Lecture NO. 4 Title Microbiology And Det
Lecture NO. 4
Title: Microbiology And Deterioration of Meat
Sources of Microbial contamination:
The muscle of healthy animal is considered to be free
of bacteria or other contaminations. Contamination
mostly came during the slaughtering, cutting within
the abattoir itself because of:i. Hides/skin and feet.
ii. Gastrointestinal contents.
iii. Instruments such as knives.
iv. Water used for washing carcasses and instruments.
v. Airborne contamination.
vi. Hands and clothing of the personnel.
Contamination of meat may also take place during
chilling, ageing, processing, packaging and
distribution.
Growth of Microorganisms in Meat
The microorganisms that occur in meat may be
bacteria or fungi. Fungi may be multi-cellular
filaments (mold) or large single cells with buds
(yeast). Molds are capable of producing minute
spores under unfavorable conditions. Bacteria
are unicellular microorganisms which are
spherical or ovoid or rod shaped and may occur
in chains or clusters.
Bacterial growth or multiplication takes place in
phases:*Lag phase : Bacterial cells increase in size
under favorable conditions. *Log phase: Bacterial cells
multiply and increase in number. *Stationary phase:
Growth rate becomes relatively constant due to
Environmental limitations. *Decline or death phase:
There is destruction of bacterial cells either; Due to
nutritional depletion or application of Some
preservation technique. An understanding of growth
curve enables the meat technologists to apply suitable
preservation technique to prolong the lag phase. So
that bacterial multiplication is retarded or if conditions
have already favored some growth, then to hasten the
death phase.
M
. icrobial growth activity in meat depends on various
extrinsic and intrinsic factors. The extrinsic factors are
temperature, oxygen, moisture and physical stage of
meat. Different groups of bacteria have their own
growth optima. Psychrophiles have their optimum
growth temperature below 20oC, thermophiles above
45oC and mesophiles an optima ranging between these
two. A refrigerated temperature of nearly 5oC greatly
retards the growth of most psychrophilic organisms
responsible for the spoilage of meat. These bacteria
generally belong to genera Pseudomonas,
Achromobactor, Flavobacterirum, Micrococcus,
Streptococcus, in cured or vacuum packed meat
products.
. It may be remembered that meat spoilage
molds are also psychrophiles. On the contrary,
food pathogens generally belong to the
thermophilic group of bacteria.
Oxygen environment around the meat will
determine the type of micro-flora that found. All
molds and yeast that grow in meat are aerobic in
nature. Bacteria found in meat may be aerobic,
anaerobic and sometimes facultative.
Physical state of meat such as whole carcass or
primal cuts or retail cuts or comminuted form
also influence the rate of microbial growth.
Microbial load increases with the increase in
exposed surface area of meat.
Important intrinsic factors which affect the
growth of microorganisms in meat are pH, water
activity, Oxidation-reduction potential and the
interaction.
Water is an absolute requirement for microbial
growth The amount of water available in a food
system for the growth of microorganisms is
generally expressed in terms of water activity.
Bacteria generally require highest water activity
(>0.90), most yeast thrives in the range 0.870.92 while molds grow at Aw of 0.84 or less.
Meat pH is yet another intrinsic factor which
influences the growth of microorganisms; Bacterial
growth is best at neutral pH (i.e. 7.0). It keeps on
diminishing as meat pH goes down. If ultimate pH is
6.0 or so, a large number of bacteria can still grow in
meat. However, when normal ultimate pH of nearly
5.5 is achieved in meat, bacterial growth is reduced to
a large extent and the growth of mold and yeast is
favored. At temperature near growth minima or
maxima, microorganisms generally become more
sensitive to Aw, oxygen availability, and pH. Under
anaerobic condition facultative bacteria may require
high pH, Aw and temperature for growth than when
aerobic conditions prevail.
Deteriorative Changes in Meat
When meat depicts signs of decomposition and
putrefaction, it is referred as spoiled and
becomes unfit for human consumption. Besides
microorganisms, intrinsic enzymes and insects,
chemical reaction, and physical changes.
Chemical changes:
Degradation of proteins, lipids, carbohydrates, and
other complex molecules into simpler ones is
accomplished by action of endogenous hydrolytic
enzymes present in meat, as well as by enzymes
produced by microorganisms. The simpler compounds
that are used as nutrient and energy sources for
microbial growth and activity.
The changes may appear in color, odor, flavor,
tenderness and processing properties. Meat spoilage
classified as being either aerobic or anaerobic,
depending on conditions under which it occur as well
as principal organisms causing spoilage: bacteria,
molds, or yeasts.
Chemical reactions affecting deteriorative
changes in meat; are Oxidative rancidity and
Discoloration.
Physical deteriorative changes are Dehydration,
Freezer Burn, Drip and Absorption of OffFlavors.
Commonly found insects in meat are; "skippers"
leaping larvae that feed on muscle and other soft
tissues. Other insects found in pork products
include larder beetles, cheese or ham mites, and
blow flies. In addition to structural damage,
discoloration and weight loss also occur..
Title: Microbiology And Deterioration of Meat
Sources of Microbial contamination:
The muscle of healthy animal is considered to be free
of bacteria or other contaminations. Contamination
mostly came during the slaughtering, cutting within
the abattoir itself because of:i. Hides/skin and feet.
ii. Gastrointestinal contents.
iii. Instruments such as knives.
iv. Water used for washing carcasses and instruments.
v. Airborne contamination.
vi. Hands and clothing of the personnel.
Contamination of meat may also take place during
chilling, ageing, processing, packaging and
distribution.
Growth of Microorganisms in Meat
The microorganisms that occur in meat may be
bacteria or fungi. Fungi may be multi-cellular
filaments (mold) or large single cells with buds
(yeast). Molds are capable of producing minute
spores under unfavorable conditions. Bacteria
are unicellular microorganisms which are
spherical or ovoid or rod shaped and may occur
in chains or clusters.
Bacterial growth or multiplication takes place in
phases:*Lag phase : Bacterial cells increase in size
under favorable conditions. *Log phase: Bacterial cells
multiply and increase in number. *Stationary phase:
Growth rate becomes relatively constant due to
Environmental limitations. *Decline or death phase:
There is destruction of bacterial cells either; Due to
nutritional depletion or application of Some
preservation technique. An understanding of growth
curve enables the meat technologists to apply suitable
preservation technique to prolong the lag phase. So
that bacterial multiplication is retarded or if conditions
have already favored some growth, then to hasten the
death phase.
M
. icrobial growth activity in meat depends on various
extrinsic and intrinsic factors. The extrinsic factors are
temperature, oxygen, moisture and physical stage of
meat. Different groups of bacteria have their own
growth optima. Psychrophiles have their optimum
growth temperature below 20oC, thermophiles above
45oC and mesophiles an optima ranging between these
two. A refrigerated temperature of nearly 5oC greatly
retards the growth of most psychrophilic organisms
responsible for the spoilage of meat. These bacteria
generally belong to genera Pseudomonas,
Achromobactor, Flavobacterirum, Micrococcus,
Streptococcus, in cured or vacuum packed meat
products.
. It may be remembered that meat spoilage
molds are also psychrophiles. On the contrary,
food pathogens generally belong to the
thermophilic group of bacteria.
Oxygen environment around the meat will
determine the type of micro-flora that found. All
molds and yeast that grow in meat are aerobic in
nature. Bacteria found in meat may be aerobic,
anaerobic and sometimes facultative.
Physical state of meat such as whole carcass or
primal cuts or retail cuts or comminuted form
also influence the rate of microbial growth.
Microbial load increases with the increase in
exposed surface area of meat.
Important intrinsic factors which affect the
growth of microorganisms in meat are pH, water
activity, Oxidation-reduction potential and the
interaction.
Water is an absolute requirement for microbial
growth The amount of water available in a food
system for the growth of microorganisms is
generally expressed in terms of water activity.
Bacteria generally require highest water activity
(>0.90), most yeast thrives in the range 0.870.92 while molds grow at Aw of 0.84 or less.
Meat pH is yet another intrinsic factor which
influences the growth of microorganisms; Bacterial
growth is best at neutral pH (i.e. 7.0). It keeps on
diminishing as meat pH goes down. If ultimate pH is
6.0 or so, a large number of bacteria can still grow in
meat. However, when normal ultimate pH of nearly
5.5 is achieved in meat, bacterial growth is reduced to
a large extent and the growth of mold and yeast is
favored. At temperature near growth minima or
maxima, microorganisms generally become more
sensitive to Aw, oxygen availability, and pH. Under
anaerobic condition facultative bacteria may require
high pH, Aw and temperature for growth than when
aerobic conditions prevail.
Deteriorative Changes in Meat
When meat depicts signs of decomposition and
putrefaction, it is referred as spoiled and
becomes unfit for human consumption. Besides
microorganisms, intrinsic enzymes and insects,
chemical reaction, and physical changes.
Chemical changes:
Degradation of proteins, lipids, carbohydrates, and
other complex molecules into simpler ones is
accomplished by action of endogenous hydrolytic
enzymes present in meat, as well as by enzymes
produced by microorganisms. The simpler compounds
that are used as nutrient and energy sources for
microbial growth and activity.
The changes may appear in color, odor, flavor,
tenderness and processing properties. Meat spoilage
classified as being either aerobic or anaerobic,
depending on conditions under which it occur as well
as principal organisms causing spoilage: bacteria,
molds, or yeasts.
Chemical reactions affecting deteriorative
changes in meat; are Oxidative rancidity and
Discoloration.
Physical deteriorative changes are Dehydration,
Freezer Burn, Drip and Absorption of OffFlavors.
Commonly found insects in meat are; "skippers"
leaping larvae that feed on muscle and other soft
tissues. Other insects found in pork products
include larder beetles, cheese or ham mites, and
blow flies. In addition to structural damage,
discoloration and weight loss also occur..