16 - biological control of foodborn bacteria Flashcards
What is biopreservation
The use of microorganisms, their metabolic products or both to preserve foods (exclude fermentation).
What is controlled aciditication
the production of acids by LAB and then these acids are used as a preservative in food.
What is microgard ?
it is a small bundle composed of a fermentable carbohydrte and a bacterial culture added to regfrigerated foods to for preservation
What are the benefits of microGARD?
- protect shelf life
- maintain the organileptic qualities of food
- meet consumer’s demand for natural products
what will be the factors that influence the effectiveness of microGARD?
1-products pH
2- buffering capacity
3- target spoilage microorganisms
4- concentration of fermentable CHO
T or F : the microGARD is effective against clostridium bottulinum
true
What is the wisconsin process ?
the reducement in nitrites in bacon by adding sucrose and LAB to prevent the growth of clostridium bottulinum
what are bacteriocins?
antimicrobial peptides that can be lethal to bacteria.
T or F : bacteriocins are produced virtually by all bacteria
true
What are the four classes of bacteriocins?
Class I-IV
Nisin and subtilin are found in the class ___ of bacteriocins
Class I
Nisin is effective against gram ___
positive
What is the class I of bacteriocins?
contains unsual amino acids like lanthionine that are produced by modification after the translation.
What are lantibiotics ?
bacteriocins that contain lanthionine rings. Lanthionine rings are amino acids that have reacted with cysteine to form thioether lanthionine.
What is the class II of bacteriocins?
bacteriocins in this class are small heat stable proteins with a consensus lader sequence
What are the three sub-classes of class II bacteriocins
IIa : bacteriocins active against listeria monocytogenes
IIb : require 2 peptides for activity
IIc : require cystein for activity
What are the class III bacteriocins
really big proteins and heat liable
What are classs IV ?
proteins with lipid and cho moieties
How are bacteriocin discovered?
overlap of the colony producing the bacteriocin on a agar inoculated with the colony that the bacteriocin is against
How can you be sure the inhibition zone is due to a bacteriocin
putting proteolyitic enzyme at the center of the inhibition zone and if there is growth then the colony was producing a bacteriocin
Bacteriocin inhibition zone edges are _____
sharp
Bacteriophage inhibition zone edges are _____
clear but there is no colony at the center
Inhibition zone produced by organic acids have edges that are _____
fuzzy
how does the bacteriocin produced by LAB work?
they work by disrupting the cytoplasmic membrane
T or F : all the bacteriocins produced by LAB have the same mechanism
true
What are the two proposed model for the perforation by LAB bacteriocins
1- pore formation model
2- membrane solubulization model
What is the mechanism of action of the LAB’s bacteriocins
the will distrupt the integrity of the cytoplasmic membrane
what is the mechanism of action of nisin?
it will make the spore germinate into the preemergent spore (which is less resistant) and will inhibit the transformation of the preemergent spore into viable cells
T or F : nisin will allow spores to germinate and encourage germination
true
what is the mechnanism of colicin
they wil bind to receptor and then enter the cell by the tonB toI system and then have a endonuclease action or impant voltage dependant chanels in the iner membrane
What are the target of the endonuclease of the colicin
- protein syntehsis rRNA
- protein synthesis tRNA
- peptidoglycan syntehsis block
- DNA degradation
What is nisin usually good against
1- anti-listerial
2- anti-clostridium
What is nisin combined with to reduce the clostriudum and listeria
combined with modified atmosphere
T or F : nisin as GRAS in several countries
true
What are pediocins effective against
against L. monocytogenes vegetative cells
Why is starter culture with bacteriocins good for fermentation
because it can inactivate the sarter culture
what is one drawback of the use of bacteriocins
some bacteria can be resistant to bacteriocins
What are the challenges of using bacteriophages
possible resistance
low number of bacteria in food (phage need minimal 10^5 CFU to work)
Resistance to bacteriophages is generally created by :
changes in the bacteriophage receptor site
