New insights on Listeria monocytogenes growth in pressurised cooked ham: A piezo-stimulation effect enhanced by organic acids during storage

Abstract

The aim of the present study was to understand growth and survival responses of Listeria monocytogenes during the storage of high pressure processed (HPP) cooked ham formulated with organic acids to inhibit growth of the pathogen. Cooked ham batches were manufactured without organic acids (control), with potassium lactate (2.8% or 4%) or with potassium lactate and sodium diacetate (2.0% + 0.11% or 2.0% + 0.45%). Products were aseptically sliced and inoculated with 10 7 cfu/g or 10 2 cfu/g of either L. monocytogenes CTC1034 (a meat isolate) or a cocktail of three isolates (12MOB045Lm, 12MOB089Lm and Scott A). Vacuum-packed samples with 10 7 cfu/g were HPP at 600 MPa for 3 min, whereas samples with 10 2 cfu/g were not HPP. Growth or survival of L. monocytogenes was determined during subsequent storage at 8, 12 and 20 ºC. Growth or survival was characterized by fitting the experimental data using the primary logistic model and the log-linear with shoulder model, respectively. Secondary models were fitted to characterize the effect of temperature on growth kinetic parameters without or with HPP. For cooked ham without organic acids, growth rates of L. monocytogenes were slightly increased by HPP and lag times were longer. Interestingly, for cooked ham with organic acids, the HPP had a significant stimulating effect on subsequent growth of L. monocytogenes (piezo-stimulation). At 20 ºC, the growth rates of L. monocytogenes in cooked ham with lactate were up to 4-fold higher than those of the same product without HPP. The observed enhancement of the piezo-stimulating effect of organic acids on growth rates during storage of HPP cooked ham represents a challenge for the use of organic acids as antimicrobials in these products. A predictive model available as part of the Food Spoilage and Safety Predictor (FSSP) software seemed useful to predict growth and growth boundary of L. monocytogenes in non-pressurised cooked ham. This model was calibrated to take into account the observed piezo-stimulating effect and to predict growth of L.

Quality and Safety of Fresh Chicken Fillets after High Pressure Processing: Survival of Indigenous Brochothrix thermosphacta and Inoculated Listeria monocytogenes

“…Similar results were observed in the study of Hayman et al [20] in a variety of RTE meats inoculated with 4 log CFU/g of L. monocytogenes , where after HPP treatment (600 MPa/180 s/20 °C) L. monocytogenes was found sporadically present after enrichment for a storage period of 91 days at 4 °C. Reduction of 7 log units of a 3-strain cocktail of L. monocytogenes (7 log CFU/g initial inoculum level) was observed at 600 MPa/3 min on cooked ham in the study of Bover-Cid et al [40]. Yet, the cells that survived were able to initiate growth just after HPP treatment [40].…”

“…Reduction of 7 log units of a 3-strain cocktail of L. monocytogenes (7 log CFU/g initial inoculum level) was observed at 600 MPa/3 min on cooked ham in the study of Bover-Cid et al [40]. Yet, the cells that survived were able to initiate growth just after HPP treatment [40]. Schneinberg et al [41] reported that inoculated beef jerky which was treated with two cycles of HPP (550 MPa/60 sec/22 °C) resulted in a reduction of approximately 1 log of L. monocytogenes (7 log CFU/g initial inoculum level) and subsequently it increased during storage under vacuum packaging, in contrast to the other examined inoculated pathogens that exhibited a significant reduction in the population levels.…”

“…Several studies have monitored the survival of L. monocytogenes strains, however, to our knowledge, no work until now has implemented in typing with molecular methods the survival of Listeria strains after HPP treatment, although, the survival of different strains of the pathogen has been studied when pathogen was inoculated either as a monoculture [46,47] or as mixed culture [40] in a variety of products after different HPP treatments. Thus, PFGE typing revealed the distribution of the inoculated pathogenic strains and it was evident that pathogen survival was strain dependent.…”

Enabling Cost-Effective Screening for Antimicrobials against Listeria monocytogenes in Ham

“…However, screening methods to study the effect of antimicrobials to control the growth of LM on RTE meat products are laborious and expensive, since they typically require the use of whole food products, such as slices of deli ham (6,11,17). Antimicrobials and pathogen cultures are applied to the surface of the slice of ham.…”

High-Hydrostatic-Pressure (HHP) Processing Technology as a Novel Control Method for Listeria monocytogenes Occurrence in Mediterranean-Style Dry-Fermented Sausages

“…The combination of enterocin and HHP (400 MPa/10 min/ 17 • C) was successful in preventing the growth of L. monocytogenes and widening the shelf life of treated samples at 90 days in comparison with control samples. More recently, Bover-Cid et al [151] evaluated the elimination of spiked L. monocytogenes (10 7 CFU/g) in HHP-treated (600 MPa/3 min) sliced standard cooked hams. Standard hams were produced with organic acids and control samples without organic acids, but including potassium lactate and sodium diacetate.…”