Combined effect of temperature, water activity and salt content on the growth and gene expression of Listeria monocytogenes in a dry-cured ham model system

Listeria monocytogenes population and the expression patterns of three virulence (plcA, hly, and iap) and one stress-related (sigB) genes in dry-cured ham with different water activity (aw) values (0.92, 0.88, and 0.84) and treated with high pressure processing (HPP, 450 MPa/10 min and 600 MPa/5 min) were monitored throughout 30 days (d) at 4 °C. The antimicrobial effect of HPP at 600 MPa against L. monocytogenes S4-2 (serotype 1/2b) and S12-1 (serotype 1/2c) was greater in dry-cured ham with aw values of 0.92, with reductions of 2.5 and 2.8 log units, respectively. The efficacy of HPP treatments decreased at lower aw values. Regarding gene expression, L. monocytogenes strains responded differently to HPP. For strain S4-2, the four target genes were generally overexpressed in dry-cured ham immediately after HPP treatments at the three aw values investigated, although the extent of this induction was lower in the samples pressurized at 600 MPa and with aw values of 0.84. For strain S12-1, the expression of all target genes was repressed at the three aw values investigated. The antimicrobial efficacy of HPP against L. monocytogenes could be compromised by low aw values in food products. However, no growth of HPP-survival cells was observed during refrigerated storage in low-aw dry-cured ham, and the overexpression of virulence and stress-related genes decreased.

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The effect of temperature, water activity and sorbic acid on ketone rancidity produced byPenicillium crustosumThom in coconut and palm kernel oils

Journal of Applied Bacteriology ◽

10.1111/j.1365-2672.1991.tb02747.x ◽

1991 ◽

Vol 70 (6) ◽

pp. 502-506 ◽

Cited By ~ 5

Author(s):

Judith L. Kinderlerer ◽

P.V. Hatton

Keyword(s):

Water Activity ◽

Sorbic Acid ◽

Palm Kernel ◽

Effect Of Temperature ◽

Temperature Water

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Relationship Between Water Activity, Salts of Lactic Acid, and Growth of Listeria monocytogenes in a Meat Model System

Journal of Food Protection ◽

10.4315/0362-028x-55.8.574 ◽

1992 ◽

Vol 55 (8) ◽

pp. 574-578 ◽

Cited By ~ 74

Author(s):

NING CHEN ◽

LEORA A. SHELEF

Keyword(s):

Lactic Acid ◽

Listeria Monocytogenes ◽

Moisture Content ◽

Water Activity ◽

Sodium Lactate ◽

Model System ◽

Cell Numbers ◽

Maximum Cell ◽

The Relationship ◽

Control Samples

The relationship between water activity (aw), lactate, and growth of Listeria monocytogenes strain Scott A was studied in a meat model system consisting of cooked strained beef ranging in moisture content from 25 to 85% (wt/wt). Lactate (4%) depressed meat aw, and differences between aw values in control and lactate-treated samples at each moisture level increased progressively with decrease in moisture, from 0.003 (85% moisture) to 0.046 (25% moisture). Maximum cell numbers per g in control samples stored at 20°C for 7 d were about 109 (45–85% moisture, aw= 0.981–0.994) and 107 (35% moisture, aw = 0.965); there was no growth in meat with 25% moisture (aw = 0.932). Sodium lactate (4%) suppressed listerial growth at >55% and inhibited growth in samples with 25–55% moisture (a < 0.964). Lactate concentrations less than 4% were not listeristatic, but combinations of 2 or 3% lactate with 2% NaCl in samples with 55% moisture inhibited growth. Potassium and calcium lactate were as effective as the sodium salt in suppressing growth and aw.

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