chemical preservatives and natural antimicrobial compounds Flashcards
preservative
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
traditional preservatives
- used for many years
- approved for use in many countries
- produced by synthetic processes.
naturally occurring preservatives
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
organic acids
- 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
Best acids for preservatives
weak monoprotic acids (acetic, lactic, propionic, sorbic, benzoic)
pKa?
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
acetic acid
- bacteria and yeast
- LAB and AAB are resistant
- Added to condiments: relish, gravy, sauces
Benzoic acid
- antifungals (though most bacteria are susceptible and some fungi are resistant)
- ex: apple cider, mold spoilage
lactic acid
- 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)
sorbic acid
- 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
dimethyl dicarbonate
- mainly targets yeast
- unclear mechanism, but likely enzyme inactivation
- added to alcoholic beverages
Lactoferrin
- 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
Lysozyme
- peptidoglycan hydrolase: digests the cell wall peptidoglycan
- Gram-positive are more susceptible
- used in cheeses to prevent late blowing
nitrites
- sodium and podium nitrite used in meat products
- inhibits C. botulinium
- inhibit the ability of bacteria to generate ATP - starve cells of energy
para-hydroxybenzoic acid esters (parabens)
- 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
sulfites
- 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
Naturally occurring preservatives sources
animals : lactoperoxidase, chitosan
plants: spices, essential oils, allicin, hops, isothiocyanates
lactoperoxidase
- 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
Chitosan
- natural component f fungal cell walls
- inhibits foodborne fungi and bacteria esp when combined with other organic acids or antimicrobials
spices
roots, bark, seeds, buds, leaves, fruit that are added to foods as flavouring agents
spices and essential oils
greatest antimicrobial activity - cloves, cinnamon, oregano, thyme
-cinnamon/cloves: eugenol and cinnamic aldehyde inhibit B,F,Y
Allicin
- found in onions and garlic
- can inhibit C. botulinum
- inhibition of disulfide-containing enzymes: inactivates proteins by oxidizing thiols to disulfides
Hops
- 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
isothiocyanates
- derived from plants in the family brassicaceae
- synthesized when the plant tissue is injured or machanically disrupted
- inhibits BFY
factors affecting activity
- 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
