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5) Food Microbiology > 17) Chemical Preservative and Natural Antimicrobial Compounds > Flashcards

17) Chemical Preservative and Natural Antimicrobial Compounds Flashcards

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1
Q

define a preservative

A

chemical added to food that slows growth of or kills MOs

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2
Q

most preservatives are added at levels that are ____ or _____ and thus don’t kill the organisms

A

bacteriostatic or fungistatic

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3
Q

what are 2 classes of preservatives?

A

traditional

naturally occurring

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4
Q

describe a traditional preservative

A
  • used for many yeasrs
  • approved for use in many countries
  • ## can be produced by synthetic processes or found in nature (eg. acetic or benzoic acid in cranberries)
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5
Q

define a naturally occurring preservative

A

when a food pdt naturally contains a compound that extends it’s shelf life

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6
Q

what are examples of traditional antimicrobials?

A
  • organic acids and derivatives
  • dimethyl bicarbonate (DMDC)
  • lactoferrin
  • nitrites
  • para-hydroxybenzoic acid esters
  • sulfites
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7
Q

describe how undissociated weak organic acids functions to inactivate cells

A
  1. they have no charge and are hydrophobic, allowing them to easily diffuse through the cytoplasmic membrane into the cell
  2. enters into cell where H can easily dissociate
  3. bacterial cells spend excessive energy to pump on extra H, which inhibits growth and inactivates the c ell
  4. if H is not pumped out, there will be structural changes to proteins, enzymes, nucleic acids and phospholipids
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8
Q

which state should weak organic acids be in to be the most effective antimicrobial?

A

undissociated state

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9
Q

what are the best acids for preservatives? what are examples?

what is less effective?

A

more effective: monoprotic acids (acetic, lactic, propionic, sorbic, benzoic)

less effective: multiprotic (citric, malic, tartaric, fumaric)

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10
Q

what two factors is very important in choosing an organic acid for use as an additive?

A
  1. pH of the product

2. pKa of the acid

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11
Q

using organic acids as preservatives is limited to what foods? why?

A

foods w/ a pH < 5.5

since most organic acids have pKa of 3-5

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12
Q

what is a limitation of naturally occurring preservatives?

how can this be changed? what is a drawback of this?

A

few of them exist in nature at concentrations high enough to inhibit microbial growth w/o purification/refining

adding natural substances. But this can lead to adverse sensory changes in food

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13
Q

what two factors affect activity of antimicrobials?

what is an example of each?

A

factors associated with…
1. the MO (vegetative vs. sporulated cells, interactions w/ other microbes, cell structure)

  1. the physiochemistry of the preservative (physical barriers, pH, buffering capacity, redox potential)
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14
Q

what does acetic acid target as an anti-microbial?

what is it not effective against?

what are resistant bacteria?

A

targets: bacteria and yeast
not effective to: molds
resistant: LAB and AAB

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15
Q

what are common uses of acetic acid as an antimicrobial?

A
  • scald tank in chicken processing to lower salmonella

- bread dough to reduce rope forming bacillus subtilis

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16
Q

what does benzoic acid target?

what is resistant?

A

targets: fungi and some bacteria
resistant: some fungi

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17
Q

what are common uses of benzoic acid as an antimicrobial?

A
  • reducing e.coli in apple cider

- reducing mold spoilage in grape juice

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18
Q

what is the function of lactic acid as an anti-microbial?

A

reduces Aw of food system which limits microbial growth

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19
Q

what is a beneficial property of lactic acid?

what is a common application due to this property?

A

limited taste

used to extend shelf life of meats

20
Q

what does sorbic acid target?

A

fungi, bacteria, most yeast and production of mycotoxins by molds

21
Q

how can sorbic acid be applied to foods?

A 
direct addition
dipping
spraying
dusting
incorporation into packaging films
22
Q

what are common uses of sorbic acid?

A

inhibiting fungi in bakery pdts

salad dressings

23
Q

what does DMDC stand for?

what are it’s properties?

A

dimethyl dicarbonate

properties

  • colorless lquid
  • slightly soluble in water
  • v reactive with many substances (h2o, ethyl alcohol, aromatic amines, SH groups)
24
Q

what is the function of DMDC?

A

enzyme inactivatino

25
Q

what are common uses of DMDC?

A

inhibiting growth of spoilage yeast in alcoholic beverages

26
Q

describe lactoferrin

where is it found?

what is its function?

A
  • primary iron-chelating protein in milk and colostrum
  • found naturally in milk or produced commercially
  • prevents infection in mammary gland (mother) and intestines (infant)

function: inhibits access to iron = restricts microbial access to nutrients = decreases cell growth and division

27
Q

what is lysozyme?

where is it found?

what is it’s function?

A
  • naturally occurring peptidoglycan hydrolase
  • found in avian eggs mammalian milk, tears and other secretions
  • function: digests bonds in cell wall peptidoglycan = results in cellular lysis on hypotonic systems
28
Q

what are common uses of lysozyme?

A
  • prevents late blowing caused by fermentation of C. tyrobutyricum in cheese
  • reduce L. monocytogenes in meat
29
Q

what are nitrite compounds used in cured meats?

A

sodium nitrite

potassium nitrite

30
Q

what is produced when nitrite reacts with myoglobin?

A

nitrosomyoglobin

31
Q

what is the primary function of nitrite in cured meats?

A
  • inhibit C. bot spore germination, growth and toxin production
  • inhibit ATP generation in bacteria = depeletes energy stores
  • stabilizes color and flavor
32
Q

what compounds are commonly added with nitrites? why?

A

ascorbates

- accelerates curing process by reducing nitrite, which slows formation of nitrosamines (carcinogens)

33
Q

what are nitrosamines? how are they formed in cured meats? what is a solution to this?

A

carcinogens formed by nitrite with secondary or tertiary amines

solution: add ascorbates to slow formation

34
Q

which are parabens more effective to?

1a) fungi
1b) bacteria

2a) gram pos bacteria
2b) gram neg bacteria

A

fungi > bacteria

gram pos > gram neg

35
Q

describe the mechanism of parabens

A

causes interface w/ cytoplasmic membrane which causes interfering with electrochemical gradient

36
Q

what are common applications of parabens?

A

inhibits fungal growth in beverages (beer, soft drinks)

37
Q

what is the function of sulfites?

A

1) controls growth of fermentative fungi, AAB and malolactic bacteria
2) inhibits enzymatic and non-enzymatic browning of foods

38
Q

what are naturally occurring preservatives from animal sources?

A

lactoperoxidase

chitosan

39
Q

what are naturally occurring preservatives from plant sources?

A

spices + essential oils

allicin (onions and garlic)

hops

isothiocyanates

40
Q

what is lactoperoxidase?

where is it naturally found?

how does it function?

A
  • glycoprotein enzyme
  • found in raw milk, clostrum saliva, other secretions
  • function: oxidizes thiocyanate (in presence of H2O2) –> hypothiocyanite (reactive oxidant and antimicrobial)
41
Q

what is chitosan?

how can it be derived?

function?

mechanism?

common uses?

A
  • natural component of the fungal cell wall
  • derived from chitin (from shellfish processing)
  • function: inhibits fungi and bacteria
  • mechanism: chelates LPS-associated cations
  • uses: add to edible films for inhibition of MOs
42
Q

where are spices found?

A 
roots
bark
seeds
buds
leaves
fruit

added to food for flavor

43
Q

what spices have greatest antimicrobial activity?

A

cloves
cinnamon
oregano
thyme

44
Q

describe antimicrobial compounds in cinnamon and cloves

what do they target?

A

eugenol and cinnamic aldehyde

targets bacterial, fungi and yeast

45
Q

where is allicin found?

what do they target?

how does it function?

A

onions and garlic

targets growth and toxin production of MOs (including C. bot)

function: oxidizes thiols to disulfides which inactivates disulfide containing enzymes (eg. alcohol dehydrogenase and urease)

46
Q

besides allicin, what other antimicrobial compounds do onions have?

A

phenolic compounds (catechol)

47
Q

what are isothiocyanates derived from?

how are they synthesized?

what do they target?

A

plants in the Brassicaceae family (cabbage, broccoli, kale…)

synthesized when plant tissue is injured or mechanically disrupted

targets fungi, yeast, bacteria

5) Food Microbiology (21 decks)

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