Survival of Listeria monocytogenes introduced as a post-aging contaminant during storage of low-salt Cheddar cheese at 4, 10, and 21°C

Abstract

Traditional aged Cheddar cheese does not support Listeria monocytogenes growth and, in fact, gradual inactivation of the organism occurs during storage due to intrinsic characteristics of Cheddar cheese, such as presence of starter cultures, salt content, and acidity. However, consuming high-salt (sodium) levels is a health concern and the dairy industry is responding by creating reduced-salt cheeses. The microbiological stability of low-salt cheese has not been well documented. This study examined the survival of L. monocytogenes in low-salt compared with regular-salt Cheddar cheese at 2 pH levels stored at 4, 10, and 21°C. Cheddar cheeses were formulated at 0.7% and 1.8% NaCl (wt/wt) with both low and high pH and aged for 10 wk, resulting in 4 treatments: 0.7% NaCl and pH 5.1 (low salt and low pH); 0.7% NaCl and pH 5.5 (low salt and high pH); 1.8% NaCl and pH 5.8 (standard salt and high pH); and 1.8% NaCl and pH 5.3 (standard salt and low pH). Each treatment was comminuted and inoculated with a 5-strain cocktail of L. monocytogenes at a target level of 3.5 log cfu/g, then divided and incubated at 4, 10, and 21°C. Survival or growth of L. monocytogenes was monitored for up to 90, 90, and 30 d, respectively. Listeria monocytogenes decreased by 0.14 to 1.48 log cfu/g in all treatments. At the end of incubation at a given temperature, no significant difference existed in L. monocytogenes survival between the low and standard salt treatments at either low or high pH. Listeria monocytogenes counts decreased gradually regardless of a continuous increase in pH (end pH of 5.3 to 6.9) of low-salt treatments at all study temperatures. This study demonstrated that post-aging inoculation of L. monocytogenes into low-salt (0.7%, wt/wt) Cheddar cheeses at an initial pH of 5.1 to 5.5 does not support growth at 4, 10, and 21°C up to 90, 90, and 30 d, respectively. As none of the treatments demonstrated more than a 1.5 log reduction in L. monocytogenes counts, the need for good sanitation practices to prevent post-manufacturing cross contamination remains.

Behaviour of Listeria monocytogenes in raw milk Cantal type cheeses during cheese making, ripening and storage in different packaging conditions

“…It was in the same range than those found in Cantal cheeses by De Freitas et al (2007). As discussed by Wemmenhove et al (2013) and by Shrestha, Grieder, McMahon, and Nummer (2011), such concentrations alone cannot affect the behaviour of L. monocytogenes.…”

Effect of Reduced Sodium Cheese on the Growth of Pathogenic Bacteria and Inactivation of Listeria Innocua Using Supercritical Fluid Extraction With Co2

“…There was no significant difference in pH between reduced and regular sodium Mozzarella cheeses stored at 4 and 12 °C at either 90 or 30 days (Table 2-10). 14 log CFU/g in low and standard salt Cheddar cheese (0.7% and 1.8%), with a pH similar to this study, stored at 4, 10, and 21 °C, respectively (Shrestha et al, 2011a). However, the salt concentration and cheese type used differed from the present study, which caused a significantly higher reduction at higher temperatures.…”

“…Other researchers also studied the fate of L. monocytogenes and Salmonella in low (0.7 %) and regular (1.8 %) Cheddar cheese. Listeria monocytogenes and Salmonella counts gradually decreased for each treated cheese regardless of salt concentration (Shrestha et al 2011a ;Shrestha et al, 2011b). However, Hystead et al (2013) reported that L. monocytogenes inoculated in Cheddar cheese after two and three weeks of cheese aging survived and grew better in low sodium (between 1.26 to 1.65%) cheese compared to regular sodium Cheddar cheese during storage day at 4 °C, but growth was not enhanced at 12°C.…”

“…Dairy products were also rated as the number one cause of hospitalization and the second highest to cause death (Gould et al, 2014;CDC, 2012). Lowering the sodium content of cheese may cause an increase in the growth and or survival of pathogenic bacteria (Shrestha et al 2011a ;Shrestha et al, 2011b). Therefore, it is essential to investigate whether lowering the salt content of Mozzarella cheese affects the survival of pathogenic bacteria since foodborne illness due to cheese consumption is already a risk.…”

Effect of Antimicrobials and Sodium Replacement Agents on the Survival of Pathogenic Bacteria in Low Sodium Low-Moisture Part-Skim (LMPS) Mozzarella Cheese

“…monocytogenes survived for 90, 90 and 30 days in cheddar cheese when incubated at 4°, 10° and 21°C, respectively (Shrestha et al, 2011a). No decrease in L. monocytogenes counts was observed over the 12 day incubation at 10°C when the organism was artificially inoculated into cuajada, a semisolid dairy product (Arques et al, 2008a).…”