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39 Cards in this Set

  • Front
  • Back
What are the two classifications of protein antimicrobials?
-Naturally in food
-Bacteriocins (made by bacteria)
What are antimicrobial proteins found in food naturally?
-other Fe chelators
(transferrin, ovoferrin)
What are the classifications of bacteriocins?
-non-post-translationally modified
How does lysozyme work?
It hydrolizes the beta-1-4-glycosidic bond between n-acetylmuramic acid and n-acetulglucosamine in peptidoglycan.
How can lysozyme activity be enhances in g- orgs?
By using something - ie EDTA - to get through LPS membrane.
How does EDTA work to get through g- LPS membrane of g-?
the membrane is stabilized by cations. EDTA chelates these ions and destabilized the membrane.
How does Avidin work?
By binding to 4 molecules of biotin, making it unavailable? for the bacteria

It's bacteriostatic and not bactericidal
How does lactoferrin work?
What is limitation to its use?
By binding to iron; but only works in neutral pH!! Otherwise, iron soluble and it doesn't matter.

Binding involves bicarbonate (HCO3-)
Descibe what a lantibiotic is. What bacteria often make these?
Lantibiotic is a small protein made by bacteria, and quite often, by LAB. Sometimes they're specific, othertime broad.
Name a lantibiotic/ what organism?

By stimulates its production? What is the mechanism called?
What does it also stimulate?
Bactericidal. Works in low pH. Made in response to the presence of Nisin (signal transduction)

Nisin made by lactococcus lactis - it's fairly broad and effective against gram +'s

Also stimulates production of immunity thingies.
Describe the post-translational modification
A small pre-nicin protein is made
Two Serine, threonine dehydrated to Dha, Dhb
Five lanthionine rings formed
Transported out of cell
Cleaved to remove N-terminal peptide
cell also produces immunity
How does Nisin work?
Nisin can get through cell wall of g+; then starts forming pores in cell membranes. It cannot get through LPS membrane of g- unless helped. Pore formation facilitated by Lipid II which binds and anchors.

Essentially, proton motor force depleted. No driving force to make ATP
Name a non post-translationally modified bacteriocin.

How does these work?
Pediocin (from Pediococcus)

They have a leader glycine-glycine motif that allows cell membrane penetration
What is Pediocin effective against?
Name some non-thermal techniques to reduce microbial loads
Irradation: gamma-radiation, High E electrons, xrays, uV

Pulsed High intensity light or electrical fields
Additives - chemical preservation
What are the "levels" of irradiation treatment?
1. Radurization 0.7-2.5 kGy
2 Radicidation 2.5-10 kGy
3. Radappertization 30-40 kGy
What is a kGy
# of Joules absorbed per kg of food
What are the different types of irradiation?
gamma-radiation: cobalt60 or cesium137/ food processed in-package/ time 5-15 min

high e- electrons - "electronic pasteurization"/surebeam
What is the benefit of one vs other?
gamma radiaton: cheaper and higher penetration (>3") vs 1.5". But results in radioactive waste
What is the relationship between microbe size and kGy dose?
The smaller the organism, the biggest the does needed
Name some current applications of irraditation
insect disinfestation of wheat
Spices, herbs (30kGy)
Keep potatoes from sprouting
Fresh produce
What needs to be on the label if a food irradiated?
The radura symbol
Name some common food additives for chemical preservation
Organic acids - benzoate, proprionate, sorbate
What are the two main effects that organic acids have on the target microbe?
* Depletion of proton motor force
* Disrupts transport
What is a big drawback of organic acids?
They are only effective in acidic conditions: below their pKa. They must be protonated (uncharged) to enter bacterial cell.
Describe benzoic acid
-structure/pka/where found/inhibits what
Benzene ring + COOH
PKA = 4.76
Found in cranberries
inhibits yeast and molds
Describe propionic acid
-structure/pka/where used/inhibits what
pKa = 4.8
Used in Cheese/Bakery
Describe sorbate
-structure/pks/where found/inhibits what
pKa= 4.73

wide use
inhibits fungi, catalase + bacteria, and spore germination
What does it do?
Conditions most effective?
Reacts with myoglobin/ inhibits e-transport chain

Most effective anaerobically
Main mode of action
Where used
Effective against
v reactive; Break S-S bonds
Fruit juices/wine
Fungi, bacteria
Name a fumigant
Used for what?
Dry goods: spices, grains
Not used so much anymore due to greenhouse effect
How does irradiation work? (i.e. why is it lethal to microbes?
the radiation causes water for form free radicals and the free radicals attach proteins, DNA. The cells die as DNA disrupted.
D-value (in kGy) in Listeria? C. bot spores?
0.45 kGy
3.56 kGy
What kills microbes when non-thermal techniques used? (think BROAD)
Some form of energy
What type of log reduction is possible with pulsed-high intensity light?
Only 1-3. 20000x intensity of sun.
What pressures are HPP run at?
300-1700kPA / sometimes high T used too -- but it's PULSED
What are some applications of HHP?
Juices, guac, delimeats, oysters. Not applicable for veggies
How does HHP work?
Disruption of cell membranes
Denaturation of proteins
Ribosomes inactivated
Enzymes inactivated
What are typical D values of HHP?
2-10 min
but hard to model due to tail end