Biological methods for Food Preservation

Question 1

Biopreservation is the :

Answer 1

use of microorganisms, their metabolic products, or both to preserve foods

Question 2

What is the exception to biopreservation?

Answer 2

Controlled acidification where acid is produced by LAB in controlled-abused foods

Question 3

What is MICROGARD:

Answer 3

it is a family of products that can be added to refrigerated food products

Question 4

What to MICROGARD products include:

Answer 4

• a fermentable CHO (lactose or dextrose)

- bacterial culture

Question 5

MicroGARD is a _____, ________ product designed to improve shelf-life protection

Answer 5

natural

clean-label

Question 6

key benefits of MICROGARD (3):

Answer 6

1) Protect shelf-life
2) Maintain the organoleptic qualities of food
3) Meet consumer’s demand for natural products

Question 7

The LAB do not grow under __________ conditions and will only grow if foods are _____________

Answer 7

refrigeration

temperature abused

Question 8

Carcinogenic nitrosamines can be formed from ________________, and this has led to a search for nitrite substitutes for bacon preservation (particularly temperature abused bacon)

Answer 8

nitrites in cured meats

Question 9

Explain the Wisconsin process

Answer 9

Inoculating bacon with less nitrite, 0.7% sucrose, and LAB starter culture is even better than inoculating the bacon only with nitrites

Question 10

What are bacteriocins ?

Answer 10

Bacteriocins are antimicrobial peptides of bacterial origins that are lethal to some bacteria, but not the host that produced them

Question 11

T OR F : Many bacteriocins are able to inhibit pathogens of serious concern, like L. monocytogenes, and are therefore of interest for food safety

Answer 11

T

Question 12

Are bacteriocins antibiotics?

Answer 12

nope

Question 13

________ is the best-characterized LAB bacteriocin

Answer 13

Nisin

Question 14

Class 1 bacteriocins:

Answer 14

-contain unusual AA produced by posttranslational modification

Question 15

How is nisin obtained in the food industry ?

Answer 15

From the culturing of L.lactis on natural substrates and is not chemically synthesized

Question 16

Nisin extends shelf-life by suppressing ________ spoilage and pathogenic bacteria

Answer 16

gram +

Question 17

Subtilin:

Answer 17

(produced by Bacillus subtilis) is also a lantibiotic, but is also an effective protease and can be used in food, laundry detergent, and contact lens cleaners

Question 18

Class 2 bacteriocins:

Answer 18

• small heat stable proteins with a consensus leader sequence that signals to the producing cell that the protein must be exported
• 2a : active against L.monocytogenes
• 2b : require 2 different peptides for activity
• 2c: require reduced cysteine for activity

Question 19

Class 3 bacteriocins:

Answer 19

Are larger >30kDa heat-liable antimicrobial proteins

Question 20

Class 4 bacteriocins:

Answer 20

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

Question 21

What is the method for bacteriocin discovery:

Answer 21

• overlay a colony of the putative bacteriocin producer with an agar medium containing a bacterium being tested for sensitivity
• bacteriocin will form an inhibition zone with sharp edges in the confluent growth
• verification test: hole is poked in the center of the inhibition zone and the hole is filled with a proteolytic enzyme.
• as the enzyme moves out it cleaves bacteriocin and inactivates it, allowing the bacteria to grow where it was once inhibited

Question 22

All bacteriocins produced by LAB act by __________________________-

Answer 22

disrupting the integrity of the cytoplasmic membrane

Question 23

The addition of bacteriocins to vegetative cells results in rapid and non-specific efflux of _________________________ this rapidly dissipates chemical and electrical gradients

*the cell is unable to regenerate the pmf and ultimately increases in permeability / unable to protect its cytoplasm and this leads to cell inhibition and death

Answer 23

pre-accumulated ions, amino acids, and ATP molecules

Question 24

What are the 2 proposed models for bacteriocin mechanism of Action:

Answer 24

1) Pore forming model 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 cell lysis

Question 25

What happens to the mechanism of nisin in spores ?

Answer 25

• in spores nisin allows spores to germinate
• however it inhibits the outgrowth of the preemergent spore
• the preemergent spore is much less resistant to environmental stresses (heat) than the spore

Question 26

Colicins (what are they?)

Answer 26

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
• release

Question 27

How do colicins exert their lethal action?

Answer 27

• binding to specific receptors (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
• reach their lethal target and act by forming a voltage-dependent channel into the inner membrane or by using their endonuclease activity on DNA, rRNA and tRNA

Question 28

Colicins can be divided into:

Answer 28

enzymatic colicins or pore-forming colicins

Question 29

For enzymatic colicins the mode of action can be:

Answer 29

• peptidoglycan synthesis block (M)
• Protein synthesis block by cleavage of tRNA (D and E5)
• Protein synthesis block by cleavage of 16sRNA (E3, E4, E6)
• DNA degradation (E2,E7,E9)

Question 30

what are the three ways that are approved methods to add bacteriocins to foods:

Answer 30

1) Purified bacteriocins can be added directly to the food product
2) Bacteriocinogenic cultures can be added to non-fermented products so that bacteriocins can be produced in situ
3) Starter cultures that encode bacteriocins can be chosen for fermentation reactions

Question 31

Nisin has _________ properties, and it sensitizes spores to ______, so that thermal processing times can be reduced and nisin generally gets used in products where botulism is a concern

Answer 31

anti-listerial

heat

Question 32

Give an example of a bacteriocinogenic culture :

Answer 32

pediocins (not active against spores but active against vegetative L.monocytogenes cells

Question 33

How can you overcome resistance to bacteriocins?

Answer 33

It has been suggested that bacteriocins be used in combination to overcome this problem, but this is only effective if resistance to each bacteriocin is conferred by different mechanisms (straight chain fatty acids example)

Question 34

nisin-resistant bacteria are likely less resistant to ______

Answer 34

cold

Question 35

Bacteriophages are ___________________________

Answer 35

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

Question 36

Resistance to bacteriophages is generally created by ______________

Answer 36

changes in the bacteriophage receptor site

Question 37

What should be done to control bacteriophage resistant

Answer 37

-phage should be used in cocktails containing several different strains and types