Food Microbiology Exam 2

lag

microbial growth phase of getting used to environment, isn’t much noticeable growth

obligate aerobe

require oxygen for growth

molds

what are commonly obligate aerobes

obligate anaerobe

oxygen is detrimental/fatal

facultative anaerobe

not strict aerobes or anaerobes

clostridium (oa)

example of obligate anaerobe

with

do facultative anaerobes grow best with or without oxygen

saccharomycess, E coli, salmonella, listeria

4 facultative anaerobes

microaerophilic

require oxygen levels lower than that found under normal atmospheric conditions

campylobacter (in chicken intestine)

ex of microaerophilic bacteria

aerotolerant anaerobe

don’t use oxygen but not killed by it

LAB (aa)

an aerotolerant anaerobe

aerobic plate count

estimates number of microorganisms in food, only estimates certain category of microorganisms, not anaerobes

fermentation (o)

if no oxygen is present, what happens after glycolysis

aerobic respiration (o)

if oxygen is present, what happens after glycolysis

cytoplasm

where does glycolysis occur

2

how many ATP per glucose of hydrolysis

mitochondria

where does aerobic respiration take place

oxidative phosphorylation

what is the reason aerobic respiration produces so much more energy

oxygen

______ is terminal e acceptor in oxidative phosphorylation

slow

is aerobic respiration fast or slow

32

how much ATP does oxidative phosphorylation produce

fast

is fermentation fast or slow

lactate (usually)

what is pyruvate converted to in anaerobic fermentation

2

how much ATP does fermentation produce

substrate level phosphorylation

what phosphorylation does fermentation use

no

is energy the main byproduct in fermentation

diacetyl

byproduct from fermentation involving LAB, buttery

lipids

metabolized by lipases secreted by molds

butyric acid

what acid can be produced by clostridium

molds

what are lipids secreted by in fermentation

amino acid

____ ____ metabolism - flavors in cheese

injured cells

may not be able to form visible colonies, but could still cause disease

viable but nonculturable (VBNC)

category of injured, vegetative or dormant state, cannot be cultured by normal methods

campylobacter

what bacteria is sometimes VBNC

aseptically

how are samples collected

enrich

if we are interested in presence and have a small number we ______

dilute

if high quantities are expected and we want to quantify we

enrich

when doing surface testing, do you dilute or enrich

no

is surface testing destructive

a single cell

standard plate count assumption - each colony forming unit arises from

pour plate

does LAB prefer pour plate or spread plate method

obligate aerobe

what is best for spread plate method

anaerobe

what is best for pour plate method

selective media

incorporation of ingredients that favor or inhibit growth of particular microorganisms

differential media

incorporation of ingredients that allow differentiation between microorganisms due to biochemical reactions

long process

what’s the issue with detection and enumeration for food

most probable number

relatively fast screening method, mix between rapid and traditional, estimates low number of microorganisms, uses test tubes of broth that enrich and select for particular microorganisms

small

is most probable number best for small or large numbers

alive

nucleic acid based methods limitation is that DNA doesn’t have to be _____

viruses

what is looked for in electron microscopy

fecal exam

how do people look for parasites

binary fission

how does bacteria reproduce

positive

bacterial growth for food fermentations

negative

bacterial growth for spoilage or safety

generation time

doubling time

growth

proliferation and metabolism, rates differ for microorganisms

survival

injured; viable but nonculturable, membrane integrity compromised, slowed metabolism, focused on repair

psychrophile

love cold

psychrotroph

likes 20-30 degrees Celsius, but can grow lower

listeria

ex of psychrotroph

mesophile

likes 30-40 degrees Celsius, GI tract

e coli and salmonella

examples of mesophiles

thermophile

associated with spoilage, likes 55-65 degrees Celsius

pseudomonas, molds, bacillus

3 obligate aerobes

listeria, salmonella, e coli

3 facultative anaerobes

lactobacilli

an aerotolerant anaerobe

campylobacter

a microaerophile

vacuum packaging

slows spoilage and controls oxidation

modified atmosphere packaging

instead of removing air from package, control

controlled atmosphere storage

stored in facility, ex apples out of season

nutrients

slicing, macerating and inclusions impact availability of

LAB

what spoilage microorganism grows well in acid foods

high

are low or high pH foods typically associated with outbreaks

acidified food

addition of acid to lower pH results in

acid food

foods with naturally low pH

antimicrobials

substances natural to the foods with inhibitory or inactivating properties

preservative

if you add antimicrobials, it’s called a

lysozyme

antimicrobial enzyme we discuss

lactoperoxidase system

naturally occurring inhibitory system in milk

redox potential (Eh)

measure of tendency to gain or lose electrons

Eh

short form of redox potential

reduced

negative electric potential, favors anaerobic growth

oxidized

positive electric potential, favors aerobic growth

anaerobic

does reduction favor aerobic or anaerobic growth

water activity

ratio of free, available water within a food

clostridium

what bacteria needs the highest water activity

anaerobic

does aerobic or anaerobic staphylococcus need higher water activity

cross protection

same protein used to respond to multiple stresses

oxidative phosphorylation

oxygen serves as terminal electron acceptor and yields energy

LAB and yeasts

2 key players in fermentation

alcoholic fermentation

what is yeast involved with

lactobacillus, leuconostoc, pediococcus

main fermenters associated with LAB

homolactic

lactic acid is primary byproduct

leuconostoc

ex of a fermenter associated with heterolactic fermentation

back slopping

using part of a finished product to start a new

lab grown

starter culture with highest consistency

homogenization

prevents ingredient separation during fermentation

coagulation

microbes and enzymes hydrolyze casein

live cultures

fermentation of milk to make yogurt uses ____ _____