Chemical preservatives and Natural Antimicrobial compounds Flashcards
What are preservatives ?
Chemicals that are added to foods that retard the growth of, or kill, microorganisms.
Most preservatives are added at levels that are ___________, or ________ and do not actually kill the organisms
bacteriostatic
fungistatic
T or F, most food preservatives preserve food indefinitely
F
What are the 2 classes of preservatives?
Traditional and naturally occurring
Naturally occurring preservatives are when:
a specific food product naturally contains a compound that extends it’s shelf life
Name some traditional antimicrobials: (7)
- organic acids and derivatives (acetic acid, benzoic acid, lactic acid, propionic acid, sorbic acid)
- dimethyl dicarbonate (DMDC)
- lactoferrin
- lysozyme
- nitrites
- para-hydroxybenzoic acid esters
- sulfites
Weak organic acids are the most effective antimicrobials in their _________ state
undissociated
Explain how undissociated weak organic acids dissociate and become toxic for the bacterial cells:
- Undissociated acids have no charge and are hydrophobic allowing them to easily diffuse through the cytoplasmic membrane and into the cell
- Once inside the conditions are favorable for the hydrogen to dissociate
- bacterial cells expend excessive energy trying to pump out the extra hydrogens, and eventually growth is inhibited or the cell is inactivated
- if the bacteria does not pump out the extra hydrogens there will be structural changes to proteins, enzymes, nucleic acids, and phospholipids
The best acids for preservatives are _______________ (acetic, lactic, propionic, sorbic, and benzoic)
monoprotic acids
___________ are less effective (citric, malic, tartaric, and fumaric)
Multiprotic acids
What do we have to consider in choosing an organic acid for use as an additive:
- the pH of the product
- pKa of the acid
The use of organic acids as preservatives is generally limited to foods with a pH
5.5
Acetic acid is more effective against ________ and ________ than molds
bacteria and yeast
Bacteria resistant against acetic acid are:
LAB + AAB
What are common uses of acetic acid:
- scald tank in chicken to prevent salmonella
- added to bread dough to reduce rope forming bacillus subtilis
- routinely added to condiments, relishes, gravy, and sauces
benzoic acid are commonly added as __________
antifungals
What are common uses of benzoic acid:
- reducing E.coli in apple cider
- reduce mold spoilage by 3-log in grape juice
Which acid has limited taste and is used in meats for shelf-life extension?
lactic acid
______________ also reduce the aw of the food system further limiting microbial growth
Lactic acids
Sorbic acids are able to inhibit both _____, ________, and most _______
fungi
bacteria
yeasts
How can sorbic acid be applied to foods?
- direct addition
- dipping
- spraying
- dusting
- incorporation into packaging films
What are common uses of sorbic acid:
- bakery products to inhibit fungi
- beverages syrups, cakes, cheese, fried fruits, margarine
What is DMDC and what does it do?
It is a colorless liquid that is only slightly soluble in water, and is very reactive with many substances (water, ethyl alcohol, aromatic amines)
It mainly targets yeasts but is also bactericidal
- It leads to enzyme inactivation
- Added to alcoholic beverages
Talk to me about lactoferrin:
- It is the primary iron-chelating protein in milk and colostrum
- It can occur naturally in milk, but can also be produced commercially
- in nature it prevent infection in the mammary gland and intestinal infection in infant
- it restricts microbial access to nutrients, via sequestration of iron, bacterial cells cannot grow or divide
What is lysozyme and whats in main action:
It is a peptidoglycan hydrolase that occurs in avian eggs, mammalian milk, tears and other secretions
Peptidoglycan hydrolases digest the bonds in the cell wall peptidoglycan resulting in cellular lysis in hypotonic systems
Sodium nitrite (NaNO2) and potasium nitrite (KNO2) have a specialized use in __________
cured meat products
Both nitrites have antimicrobial properties but are also used in cured meats for other purposes like :
nitrite reacts with the muscle protein myoglobin to form nitrosomyoglobin, which stabilizes the cured meat colour. Nitrites also contribute to that (yummy) cured meat taste
The primary application of nitrite is for the inhibition of ________ spore germination, growth, and toxin production in cured and fermented meats
C. botulinum
Why add ascorbates in cured meats?
- to accelerate the curing process by reducing nitrite
- slow the formation of nitrosamines, carcinogens formed by the reaction of nitrite with secondary or tertiary amines
Which type of bacteria is more sensitive to parabens?
gram +
What is the mechanism behind parabens?
paraben-directed interference with the cytoplasmic membrane, likely through interfering with the electrochemical gradient
Sulfites are mainly used in what kind of products ?
mainly fruits and vegetables products (fruits, juices, wines) to control the growth of fermentative fungi, AAB, and malolactic bacteria
sulfites have _________ properties that inhibit the enzymatic and non-enzymatic browning of foods
antioxidant
What are the 2 naturally occurring preservatives from animal source (2):
chitosan + lactoperoxidase
What are the 4 naturally occurring preservatives from plant source (4):
- Spices and essential oils (thymol, eugenol, carvacrol and cinnamic adehyde)
- Allicin
- Hops
- Isothiocyanates
The addition of some natural substances can lead to ________________
adverse sensory changes in the food
What is lactoperoxidase, what does it do ?
- It is a glycoprotein enzyme that occurs naturally in milk, colostrum
- It oxidizes thiocyanate in the presence of available hydrogen peroxide to hypothiocyanite which is a highly reactive oxidant and therefore antimicrobial
- To effectively use this system you must add extra hydrogen peroxide
Chitosan is :
a natural component of the fungal cell wall that can be derived from chitin, a by-product of shellfish processing
Chitosan can inhibit the growth of
foodborne fungi and bacteria, especially when combined with other organic acids or antimicrobials (ability to chelate LPS-associated cations)
Allicin appears to work through:
inhibition of disulfide-containing enzymes, it inactivates these proteins by oxidizing thiols to disulfides
Isothiocyanates are derived from plants in the family : _______
Brassicaceae
___________ are synthesized when the plant tissue is injured or mechanically disrupted
isothiocyanates (affective against yeast, fungi and bacteria)
There are a number of factors known to affect the activity of antimicrobials, but these can be subdivided into:
- Factors associated with the microorganism (vegetative vs sporulated cells, interactions with other microbes)
- Factors associated with the physiochemistry of the preservative (pH, redox potential, buffering capacity
