Biopreservation

Question 1

What is biopreservation? What is excluded in the definition

Answer 1

-is the use of microorganisms, their metabolic products, or both to preserve foods.
-However, this definition usually excludes fermentation
An exception is controlled acidification where acid is produced by LAB in temperature-abused foods
-Other examples of biopreservation are the use of bacteriocins, and bacteriophages

Question 2

What is controlled acidification?

Answer 2

Organic acids can be added to foods, can be produced via fermentation, or LAB can produce lactic acid in situ and the controlled production of lactic acid can be an important form of biopreservation

Question 3

What is Microgard?

Answer 3

• MicroGARD is a family of products that can be added to refrigerated food products
• MicroGARD products include a fermentable carbohydrate (usually lactose or dextrose), and a bacterial culture that are combined to offer customizable protection for a variety of food products
• If the food is temperature abused the bacteria will grow and produce lactic acid, acetic acid, propionic acid, and bacteriocins to ensure the safety of the product despite the temperature abuse
• MicroGARD is a natural, clean-label product designed to improve shelf-life protection

Question 4

Advantages of Microguard?

Answer 4

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

Question 5

What was the idea behind microguard?

Answer 5

was a way to use LAB to prevent the growth of C. botulinum in certain foods that could be temperature abused
The LAB do not grow under refrigeration conditions and will only grow if foods are temperature abused

Question 6

The effectiveness of in situ acidification depends on

Answer 6

on the products pH, buffering capacity, target spoilage microorganisms, and the concentration of fermentable carbohydrates (therefore a custom solution is required)

Question 7

What is the wisonsin process

Answer 7

Carcinogenic nitrosamines can be formed from nitrites in cured meats, and this has led to a search for nitrite substitutes for bacon preservation (particularly temperature abused bacon)
When bacon without nitrites was inoculated with C. botulinum and incubated at 28C, 58% turned toxic
When bacon was prepared with less nitrite, 0.7% sucrose, and LAB starter cultures <2% became toxic
This is known as the Wisconsin process and was approved by the FDA for use in 1986

Question 8

what are bacteriocins

Answer 8

antimicrobial peptides of bacterial origins that are lethal to some bacteria, but not the host that produced them. They are produced by virtually all bacterial species. Although, the bacteriocins produced by LAB are of particular interest to the food industry.

Question 9

Many bacteriocins are able to inhibit___ and therefore are of interest for food safety

Answer 9

pathogens of serious concern like L monocytogenes

Question 10

T or F: bacteriocins are not antibiotics.

Answer 10

T

Question 11

What are the 4 main classes of bacteriocins

Answer 11

1. class 1; contain unusual amino acids produced by post translational modification. lantibiotics.
2. class 2; small heat stable proteins with a consensus leader sequence that signals to the producing cell that the protein must be exported.
3. larger, heat liable antimicrobial proteins
4. have lipid or carbohydrate moieties and the function of these non protein portions are unknown

Question 12

what are the 3 sub classes of class 2 bacteriocins

Answer 12

11a; bacteriocins active against L monocytogenes
11b; bacteriocins that require 2 diff peptides for activity
11c; bacteriocins that require cysteine for actvity.

Question 13

How to discovery the presence of bacteriocins

Answer 13

overlay colony of the putative bacteriocin producer with an agar medium containing the bacterium being tested for sensitvity.

Bacteriocin producers will form an inhibition zone with sharp edges and confluent growth.

• egdes by acids = fuzzy
• bacteriophages= no colony at center

Question 14

verification test for presence of bacteriophages

Answer 14

The verification test can be done on the same plate. A hole is poked in the center of the inhibition zone (where the colony is) and the hole is filled with a proteolytic enzyme. As this enzyme moves out it cleaves the bacteriocin and inactivates it, allowing the bacteria to grow where it once was inhibited

Question 15

All bacteriocins produced by LAB act by

Answer 15

disrupting the integrity of the cytoplasmic membrane

Question 16

what happens when bacteriocins are added to vegetative cells

Answer 16

• results in rapid, non specific efflux of pre-accumulated ions, amino acids and ATP molecules
• dissipates chemical and electrical gradients
• unable to regenerate pmf and increase permeability, less functional cytoplasm so cell inhibition and death.
• amphiphillic cationic peptides = insert to the membrane for permeallization too.

Question 17

2 proposed models of attack by bacteriocins

Answer 17

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

Question 18

what is the mechanism of action of bacteriocins on spores

Answer 18

in spores, nisin allows spores to germinate but inhibit the outgrowth of the preemergent spore. the pre emergent spore is much less resistant to environmental stresses (ie heat ) than the spore

Question 19

what are colicins

Answer 19

Colicins are proteins produced by and toxic for some strains ofEscherichia coli. They are produced by strains ofE. colicarrying a colicinogenic plasmid that bears the genetic determinants for:
Colicin synthesis,
Immunity, and
Release

Question 20

how do collicins work

Answer 20

-Colicins exert their lethal action by first binding to specific receptors, which are outer membrane proteins used for the entry of specific nutrients
-They are then translocated through the outer membrane and transit through the periplasm by either the Tol or the TonB system
Colicins then reach their lethal target and act either by forming a voltage-dependent channel into the inner membrane or by using their endonuclease activity on DNA, rRNA, or tRNA.

Question 21

colicins can be divided into what 2 classes?

Answer 21

enzymatic colicins or pore-forming colicins

Question 22

mode of action of enzymatic colicins

Answer 22

peptidoglycan synthesis block [M]
protein synthesis block by cleavage of tRNA [D and E5]
Protein synthesis block by cleavage of 16S rRNA [E3, E4, and E6], or
DNA degradation [E2 and E7 to E9]) is also indicated

Question 23

3 ways to add bacteriocins to food

Answer 23

1. Purified bacteriocins can be added directly to the 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 24

example of purified bacteriocin

Answer 24

nisin

Question 25

explain some properties of nisin

Answer 25

• added to milk and cheese, canned foods
• GRAS
• anti listerial properties
• sensitizes spores to heat so that thermal processing times can be reduced
• used when c bot is a concern

Question 26

give examples of bacteriogenic cultures

Answer 26

pediocins

Question 27

when would starter cultures that encode bacteriocins be used?

Answer 27

This is particularly useful in fermented meat and vegetable products where the indigenous communities are not inactivated (i.e. by pasteurization) therefore, using a starter that makes a bacteriocin can help to inactivate the bacteria that are already there and give the fermentation reaction a better chance of success

Question 28

how can bacteriocin resistance be overcome?

Answer 28

by combining bacteriocins. this is only effective if resistance to each bacteriocin is conferred by a different mechanism

Question 29

most resistance to bacteriocins has to do with?

Answer 29

changes in membrane permeability and generalized mechanisms

Question 30

what are bacteriophages

Answer 30

a natural component of food microbiota and are routinely consumed as part of our diet

Question 31

name some commercial bacteriophages + problems

Answer 31

Commercial bacteriophages to control the growth of salmonella, ecoli and listeria. There are several challenges associated with bacteriophage use in foods, including:
Possible resistance
Low numbers of bacteria in food (phage need 105 to 106 CFU of actively growing bacteria to be effective)

Question 32

explain the causes of bacteriophage resistance + how is resistance controlled

Answer 32

-Resistance to bacteriophages is generally created by changes in the bacteriophage receptor site
The receptor site can be proteins, LPS, or lipoproteins
-Luckily there are an abundance of bacteriophage strains in existence, and resistance to one does not affect the efficacy of the remaining phage types
-Therefore to control resistance, phage should be used in cocktails, containing several different strains and types
If a bacteria is resistant to one type, the other types should still be functional, and this strategy should curb the emergence of resistance