chemical preservatives and natural antimicrobial compounds

Question 1

preservative

Answer 1

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

• usually bacteriostatic: do not preserve food indefinitely
• two classes: traditional and naturally occurring

Question 2

traditional preservatives

Answer 2

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

Question 3

naturally occurring preservatives

Answer 3

when a specific food product naturally contains a compound that extends its shelf life
-few preservatives exist in natural sources at concentrations that are high enough to inhibit microbes

Question 4

organic acids

Answer 4

• best: weak organic acids
• undissociated acids have no charge: diffuse across the cytoplasmic membrane
• inside the cells, H+ dissociates
• Because the cell is spending time/energy pumping out the H, it inhibits cell growth - inactivated cell
• if it is not pumped out, the proteins etc change structure

Question 5

Best acids for preservatives

Answer 5

weak monoprotic acids (acetic, lactic, propionic, sorbic, benzoic)

Question 6

pKa?

Answer 6

pKa must be considered because it is best that the acid is undissociated outside the cell.
-Most organic acids have a pKa of 3-5, so they are used in foods with a pH <5.5

Question 7

acetic acid

Answer 7

• bacteria and yeast
• LAB and AAB are resistant
• Added to condiments: relish, gravy, sauces

Question 8

Benzoic acid

Answer 8

• antifungals (though most bacteria are susceptible and some fungi are resistant)
• ex: apple cider, mold spoilage

Question 9

lactic acid

Answer 9

• limited taste associated with it
• added to meats for shelf-life extension
• added to carcasses pre or post chilling
• reduces the a_w (further limiting microbial growth)

Question 10

sorbic acid

Answer 10

• inhibits growth of fungi, bacteria, and most yeasts
• molds cannot produce mycotoxins in the presence of sorbates
• ex. bakery products have sorbic acid for the inhibition of fungi, salad dressings

Question 11

dimethyl dicarbonate

Answer 11

• mainly targets yeast
• unclear mechanism, but likely enzyme inactivation
• added to alcoholic beverages

Question 12

Lactoferrin

Answer 12

• the primary iron-chelating protein in milk
• prevents infection in the mammary gland
• restricts microbial access to nutrients via sequestration of iron - bacteria cannot grow or divide

Question 13

Lysozyme

Answer 13

• peptidoglycan hydrolase: digests the cell wall peptidoglycan
• Gram-positive are more susceptible
• used in cheeses to prevent late blowing

Question 14

nitrites

Answer 14

• sodium and podium nitrite used in meat products
• inhibits C. botulinium
• inhibit the ability of bacteria to generate ATP - starve cells of energy

Question 15

para-hydroxybenzoic acid esters (parabens)

Answer 15

• more effective against fungi than bacteria, Gram pos more sensitive
• interfere with the electrochemical gradient of the cell membrane
• used in beers, fruit mased beverages, baked goods, fruit products

Question 16

sulfites

Answer 16

• control growth of fermentative fungi, AAB, and malolactic bacteria
• inhibit enzymatic and non-enzymatic browning of foods
• aqueous solutions of sulfur dioxide yield sulfurous acid and have similar mechanism to organic acids

Question 17

Naturally occurring preservatives sources

Answer 17

animals : lactoperoxidase, chitosan

plants: spices, essential oils, allicin, hops, isothiocyanates

Question 18

lactoperoxidase

Answer 18

• glycoprotein enzyme
• occurs in raw milk
• oxidizes thiocyanate in the presence of available H2O2 and forms hypothiocyanite, which is a highly reactive oxidant and antimicrobial
• to effectively use this system, you must add extra H2O2

Question 19

Chitosan

Answer 19

• natural component f fungal cell walls

- inhibits foodborne fungi and bacteria esp when combined with other organic acids or antimicrobials

Question 20

spices

Answer 20

roots, bark, seeds, buds, leaves, fruit that are added to foods as flavouring agents

Question 21

spices and essential oils

Answer 21

greatest antimicrobial activity - cloves, cinnamon, oregano, thyme
-cinnamon/cloves: eugenol and cinnamic aldehyde inhibit B,F,Y

Question 22

Allicin

Answer 22

• found in onions and garlic
• can inhibit C. botulinum
• inhibition of disulfide-containing enzymes: inactivates proteins by oxidizing thiols to disulfides

Question 23

Hops

Answer 23

• resin from the hop vine is composed of bitter acids, have antibaterial activity against bacteria and fungi at a reduced a_w
• LAB that spoil beer are resistant

Question 24

isothiocyanates

Answer 24

• derived from plants in the family brassicaceae
• synthesized when the plant tissue is injured or machanically disrupted
• inhibits BFY

Question 25

factors affecting activity

Answer 25

• factors associated with the microbe and with the physiochemistry of the preservative
  microbe: spore vs vegetative, biofilm, cellular structure
  preservative: pH, redox potential, buffering capacity