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Food Microbiology > Chemical preservation > Flashcards

Chemical preservation Flashcards

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1
Q

What are preservatives?

A

chemicals added to food to retard growth/kill bacteria

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2
Q

Why can’t preservatives extend the shelf life of foods indefinitely?

A

Most don’t kill microbes; only bacteriostatic/fungistatic

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3
Q

2 classes of preservatives:

What is the difference?

A 
naturally occurring (found already within the food)
traditional (approved substances added to food)

*traditional preservatives can be synthetic compounds that also occur naturally

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4
Q

Traditional antimicrobials include: (7)

A 
Organic acids (+ derivatives)
Dimethyl bicarbonate (DMDC)
lactoferrin
Lysozyme
Nitrites
para-hydroxybenzoic acid esters
sulfites
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5
Q

(strong/weak) organic acids are more effective antimicrobials. Why?

A

Weak

remain undissociated outside cell -> easily cross membrane (no charge) -> dissociate inside due to higher pH

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6
Q

What is the antimicrobial mechanism of organic acids?

A

dissociate inside cell -> release H+ ions
bacteria must spend energy to pump out ions; buildup will eventually cause damage to proteins, enzymes, nucleic acids, phospholipids -> cell stop growing/death

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7
Q

use of organic acids is limited to foods with a pH of _____. Why?

A

pH <5.5

pKa of 3.0 to 5.0 (needs to remain undissociated to be effective)

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8
Q

(monoprotic/polyprotic) organic acids are more effective. Give examples of each.

A

monoprotic more effective

monoprotic: lactic, acetic, propionic, benzoic, sorbic
polyprotic: tartaric, fumaric, citric, malic

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9
Q

Acetic acid is more effective against ____ than _____. What are exceptions?

A

bacteria+ yeast

mold

exceptions: LAB, AAB are resistant

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10
Q

Some examples of acetic acid as a preservative:

A

0.1% in scalding tanks for chicken (prevent salmonella)
0.1% in moist bread dough (prevent bacillus)
added to condiments, gravy, sauces, etc

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11
Q

What organic acid is usually used as an antifungal? Give examples of its use.

A

benzoic acid (some bacteria also susceptible)

  1. 1% in apple cider (prevent E coli)
  2. 1% in grape juice (prevent mold)
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12
Q

What is the advantage of lactic acid, and what are its applications?

A

relatively tasteless, reduces Aw

added to meat/carcasses

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13
Q

Advantages of sorbic acid and its uses:

A

effective against most microbes, also inhibits mycotoxin production

baked goods, syrups, cheese, dry fruit, salad dressing, wine, etc
(applied by direct addition, spraying, dipping, or in packaging)

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14
Q

Describe the properties of DMDC:

What does it target, and what is the mechanism? What is it added to?

A

colorless liquid, slightly water soluble, very reactive

target yeast (some bacteria); enzyme inactivation

added to alcoholic beverage to prevent yeast spoilage

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15
Q

What is an important antimicrobial compound in human milk that is also produced commercially as a preservative? How does it function?

A

lactoferrin (prevents infection in mammary gland and infant intestine)

binds iron (limiting nutrient for bacterial growth)

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16
Q

Where does lysozyme occur naturally? What uses does it have in food?

A

tears, milk, avian eggs, other secretions
can occur naturally or added (GRAS)
Used in cheese to prevent late blowing (C. tyrobutyricum)

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17
Q

What is the antimicrobial mechanism of lysozyme? What type of bacteria is this most effective against?

A

peptidoglycan hydrolase: it digests bonds in peptidoglycan layer (cell wall) -> result in cell lysis
most effective against Gram positive (gram negative don’t have cell wall)

18
Q

In what forms are nitrites added to meats?

A

sodium nitrite

potassium nitrite

19
Q

What purposes does nitrites serve in meat? What is the main purpose?

A 
antimicrobial 
pink color (react with myoglobin -> nitrosomyoglobin)
characteristic flavor

main purpose is to prevent C. botulinum growth and toxin production

20
Q

How do nitrites act as antimicrobials?

A

inhibit ATP generation in bacteria -> deplete energy stores

21
Q

What is often added along with nitrites to cured meat? Why?

A

ascorbate - antioxidant agent (reduce nitrite)

  • accelerate curing process
  • less formation of nitrosamines (carcinogen)
22
Q

para-hydroxybenzoic acid esters are also known as ______. What forms is it found in? What products is this used in?

A

parabens - methyl paraben, propyl paraben

beer, juice, beverages (inhibit fungi)
baked goods, fruit products, fermented food, syrup, dressing, etc

23
Q

What microbes are parabens effective against? What is the mode of action?

A

effective against fungi > Gram + > Gram -

interfere with cytoplasmic membrane (disrupt membrane gradient)

24
Q

sulfites are salts of ______. give examples used in food.

A

sulfur dioxide

potassium sulfite, sodium sulfite, potassium metabisulfite, sodium bisulfite, sodium metabisulfite

25
Q

What products are sulfites added to, and what are they effective against?

A

mostly fruit/veg products (fruit, juice, wine, pickles), also sausage, shrimp

protect from fungi, AAB, malolactic bacteria
antioxidant: prevent browning (enzymatic and non enzymatic)

26
Q

What is the mechanism of sulfite against microbes?

A

form aqueous solution of sulfur dioxide -> yields sulfurous acid -> functions like organic acid

27
Q

What are 2 examples of naturally occuring antimicrobials in animal sources?

A

lactoperoxidase

chitosan

28
Q

What are 4. examples of natural occurring antimicrobials in plant sources?

A

Spices/essential oils
Allicin
Hops
Isothiocyanates

29
Q

What are the current challenges with naturally occurring antimicrobials?

A
  1. does not occur in levels high enough in food (must refine and add more to be effective)
  2. adding to food can cause adverse sensory changes
30
Q

Lactoperoxidase is a _____ enzyme. It is found in: ______. How does it work as an antimicrobial?

A

glycoprotein/oxidative
found in milk, colostrum, saliva, other secretions

oxidizes thiocyanate (in presence of H peroxide) -> hypothiocyanate (highly reactive oxidative species) -> attacks microbes

31
Q

Chitosan is a natural component of ______, and can be derived from: _____

A

fungal cell wall

derive from chitin (by-product from shellfish)

32
Q

What are the applications of chitosan in food?

A

antimicrobial against fungi, bacteria (use in combination with other antimicrobials)

Can also be added to edible films

33
Q

What is a proposed mechanism of action of chitosan against bacteria?

A

chelates LPS associated cations

34
Q

What are spices? Which have the greatest antimicrobial activity and what compounds are responsible?

A

roots/bark/leaves/seeds/buds/fruit: added as flavor agents

greatest activity: thyme (thymol), oregano (carvacrol), cinnamon (cinnamic aldehyde), cloves (eugenol)

less from rosemary (bornel, camphene, camphor) and sage (thujone)

35
Q

Allicin is found in foods such as: ______. They inhibit:

A

onion and garlic (alliums)

inhibit growth and toxin production of several microbes, including C. botulinum.

36
Q

onions contain allicin, and also ____, which may also have antimicrobial effects.

A

catechol

37
Q

How does allicin function as an antimicrobial?

A

oxidize thiols -> disulfides (inhibits disulfide containing enzymes, such as alcohol dehydrogenase, urease, etc)

38
Q

What is the antimicrobial compound in hops? What is it effective against?

A 
bitter acids (3-12%)
effective against most bacteria; but not LAB that spoil beer
39
Q

Where do isothiocyanates come from?

A 
Brassica family (broccoli, kale, cabbage, etc)
produced when plant is injured
40
Q

What are the main factors affecting activity of antimicrobials?

A
  1. based on microorganism:
    - spore vs vegetative
    - biofilms
    - species interaction
    - cell structure
  2. based on physiochemistry of preservative:
    - physical barrier (shell, husk, etc)
    - pH
    - buffering capacity
    - redox potential

Food Microbiology (21 decks)

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