Biological methods for Food Preservation Flashcards
Biopreservation is the :
use of microorganisms, their metabolic products, or both to preserve foods
What is the exception to biopreservation?
Controlled acidification where acid is produced by LAB in controlled-abused foods
What is MICROGARD:
it is a family of products that can be added to refrigerated food products
What to MICROGARD products include:
- a fermentable CHO (lactose or dextrose)
- bacterial culture
MicroGARD is a _____, ________ product designed to improve shelf-life protection
natural
clean-label
key benefits of MICROGARD (3):
1) Protect shelf-life
2) Maintain the organoleptic qualities of food
3) Meet consumer’s demand for natural products
The LAB do not grow under __________ conditions and will only grow if foods are _____________
refrigeration
temperature abused
Carcinogenic nitrosamines can be formed from ________________, and this has led to a search for nitrite substitutes for bacon preservation (particularly temperature abused bacon)
nitrites in cured meats
Explain the Wisconsin process
Inoculating bacon with less nitrite, 0.7% sucrose, and LAB starter culture is even better than inoculating the bacon only with nitrites
What are bacteriocins ?
Bacteriocins are antimicrobial peptides of bacterial origins that are lethal to some bacteria, but not the host that produced them
T OR F : Many bacteriocins are able to inhibit pathogens of serious concern, like L. monocytogenes, and are therefore of interest for food safety
T
Are bacteriocins antibiotics?
nope
________ is the best-characterized LAB bacteriocin
Nisin
Class 1 bacteriocins:
-contain unusual AA produced by posttranslational modification
How is nisin obtained in the food industry ?
From the culturing of L.lactis on natural substrates and is not chemically synthesized
Nisin extends shelf-life by suppressing ________ spoilage and pathogenic bacteria
gram +
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
Class 2 bacteriocins:
- 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
Class 3 bacteriocins:
Are larger >30kDa heat-liable antimicrobial proteins
Class 4 bacteriocins:
Have lipid or carbohydrate moieties and the function of these non-protein portions are unknown
What is the method for bacteriocin discovery:
- 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
All bacteriocins produced by LAB act by __________________________-
disrupting the integrity of the cytoplasmic membrane
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
pre-accumulated ions, amino acids, and ATP molecules
What are the 2 proposed models for bacteriocin mechanism of Action:
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
What happens to the mechanism of nisin in spores ?
- 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
Colicins (what are they?)
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
How do colicins exert their lethal action?
- 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
Colicins can be divided into:
enzymatic colicins or pore-forming colicins
For enzymatic colicins the mode of action can be:
- 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)
what are the three ways that are approved methods to add bacteriocins to foods:
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
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
anti-listerial
heat
Give an example of a bacteriocinogenic culture :
pediocins (not active against spores but active against vegetative L.monocytogenes cells
How can you overcome resistance to 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 (straight chain fatty acids example)
nisin-resistant bacteria are likely less resistant to ______
cold
Bacteriophages are ___________________________
a natural component of food microbiota and are routinely consumed as part of our diet
Resistance to bacteriophages is generally created by ______________
changes in the bacteriophage receptor site
What should be done to control bacteriophage resistant
-phage should be used in cocktails containing several different strains and types
