17) Chemical Preservative and Natural Antimicrobial Compounds Flashcards
define a preservative
chemical added to food that slows growth of or kills MOs
most preservatives are added at levels that are ____ or _____ and thus don’t kill the organisms
bacteriostatic or fungistatic
what are 2 classes of preservatives?
traditional
naturally occurring
describe a traditional preservative
- 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)
define a naturally occurring preservative
when a food pdt naturally contains a compound that extends it’s shelf life
what are examples of traditional antimicrobials?
- organic acids and derivatives
- dimethyl bicarbonate (DMDC)
- lactoferrin
- nitrites
- para-hydroxybenzoic acid esters
- sulfites
describe how undissociated weak organic acids functions to inactivate cells
- they have no charge and are hydrophobic, allowing them to easily diffuse through the cytoplasmic membrane into the cell
- enters into cell where H can easily dissociate
- bacterial cells spend excessive energy to pump on extra H, which inhibits growth and inactivates the c ell
- if H is not pumped out, there will be structural changes to proteins, enzymes, nucleic acids and phospholipids
which state should weak organic acids be in to be the most effective antimicrobial?
undissociated state
what are the best acids for preservatives? what are examples?
what is less effective?
more effective: monoprotic acids (acetic, lactic, propionic, sorbic, benzoic)
less effective: multiprotic (citric, malic, tartaric, fumaric)
what two factors is very important in choosing an organic acid for use as an additive?
- pH of the product
2. pKa of the acid
using organic acids as preservatives is limited to what foods? why?
foods w/ a pH < 5.5
since most organic acids have pKa of 3-5
what is a limitation of naturally occurring preservatives?
how can this be changed? what is a drawback of this?
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
what two factors affect activity of antimicrobials?
what is an example of each?
factors associated with…
1. the MO (vegetative vs. sporulated cells, interactions w/ other microbes, cell structure)
- the physiochemistry of the preservative (physical barriers, pH, buffering capacity, redox potential)
what does acetic acid target as an anti-microbial?
what is it not effective against?
what are resistant bacteria?
targets: bacteria and yeast
not effective to: molds
resistant: LAB and AAB
what are common uses of acetic acid as an antimicrobial?
- scald tank in chicken processing to lower salmonella
- bread dough to reduce rope forming bacillus subtilis
what does benzoic acid target?
what is resistant?
targets: fungi and some bacteria
resistant: some fungi
what are common uses of benzoic acid as an antimicrobial?
- reducing e.coli in apple cider
- reducing mold spoilage in grape juice
what is the function of lactic acid as an anti-microbial?
reduces Aw of food system which limits microbial growth
what is a beneficial property of lactic acid?
what is a common application due to this property?
limited taste
used to extend shelf life of meats
what does sorbic acid target?
fungi, bacteria, most yeast and production of mycotoxins by molds
how can sorbic acid be applied to foods?
direct addition dipping spraying dusting incorporation into packaging films
what are common uses of sorbic acid?
inhibiting fungi in bakery pdts
salad dressings
what does DMDC stand for?
what are it’s properties?
dimethyl dicarbonate
properties
- colorless lquid
- slightly soluble in water
- v reactive with many substances (h2o, ethyl alcohol, aromatic amines, SH groups)
what is the function of DMDC?
enzyme inactivatino
what are common uses of DMDC?
inhibiting growth of spoilage yeast in alcoholic beverages
describe lactoferrin
where is it found?
what is its function?
- 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
what is lysozyme?
where is it found?
what is it’s function?
- 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
what are common uses of lysozyme?
- prevents late blowing caused by fermentation of C. tyrobutyricum in cheese
- reduce L. monocytogenes in meat
what are nitrite compounds used in cured meats?
sodium nitrite
potassium nitrite
what is produced when nitrite reacts with myoglobin?
nitrosomyoglobin
what is the primary function of nitrite in cured meats?
- inhibit C. bot spore germination, growth and toxin production
- inhibit ATP generation in bacteria = depeletes energy stores
- stabilizes color and flavor
what compounds are commonly added with nitrites? why?
ascorbates
- accelerates curing process by reducing nitrite, which slows formation of nitrosamines (carcinogens)
what are nitrosamines? how are they formed in cured meats? what is a solution to this?
carcinogens formed by nitrite with secondary or tertiary amines
solution: add ascorbates to slow formation
which are parabens more effective to?
1a) fungi
1b) bacteria
2a) gram pos bacteria
2b) gram neg bacteria
fungi > bacteria
gram pos > gram neg
describe the mechanism of parabens
causes interface w/ cytoplasmic membrane which causes interfering with electrochemical gradient
what are common applications of parabens?
inhibits fungal growth in beverages (beer, soft drinks)
what is the function of sulfites?
1) controls growth of fermentative fungi, AAB and malolactic bacteria
2) inhibits enzymatic and non-enzymatic browning of foods
what are naturally occurring preservatives from animal sources?
lactoperoxidase
chitosan
what are naturally occurring preservatives from plant sources?
spices + essential oils
allicin (onions and garlic)
hops
isothiocyanates
what is lactoperoxidase?
where is it naturally found?
how does it function?
- glycoprotein enzyme
- found in raw milk, clostrum saliva, other secretions
- function: oxidizes thiocyanate (in presence of H2O2) –> hypothiocyanite (reactive oxidant and antimicrobial)
what is chitosan?
how can it be derived?
function?
mechanism?
common uses?
- 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
where are spices found?
roots bark seeds buds leaves fruit
added to food for flavor
what spices have greatest antimicrobial activity?
cloves
cinnamon
oregano
thyme
describe antimicrobial compounds in cinnamon and cloves
what do they target?
eugenol and cinnamic aldehyde
targets bacterial, fungi and yeast
where is allicin found?
what do they target?
how does it function?
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)
besides allicin, what other antimicrobial compounds do onions have?
phenolic compounds (catechol)
what are isothiocyanates derived from?
how are they synthesized?
what do they target?
plants in the Brassicaceae family (cabbage, broccoli, kale…)
synthesized when plant tissue is injured or mechanically disrupted
targets fungi, yeast, bacteria
