Handbook of Meat Processing

Canned Products and Pâté 339

temperatures; this is the case with tropical

preserves (Manev 1983 ). Heat treatment

conditions destroying C. botulinum and

Clostridium sporogenes result in a thermo-

stable food, with considerably long shelf

life and without the need of other preserva-

tion processing. Inactivation of either patho-

gen or spoilage - causing microorganisms is

calculated by the heat penetration rate.

Vegetative cells are destroyed at tempera-

tures slightly higher than optimum growth

temperatures, whereas spores can survive at

higher temperatures (Zamudio 2006 ). Heat

treatments depend on a time - temperature

relationship.

Traditionally, process calculations con-

sider that, since heat application involves the

destruction of at least one microbial enzyme

necessary to the bacterial metabolism, vege-

tative cells and spores are inhibited according

to a fi rst - order reaction rate equation (Baranyi

and Roberts 1995 ), even though Peleg (2006)

stated that there is evidence bacterial spore

inactivation, including C. botulinum spores,

does not follow fi rst - order kinetics. The

author states that the exponential inacti-

vation rate depends on the spores ’ previous

thermal history, which is not considered in

the exponential inactivation rate equations

that follow a log - linear Arrhenius model.

However, the author concluded canning

operations are generally a safe procedure due

to over - processing.

When microbial populations are treated

with humid heat at a temperature slightly

higher than the maximum for growth, vegeta-

tive cells and spores are destroyed according

to the equation:

−=

dc

dt

kc (19.1)

This means that cell concentration (dc)

decreases (hence, the negative sign) with

time (dt) in a direct proportion to viable cell

concentration (c). This is a logarithmic cell

destruction rate (for example: 10^3 to 10^2 ), but

time increases linearly.

metabolism of certain microorganisms.
Several of these toxins are thermostable,
whereas others can be destroyed by heat
treatments. The toxin Aeromonas hydrophila
is heat sensitive ; Escherichia coli 0157:H7
and C. botulinum (proteolytic types A, B, F,
and nonproteolytic types B, E, F) toxins are
medium heat resistant; Vibrio sp. ( V. cholera
and V. parahaemolyticus) and Staphyloccocus
aureus toxins are highly heat resistant.

Microbial and Enzyme Destruction

in Canned Foods

As stated before, heat treatment ’ s fi rst aim is
to destroy pathogens, spoilage microorgan-
isms, and enzymes. Theoretical consider-
ations for microbial destruction are also valid
for enzyme inactivation (Dziezak 1991 ). The
main criteria for thermal destruction are: (1)
all spores and viable cells able to grow and
produce toxins must be eliminated, taking as
a calculation basis C. botulinum , the most
dangerous microorganism from the public
health point of view; (2) spoilage microor-
ganisms must be reduced to a limit that
ensures food quality for a given time. From
a commercial point of view, a food can
be considered sterile if it is free from
Bacillus stearothermophilus or Clostridium
perfringens.
In general, the strict anaerobe C. botuli-
num is taken as the target microorganism due
to its pathogenicity; however, other target
microorganisms are B. stearothermophilus,
B. thermoacidurans , B. macerans, and B.
polymyxa (Guerrero Legarreta 2001 ), in
addition to specifi c pathogens most likely
to colonize a specifi c food. In the case of
raw poultry meat and poultry products,
these are C. prefringens , Salmonella spp.,
Staphylococcus spp., and Campylobacter
spp. Microbial inactivation calculations are
based on how long the food shelf life must
be extended.
Sporulated thermophiles must also be
considered if the food will be stored at high