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39 Cards in this Set
- Front
- Back
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What are the two classifications of protein antimicrobials?
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-Naturally in food
-Bacteriocins (made by bacteria) |
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What are antimicrobial proteins found in food naturally?
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-Lysozyme
-Avidin -lactoferrin -other Fe chelators (transferrin, ovoferrin) |
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What are the classifications of bacteriocins?
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-Lantibiotics
and -non-post-translationally modified |
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How does lysozyme work?
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It hydrolizes the beta-1-4-glycosidic bond between n-acetylmuramic acid and n-acetulglucosamine in peptidoglycan.
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How can lysozyme activity be enhances in g- orgs?
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By using something - ie EDTA - to get through LPS membrane.
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How does EDTA work to get through g- LPS membrane of g-?
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the membrane is stabilized by cations. EDTA chelates these ions and destabilized the membrane.
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How does Avidin work?
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By binding to 4 molecules of biotin, making it unavailable? for the bacteria
It's bacteriostatic and not bactericidal |
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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-) |
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Descibe what a lantibiotic is. What bacteria often make these?
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Lantibiotic is a small protein made by bacteria, and quite often, by LAB. Sometimes they're specific, othertime broad.
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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. |
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Describe the post-translational modification
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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 |
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How does Nisin work?
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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 |
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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 |
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What is Pediocin effective against?
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Listeria
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Name some non-thermal techniques to reduce microbial loads
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Irradation: gamma-radiation, High E electrons, xrays, uV
Pulsed High intensity light or electrical fields HHP Additives - chemical preservation |
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What are the "levels" of irradiation treatment?
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1. Radurization 0.7-2.5 kGy
2 Radicidation 2.5-10 kGy 3. Radappertization 30-40 kGy |
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What is a kGy
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# of Joules absorbed per kg of food
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What are the different types of irradiation?
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gamma-radiation: cobalt60 or cesium137/ food processed in-package/ time 5-15 min
high e- electrons - "electronic pasteurization"/surebeam |
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What is the benefit of one vs other?
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gamma radiaton: cheaper and higher penetration (>3") vs 1.5". But results in radioactive waste
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What is the relationship between microbe size and kGy dose?
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The smaller the organism, the biggest the does needed
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Name some current applications of irraditation
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insect disinfestation of wheat
Poultry Beef Spices, herbs (30kGy) Keep potatoes from sprouting Fresh produce |
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What needs to be on the label if a food irradiated?
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The radura symbol
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Name some common food additives for chemical preservation
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Organic acids - benzoate, proprionate, sorbate
Sulfites Nitrites |
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What are the two main effects that organic acids have on the target microbe?
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* Depletion of proton motor force
* Disrupts transport |
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What is a big drawback of organic acids?
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They are only effective in acidic conditions: below their pKa. They must be protonated (uncharged) to enter bacterial cell.
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Describe benzoic acid
-structure/pka/where found/inhibits what |
Benzene ring + COOH
PKA = 4.76 Found in cranberries inhibits yeast and molds |
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Describe propionic acid
-structure/pka/where used/inhibits what |
CH3-CH2-Cooh
pKa = 4.8 Used in Cheese/Bakery Molds |
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Describe sorbate
-structure/pks/where found/inhibits what |
CH3-CH=CH-CH=CH-COOH
pKa= 4.73 wide use inhibits fungi, catalase + bacteria, and spore germination |
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Nitrite:
What does it do? Conditions most effective? |
Reacts with myoglobin/ inhibits e-transport chain
Most effective anaerobically |
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Sulfites:
Main mode of action Where used Effective against |
v reactive; Break S-S bonds
Fruit juices/wine Fungi, bacteria |
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Name a fumigant
Used for what? |
Ethylene
Dry goods: spices, grains Not used so much anymore due to greenhouse effect |
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How does irradiation work? (i.e. why is it lethal to microbes?
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the radiation causes water for form free radicals and the free radicals attach proteins, DNA. The cells die as DNA disrupted.
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D-value (in kGy) in Listeria? C. bot spores?
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0.45 kGy
3.56 kGy |
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What kills microbes when non-thermal techniques used? (think BROAD)
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Some form of energy
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What type of log reduction is possible with pulsed-high intensity light?
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Only 1-3. 20000x intensity of sun.
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What pressures are HPP run at?
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300-1700kPA / sometimes high T used too -- but it's PULSED
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What are some applications of HHP?
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Juices, guac, delimeats, oysters. Not applicable for veggies
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How does HHP work?
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Disruption of cell membranes
Denaturation of proteins Ribosomes inactivated Enzymes inactivated |
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What are typical D values of HHP?
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2-10 min
but hard to model due to tail end |
