4. Conclusions
Limited to the considered species, the microbial cell inactivation
predicted in this study for some pressure and temperature combinations
is in compliance with the FDA requirement of a 5 Log
reduction of microorganisms in fruit juices and beverages (USFDA,
2004). The appropriate temperature selection in the pressure
treatment of smoothies permits cold pasteurization to be obtained
at pressure levels below 300 MPa, thus enabling HHP plant cost
reduction that is favourable for the industrialization of the process.
The conditions adopted in the present research for the recovery of
L. monocytogenes injured cells confirmed their effectiveness,
allowing the sub-lethal injury evolution in the surviving population
to be followed as the severity of the treatment increases. Additionally,
fluorescent cell staining methods provide additive information
on the injured cell physiology.
To the best of our knowledge, while some authors obtained
promising results applying pressures as high as 600 MPa at room
temperature, little is known about the effects of sub-zero temperature
HHP treatments on the maintenance of the organoleptic and
functional traits of smoothies, and such an intriguing aspect remains
to be investigated.
Concerning the problem of sub-lethal injured cells, their
behaviour during the storage of the smoothies should not be
overlooked. Such an intermediate physiological state prevailing in
the survivor population of the most effective treatments could be
recovered by the residual metabolic activity in permissive environmental
conditions, which differs from the conditions of
smoothies. These aspects have been investigated in our laboratory
(Zacconi & Scolari, submitted for publication) as an important
factor in determining the applicability and safety of pressure
treatments in the smoothies industry.