Abstract:
High hydrostatic pressure (HHP) affects the pH of weak acids due to an
increased degree of acid dissociation while under pressure. The temporary pH
reduction by high pressure in such a case may influence the barotolerance of
microorganisms. The objective of this study was to determine the impact of weak
and strong acids on the barotolerance of lactic acid bacteria across a range of pH
under high hydrostatic pressure conditions. The effect of two acid groups (weak
and strong) was studied on Lactobacillus plantarum (strain MDOS 32) at different
pH levels (3.5 to 5). All high pressure treatments were carried for 1 minute over a
range of pressures (350 – 525 MPa) at 25°C (at pressure). Population reductions
were assessed by serial dilution followed by spiral plating, and pressure
dependency of these reductions was modeled using the Weibull equation.
Microbial inactivation was significantly affected by the type of acid (weak vs.
strong), pH and pressure. In general, high pressure lethality of weak acids was greater compared to that of strong mineral acids. As the pH decreased from 5 to
3.5, high pressure lethality increased. The presence of whey protein isolate did not
alter the lethality of the acid buffer systems.
