Chemical preservation Flashcards
What are preservatives?
chemicals added to food to retard growth/kill bacteria
Why can’t preservatives extend the shelf life of foods indefinitely?
Most don’t kill microbes; only bacteriostatic/fungistatic
2 classes of preservatives:
What is the difference?
naturally occurring (found already within the food) traditional (approved substances added to food)
*traditional preservatives can be synthetic compounds that also occur naturally
Traditional antimicrobials include: (7)
Organic acids (+ derivatives) Dimethyl bicarbonate (DMDC) lactoferrin Lysozyme Nitrites para-hydroxybenzoic acid esters sulfites
(strong/weak) organic acids are more effective antimicrobials. Why?
Weak
remain undissociated outside cell -> easily cross membrane (no charge) -> dissociate inside due to higher pH
What is the antimicrobial mechanism of organic acids?
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
use of organic acids is limited to foods with a pH of _____. Why?
pH <5.5
pKa of 3.0 to 5.0 (needs to remain undissociated to be effective)
(monoprotic/polyprotic) organic acids are more effective. Give examples of each.
monoprotic more effective
monoprotic: lactic, acetic, propionic, benzoic, sorbic
polyprotic: tartaric, fumaric, citric, malic
Acetic acid is more effective against ____ than _____. What are exceptions?
bacteria+ yeast
mold
exceptions: LAB, AAB are resistant
Some examples of acetic acid as a preservative:
0.1% in scalding tanks for chicken (prevent salmonella)
0.1% in moist bread dough (prevent bacillus)
added to condiments, gravy, sauces, etc
What organic acid is usually used as an antifungal? Give examples of its use.
benzoic acid (some bacteria also susceptible)
- 1% in apple cider (prevent E coli)
- 1% in grape juice (prevent mold)
What is the advantage of lactic acid, and what are its applications?
relatively tasteless, reduces Aw
added to meat/carcasses
Advantages of sorbic acid and its uses:
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)
Describe the properties of DMDC:
What does it target, and what is the mechanism? What is it added to?
colorless liquid, slightly water soluble, very reactive
target yeast (some bacteria); enzyme inactivation
added to alcoholic beverage to prevent yeast spoilage
What is an important antimicrobial compound in human milk that is also produced commercially as a preservative? How does it function?
lactoferrin (prevents infection in mammary gland and infant intestine)
binds iron (limiting nutrient for bacterial growth)
Where does lysozyme occur naturally? What uses does it have in food?
tears, milk, avian eggs, other secretions
can occur naturally or added (GRAS)
Used in cheese to prevent late blowing (C. tyrobutyricum)
What is the antimicrobial mechanism of lysozyme? What type of bacteria is this most effective against?
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)
In what forms are nitrites added to meats?
sodium nitrite
potassium nitrite
What purposes does nitrites serve in meat? What is the main purpose?
antimicrobial pink color (react with myoglobin -> nitrosomyoglobin) characteristic flavor
main purpose is to prevent C. botulinum growth and toxin production
How do nitrites act as antimicrobials?
inhibit ATP generation in bacteria -> deplete energy stores
What is often added along with nitrites to cured meat? Why?
ascorbate - antioxidant agent (reduce nitrite)
- accelerate curing process
- less formation of nitrosamines (carcinogen)
para-hydroxybenzoic acid esters are also known as ______. What forms is it found in? What products is this used in?
parabens - methyl paraben, propyl paraben
beer, juice, beverages (inhibit fungi)
baked goods, fruit products, fermented food, syrup, dressing, etc
What microbes are parabens effective against? What is the mode of action?
effective against fungi > Gram + > Gram -
interfere with cytoplasmic membrane (disrupt membrane gradient)
sulfites are salts of ______. give examples used in food.
sulfur dioxide
potassium sulfite, sodium sulfite, potassium metabisulfite, sodium bisulfite, sodium metabisulfite
What products are sulfites added to, and what are they effective against?
mostly fruit/veg products (fruit, juice, wine, pickles), also sausage, shrimp
protect from fungi, AAB, malolactic bacteria
antioxidant: prevent browning (enzymatic and non enzymatic)
What is the mechanism of sulfite against microbes?
form aqueous solution of sulfur dioxide -> yields sulfurous acid -> functions like organic acid
What are 2 examples of naturally occuring antimicrobials in animal sources?
lactoperoxidase
chitosan
What are 4. examples of natural occurring antimicrobials in plant sources?
Spices/essential oils
Allicin
Hops
Isothiocyanates
What are the current challenges with naturally occurring antimicrobials?
- does not occur in levels high enough in food (must refine and add more to be effective)
- adding to food can cause adverse sensory changes
Lactoperoxidase is a _____ enzyme. It is found in: ______. How does it work as an antimicrobial?
glycoprotein/oxidative
found in milk, colostrum, saliva, other secretions
oxidizes thiocyanate (in presence of H peroxide) -> hypothiocyanate (highly reactive oxidative species) -> attacks microbes
Chitosan is a natural component of ______, and can be derived from: _____
fungal cell wall
derive from chitin (by-product from shellfish)
What are the applications of chitosan in food?
antimicrobial against fungi, bacteria (use in combination with other antimicrobials)
Can also be added to edible films
What is a proposed mechanism of action of chitosan against bacteria?
chelates LPS associated cations
What are spices? Which have the greatest antimicrobial activity and what compounds are responsible?
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)
Allicin is found in foods such as: ______. They inhibit:
onion and garlic (alliums)
inhibit growth and toxin production of several microbes, including C. botulinum.
onions contain allicin, and also ____, which may also have antimicrobial effects.
catechol
How does allicin function as an antimicrobial?
oxidize thiols -> disulfides (inhibits disulfide containing enzymes, such as alcohol dehydrogenase, urease, etc)
What is the antimicrobial compound in hops? What is it effective against?
bitter acids (3-12%) effective against most bacteria; but not LAB that spoil beer
Where do isothiocyanates come from?
Brassica family (broccoli, kale, cabbage, etc) produced when plant is injured
What are the main factors affecting activity of antimicrobials?
- based on microorganism:
- spore vs vegetative
- biofilms
- species interaction
- cell structure - based on physiochemistry of preservative:
- physical barrier (shell, husk, etc)
- pH
- buffering capacity
- redox potential