Biological methods of food preservation Flashcards
What is biopreservation
Explain what is controlled acidification
- 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)
What is MicroGARD? What is the science behind it?
Advantages of MicroGARD
The effectiveness of MicroGARD depend on what
•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)
What is a Wisconsin process for bacon?
What are bacteriocins? Which ones are more of interest to food industry
•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.
What LAB that has been mentioned in lectures produces bacteriocin that inhibits pathogens of serious concern
•Many bacteriocins are able to inhibit pathogens of serious concern, like L. monocytogenes, and are therefore of interest for food safety
Is there a resistance to bacteriocins?
- 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
What is considered bacteriocins class I? What is their name in terms of structure?
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.
What is the name of the best-characterized LAB bacteriocin
Nisin
How nisin is produced, where it is added to inhibit what
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.
What subtilin? What bacteriocin class, mode of action, produced by who and against what
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
Bacteriocins: class II what are they
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
How bacteriocins class II can be further subdivided?
Bacteriocins class III and IV, what are they, are they used in food
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
How bacteriocin can be discovered in the lab? (it’s long, I am sorry)
Bacteriocin mechanism of action
Two models of bacteriocin action on vegetative cells
- 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
How bacteriocin inhibits spores
What are colicins, but whom they are produced? (mention genetic and determinants), and when expressed
two classes of colicins
•Colicins can be divided into enzymatic colicins or pore-forming colicins
What is action of pore forming colicins
- 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
What is endonuclease activity of colicins
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
Three ways that are approved methods to add bacteriocins to foods
- Purified bacteriocins can be added directly to the food product
- Bacteriocinogenic cultures can be added to non-fermented food products, so that bacteriocins can be produced in situ
- Starter cultures that encode bacteriocins can be chosen for fermentation reactions
In what foods nisin is applied? what properties it has
- 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
Is nisin usually used alone in food? How is it used with other substances
- 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
How pediocins is active, against what organism, where it is added
- 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
Give example of starter cultures that encode bacteriocins and when it is better to use them (2 examples)
What strains of bacteria have nisin-resistant
Nisin-resistant L. monocytogenes, Staphylococcus aureus, and C. botulinum exist
How it has been suggested to overcome resistance of bacteriocins
- 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
What is the main resistant mechanism against bacteriocins
- 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
If resistance to bacteriocins exist, is there a solution to it
- 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
Are bacteriophages dangerous to us?
•Bacteriophages are a natural component of food microbiota and are routinely consumed as part of our diet
Against what bacteria are there bacteriophages
•There are commercial bacteriophages to control the growth of Salmonella, E. coli, and Listeria
Are there several challenges associated with bacteriophage?
- Possible resistance
- Low numbers of bacteria in food (phage need 105 to 106 CFU of actively growing bacteria to be effective)
Is bacteriophage used as a food additive?
•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
How resistance to bacteriophages is developed
- Resistance to bacteriophages is generally created by changes in the bacteriophage receptor site
- The receptor site can be proteins, LPS, or lipoproteins
Is there a way to overcome resistance of bacteriophages?
- 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
