Thermal Inactivation of Listeria monocytogenes in Chicken Gravy

Abstract

Heat resistance of Listeria monocytogenes strains V7 and Scott A in chicken gravy and changes in heat resistance during refrigerated storage were studied. After chicken gravy was made, it was cooled to 40°C, inoculated with 105 CFU L. monocytogenes per ml of gravy, and then stored at 7°C for 10 d. Gravy was heated at 50, 55, 60, and 65°C immediately after inoculation and after 1, 3, 5, and 10 d of refrigerated storage. The D values for strains Scott A and V7 in gravy heated at 50°C at day 0 were 119 and 195 min and at day 10 they were 115 and 119 min, respectively, whereas at 65°C comparable values at day 0 were 0.48 and 0.19 min and at day 10 they were 0.014 and 0.007 min. Heat resistance (expressed as D values) was greater at day 0 than at the end of refrigerated storage. The z values ranged from 3.41 to 6.10°C and were highest at the early stages of chill storage and then decreased at the later stages. Strain V7 was more heat resistant than Scott A at 50°C. Strain Scott A always had a higher z value than did strain V7 at the same storage interval. A heat treatment greater than the 4-D process recommended by the U.S. Department of Agriculture was required to inactivate the large numbers of L. monocytogenes that developed in chicken gravy during refrigerated storage.

Heat‐Resistance of Escherichia Coli O157:H7 in Meat and Poultry as Affected by Product Composition

“…Higher fat levels in all products resulted in higher D-values, consistent with other reports on this and other foodbome bacterial pathogens (Line, 1991;Doyle and Schoeni, 1987;Huang et al, 1992). Filppi (1973) showed that increasing the fat content of hamburger increased the D-value of poliovirus.…”

Factors affecting the heat resistance of Escherichia coli O157 : H7

“…There were some practical difficulties with this experiment but survivors were detected after heating at 60°C for 1 h or at 70°C for 5 min (Table 3), suggesting the importance of fat content of a food product in determining the efficiency of a cooking process. Higher fat levels in food products have resulted in higher D-values of this and other food-borne bacterial pathogens (Doyle and Schoeni 1987 ;Line et al 1991 ;Huang et al 1992 ;Ahmed et al 1995). That the heat protection phenomenon of fats is due to reduced water activity in the fat during heating has been proved by -------------------------------------------------- ---------------------------- ----------------------------------------------------- -------------------------------------------------- Senhaji (1977).…”

Some Like It Hot: Heat Resistance of Escherichia coli in Food

“…An increased fat content in food products increased the heat resistance of E. coli in some studies (Line et al, 1991; Huang et al, 1992; Ahmed et al, 1995; Smith et al, 2001; Liu et al, 2015), while other studies reported decreased resistance, no effect, or strain-specific effects (Kotrola and Conner, 1997; Vasan et al, 2014; Liu et al, 2015). The potential direct effects of fat on heat resistance of E. coli are confounded by the strong effect of fat on heat transfer in solid foods.…”