The objective of this study was to obtain dry inocula of Salmonella Tennessee and Enterococcus faecium, a surrogate for thermal inactivation of Salmonella in low-moisture foods, and to compare their thermal resistance and stability over time in terms of survival. Two methods of cell growth were compared: cells harvested from a lawn on tryptic soy agar (TSA-cells) and from tryptic soy broth (TSB-cells). Concentrated cultures of each organism were inoculated onto talc powder, incubated at 35°C for 24 h, and dried for additional 24 h at room temperature (23 ± 2°C) to achieve a final water activity of ≤0.55 before sieving. Cell reductions of Salmonella and E. faecium during the drying process were between 0.14 and 0.96 log CFU/g, depending on growth method used. There was no difference between microbial counts at days 1 and 30. Heat resistance of the dry inoculum on talc inoculated into a model peanut paste (50% fat and 0.6 water activity) was determined after 1 and 30 days of preparation, using thermal death time tests conducted at 85°C. For Salmonella, there was no significant difference between the thermal resistance (D85°C) for the TSB-cells and TSA-cells (e.g. day 1 cells D85°C = 1.05 and 1.07 min, respectively), and there was no significant difference in D85°C between dry inocula on talc used either 1 or 30 days after preparation (P > 0.05). However, the use the dry inocula of E. faecium yielded different results: the TSB-grown cells had a significantly (P < 0.05) greater heat resistance than TSA-grown cells (e.g. D85°C for TSB-cells = 3.42 min versus 2.60 min for TSA-cells). E. faecium had significantly (P < 0.05) greater heat resistance than Salmonella Tennessee regardless what cell type was used for dry inoculum preparation; therefore, it proved to be a conservative but appropriate surrogate for thermal inactivation of Salmonella in low-moisture food matrices under the tested conditions.
Skip Nav Destination
Close
Article navigation
Research Article|
June 01 2015
Development of a Dry Inoculation Method for Thermal Challenge Studies in Low-Moisture Foods by Using Talc as a Carrier for Salmonella and a Surrogate (Enterococcus faecium)
ELENA ENACHE;
ELENA ENACHE
*
Grocery Manufacturers Association, 1350 I Street N.W., Suite 300, Washington, D.C. 20005, USA
* Author for correspondence. Tel: 202-639-5969; Fax: 202-639-5991; E-mail: eenache@gmaonline.org.
Search for other works by this author on:
AI KATAOKA;
AI KATAOKA
Grocery Manufacturers Association, 1350 I Street N.W., Suite 300, Washington, D.C. 20005, USA
Search for other works by this author on:
D. GLENN BLACK;
D. GLENN BLACK
Grocery Manufacturers Association, 1350 I Street N.W., Suite 300, Washington, D.C. 20005, USA
Search for other works by this author on:
CARLA D. NAPIER;
CARLA D. NAPIER
Grocery Manufacturers Association, 1350 I Street N.W., Suite 300, Washington, D.C. 20005, USA
Search for other works by this author on:
RICHARD PODOLAK;
RICHARD PODOLAK
Grocery Manufacturers Association, 1350 I Street N.W., Suite 300, Washington, D.C. 20005, USA
Search for other works by this author on:
MELINDA M. HAYMAN
MELINDA M. HAYMAN
Grocery Manufacturers Association, 1350 I Street N.W., Suite 300, Washington, D.C. 20005, USA
Search for other works by this author on:
J Food Prot (2015) 78 (6): 1106–1112.
Article history
Received:
August 21 2014
Accepted:
February 12 2015
Citation
ELENA ENACHE, AI KATAOKA, D. GLENN BLACK, CARLA D. NAPIER, RICHARD PODOLAK, MELINDA M. HAYMAN; Development of a Dry Inoculation Method for Thermal Challenge Studies in Low-Moisture Foods by Using Talc as a Carrier for Salmonella and a Surrogate (Enterococcus faecium). J Food Prot 1 June 2015; 78 (6): 1106–1112. doi: https://doi.org/10.4315/0362-028X.JFP-14-396
Download citation file:
Close