1. IntroductionHigh pressure proces

1. Introduction
High pressure processing (HPP) treatment is an emerging food
preservation method able to meet not only the increasing consumer
demand for microbiologically safe foods, but also to produce
foods with fresh-like appearance and with minimal modification of
nutritional and organoleptic properties (Daryaei et al., 2007;
Neetoo et al., 2011; Pulido et al., 2008; Sharma et al., 2002; Syed
et al., 2012). HPP treatments of food are carried out with intense
pressure (commercially ranging from 100 to 600 MPa) with or
without heat, inactivating efficiently microorganisms and, consequently,
extending food products shelf-life (Campus, 2010; Hugas
et al., 2002). The susceptibility of microorganisms to high hydrostatic
pressure varies considerably depending on the pressure
range applied, temperature and duration of the treatment
(Considine et al., 2008; Fonberg-Broczek et al., 2005; Karatzas and
Bennik, 2002; Rodriguez et al., 2005), but also depends on each
microorganism characteristics, growth phase and suspending medium
(Alpas et al., 1999; Jofre et al., 2010; Pulido et al., 2008;
Rodriguez et al., 2005). It is generally assumed that Gram-positive
bacteria and cells in the stationary growth phase are more resistant
than Gram-negative and cells in the exponential growth phase
(Campus, 2010). It has also been stated that bacterial protective
effect against HPP may be given by carbohydrates, proteins, lipids
and other constituents of the suspending medium or food (which,
when caught up by the bacteria decrease their sensitivity to HPP)
(Garriga et al., 2004; Pulido et al., 2008; Van Opstal et al., 2005).
HPP affects bacterial cellular processes such as protein and DNA
synthesis, membrane-associated processes, macromolecular quaternary
structures (e.g., protein denaturation) and cellular membrane
structure. Cell external structures are the primary sites that
are damaged by pressure, altering cell permeability, transport
systems, osmotic pressure and ability to preserve pH, resulting in
leakage of cell contents (Bowman et al., 2008; Hauben et al., 1997;
Karatzas and Bennik, 2002; Pulido et al., 2008; Ritz et al., 2002;
Yang et al., 2012). As the main targets of HPP are the external
* Corresponding author.
E-mail addresses: mines.baptista@ua.pt (I. Baptista), rui.queiros@ua.pt
(R.P. Queiros), acunha@ua.pt (A. Cunha), ^ smrocha@ua.pt (S.M. Rocha),
jorgesaraiva@ua.pt (J.A. Saraiva), aalmeida@ua.pt (A. Almeida).
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Food Microbiology
journal homepage: www.elsevier.com/locate/fm
http://dx.doi.org/10.1016/j.fm.2014.09.016
0740-0020/© 2014 Elsevier Ltd. All rights reserved.
Food Microbiology 46 (2015) 515e520