In Situ Determination of the Intracellular pH ofLactococcus lactisandLactobacillus plantarumduring Pressure Treatment

• DOI: 10.1128/aem.68.9.4399-4406.2002
• Publication Date: 2002-08-28T21:43:24Z
• Authors: Adriana Molina-Gu...; Volker Stippl; Antonio Delgado; Michael G. Gänzle; Rudi F. Vogel
• Keywords: 0301 basic medicine; Buffers; Hydrogen-Ion Concentration; Lactococcus lactis; Lactobacillus; 03 medical and health sciences; Milk; Calibration; Pressure; Animals; Homeostasis; Cattle

ABSTRACTHydrostatic pressure may affect the intracellular pH of microorganisms by (i) enhancing the dissociation of weak organic acids and (ii) increasing the permeability of the cytoplasmic membrane and inactivation of enzymes required for pH homeostasis. The internal pHs ofLactococcus lactisandLactobacillus plantarumduring and after pressure treatment at 200 and 300 MPa and at pH values ranging from 4.0 to 6.5 were determined. Pressure treatment at 200 MPa for up to 20 min did not reduce the viability of either strain at pH 6.5. Pressure treatment at pH 6.5 and 300 MPa reduced viable cell counts ofLactococcus lactisandLactobacillus plantarumby 5 log after 20 and 120 min, respectively. Pressure inactivation was faster at pH 5 or 4. At ambient pressure, both strains maintained a transmembrane pH gradient of 1 pH unit at neutral pH and about 2 pH units at pH 4.0. During pressure treatment at 200 and 300 MPa, the internal pH ofL. lactiswas decreased to the value of the extracellular pH during compression. The same result was observed during treatment ofLactobacillus plantarumat 300 MPa.Lactobacillus plantarumwas unable to restore the internal pH after a compression-decompression cycle at 300 MPa and pH 6.5.Lactococcus lactislost the ability to restore its internal pH after 20 and 4 min of pressure treatment at 200 and 300 MPa, respectively. As a consequence, pressure-mediated stress reactions and cell death may be considered secondary effects promoted by pH and other environmental conditions.