title: Use of mild-heat treatment following high-pressure processing to prevent recovery of pressure-injured Listeria monocytogenes in milk.
abstract: This study examined the inactivation of Listeria monocytogenes in milk by high-pressure processing (HPP) and bacterial recovery during storage after HPP. We developed a technique to inhibit the bacterial recovery during storage after HPP (550 MPa for 5 min) using a mild-heat treatment (30-50 degrees C). Various mild-heat treatments were conducted following HPP to investigate the condition on which the bacterial recovery was prevented. Immediately after HPP of 550 MPa at 25 degrees C for 5 min, no L. monocytogenes cells were detected in milk regardless of the inoculum levels (3, 5, and 7 log(10)CFU/ml). However, the number of L. monocytogenes cells increased by >8 log(10)CFU/ml regardless of the inoculum levels after 28 days of storage at 4 degrees C. Significant recovery was observed during storage at 25 degrees C; the bacterial number increased by >8 log(10)CFU/ml after 3 days of storage in the case of an initial inoculum level of 7 and 5 log(10)CFU/ml. Even in the case of an initial inoculum level of 3 log(10)CFU/ml, the bacterial number reached the level of 8 log(10)CFU/ml after 7 days of storage. No bacterial recovery was observed with storage at 37 degrees C for 28 days. Milk samples were treated by various mild-heat treatments (30-50 degrees C for 5-240 min) following HPP of 550 MPa at 25 degrees C for 5 min, and then stored at 25 degrees C for 70 days. The mild-heat treatment (e.g., 37 degrees C for 240 min or 50 degrees C for 10 min) inhibited the recovery of L. monocytogenes in milk after HPP. No recovery of L. monocytogenes in milk was observed during 70-day storage at 25 degrees C in samples that received mild-heat treatments such as mentioned above following HPP (550 MPa for 5 min). Moreover, the mild-heat treatment conditions (temperature and holding time) required to inhibit the recovery of L. monocytogenes in milk was modelled using a logistic regression procedure. The predicted interface of recovery/no recovery can be used to calculate the mild-heat treatment condition to control bacterial recovery during storage at 25 degrees C after HPP (550 MPa for 5 min). The results in this study would contribute to enhance the safety of high-pressure-processed milk.
authors.affiliation: National Food Research Institute, 2-1-12, Kannondai, Tsukuba, Ibaraki 305-8642, Japan. koseki@affrc.go.jp
authors.forename: Shigenobu
authors.initials: S
authors.lastname: Koseki
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Mizuno
authors.forename: Kazutaka
authors.initials: K
authors.lastname: Yamamoto
mesh_terms: D000818:Animals; D015169:Colony Count, Microbial; D003257:Consumer Product Safety; D005511:Food Handling / Q000379:methods*; D005516:Food Microbiology; D005519:Food Preservation / Q000379:methods; D006358:Hot Temperature; D006801:Humans; D006874:Hydrostatic Pressure; D007700:Kinetics; D008089:Listeria monocytogenes / Q000254:growth & development*; D016015:Logistic Models; D008892:Milk / Q000382:microbiology*; D013997:Time Factors