64 research outputs found
Recommended from our members
High Pressure Effects on Proteolytic and Glycolytic Enzymes Involved in Cheese Manufacturing
The activity of chymosin, plasmin, and Lactococcus
lactis enzymes (cell envelope proteinase, intracellular
peptidases, and glycolytic enzymes) were determined
after 5-min exposures to pressures up to 800 MPa.
Plasmin was unaffected by any pressure treatment.
Chymosin activity was unaffected up to 400 MPa and
decreased at 500 to 800 MPa. Fifty percent of control
chymosin activity remained after the 800 MPa treatment.
The lactococcal cell envelope proteinase (CEP)
and intracellular peptidase activities were monitored
in cell extracts of pressure-treated cells. A pressure
of 100 MPa increased the CEP activity, whereas 200
MPa had no effect. At 300 MPa, CEP activity was
reduced, and 400 to 800 MPa inactivated the enzyme.
X-Prolyl-dipeptidyl aminopeptidase was insensitive
to 5-min pressure treatments of 100 to 300 MPa, but
was inactivated at 400 to 800 MPa. Aminopeptidase
N was unaffected by 100 and 200 MPa. However, 300
MPa significantly reduced its activity, and 400 to 800
MPa inactivated it. Aminopeptidase C activity increased
with increasing pressures up to 700 MPa.
High pressure did not affect aminopeptidase A activity
at any level. Hydrolysis of Lys-Ala-ρ-NA doubled
after 300-MPa exposure, and was eliminated at 400
to 800 MPa. Glycolytic enzyme activities of pressure-treated
cells were evaluated collectively by determining
the titratable acidity as lactic acid produced by
cell extracts in the presence of glucose. The titratable
acidities produced by the 100 and 200 MPa samples
were slightly increased compared to the control. At
300 to 800 MPa, no significant acid production was
observed. These data demonstrate that high pressure
causes no effect, activation, or inactivation of proteolytic
and glycolytic enzymes depending on the pressure
level and enzyme. Pressure treatment of cheese may alter enzymes involved in ripening, and pressure-treating
L. lactis may provide a means to generate
attenuated starters with altered enzyme profiles.Keywords: protease, cheese ripening, Lactococcus, peptidaseKeywords: protease, cheese ripening, Lactococcus, peptidas
GIANT SEQUOIA (SEQUOIADENDRON GIGANTEUM [TAXODIACEAE]) SEEDLING SURVIVAL AND GROWTH IN THE FIRST FOUR DECADES FOLLOWING MANAGED FIRES
Volume: 53Start Page: 342End Page: 35
SURVIVORSHIP AND GROWTH OF GIANT SEQUOIA (SEQUOIADENDRON GIGANTEUM (LINDL.) BUCHH.) SEEDLINGS AFTER FIRE
Volume: 38Start Page: 14End Page: 2
Effects of High Pressure on the Viability, Morphology, Lysis, and Cell Wall Hydrolase Activity of Lactococcus lactis subsp. cremoris
Viability, morphology, lysis, and cell wall hydrolase activity of Lactococcus lactis subsp. cremoris MG1363 and SK11 were determined after exposure to pressure. Both strains were completely inactivated at pressures of 400 to 800 MPa but unaffected at 100 and 200 MPa. At 300 MPa, the MG1363 and SK11 populations decreased by 7.3 and 2.5 log cycles, respectively. Transmission electron microscopy indicated that pressure caused intracellular and cell envelope damage. Pressure-treated MG1363 cell suspensions lysed more rapidly over time than did non-pressure-treated controls. Twenty-four hours after pressure treatment, the percent lysis ranged from 13.0 (0.1 MPa) to 43.3 (300 MPa). Analysis of the MG1363 supernatants by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirmed pressure-induced lysis. Pressure did not induce lysis or membrane permeability of SK11. Renaturing SDS-PAGE (zymogram analysis) revealed two hydrolytic bands from MG1363 cell extracts treated at all pressures (0.1 to 800 MPa). Measuring the reducing sugars released during enzymatic cell wall breakdown provided a quantitative, nondenaturing assay of cell wall hydrolase activity. Cells treated at 100 MPa released significantly more reducing sugar than other samples, including the non-pressure-treated control, indicating that pressure can activate cell wall hydrolase activity or increase cell wall accessibility to the enzyme. The cell suspensions treated at 200 and 300 MPa did not differ significantly from the control, whereas cells treated at pressures greater than 400 MPa displayed reduced cell wall hydrolase activity. These data suggest that high pressure can cause inactivation, physical damage, and lysis in L. lactis. Pressure-induced lysis is strain dependent and not solely dependent upon cell wall hydrolase activity
UNUSUAL FACTORS CONTRIBUTING TO THE DESTRUCTION OF YOUNG GIANT SEQUOIAS
Volume: 20Start Page: 408End Page: 41
- …