BLBS102-c39 BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm Printer Name: Yet to Come
756 Part 7: Food Processinghypochlorite in inhibitingListeria monocytogenes,Salmonella,
E. coliO157:H7, and the bacteriaErwinia carotovorain lettuce
and fresh-cut products (Abadias et al. 2008). Comparison of
bacterial reduction potency of strongly acidic electrolyzed wa-
ter (SAEW), sodium hypochlorite solution (NaOCl), and slightly
acidic electrolyzed water (StAEW) yielded the following order:
StAEW>NaOCl>SAEW (Issa-Zacharia et al. 2010). The
level of implementation of these techniques at commercial scale
has been limited.QUALITY AND SAFETY
CONSIDERATIONS: THE HURDLE
CONCEPTAlthough food safety is critical, it is known that quality is a top-
of-mind consideration when consumers purchase food products.
A successful processing technique must therefore not only en-
sure that the product is safe, it must also maintain appropriate
quality attributes that can be acceptable by consumers. Thermal
treatment is a broad-spectrum antimicrobial process. However,
novel nonthermal or minimal processing techniques have been
developed due to the potential of thermal processing to degrade
nutritive quality and functional properties of foods. The indi-
vidual use of most of the new techniques may not provide the
inactivation level required for commercial processing. Recently,
combined inactivation techniques of microorganisms have been
widely investigated since a combination of different “hurdles” is
a more effective means of inhibiting microorganisms than using
each “hurdle” alone (Alakomi et al. 2002, Leistner 2000). The
hurdle concept is based on the imposition of certain hurdles to
restrict the growth of food spoiling microorganisms as illustrated
in Figure 39.2. Any microbial inactivation factor can potentially
be adapted as a hurdle. Nearly 60 potential hurdles have been
identified for food preservation. The hurdles must be applied
in a logical sequence to ensure safety of the food product. The
resistance of different pathogens should be considered when a
hurdle is the lone preservation factor. For instance, PEF as well
as high-pressure treatment effectively inactivate bacteria andTime, treatment intensitySurvival fractionFigure 39.2.Schematic of enhanced microbial inactivation using
different hurdles in food processing.yeast but are ineffective against bacterial and mold spores and
some enzymes. Ultrasound is ineffective against wide-ranging
pathogens. Although heating is the most broad-spectrum inacti-
vation method, cells ofClostridium botulinumare highly resis-
tant even to thermal treatment. Moreover, there is an inactivation
threshold after which further hurdle application and energy input
do not inactivate microorganisms or degrade nutritive quality of
the treated foods.
A synergistic relationship between different nonthermal phys-
ical and chemical hurdles has been observed for both foods
(Fielding et al. 1997, Raso et al. 1998, Dutreux et al. 2000,
Heinz and Knorr 2000, Aronsson and Ronner 2001, Fernanda ̈
et al. 2001) as well as nonfoods liquids (wastes, poultry chiller
water, and others) (Liltved et al. 1995, Unal et al. 2001, Lar-
son and Mari ̃nas 2003). Although the simultaneous application
of different nonthermal technologies has been shown to have
a significant bactericidal effect, thermal treatment may still be
required to achieve the level of inactivation of different mi-
croorganisms necessary for practical use. Thus, combination of
thermal treatment with PEF (thermoelectrical treatment), pres-
sure (manothermal treatment), ultrasound (thermoultrasonica-
tion), irradiation (thermoradiation), and other hurdles have been
reported (Raso et al. 1998, Hoover 2000, Aronsson and Ronner ̈
2001, Kim et al. 2001, Ohshima et al. 2002). Synergistic bacte-
ricidal effects have also been observed between heat and ultra-
sound (Wrigley and Llorca 1992), heat and radiation (Schaffner
et al. 1989), heat and nisin (Knight et al. 1999), high hydro-
static pressure and nisin (Ponce et al. 1998), and PEF and nisin
(Calder ́on-Miranda et al. 1999). Some general approaches for
understanding hurdle concept can be found in Barbosa-Canovas
et al. (1998) and Leistner and Gorris (1995).Microbial StressWhen microorganisms present in food encounter stress in the
form of various hurdles, they undergo homeostasis. The organ-
isms try to prevail over inclement conditions caused by hurdles,
but metabolic exhaustion due to repair action leads to death of the
microorganisms. However, when bacteria are under stress, they
can become more resistant and synthesize stress shock proteins.
These proteins play the role of molecular chaperons by folding
distorted proteins into a shape that retains the cell functionality
under stress (Hightower 1991). But if the food is exposed to
different stresses simultaneously, the microorganism generates
more shock protein using all the cell energy and dies due to
metabolic exhaustion (Leistner 2000).Multitarget Preservation of FoodsHurdle technology emphasizes intelligent combination of vari-
ous preservation techniques. Leistner (1995) proposed concept
of multitarget preservation of foods and suggested that different
hurdles rather than having an accruing effect may have synergis-
tic action. It has been suggested that different preservative factors
of variable intensity be used for the synergistic action, instead
of using a single high-impact preservative. These targets include
cell components, enzymes, pH, water activity, redox potential,