Effect of water activity on inactivation of Listeria monocytogenes and lactate dehydrogenase during high pressure processing

Melinda M. Hayman, Gilles K. Kouassi, Ramaswamy C. Anantheswaran, John D. Floros, Stephen John Knabel

Research output: Contribution to journalArticle

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Abstract

The aim of this study was to investigate the effect of water activity (aw) on the inactivation of Listeria monocytogenes and lactate dehydrogenase (LDH) during high pressure processing (HPP). For microbial inactivation lyophilized cells of L. monocytogenes 19,115 were left dry or were suspended in 10 ml of 0.1% peptone water, 10 ml of glycerol, or mixtures of glycerol and peptone water. All samples of various aws were high pressure (HP) processed at ambient temperature at 600 MPa for 300 s. Following HPP, samples were serially diluted in 0.1% peptone and spread-plated on Tryptic Soy agar supplemented with Yeast Extract. For enzyme inactivation, 4.2 mg of lyophilized LDH was suspended in 2 ml of 100 mM phosphate buffer (pH 7.4), 2 ml of peptone water or glycerol, or in 2 ml mixtures of glycerol and peptone water. A lyophilized sample with no added liquid was also included. All enzyme samples were subjected to HPP as described above. After HPP, LDH was diluted to 0.28 μg/ml in 100 mM phosphate buffer (pH 7.4). LDH activity was assessed by measuring the change in concentration of β-NADH as a function of time. Dynamic light scattering analysis (DLS) was performed to examine the size distribution, polydispersity, and hydrodynamic radius of LDH before and after HPP. No significant difference in CFU/g was observed between lyophilized cells not subjected to HPP and lyophilized cells subjected to 600 MPa for 300 s (P < 0.05). However, lyophilized cells that were suspended in 100% to 60% peptone water showed a ~ 7.5-log10 reduction when subjected to HPP. Survival of L. monocytogenes following HPP significantly increased (P < 0.05) when the peptone water concentration was decreased below 60% (aw ~ 0.8). DLS results revealed that LDH suspended in buffer underwent aggregation following HPP (600 MPa, 300 s). Inactivation rate constants obtained using a first-order kinetic model indicated that untreated and HP processed lyophilized LDH had similar activities. When LDH was subject to HPP in solutions containing glycerol, enzyme activity decreased as the water content increased (r2 = 0.95). Lyophilization completely protected L. monocytogenes and LDH from inactivation by high pressure. Furthermore, enzyme activity and cell survival increased as water activity was decreased. We postulate low aw results in protein stabilization, which prevents protein denaturation and cell death during HPP.

Original languageEnglish (US)
Pages (from-to)21-26
Number of pages6
JournalInternational journal of food microbiology
Volume124
Issue number1
DOIs
StatePublished - May 10 2008

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high pressure treatment
Listeria monocytogenes
lactate dehydrogenase
L-Lactate Dehydrogenase
water activity
inactivation
peptones
Pressure
Peptones
Water
glycerol
Glycerol
buffers
water
light scattering
Buffers
Enzymes
cells
phosphates
enzyme activity

All Science Journal Classification (ASJC) codes

  • Food Science
  • Microbiology

Cite this

@article{2ccc85f92864444c9e47e81c77a1fec4,
title = "Effect of water activity on inactivation of Listeria monocytogenes and lactate dehydrogenase during high pressure processing",
abstract = "The aim of this study was to investigate the effect of water activity (aw) on the inactivation of Listeria monocytogenes and lactate dehydrogenase (LDH) during high pressure processing (HPP). For microbial inactivation lyophilized cells of L. monocytogenes 19,115 were left dry or were suspended in 10 ml of 0.1{\%} peptone water, 10 ml of glycerol, or mixtures of glycerol and peptone water. All samples of various aws were high pressure (HP) processed at ambient temperature at 600 MPa for 300 s. Following HPP, samples were serially diluted in 0.1{\%} peptone and spread-plated on Tryptic Soy agar supplemented with Yeast Extract. For enzyme inactivation, 4.2 mg of lyophilized LDH was suspended in 2 ml of 100 mM phosphate buffer (pH 7.4), 2 ml of peptone water or glycerol, or in 2 ml mixtures of glycerol and peptone water. A lyophilized sample with no added liquid was also included. All enzyme samples were subjected to HPP as described above. After HPP, LDH was diluted to 0.28 μg/ml in 100 mM phosphate buffer (pH 7.4). LDH activity was assessed by measuring the change in concentration of β-NADH as a function of time. Dynamic light scattering analysis (DLS) was performed to examine the size distribution, polydispersity, and hydrodynamic radius of LDH before and after HPP. No significant difference in CFU/g was observed between lyophilized cells not subjected to HPP and lyophilized cells subjected to 600 MPa for 300 s (P < 0.05). However, lyophilized cells that were suspended in 100{\%} to 60{\%} peptone water showed a ~ 7.5-log10 reduction when subjected to HPP. Survival of L. monocytogenes following HPP significantly increased (P < 0.05) when the peptone water concentration was decreased below 60{\%} (aw ~ 0.8). DLS results revealed that LDH suspended in buffer underwent aggregation following HPP (600 MPa, 300 s). Inactivation rate constants obtained using a first-order kinetic model indicated that untreated and HP processed lyophilized LDH had similar activities. When LDH was subject to HPP in solutions containing glycerol, enzyme activity decreased as the water content increased (r2 = 0.95). Lyophilization completely protected L. monocytogenes and LDH from inactivation by high pressure. Furthermore, enzyme activity and cell survival increased as water activity was decreased. We postulate low aw results in protein stabilization, which prevents protein denaturation and cell death during HPP.",
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Effect of water activity on inactivation of Listeria monocytogenes and lactate dehydrogenase during high pressure processing. / Hayman, Melinda M.; Kouassi, Gilles K.; Anantheswaran, Ramaswamy C.; Floros, John D.; Knabel, Stephen John.

In: International journal of food microbiology, Vol. 124, No. 1, 10.05.2008, p. 21-26.

Research output: Contribution to journalArticle

TY - JOUR

T1 - Effect of water activity on inactivation of Listeria monocytogenes and lactate dehydrogenase during high pressure processing

AU - Hayman, Melinda M.

AU - Kouassi, Gilles K.

AU - Anantheswaran, Ramaswamy C.

AU - Floros, John D.

AU - Knabel, Stephen John

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Y1 - 2008/5/10

N2 - The aim of this study was to investigate the effect of water activity (aw) on the inactivation of Listeria monocytogenes and lactate dehydrogenase (LDH) during high pressure processing (HPP). For microbial inactivation lyophilized cells of L. monocytogenes 19,115 were left dry or were suspended in 10 ml of 0.1% peptone water, 10 ml of glycerol, or mixtures of glycerol and peptone water. All samples of various aws were high pressure (HP) processed at ambient temperature at 600 MPa for 300 s. Following HPP, samples were serially diluted in 0.1% peptone and spread-plated on Tryptic Soy agar supplemented with Yeast Extract. For enzyme inactivation, 4.2 mg of lyophilized LDH was suspended in 2 ml of 100 mM phosphate buffer (pH 7.4), 2 ml of peptone water or glycerol, or in 2 ml mixtures of glycerol and peptone water. A lyophilized sample with no added liquid was also included. All enzyme samples were subjected to HPP as described above. After HPP, LDH was diluted to 0.28 μg/ml in 100 mM phosphate buffer (pH 7.4). LDH activity was assessed by measuring the change in concentration of β-NADH as a function of time. Dynamic light scattering analysis (DLS) was performed to examine the size distribution, polydispersity, and hydrodynamic radius of LDH before and after HPP. No significant difference in CFU/g was observed between lyophilized cells not subjected to HPP and lyophilized cells subjected to 600 MPa for 300 s (P < 0.05). However, lyophilized cells that were suspended in 100% to 60% peptone water showed a ~ 7.5-log10 reduction when subjected to HPP. Survival of L. monocytogenes following HPP significantly increased (P < 0.05) when the peptone water concentration was decreased below 60% (aw ~ 0.8). DLS results revealed that LDH suspended in buffer underwent aggregation following HPP (600 MPa, 300 s). Inactivation rate constants obtained using a first-order kinetic model indicated that untreated and HP processed lyophilized LDH had similar activities. When LDH was subject to HPP in solutions containing glycerol, enzyme activity decreased as the water content increased (r2 = 0.95). Lyophilization completely protected L. monocytogenes and LDH from inactivation by high pressure. Furthermore, enzyme activity and cell survival increased as water activity was decreased. We postulate low aw results in protein stabilization, which prevents protein denaturation and cell death during HPP.

AB - The aim of this study was to investigate the effect of water activity (aw) on the inactivation of Listeria monocytogenes and lactate dehydrogenase (LDH) during high pressure processing (HPP). For microbial inactivation lyophilized cells of L. monocytogenes 19,115 were left dry or were suspended in 10 ml of 0.1% peptone water, 10 ml of glycerol, or mixtures of glycerol and peptone water. All samples of various aws were high pressure (HP) processed at ambient temperature at 600 MPa for 300 s. Following HPP, samples were serially diluted in 0.1% peptone and spread-plated on Tryptic Soy agar supplemented with Yeast Extract. For enzyme inactivation, 4.2 mg of lyophilized LDH was suspended in 2 ml of 100 mM phosphate buffer (pH 7.4), 2 ml of peptone water or glycerol, or in 2 ml mixtures of glycerol and peptone water. A lyophilized sample with no added liquid was also included. All enzyme samples were subjected to HPP as described above. After HPP, LDH was diluted to 0.28 μg/ml in 100 mM phosphate buffer (pH 7.4). LDH activity was assessed by measuring the change in concentration of β-NADH as a function of time. Dynamic light scattering analysis (DLS) was performed to examine the size distribution, polydispersity, and hydrodynamic radius of LDH before and after HPP. No significant difference in CFU/g was observed between lyophilized cells not subjected to HPP and lyophilized cells subjected to 600 MPa for 300 s (P < 0.05). However, lyophilized cells that were suspended in 100% to 60% peptone water showed a ~ 7.5-log10 reduction when subjected to HPP. Survival of L. monocytogenes following HPP significantly increased (P < 0.05) when the peptone water concentration was decreased below 60% (aw ~ 0.8). DLS results revealed that LDH suspended in buffer underwent aggregation following HPP (600 MPa, 300 s). Inactivation rate constants obtained using a first-order kinetic model indicated that untreated and HP processed lyophilized LDH had similar activities. When LDH was subject to HPP in solutions containing glycerol, enzyme activity decreased as the water content increased (r2 = 0.95). Lyophilization completely protected L. monocytogenes and LDH from inactivation by high pressure. Furthermore, enzyme activity and cell survival increased as water activity was decreased. We postulate low aw results in protein stabilization, which prevents protein denaturation and cell death during HPP.

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