RELATIONSHIP BETWEEN WATER ACTIVITY, SALTS OF LACTIC-ACID, AND GROWTH OF LISTERIA-MONOCYTOGENES IN A MEAT MODEL SYSTEM

The relationship between water activity (a(w)), 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 a(w), and differences between a(w) 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-degrees-C for 7 d were about 10(9) (45-85% moisture, a(w) = 0.981-0.994) and 10(7) (35% moisture, a(w) = 0.965); there was no growth in meat with 25% moisture (a(w) = 0.932). Sodium lactate (4%) suppressed listerial growth at >55% and inhibited growth in samples with 25-55% moisture (a(w) < 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 a(w).