Factors influencing the growth of microorganism in food Flashcards
Food spoilage organisms cause by
bacteria, yeasts, & molds
Food spoilage organisms are
often smelled, seen, or tasted
food spoilage organisms do not
cause life-threatening infection
Foodborne pathogens do not
affect the taste, smell, or appearance of food.
Foodborne pathogens caused by
bacteria, viruses, parasites
Intrinsic factors
*Nutrient
*pH (Acidity / alkalinity)
*Water activity / moisture content
*Antimicrobial chemical
*Oxidation-reduction potential
*Biological barriers (e.g. shells)
Extrinsic factors
*Temperature / Time
*Relative humidity
*Presence and concentration of gases
*Presence and activities of
other microorganism
example Nutrients: as the sources of energy for microbes
(carbohydrate, protein, lipid)
what is Bacterial Metabolism
The series of biochemical reactions by which the cells breaks down various biomolecules such as nutrients (carbohydrates,
fat, protein) for energy generation and the use of energy to synthesize cell material (lipids, polysaccharides, proteins) from small
molecules
Many microorganisms are inhibited by acid conditions except
lactic acid bacteria
(LAB) used in
fermentation process of food production
LAB also cause spoilage of
unpasteurized milk and other foods
pH can determine
bacteria’s ability to produce toxin
Pathogens do not grow,
or grow very slowly, at
pH below 4.6, except
- Clostridium botulinum
- Salmonella spp.
Water activity is defined as t
the ratio of the vapor pressure
of water in a material (p) to the vapor pressure of pure
water (po) at the same temperature
Modified the aw for food preservation
- Physical removal of water (drying, baking)
- Adding solutes (salt, sugar)
Biological barriers in plant and animal derived food (raw) help
to prevent the entry and growth of
microorganism
Some foods contain natural antimicrobial
chemicals / chemical preservative & additive that
inhibit microbial growth
ANTIMICROBIAL CHEMICALS in Plant-based food:
Essential oils, tannin, glycosides,
resins
ANTIMICROBIAL CHEMICALS in animal-based food:
Lactoferrin, conglutinin and the lactoperoxidase system (lactoperoxidase, thiocyanate, and hydrogen peroxide) in milk - innate immunity, killing bacteria in milk
Lysozyme in eggs and milk (enzyme that can hydrolyze the cell wall of bacteria)
Bacteriocin (from LAB), antibiotics (from mold) –inactivate other microorganism
Redox potential (Eh) is a
a measurement of the ease
for a substance to gain or loses electrons
The redox potential of food is closely linked to
availability of oxygen and influences the types of microorganisms that can grow and thrive in that environment.
Major group of microorganism based on their relationship to redox potential:
Aerobes +500 to +300 mV
Anaerobes +100 to < -250mV
Facultative anerobes +300mV to -100mV
Bacterial proliferation can be controlled by
both heat and cold temperature
