monocytogenes in dry and hydrated nonfat dry milk and whole milk powder during extended storage

Abstract

The survivability and thermal resistance of Listeria monocytogenes was determined in dry and hydrated nonfat dry milk (NFDM) and whole milk powder (WMP) during 180 days of storage. The hydrated milks were prepared from stored, inoculated milk powders on the day of D- and z-value analyses. The overall L.monocytogenes population in milk powders was 7.0 log cfu g−1 on day 1, which reduced by ∼2.2 log cfu g−1 at the end of storage. The D70°C, D75°C, and D80°C of L. monocytogenes in NFDM at day 1 were 13.1, 6.0, and 4.0 min, respectively, and the D70°C, D75°C, and D80°C for WMP were 12.0, 6.3, and 3.3 min, respectively. Whereas the D70°C, D75°C, and D80°C of L. monocytogenes in NFDM at day 180 were 19.2, 10.4, and 3.8 min, respectively, and for WMP, the D70°C, D75°C, and D80° were 16.4, 9.1 and 5.2 min, respectively.