biological methods of food preservation

Question 1

biopreservation

Answer 1

the use of microorganisms, their metabolic products, or both, to preserve food (usually excludes fermentation)
ex. bacteriocins, bacteriophage, controlled acidification

Question 2

controlled acidification

Answer 2

organic acids can be added to foods, can be produced via fermentation, or LAB

Question 3

MicroGARD

Answer 3

-family of products that can be added to refrigerated food products

Question 4

key benefits of microGARD

Answer 4

1. protect shelf life
2. maintain the organoleptic qualities of food
3. meet consumers demands for natural products

Question 5

bacteriocins

Answer 5

antimicrobial peptides of bacterial origins that are lethal to some bacteria but not to the host that produced them. They are produced by virtually all bacterial species.

Question 6

Bacteriocins: class 1

Answer 6

contain unusual amino acids produced by posttranslational modification

ex. Nisin: the best-characterized LAB bacteriocin. Nisin is not chemically synthesized. Used in the processing of cheese, meats, beverages - supresses gram-pos bac.
ex. Subtilin: (bacillus subtilis). lantibiotic (produced by LAB). effective protease and can be used in food, laundry detergent, and contact lens cleaners

Question 7

Bacteriocins: Class 2

Answer 7

-small heat-stable proteins with a consensus leader sequence (signal sequence) that signals to the producing cell that the protein must be exported

Question 8

Class 2: subclasses (3)

Answer 8

IIa: bacteriocins active against Listeria monocytogenes
IIb: bacteriocins that require two different peptides for activity
IIc: bacteriocins that require reduced cysteine for activity

Question 9

Bacteriocins: class 3

Answer 9

are larger than 30kDa heat-labile antimicrobial proteins

Question 10

Bacteriocins: Class 4

Answer 10

have lipid or carbohydrate moieties and the function of these non-protein portions are unknown

Question 11

How were bacteriocins discovered/identified?

Answer 11

• zone of inhibition with a colony in the center and sharp edges
• organic acids have fuzzy edges
• bacteriophage have no colony in center
• to check you can put a protease in the colony that will cleave and inactivate the bacteriocin

Question 12

Mechanism of action: bacteriocin

Answer 12

• bacteriocins produced by LAB disrupt membrane integrity
• vegetative cells: rapid and non-specifin efflux of ions, AA, and ATP
• therefore dissipates chemical and electrical gradients
• *Bacteriocins are diverse, but all have basically the same mechanism
• most bacteriocins have amphiphili cataionic peptides which allow for insertion into the membrane and permeabilization

Question 13

what are the 2 mechanism models for bacteriocins?

Answer 13

1. pore formation model: bacteriocins bind, insert into the membrane, and oligomerize to form a pore
2. membrane solubilization model: bacteriocins act as detergents resulting in lysis of the cell

Question 14

mechanism in spores? bacteriocins

Answer 14

allows spores to germinate or encourages germination. Inhibits the outgrowth of the preemergent spore, which is less resistant to environmental stresses than the spore

Question 15

Colicin

Answer 15

• def: proteins produced by and toxic for some strains of E. coli. Produced y strains of E. coli carrying a colicinogenic plasmid that bears the genetic deterinants for: colicin synthesis, immunity, and release.
• mechanism: bind to specific receptors, which are outer membrane proteins used for the entry of nutrients. They are then translocated through the outer membrane and transit through the periplasm by either the Tol or the TonB system
• Act by forming a voltage-dependent channel into the inner membrane or by using their endonuclease activity on DNA, rRNA, or tRNA

Question 16

Colicins - list of mechanisms

Answer 16

Enzymatic or pore-forming
Enzymatic:
1. block peptidoglycan synthesis
2. block protein synthesis by cleavage of tRNA or 16S rRNA
3. DNA degradation

Question 17

How to add bacteriocins to food?

Answer 17

1. purified bacteriocins added directly to food product
2. bacteriocinogenic cultures can be added to non-fermented food products so that bacteriocins can be produced in situ
3. starter cultures that encode bacteriocins can be chosen for fermentation reactions

Question 18

Bacteriophage

Answer 18

• natural component of the food microbiota and are routinely consumed as part of our diet
• challenges associated: 1. possible resistance, low numbers of bacteria in food (phage need 10^5-10^6 CFU of actively growing bacteria to be effective

Question 19

Bacteriophage resistance

Answer 19

• created by changes in the bacteriophage receptor site - could be proteins, LPS, lipoproteins
• resistance to one phage does not mean resistance to another because there is great variety and abundance of phage.
• phages should be used in cocktails containing several different strains and types.