Chapter 2: Food Microbiology Flashcards
Microbial population show a characteristic type of growth pattern, called?
exponential growth
little or no apparent growth for a period following the initial contact between the microbes and the environment
length of this phase varies with the condition of the microorganisms and the nature of the environment
stage 1: lag phpase
microorganisms are growing and dividing at the maximal rate
constant growth rate is observed
cells are in their healthiest state
stage 2: log phase (exponential phase)
no net increase or decrease in cell number
accumulation of wastes that are toxic and nutrient depletion
stage 3: stationary phase
decline in the number of viable cells
rate of death exceeds rate of growth
many of the numbers essential for survival are no longer available
stage 4: death phase
characteristic of the growth substrate
intrinsic factors
microorganisms require this type of moisture
free/available water
free water may be expressed as
water activity (aw)
amount of free or available water in a product, which can affect its shelf life, safety, and quality. It is measured on a scale from 0 (completely dry) to 1.0 (pure water)
water activity (aw)
ratio of the water vapor pressure over a food at equilibrium with the atmosphere above it to the water vapor pressure at the same temperature
water activity (aw)
aw of water is?
aw = 1.0
aw of a completely dehydrated food (e.g. crackers and powdered products)
aw = 0
Most bacteria, yeasts, and molds cannot grow. This is important for food preservation
aw = 6
an organism that grows in high concentration of salt
halophiles
salt tolerant organism
haloduric
organisms that can grow over a fairly wide range of Aw or solute concentrations
osmotolerant
aw of fresh foods
0.99
organic and inorganic compounds found in any substrate provide energy that supports microbial existence
release of energy consists of oxidizing one compound and reducing another
oxidation-reduction (redox) potential (Eh)
require positive Eh values
aerobes
will not start to grow until the redox has reached a critical maximum, much lower than facultative aerobes
anearobes
requires negative Eh values
anaerobes and facultative anaerobes
microorganisms need these nutrients to survive (conspim)
carbon, oxygen, nitrogen, sulfur, phosphorous, iron, magnesium
Water activity where yeasts can grow at lower aw levels compared to bacteria
aw = 0.88
Antimicrobial constituent in cloves, cinnamon, and sage
eugenol
Antimicrobial constituent in cinnamon
cinnamic aldehyde
Antimicrobial constituent in sage and oregano
thymol
Antimicrobial constituent in garlic
thymol
Antimicrobial constituent in mustard
allyl isothiocyanate
Antimicrobial constituent in eggs and milk
lysozyme
Antimicrobial constituent in milk
lactoperoxidase
imposed from outside
extrinsic factors
organisms with a narrow temperature range for growth
constant temperature
sa isang temperature lang makaka-survive (either cold or hot)
stenothermal
organisms growing from environments with greater natural variation of temperature
eurythermal
microorganisms that can grow at subzero to 20C with optimum at 10-15C
psychrophiles
psychrophiles are microorganisms that can grow at what temperature
subzero to 20C
optimum at 10-15C
microorganisms that can grow at and below 7C with optimum at 20-30C
psychrotrophs
psychrotrophs can grow at what temperature
at and below 7C
optimum at 20-30C
microorganisms that can grow at 20-45C with optimum at 30-40C
thrive best at rom temp and are more common spoilage organisms
mesophiles
mesophiles are. microorganisms that can grow best at what temperature
20-45C
optimum at 30-40C
microorganisms that can grow at and above 45C with optimum at 55-65C
cause of spoilage in thermally processed foods
when they multiply, they produce spores that are heat-resistant
thermophiles
thermophiles are microorganisms that can grow best at what temperature
at and above 45C optimum at 55-65C
two main gases that affect microbial activity
oxygen and carbon dioxide
Must have oxygen to survive and grow
obligate aerobe