Servizio Comunitario di Informazione in materia di Ricerca e Sviluppo - CORDIS

Pre-adaptation treatment for stress induction to improve tolerance against harsh conditions

It has been demonstrated for many bacteria that responses induced by one type of stress may then confer protection to the bacteria against other different stress challenges. This phenomenon is known as cross tolerance. The protection responses induced by bile salts, heat or NaCl improved the capacity of the probiotic bacteria in withstanding stressful processing techniques such as spray drying were investigated.

Log-phase cells of probiotic lactobacilli strains were re-suspended in 20% RSM and were either spray dried immediately or exposed for one hour to sub-lethal levels of heat (48°C), NaCl (5%), bile salts (1mM GDCA) or heat (4ºC) + NaCl (5%) prior to spray drying. Cells were spray dried at two different outlet temperatures, 90°C and 95°C. Higher levels of survival of the spray drying process relative to the un-induced cells were obtained. Heat afforded the lowest level of survival of the induced cells, with the greatest level of survival being observed for cells induced with heat + NaCl. Moreover, in the frame of the work it was observed that even though induction of a heat tolerance response prior to spray drying increases the ability of the cells to survive the drying process, it did not significantly effect survival of the dried cells during storage.

The effect of mild pressure pre-treatments on technological behaviour of L. rhamnosus GG was evaluated. With respect to heat tolerance pressure pre-treated cells (at 100MPa and 37°C) showed higher survivability than untreated ones when both were exposed to lethal heat treatment. Flow cytometric analysis showed that the acquisition of pressure-induced heat tolerance was related to membrane stabilization and protein biosynthesis. Pressure induced thermotolerance occurred as a consequence of stabilization of cellular membranes - presumably by incorporation of heat shock proteins into cytoplasmic membrane - which in turn led to an enhanced transient protection against degradative effects of heat on cell membrane. The absence of induced thermal tolerance upon addition of Chloramphenicol suggested that the proteins expressed during pressure adaptation was involved in the prevention of thermal degradation on cell membrane. Pressure pre-treated LGG showed also an improved tolerance against chemical compounds which are able to degrade cytoplasmic membranes, such as bile acid and nisin. This result confirmed the positive role of protein synthesis during pressure adaptation in protecting this vital cellular component. The potential of utilising pressure shock response in increasing the survivability of LGG during spray drying, which poses multiple environmental stresses (including heat, osmotic and oxidative stress) was also demonstrated.


Dietrich KNORR, (Professor and Head of Department)
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