Biological methods of food preservation

Question 1

What is biopreservation

Answer 1

Question 2

Explain what is controlled acidification

Answer 2

• In controlled acidification, it is not like normal fermentation, because LAB is not naturally there, they are added
• Organic acids can be added to foods, can be produced via fermentation (traditional preservation method by fermention, not biological or chemical),
• or LAB can produce lactic acid in situ and the controlled production of lactic acid can be an important form of biopreservation
• Organic acids can be produced separately from food and then added (then it is considered chemical preservation)

Question 3

What is MicroGARD? What is the science behind it?

Answer 3

Question 4

Advantages of MicroGARD

Answer 4

Question 5

The effectiveness of MicroGARD depend on what

Answer 5

•The effectiveness of in situ acidification will depend on the products pH, buffering capacity, target spoilage microorganisms, and the concentration of fermentable carbohydrates (therefore a custom solution is required)

Question 6

What is a Wisconsin process for bacon?

Answer 6

Question 7

What are bacteriocins? Which ones are more of interest to food industry

Answer 7

•Bacteriocins are 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 8

What LAB that has been mentioned in lectures produces bacteriocin that inhibits pathogens of serious concern

Answer 8

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

Question 9

Is there a resistance to bacteriocins?

Answer 9

• However, there are regulatory concerns about the use of bacteriocins, including the development of bacteriocin-resistant pathogens. But there is very little bacteria that become resistant to them
• Bacteriocins are not antibiotics

Question 10

What is considered bacteriocins class I? What is their name in terms of structure?

Answer 10

Class I: Contain unusual amino acids (dehydroalanine, dehydrobutyrine, lanthionine, and methyllanthione) produced by posttranslational modification. Dehydro- amino acids react with cysteine to form thioether lanthionine. Bacteriocins containing lanthionine rings are commonly referred to as lantibiotics.

Question 11

What is the name of the best-characterized LAB bacteriocin

Answer 11

Nisin

Question 12

How nisin is produced, where it is added to inhibit what

Answer 12

In the food industry, nisin is obtained from the culturing of L. lactis on natural substrates and is not chemically synthesized.

Nisin is used in processed cheese, meats, beverages, etc. during production to extend shelf life by suppressing Gram-positive spoilage and pathogenic bacteria.

Question 13

What subtilin? What bacteriocin class, mode of action, produced by who and against what

Answer 13

Subtilin (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 14

Bacteriocins: class II what are they

Answer 14

Class II: bacteriocins are small heat-stable proteins with a consensus leader sequence that signals to the producing cell that the protein must be exported

Question 15

How bacteriocins class II can be further subdivided?

Answer 15

Question 16

Bacteriocins class III and IV, what are they, are they used in food

Answer 16

Class III: Are larger >30kDa heat-liable antimicrobial proteins, not used in foods so much, because large and not heat stable

Class IV: Have lipid or carbohydrate moieties and the function of these non-protein portions are unknown, not used in food

Question 17

How bacteriocin can be discovered in the lab? (it’s long, I am sorry)

Answer 17

Question 18

Bacteriocin mechanism of action

Answer 18

Question 19

Two models of bacteriocin action on vegetative cells

Answer 19

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

Question 20

How bacteriocin inhibits spores

Answer 20

Question 21

What are colicins, but whom they are produced? (mention genetic and determinants), and when expressed

Answer 21

Question 22

two classes of colicins

Answer 22

•Colicins can be divided into enzymatic colicins or pore-forming colicins

Question 23

What is action of pore forming colicins

Answer 23

• 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 (pore-forming systems)

Colicins then reach their lethal target and act either by forming a voltage-dependent channel into the inner membrane

Question 24

What is endonuclease activity of colicins

Answer 24

For enzymatic colicins the mode of action can be:

• peptidoglycan synthesis block , like penicillin [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 25

Three ways that are approved methods to add bacteriocins to foods

Answer 25

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 26

In what foods nisin is applied? what properties it has

Answer 26

* Nisin can be directly added to milk, cheese, and dairy products, canned foods, smoked fish, mayonnaise, and baby foods throughout the world (it is GRAS in several countries) * Nisin has anti-listerial properties, and it sensitizes spores to heat, so that thermal processing times can be reduced and nisin generally gets used in products where botulism is a concern

Question 27

Is nisin usually used alone in food? How is it used with other substances

Answer 27

* Nisin is rarely used on it’s own, it’s generally part of a multiple-barrier inhibitory system * It is used with modified-atmosphere (CO₂) storage for delaying toxin production by *C. botulinum* in fresh fish * Nisin is also added to ground pork stored in modified-atmosphere storage to delay or stop the growth of *L. monocytogenes*

Question 28

How pediocins is active, against what organism, where it is added

Answer 28

* Pediocins are not active against spores, but are active against vegetative *L. monocytogenes* cells * European products use pediocin producing cultures as a dried powder or culture liquid and apply it to several products such as: salad dressing, cream, cottage cheese, meat, and RTE salads

Question 29

Give example of starter cultures that encode bacteriocins and when it is better to use them (2 examples)

Answer 29

Question 30

What strains of bacteria have nisin-resistant

Answer 30

Nisin-resistant *L. monocytogenes*, *Staphylococcus aureus*, and *C. botulinum* exist

Question 31

How it has been suggested to overcome resistance of bacteriocins

Answer 31

* 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 * The issue of cross-resistance with antibiotics has been considered, but bacteriocins are different from antibiotics, and multidrug resistant bacteria are sometimes sensitive to bacteriocins

Question 32

What is the main resistant mechanism against bacteriocins

Answer 32

* Most resistance mechanisms likely have to do with changes in membrane permeability, and generalized mechanisms may also confer resistance to other preservatives * i.e. Membranes in nisin-resistant *L. monocytogenes* have more straight-chain fatty acids, and presumably this decrease in membrane fluidity hinders nisin insertion into the membrane

Question 33

If resistance to bacteriocins exist, is there a solution to it

Answer 33

* Bacteriocin-resistant bacteria may be more sensitive to other hurdles in food preservation and this should be exploited * i.e. nisin-resistant bacteria are likely less resistant to cold

Question 34

Are bacteriophages dangerous to us?

Answer 34

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

Question 35

Against what bacteria are there bacteriophages

Answer 35

•There are commercial bacteriophages to control the growth of *Salmonella, E. coli,* and *Listeria*

Question 36

Are there several challenges associated with bacteriophage?

Answer 36

* Possible resistance * Low numbers of bacteria in food (phage need 10⁵ to 10⁶ CFU of actively growing bacteria to be effective)

Question 37

Is bacteriophage used as a food additive?

Answer 37

•In 2006 the FDA approved a novel food additive, which is combination of 6 bacteriophages with anti-Listeria activity. This product is considered effective at controlling Listeria in RTE foods

Question 38

How resistance to bacteriophages is developed

Answer 38

* Resistance to bacteriophages is generally created by changes in the bacteriophage receptor site * The receptor site can be proteins, LPS, or lipoproteins

Question 39

Is there a way to overcome resistance of bacteriophages?

Answer 39

* 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