Chemical preservatives and Natural Antimicrobial compounds

Question 1

What are preservatives ?

Answer 1

Chemicals that are added to foods that retard the growth of, or kill, microorganisms.

Question 2

Most preservatives are added at levels that are ___________, or ________ and do not actually kill the organisms

Answer 2

bacteriostatic

fungistatic

Question 3

T or F, most food preservatives preserve food indefinitely

Answer 3

F

Question 4

What are the 2 classes of preservatives?

Answer 4

Traditional and naturally occurring

Question 5

Naturally occurring preservatives are when:

Answer 5

a specific food product naturally contains a compound that extends it’s shelf life

Question 6

Name some traditional antimicrobials: (7)

Answer 6

• 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

Question 7

Weak organic acids are the most effective antimicrobials in their _________ state

Answer 7

undissociated

Question 8

Explain how undissociated weak organic acids dissociate and become toxic for the bacterial cells:

Answer 8

• 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

Question 9

The best acids for preservatives are _______________ (acetic, lactic, propionic, sorbic, and benzoic)

Answer 9

monoprotic acids

Question 10

___________ are less effective (citric, malic, tartaric, and fumaric)

Answer 10

Multiprotic acids

Question 11

What do we have to consider in choosing an organic acid for use as an additive:

Answer 11

• the pH of the product

- pKa of the acid

Question 12

The use of organic acids as preservatives is generally limited to foods with a pH

Answer 12

5.5

Question 13

Acetic acid is more effective against ________ and ________ than molds

Answer 13

bacteria and yeast

Question 14

Bacteria resistant against acetic acid are:

Answer 14

LAB + AAB

Question 15

What are common uses of acetic acid:

Answer 15

• 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

Question 16

benzoic acid are commonly added as __________

Answer 16

antifungals

Question 17

What are common uses of benzoic acid:

Answer 17

• reducing E.coli in apple cider

- reduce mold spoilage by 3-log in grape juice

Question 18

Which acid has limited taste and is used in meats for shelf-life extension?

Answer 18

lactic acid

Question 19

______________ also reduce the aw of the food system further limiting microbial growth

Answer 19

Lactic acids

Question 20

Sorbic acids are able to inhibit both _____, ________, and most _______

Answer 20

fungi
bacteria
yeasts

Question 21

How can sorbic acid be applied to foods?

Answer 21

• direct addition
• dipping
• spraying
• dusting
• incorporation into packaging films

Question 22

What are common uses of sorbic acid:

Answer 22

• bakery products to inhibit fungi

- beverages syrups, cakes, cheese, fried fruits, margarine

Question 23

What is DMDC and what does it do?

Answer 23

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

Question 24

Talk to me about lactoferrin:

Answer 24

• 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

Question 25

What is lysozyme and whats in main action:

Answer 25

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

Question 26

Sodium nitrite (NaNO2) and potasium nitrite (KNO2) have a specialized use in __________

Answer 26

cured meat products

Question 27

Both nitrites have antimicrobial properties but are also used in cured meats for other purposes like :

Answer 27

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

Question 28

The primary application of nitrite is for the inhibition of ________ spore germination, growth, and toxin production in cured and fermented meats

Answer 28

C. botulinum

Question 29

Why add ascorbates in cured meats?

Answer 29

• 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

Question 30

Which type of bacteria is more sensitive to parabens?

Answer 30

gram +

Question 31

What is the mechanism behind parabens?

Answer 31

paraben-directed interference with the cytoplasmic membrane, likely through interfering with the electrochemical gradient

Question 32

Sulfites are mainly used in what kind of products ?

Answer 32

mainly fruits and vegetables products (fruits, juices, wines) to control the growth of fermentative fungi, AAB, and malolactic bacteria

Question 33

sulfites have _________ properties that inhibit the enzymatic and non-enzymatic browning of foods

Answer 33

antioxidant

Question 34

What are the 2 naturally occurring preservatives from animal source (2):

Answer 34

chitosan + lactoperoxidase

Question 35

What are the 4 naturally occurring preservatives from plant source (4):

Answer 35

• Spices and essential oils (thymol, eugenol, carvacrol and cinnamic adehyde)
• Allicin
• Hops
• Isothiocyanates

Question 36

The addition of some natural substances can lead to ________________

Answer 36

adverse sensory changes in the food

Question 37

What is lactoperoxidase, what does it do ?

Answer 37

• 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

Question 38

Chitosan is :

Answer 38

a natural component of the fungal cell wall that can be derived from chitin, a by-product of shellfish processing

Question 39

Chitosan can inhibit the growth of

Answer 39

foodborne fungi and bacteria, especially when combined with other organic acids or antimicrobials (ability to chelate LPS-associated cations)

Question 40

Allicin appears to work through:

Answer 40

inhibition of disulfide-containing enzymes, it inactivates these proteins by oxidizing thiols to disulfides

Question 41

Isothiocyanates are derived from plants in the family : _______

Answer 41

Brassicaceae

Question 42

___________ are synthesized when the plant tissue is injured or mechanically disrupted

Answer 42

isothiocyanates (affective against yeast, fungi and bacteria)

Question 43

There are a number of factors known to affect the activity of antimicrobials, but these can be subdivided into:

Answer 43

• 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