15 - Chemical Preservatives Flashcards
define a preservative
chemicals added to foods to retard the growth of, or kill microorganisms
most preservatives are added at levels that are _____ or _____
bacteriostatic; fungistatic
true or false: preservatives can preserve a food indefinitely
false
how are preservatives categorized?
- traditional
- naturally occuring
what are the criteria for a preservative to be categorized as traditional?
- used for many years
- approved for use in many countries
- are produced by synthetic processes
what are some traditional preservatives that can be found in nature
- acetic acid
- benzoic acid (from cranberries)
define a naturally occuring preservative
when a specific food product contains a compound that extends its shelf life
can one chemical be both a naturally occuring and a traditional preservative?
yes, depending on how it was produced
list some traidtional antimicrobials
- organic acid & derivatives
- Dimethyl Bicarbonate (DMDC)
- Lactoferrin
- Lysozyme
- Nitrites
- para-Hydroxybenzoic Acid Esters
- Sulfites
(strong/weak) organic acids are the most effective antimicrobials in their undissociated state
weak
why are weak organic acids more effective?
undissociated acids have no charge and can diffuse through cell membrane. then once inside, they dissociate
how do organic acids kill a microorganism?
- the microorganism will have to spend excessive energy trying to pump out extra H
- if it doesn’t pump, the extra H will induce structural changes to proteins, enzymes, nucleic acids, and phospholipids
the best acids for preservatives are _____ acids (referring to # of protons)
monoprotic
list some monoprotic acids
acetic, lactic, propionic, sorbic, and benzoic
list some multiprotic acids
citric, malic, tartaric, fumaric
the use of organic acids as preservatives is generally limited to foods with a pH of < ______ since most organic acids have a pKa of _____ to _____
- 5
- 0
- 0
how is acetic acid produced?
oxygenic fermentation
how is benzoic acid produced?
extracted from cranberries, plums, prunes, cinnamon, and cloves
how is lactic acid produced?
anoxic fermentation
how is propionic acid produced
heterofermentative fermentation
how is sorbic acid produced?
mountain ash berries
what kind of microorganism does acetic acid best defend against?
bacteria and yeast
where is acetic acid commonly applied?
- scald tank in chicken processing (lowers salmonella)
- bread dough for moist products (lowers Bacillus subtilis)
- condiments, gravy, sauces
what kind of microorganism does benzoic acid best defend against?
fungi
- some bacteria can be sensitive
- some fungi are resistant
where is benzoic acid commonly applied?
- apple cider (reduce E. coli)
- grape juice (reduces mold spoilage)
where is lactic acid applied?
- some studies addressed adding lactic acid to meats
how else does lactic acid limit microbial growth?
reduces aw
what microorganisms does sorbic acid best defend against?
fungi, bacteria, most yeasts; also prevents production of mycotoxins
how can sorbic acid be applied to foods?
dipping, spraying, dusting, incorporation into packaging films
where is sorbic acid commonly applied?
beverage syrups, cakes, cheese, dried fruits, margarine, pie fillings, salad dressings, wine
expand DMDC
dimethyl dicarbonate
what is DMDC?
- colorless liquid
- slightly soluble with water
- reactive with many substances (water, ethyl alcohol, aromatic amines, sulfhydryl groups)
what microorganism does DMDC best defend against?
yeasts, but is also bacericidal
what’s the suggested mode of action for DMDC?
enzyme inactivation
where is DMDC commonly applied?
- apple cider
- wine
(prevents spoilage yeasts)
what is lactoferrin?
primary iron-chelating protein in milk and colostrum
what does lactoferrin’s function?
- prevents infection of mammary glands & intestinal infection in the infant
- restricts microbial access to nutrients (make iron unavailable)
what is lysozyme?
an enzyme. it’s a peptidoglycan hydrolase
where can you find lysozyme?
- avian eggs
- mammalian milk
- tears
- other secretion
what type of bacteria are lysozymes better at inhibiting?
Gram-positive
- L. monocytogenes in meat
- C. tyrobutyricum in cheese
what are nitrites?
salts containing NO2
- NaNO2
- KNow
used in cured meat products
what function do nitrites have?
- primarily inhibits C. botulinum spore germination
- antimicrobial properties
- stabilizes cured meat color
- contributes to the taste of cured meats
how do nitrites work?
inhibit the ability of bacterial cells to generate ATP
what’s one drawback to nitrites?
they can form nitrosamines, which are carcinogens formed by the rxn of nitrite with secondary or tertiary amines
what’s the real name of parabens?
para-hydroxybenzoic acid esters
what do parabens do?
- effective against mostly fungi; gram-positive bacteria are also sensitive
how do parabens work?
interfere with cytoplasmic membrane; likely interfere with electrochemical gradient
applications of parabens?
- beers
- non-carbonated soft drinks
- fruit based beverages
- baked goods
- fruit products
- preserves
- fermented foods
- syrups
- dressings
- wines
- pie fillings
what are sulfites?
salts containing sulfur dioxide
- potassium sulfite
- sodium sulfite
- potassium metabisulfite
- sodium bisulfite
- sodium metabisulfite
function of sulfites?
- control growth of fermentative fungi AAB, and malolactic bacteria
- have antioxidant properties (inhibit browning)
where are sulfites applied?
- fruit & veggie products (juices, wines)
- fresh shrimp
- pickles
- sausages
what happens to sulfur dioxide when in aqueous solution?
forms sulfurous acid, which works similarly to organic acids
name some naturally occurring preservatives from animal and plant sources
animal - lactoperoxidase - chitosan plant - spices and essential oils - allicin - hops - isothiocyanates
limitations of using naturally occurring preservatives?
- not present in very high concentrations naturally
- addition of these substances can negatively impact organoleptic qualities
- present challenges for commercial production
what is lactoperoxidase?
glycoprotein enzyme found in raw milk, colostrum, saliva, other biological secretions
how does lactoperoxidase work?
oxidizes thiocyanate in the presence of H2O2, forming hypothiocyanite, which is a highly reactive oxidant
good to use in conjunction with H2O2 use
what is chitosan?
natural component of fungal cell walls that can be derived from chitin
how does chitosan work?
chelates LPS-associated cations
what does chitosan inhibit?
growth of foodborne fungi and bacteria
where is chitosan applied?
- in combo with organic acids or antimicrobials
- edible films
define spices
roots, bark, seeds, buds, leaves, or fruit that are added to foods as flavoring agents
what spices have greatest antimicrobial activity?
- cloves
- cinnamon
- oregano
- thyme
lesser extent: sage & rosemary
what do cinnamon and cloves contain?
- eugenol
- cinnamic aldehyde
what do cinnamon and cloves inhibit?
bacteria, fungi, and yeast
application of cinnamon?
packaging material
list the antimicrobial compounds in:
- oregano
- thyme
- sage
- rosemary
- basil
oregano: carvacrol
thyme: thymol
sage: thujone
rosemary: bornel, pinene, camphene, camphor
basil: linalool, methyl chavicol
what is allicin?
organosulfur compound found in onions and garlic
what does allicin do?
inhibits growth and toxin production of several microorganisms (including C. botulinum)
what do onions uniquely produce?
- catechol
how does allicin work?
inhibits disulfide-containing enzymes by oxidizing thiols to disulfides
what part of hops has antimicrobial activity?
- resin from hop vine contains bitter acids
which bacteria are sensitive to hops?
the LAB that spoil beer
what are isothiocyanates?
derived from brassicaceae plants when plant tissue is injured or mechanically disrupted
what do isothiocyanates protect against?
fungi, yeast, bacteria
what factors associated with the microorganism influence effectiveness of antimicrobials?
- vegetative vs. sporulated cells
- interaction w/other microbes
- cellular structure
- biofilm formation
what factors associated with the physicochemistry of the preservative influence the effectiveness of antimicrobials?
- physical barriers (membranes, shells, husks, hides)
- pH
- buffering capacity
- redox potential
