Chemical methods of preservation

Question 1

Do preservatives preserve the food indefinitely? why?

Answer 1

• Preservatives are chemicals that are added to foods that retard the growth of, or kill, microorganisms.
• Most preservatives are added at levels that are bacteriostatic, or fungistatic and do not actually kill the organisms
• Therefore, most food preservatives do not preserve the food indefinitely

Question 2

Two classes of chemical preservatives

Answer 2

Traditional and naturally occuring

Question 3

What are traditional preservatives?

Answer 3

1. Have been used for many years
2. Are approved for use in many countries
3. Are produced by synthetic processes

•Ironically, many traditional preservatives are found in nature including acetic acid or benzoic acid from cranberries

Question 4

What will determine if the chemical will fall in one or another category?

Answer 4

•Some chemicals could be either traditional or naturally occurring based on if they were synthetically produced or naturally occur in the food in question (but this is all just semantics)

Question 5

List 7 traditional antimicrobials

Answer 5

Question 6

Why weak organic acids are the most effective antimicrobials

Answer 6

Question 7

The best types of organic acids (the answer is not weak)

Answer 7

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

•Multiprotic acids are less effective (citric, malic, tartaric, and fumaric)

Question 8

What factors should be accounted for when selecting organic acid for chemical preservation

Answer 8

Question 9

List in ascending order of pKa acetic acid, benzoic, lactic, propionic and their common sources (+sorbic acid)

Answer 9

Question 10

Acetic acid: against what organisms it is effective

Answer 10

• Acetic acid is more effective against bacteria and yeast than molds
• Resistant bacteria include LAB, and AAB

Question 11

Common uses of acetic acid as a preservative in food

Answer 11

Common uses:

• 0.1% acetic acid can be added to the scald tank in chicken processing (lowers Salmonella on chicken carcasses)
• 0.1-2% can be added to bread dough for moist products and reduces the rope forming Bacillus subtilis
• Routinely added to condiments, relishes, gravy, and sauces

Question 12

Benzoic acid: what organisms are effected

Answer 12

•Benzoic acids are commonly added as antifungals, although most bacteria are susceptible, and some fungi are resistant

Question 13

Common uses of benzoic acid

Answer 13

• 0.1% benzoic acid is effective at reducing E. coli in apple cider
• 0.1% in grape juice results in a 3-log reduction in mold spoilage

Question 14

Lactic acid: where it is applied, what action it has on food as a preservative

Answer 14

Question 15

Sorbic acid is effective against what microorganisms

Answer 15

• Sorbic acids are able to inhibit both fungi, bacteria, and most yeasts
• In addition, molds cannot produce mycotoxins in the presence of sorbates

Question 16

How sorbic acid can be applied to products and common uses

Answer 16

Question 17

What is DMDC

Answer 17

•Dimethyl decarbonate (DMDC) is a colorless liquid that is only slightly soluble in water, and is very reactive with many substances (water, ethyl alcohol, aromatic amines, and sulfhydryl groups)

Question 18

DMDC targets what microorganisms and added where

Answer 18

Question 19

What is lactoferrin? What is doing in nature? can it be produced commercially? How it is applied

Answer 19

Question 20

What is lysozyme? and what is its action mechanism

Answer 20

• Lysozyme is a naturally occurring peptidoglycan hydrolase that occurs in avian eggs, mammalian milk, tears, and other secretions
• Peptidoglycan hydrolases digest the bonds in the cell wall peptidoglycan and result in cellular lysis in hypotonic systems

Question 21

What microbiological activity lysozyme has (mention Gram’s, and two types of bacteria)

Answer 21

• It has more activity against Gram-positive bacteria than Gram-negative bacteria
• Lysozyme has been found to reduce the presence of L. monocytogenes in several meat products, but is not routinely used
• Lysozyme is used in cheeses to prevent late blowing caused by fermentation of the anaerobe C. tyrobutyricum

Question 22

What government status lysozyme has

Answer 22

GRAS status

Question 23

What are nitrites? Where they are added and why (for some specific bacteria), the principle of inhibition

Answer 23

• Sodium nitrite (NaNO₂) and potasium nitrite (KNO₂) have a specialized use in cured meat products
• The primary application of nitrite is for the inhibition of C. botulinum spore germination, growth, and toxin production in cured and fermented meats
• Nitrites work by inhibiting the ability of bacterial cells to generate ATP, and therefore depleting their energy stores

Question 24

Why nitrites are added to meats apart from microbial preservation

Answer 24

•Both nitrites have antimicrobial properties but are also used in cured meats for other purposes, 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 25

Some nitrite derivate is a carcinogen, mention derivative, what is done to slow it down, how it becomes carcinogenic

Answer 25

•**Ascorbates** are often added along with nitrites to accelerate the curing process by **reducing nitrite**, and this can also slow the formation of **nitrosamines**, which are **carcinogens** formed by the r**eaction of nitrite with secondary or tertiary amines**

Question 26

What are parabens?

Answer 26

*para-*Hydroxybenzoic Acid Esters (parabens)

Question 27

what microorganisms are targeted by parabens?

Answer 27

•Parabens are generally more effective against fungi than bacteria, but Gram-positive bacteria are more sensitive to the effects of parabens than Gram-negative bacteria

Question 28

The mechanism of action of parabens

Answer 28

•The mechanism is through paraben-directed interference with the cytoplasmic membrane, likely through interfering with the electrochemical gradient

Question 29

Where parabens are applied

Answer 29

* Parabens can be used in beers, noncarbonated soft drinks, and fruit based beverages, to inhibit fungal growth * Parabens are also used in baked goods, fruit products, preserves, fermented foods, syrups, dressings, wines, and pie fillings

Question 30

Sulfites are different salts of sulfur dioxide used as antimicrobials: principle of action, where applied, to control what organisms

Answer 30

Question 31

Naturally occuring preservatives: 2 from animal source and 4 from plant source

Answer 31

Question 32

Why there cna be issues with naturally occurring preservatives, why adding if already there

Answer 32

* However, few if any exist in natural sources at concentrations that are high enough to inhibit microbial growth without prior purification or refining * The addition of some natural substances can lead to adverse sensory changes in the food * There are significant challenges to economically produce, refine, and add naturally occurring antimicrobials to microbiologically sensitive foods at levels that would be useful for preservation, but not high enough to induce negative changes in the sensory characteristics of the food

Question 33

Lactoperoxidase: what does it do, what should be added to the system

Answer 33

* Lactoperoxidase is a **glycoprotein enzyme** that occurs naturally in raw milk, colostrum, saliva, and other biological secretions * Lactoperoxidase **oxidizes thiocyanate** in the presence of available hydrogen peroxide, forming **hypothiocyanite** which is a highly reactive oxidant and therefore **antimicrobial** * To effectively use this system you must add extra hydrogen peroxide

Question 34

What is chitosan, how it is used as a preservative, mode of action

Answer 34

* 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 * Chitosan can also be added to edible films for inhibition of microbial growth * The mode of action against bacterial cells is not fully understood, but it is thought to be through its ability to **chelate LPS-associated cations**

Question 35

Where the greatest antimicrobial of spices coming from (plants)

Answer 35

•The greatest antimicrobial activity comes from cloves, cinnamon, oregano, thyme and to a lesser extent sage and rosemary

Question 36

How cinnamon and cloves are antimicrobial

Answer 36

* Cinnamon and cloves contain eugenol and cinnamic aldehyde * Eugenol and cinnamic aldehyde appear to have antibacterial, fungal and yeast activity * Packaging material can be infused with cinnamon extract to reduce through on packaged food

Question 37

Allicin, the mode of action, acts on what organisms

Answer 37

* The growth and toxin production of several microorganisms (including *C. botulinum*) are inhibited by Allicin * Allicin appears to work through the inhibition of disulfide-containing enzymes (i.e. alcohol dehydrogenase, urease). It appears to inactivate these proteins by oxidizing thiols to disulfides.

Question 38

What compound in onion can function as a antimicrobials

Answer 38

•Onions also produce chain phenolic compounds (catechol) which may also contribute to the antimicrobial activity of onion essential oils and extracts

Question 39

Hops: what action they have as a preservative, who is resistant to it

Answer 39

* About 3-12% of the resin from the hop vine is composed of bitter acids which have antibacterial activity against bacteria and fungi at reduced a_w * The **LAB that spoil** beer appear to be **resistant** to the antimicrobial effects of these bitter acids, while other bacteria appear to be sensitive

Question 40

Isothiocynates: source, when synthesized in plant, against what organisms it is effective

Answer 40

* Isothiocyanates are derived from plants in the family *Brassicaceae* * Isothiocyanates are synthesized when the plant tissue is injured or mechanically disrupted * They are effective against fungi, yeast, and bacteria

Question 41

Factors Affecting Activity of chemical preservatives

Answer 41