Salt Tolerance of Cheese Culture <i>Lactococcus lactis</i> R-604 as Influenced by Prior Salt Exposure and Lactose Deprivation

Abstract

Manufacture of some cheeses involves the use of Lactococcus lactis . During processing bacteria are subjected to environmental stresses such as acid and salt osmotic conditions. Identifying procedures and mechanisms to develop resistance to these environmental stresses, specifically salt, is important to improve the culture’s growth and performance during food manufacture and storage. Hypothesis was whether salt tolerance of Lactococcus lactis R-604 can be enhanced. Objective was to study the influence of prior salt exposure and lactose deprivation on salt tolerance of L. lactis . The culture was subjected to mild stress induced by lactose starvation or prior salt exposure for 24 hours aerobically at 30 &#176; C. A control was conducted without any stress. Cells that were prior mild stressed by lactose starvation or prior salt exposure were transferred to M17 broth with 5 concentrations of NaCl (0, 1, 3, 5 and 7% w/v) and incubated aerobically at 30 &#176; C. Plating was conducted immediately after inoculation and every 24 hours for 5 days in M17 agar supplemented with 0.5% of lactose and incubated aerobically at 30 &#176; C for 48 hours. Three replications were conducted. There was no need for lactose to grow this culture in M17 broth and it could tolerate prior exposure to 3% w/v NaCl in media without affecting its growth at different salt concentrations. Culture that was exposed to lactose starvation and then subsequently grown in 3% w/v NaCl, at day 3 showed enhanced salt tolerance which can be recommended as a pretreatment condition for obtaining daughter cells with improved salt tolerance.