Abstract #T138

# T138
Influence of osmotic adaptation and lactose deprivation on the salt tolerance of Lactococcus lactis.
Ernesto E. Gonzalez-Duran*1, Kayanush J. Aryana1, 1School of Animal Sciences, Louisiana State University Agricultural Center, Baton Rouge, LA.

Lactococcus lactis is often used in cheese and salted butter manufacture. Mediterranean cheeses can have up to 7% NaCl. Osmotic conditions generally slow down the growth of both pathogen and desirable bacteria. Studies have shown that vegetative cells exposed to a mild stress become more resistant to lethal doses of the same stress since the first exposure starts the defense mechanisms of the cells creating an effect of cross-protection. The hypothesis was whether salt tolerance of Lactococcus lactis can be enhanced. The objective was to study the influence of lactose deprivation and osmotic adaptation on salt tolerance of L. lactis. L. lactis R-604 was subjected to mild stress induced by lactose deprivation (grown with no lactose in M17 broth) or prior osmotic adaption (grown with 3% w/v NaCl in M17 broth) for 24 h aerobically at 30°C. A control was run without stress (grown in M17 broth with lactose and no NaCl and incubated aerobically for 24 h at 30°C). Lactose deprived or osmotic adapted cells were transferred to M17 broth with 5 concentrations of NaCl (0, 1, 3, 5 and 7% w/v) and incubated aerobically at 30°C for 5 d. Plating was conducted immediately after inoculation and every 24 h for 5 d in M17 agar with 0.5% of lactose and incubated aerobically at 30°C for 48 h. Three replications were conducted. After the 24 h incubation in M17 broth with no lactose or 3% NaCl an increase in 4 log cfu/mL was observed. Lactose deprived cells exposed to 0, 1,3 and 5% w/v salt had a stationary phase at 11 logs for d 1 and 2. While use of 7% w/v salt reduced cells by 2 logs by d 2. On d 5 there were no differences in counts of lactose deprived cells exposed to all salt concentrations. Osmotic adapted cells exposed to 5% salt had a stationary phase at 11 logs for d 1 and 2, while cells exposed to 0,1,3 and 7% NaCl slowly declined until d 5. On d 5 there were no differences in counts of osmotic adapted cells exposed to all salt concentrations. Different amount of NaCl and days of salt exposure had a differential effect on growth of L. lactis. From d 3 until d 5, prior exposure to either mild stress did not have an effect on salt tolerance of L. lactis R-604.

Key Words: salt tolerance, dairy culture