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Food Microbiology > Chemical methods of preservation > Flashcards

Chemical methods of preservation Flashcards

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1
Q

Do preservatives preserve the food indefinitely? why?

A
  • 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
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2
Q

Two classes of chemical preservatives

A

Traditional and naturally occuring

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3
Q

What are traditional preservatives?

A
  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

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4
Q

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

A

•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)

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5
Q

List 7 traditional antimicrobials

A
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6
Q

Why weak organic acids are the most effective antimicrobials

A
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7
Q

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

A

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

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

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8
Q

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

A
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9
Q

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

A
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10
Q

Acetic acid: against what organisms it is effective

A
  • Acetic acid is more effective against bacteria and yeast than molds
  • Resistant bacteria include LAB, and AAB
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11
Q

Common uses of acetic acid as a preservative in food

A

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
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12
Q

Benzoic acid: what organisms are effected

A

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

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13
Q

Common uses of benzoic acid

A
  • 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
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14
Q

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

A
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15
Q

Sorbic acid is effective against what microorganisms

A
  • Sorbic acids are able to inhibit both fungi, bacteria, and most yeasts
  • In addition, molds cannot produce mycotoxins in the presence of sorbates
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16
Q

How sorbic acid can be applied to products and common uses

A
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17
Q

What is DMDC

A

•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)

18
Q

DMDC targets what microorganisms and added where

A
19
Q

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

A
20
Q

What is lysozyme? and what is its action mechanism

A
  • 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
21
Q

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

A
  • 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
22
Q

What government status lysozyme has

A

GRAS status

23
Q

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

A
  • 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
24
Q

Why nitrites are added to meats apart from microbial preservation

A

•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

25
Q

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

A

•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 reaction of nitrite with secondary or tertiary amines

26
Q

What are parabens?

A

para-Hydroxybenzoic Acid Esters (parabens)

27
Q

what microorganisms are targeted by parabens?

A

•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

28
Q

The mechanism of action of parabens

A

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

29
Q

Where parabens are applied

A
  • 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
30
Q

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

A
31
Q

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

A
32
Q

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

A
  • 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
33
Q

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

A
  • 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
34
Q

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

A
  • 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
35
Q

Where the greatest antimicrobial of spices coming from (plants)

A

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

36
Q

How cinnamon and cloves are antimicrobial

A
  • 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
37
Q

Allicin, the mode of action, acts on what organisms

A
  • 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.
38
Q

What compound in onion can function as a antimicrobials

A

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

39
Q

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

A
  • 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 aw
  • The LAB that spoil beer appear to be resistant to the antimicrobial effects of these bitter acids, while other bacteria appear to be sensitive
40
Q

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

A
  • 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
41
Q

Factors Affecting Activity of chemical preservatives

A

Food Microbiology (19 decks)

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