Lecture NO. 4
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
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
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
.
Microbial 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,
. It may be remembered that meat spoilage
molds are also psychrophiles. On the contrary,
food pathogens generally belong to the
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.
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
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
Deteriorative Changes in Meat
When meat depicts signs of decomposition and
putrefaction, it is referred as spoiled and
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,
