Recovery potential of heat-injured cells of Listeria under ice cream temperature abuse conditions versus simulated gastrointestinal fluids

Document Type


Publication Date



2019 American Dairy Science Association Annual Meeting: Cincinnati, Ohio


American Dairy Science Association


Journal of Dairy Science










Listeria, recovery, injured


Serving practices in nursing homes may result in temperature abuse of ice cream before consumption. Presence of even low numbers of injured cells may pose a risk, due to their potential to recover, especially to immunocompromised patients. This investigation was conducted to evaluate injured cell recovery under temperature abuse conditions and on exposure to gastrointestinal (GI) fluids. Based on our previous studies, ice cream mix samples (42% TS), spiked with 4.54 log cfu/gram of Listeria innocua, were lab pasteurized (69°C for 30 min). Heat-injured cells were recovered in BLEB, followed by isolation on MOX. The ice cream mix samples, containing injured cells, were followed through overnight aging (7°C), freezing (−4°C), and overnight hardening (−40°C) steps. To simulate serving practices, the samples were held for 12 h at 4.4°C, followed by 30 min holding at room temperature (22°C), identified as the first cycle of temperature abuse. In all, the samples were exposed to 3 such consecutive cycles. At the end of each cycle, direct plating was done on MOX to detect any intact cells. Parallelly, the ice cream samples, containing injured cells, were mixed (1:1) with simulated gastric fluids (pH 1.0 and 2.0) and were held at 37°C in a shaker incubator. Samples were drawn at 15, 30, and 60 min intervals. For studying the effect of sequential transit through a simulated intestinal fluid, 2 mL of gastric fluid + ice cream (1:1) from gastric fluid experiments were added to 50 mL of simulated intestinal fluid (pH 6.8) and held at 37°C, as above. Samples were drawn at 30, and 360 min intervals. To ascertain the recovery of any injured cells, samples were direct plated on MOX. Experiments were conducted in replicates of 3 and counts were compared for differences. The temperature abuse or GI fluid exposure studies did not result in any recovery of injured cells in the ice cream samples. However, it was also observed that the injured cells were not eliminated during exposure to gastric fluid. Further studies are necessary to understand the exact implications of these findings.