High-Temperature Short-Time Pasteurization Inactivates Listeria monocytogenes

Abstract

Full scare commercial pasteurization equipment operated at 72–73°C with a holding time of 15–16 s was used to determine the ability of commercial thermal processing to inactivate Listeria monocytogenes strain Scott A. Three methods of providing L. monocytogenes concentration in raw milk were employed: freely suspended (extra-cellular), inside bovine phagocytes (in vitro procedure), and inside bovine phagocytes in experimentally infected cows (in vivo). Three enrichment methods were used to assay for L. monocytogenes after pasteurization: cold enrichment (4°C, 28 d), selective enrichment of Lovett et al. (FDA procedure) (17), and the USDA-FSIS two stage enrichment procedure. In addition, a 1-L sample taken just before the vacuum breaker was incubated undiluted in the original sample container (4°C, 4 weeks). None of the four assay methods could detect Listeria in the pasteurized milk.

PRESENCE OF LISTERIA IN MEXICAN CHEESES

“…These results are in agreement with a study that reported positive posphatase tests in Listeria contaminated cheese samples (Lovett et al 1990). Other factors that favor Listeria growth and multiplication in cheese are: the initial concentration of Listeria in milk, the composition of cheese and the strain of Listeria in cheese (Yousef et al 1988).…”

Inactivation Kinetics of Listeria innocua in Skim Milk in a Continuous Flow Processing System

“…Edwards et al (1965) and Busta (1967) used a steam injection pilot plant UHT sterilizer to study the thermal death kinetics of B. subtilis and B. stearothermophilus spores, respectively. The death kinetics of vegetative cells have been studied in plate-type pasteurizers (Farber et al, 1988;Doyle et al, 1987;Lovett et al, 1990). In these continuous flow systems, decimal reduction times are determined from initial and final colony counts and represent the total thermal destruction resulting from non-isothermal and isothermal functions of the' process.…”

Effect of heat treatment on Listeria monocytogenes and Gram‐negative bacteria in sheep, cow and goat milks

“…Several workers have shown that L. monocytogenes cannot survive H T S T pasteurization (71.7"C/15 s) in cow milk (Bradshaw et al 1985;J3eckers el al. 1987;Lovett et al 1990).…”