Food Protection with Chemicals, and by Biocontrol 341
A study on the incidence and prevalence of C. jejuni phages on retail poultry found phages in 34
of 300 fresh chicken parts but none were found in 150 frozen samples.
7 The efficacy of host-specific
phages to reduce numbers of C. jejuni on artificially contaminated chicken skin has been demonstrated.
7
The Campylobacter phages are dsDNA and belong to the families Myxoviridae and Siphoviridae. In
order to effect cell lysis, phages need host cells that are dividing and since C. jejuni does not grow below
ca. 30
◦ C, it appears not to be a good candidate for phage control on refrigerated products. However,
if phages attach to the refrigerated cells, they may become active during later host cell growth.
Phages have been shown to reduce numbers of foodborne pathogens such as L. monocytogenes
on surface-ripened cheeses as well as E. coli 0157:H7 and salmonellae on fresh poultry. They were
used openly in the former Soviet Union to treat certain human bacterial infections. Coliphages are
very common on fresh poultry where they apparently reduce the numbers of viable E. coli.
104 Phages
present problems for dairy and meat starter culture users if one or more starter strains is lysed leading
to faulty fermentations. The true potential of bacterial viruses to reduce spoilage and food poisoning
bacteria in foods requires more research.
Vibrio vulnificus phages have been isolated from oysters taken from estaurine waters at several
locations around the United States, and numbers/g of oyster tissue ranged from 10
1 to 10
5 . All but one
isolate was specific for this pathogen with one causing lysis of V. parahaemolyticus.
42 Two coliphages
have been demonstrated to possess a wide host range that allowed them to lyse many strains of E. coli
in addition to Proteus mirabilis, Shigella dysenteriae, and two salmonellae strains.
71
THE HURDLE CONCEPT
Under intrinsic and extrinsic growth parameters presented in Chapter 3, the effect of single factors
on the welfare of microorganisms is presented. In the hurdle concept, multiple factors or techniques
are employed to effect the control of microorganisms in foods. Barrier technology, combination
preservation, and combined methods are among some of the other descriptions of this concept. Referred
to as “hurdle technology” since the mid-1980s by L. Leistner in Germany, the practice has been applied
to some foods for over a century.
A simple example of the hurdle concept or barrier technology is demonstrated by preventing the
germination of spores of proteolytic or group I strains of Clostridium botulinum. Among the intrinsic
and extrinsic parameters that are known to prevent their germination and growth are: pH <4.6; a w
<0.94; NaCl of 10% or more; NaNO 2 ca. 120 ppm; incubation temperature <10
◦ C; and a large aerobic
bacterial biota. Foods that employ the hurdle concept in their formulation would embody a series of
the above, thus making for a multitargeted approach to preventing germination and growth of these
spores. In order for C. botulinum to grow, it must “hurdle” a series of the barriers noted. Note that the
hurdles listed above include “aerobic bacterial biota”, which is microbial interference. The important
parameters of pH and a w may be controlled by the growing food biota, especially the lactic acid
bacteria. The hurdle technology concept is much broader than the above sketch presents, and more
details can be found in Leistner and Gould.
114
The concept of growth/no growth (G/NG) has been advanced to better quantify the hurdle concept
by employing the synergy that exists between two or more parameters
125 Implicit in this concept is
the interaction between two or more parameters to a point where growth ceases—the G/NG interface.
Precise definitions and determinations of those factors/parameters that permit and prevent growth of a
given organism should make it possible to devise models for the hurdle concept. For more information,
see reference 125.
A study on the incidence and prevalence of C. jejuni phages on retail poultry found phages in 34
of 300 fresh chicken parts but none were found in 150 frozen samples.
7 The efficacy of host-specific
phages to reduce numbers of C. jejuni on artificially contaminated chicken skin has been demonstrated.
7
The Campylobacter phages are dsDNA and belong to the families Myxoviridae and Siphoviridae. In
order to effect cell lysis, phages need host cells that are dividing and since C. jejuni does not grow below
ca. 30
◦ C, it appears not to be a good candidate for phage control on refrigerated products. However,
if phages attach to the refrigerated cells, they may become active during later host cell growth.
Phages have been shown to reduce numbers of foodborne pathogens such as L. monocytogenes
on surface-ripened cheeses as well as E. coli 0157:H7 and salmonellae on fresh poultry. They were
used openly in the former Soviet Union to treat certain human bacterial infections. Coliphages are
very common on fresh poultry where they apparently reduce the numbers of viable E. coli.
104 Phages
present problems for dairy and meat starter culture users if one or more starter strains is lysed leading
to faulty fermentations. The true potential of bacterial viruses to reduce spoilage and food poisoning
bacteria in foods requires more research.
Vibrio vulnificus phages have been isolated from oysters taken from estaurine waters at several
locations around the United States, and numbers/g of oyster tissue ranged from 10
1 to 10
5 . All but one
isolate was specific for this pathogen with one causing lysis of V. parahaemolyticus.
42 Two coliphages
have been demonstrated to possess a wide host range that allowed them to lyse many strains of E. coli
in addition to Proteus mirabilis, Shigella dysenteriae, and two salmonellae strains.
71
THE HURDLE CONCEPT
Under intrinsic and extrinsic growth parameters presented in Chapter 3, the effect of single factors
on the welfare of microorganisms is presented. In the hurdle concept, multiple factors or techniques
are employed to effect the control of microorganisms in foods. Barrier technology, combination
preservation, and combined methods are among some of the other descriptions of this concept. Referred
to as “hurdle technology” since the mid-1980s by L. Leistner in Germany, the practice has been applied
to some foods for over a century.
A simple example of the hurdle concept or barrier technology is demonstrated by preventing the
germination of spores of proteolytic or group I strains of Clostridium botulinum. Among the intrinsic
and extrinsic parameters that are known to prevent their germination and growth are: pH <4.6; a w
<0.94; NaCl of 10% or more; NaNO 2 ca. 120 ppm; incubation temperature <10
◦ C; and a large aerobic
bacterial biota. Foods that employ the hurdle concept in their formulation would embody a series of
the above, thus making for a multitargeted approach to preventing germination and growth of these
spores. In order for C. botulinum to grow, it must “hurdle” a series of the barriers noted. Note that the
hurdles listed above include “aerobic bacterial biota”, which is microbial interference. The important
parameters of pH and a w may be controlled by the growing food biota, especially the lactic acid
bacteria. The hurdle technology concept is much broader than the above sketch presents, and more
details can be found in Leistner and Gould.
114
The concept of growth/no growth (G/NG) has been advanced to better quantify the hurdle concept
by employing the synergy that exists between two or more parameters
125 Implicit in this concept is
the interaction between two or more parameters to a point where growth ceases—the G/NG interface.
Precise definitions and determinations of those factors/parameters that permit and prevent growth of a
given organism should make it possible to devise models for the hurdle concept. For more information,
see reference 125.