Chemical preservatives and natural antimicrobial compounds Flashcards
what are preservatives?
chemicals that are added to foods that slow down the growth of, or kill microorganisms
what is the significance of adding preservatives that are bacteriostatic or fungistatic?
they do not actually kill the organisms, therefore food preservatives do not preserve the food indefinitely
what are the two classes of preservatives?
Traditional and naturally occuring. chemicals can be considered either or based on if they were synthetically produced or naturally occur in the food in question
what is the significance of traditional preservatives?
- have been used for many years
- are approved for use in many countries
- are produced by synthetic processes
what are some examples of traditional preservatives?
acetic acid
benzoic acid
what are naturally occurring preservatives?
preservatives that naturally exist in food products, that extend their shelf lives
What are traditional antimicrobials?
- organic acids and derivatives (acetic acid, benzoic acid, lactic acid, propionic acid, sorbic acid)
- dimethyl bicarbonate
- lactoferrin
- lysozyme
- nitrites
- para-hydroxybenzoic acid esters
- sulfites
are weak or strong organic acids more effective as antimicrobials?
weak organic acids are the most effective in their undissociated state. they can bring Hydrogen atoms into the bacterial cell, increasing acidity, leading to cell death. the bacteria cannot extensively pump out H-atoms for long but if they don’t, it leads to structural changes in proteins, enzymes, nucleic acids, and phospholipids
what are the best acids for preservatives?
monoprotic acids:
acetic, lactic, propionic, sorbic, and benzoic
are multiprotic acids effective preservatives?
no
what are examples of multiprotic acids?
citric, malic, tartaric, and fumaric
The ___ of the food system is strongly related to the preservative effect of the organic acid
pH
must be undissociated outside the cell for effectiveness
the use of organic acids as preservatives is generally limited to foods with a pH of ____ since most organic acids have a pKa of 3.0 and 5.0
<5.5
a common source of acetic acid?
oxidative fermentation
a common source of benzoic acid?
cranberries, plums, prunes, cinnamon, and cloves
a common source of lactic acid?
produced during anoxic fermentation?
a common source of propionic acid?
produced by heterofermentative fermentation
a common source of sorbic acid?
Mountain ash berries
acetic acid is more effective against ____ and ____ than molds
bacteria and yeast
what are the common uses of acetic acid?
- 0.1% can be added to the scald tank in chicken processing (lowers salmonella on chicken caracasses)
- 0.1-2% can be added to bread dough for moist products and reduces the rope forming bacillus subtilis
- routinely added to condiments, relishes, gravy, and sauces
how is benzoic acid commonly used as a food preservative?
commonly added as anti fungals, although most bacteria are susceptible, and some fungi are resistant
0.1% benzoic acid is effective at reducing ___ in apple cider
E. coli
0.1% of benzoic acid in grape juice results in a ____ reduction in mold spoilage
3-log
what is the significance of lactic acid as a food preservative?
has a limit taste associated to it so it is added to meats for shelf-life extension. FDA allows lactic acid to be applied pre- or post-chilling
what is the effect of lactic acid on the food system, further limiting microbial growth?
reducing water activity
what is the significance of sorbic acids?
inhibit both fungi, bacteria, and most yeasts
molds cannot produce mycotoxins in the presence of sorbates
what are ways sorbic acid can be applied to foods?
direct addition, dipping, spraying, dusting, or incorporation into packaging films
what are the common uses of sorbic acid?
added to bakery products for inhibition of fungi, and to beverage syrups, cakes, cheese, dried fruits, margarine, pie fillings, salad dressings, and wine
what is the significance of dimethyl dicarbonate?
colorless liquid that is only slightly soluble in water, but very reactive in water, ethyl alcohol, aromatic amines, and sulfhydryl groups
what does dimethyl dicarbonate target?
yeasts, but is also bacterialcidal. also why DMDC is added to alcoholic beverages to inhibit growth of spoilage yeast
what is Lactoferrin?
the primary iron-chelating protein in milk and colostrum. can be produced commercially or occur naturally in milk
what is an advantage of lactoferrin in nature?
prevents infection in the mammary gland, and intestinal infection in the infant. restricts microbial access to nutrients via sequestration of iron
what is the significance of lysozyme?
a naturally occurring peptidogylcan hydrolase that occurs in avian eggs, mammalian milk, tears, and other secretions. they cause cellular lysis by digesting the peptidoglycan bonds
lysozymes have more activity against gram-___ bacteria than a gram-____
gram-positive
gram-negative
lysozymes are able to reduce what population of bacteria in several meat products?
L. monocytogenes
why is lysozyme used in cheeses?
prevent late blowing caused by fermentation of the anaerobe C. tyrobutyricum
sodium nitrite and potassium nitrite have a specialized use in _____
cured meat products
what kind of properties do both nitrites have?
antimicrobial properties
what muscle protein does nitrite react with
myoglobin, to form nitrosomyoglobin
what does the formation of nitrosomyoglobin result in?
stabilization of cured meat color
what is the primary application of nitrite used for?
for the inhibition of C. botulinum spore germination, growth, and toxin production in cured and fermented meats
how do nitrites inhibit the ability of spore germination?
by inhibiting the ability of bacterial cells to generate ATP, therefore depleting their energy stores
what are some meat products that contain nitrites?
bacon, corned beef, bologna, frankfurters and other cold cured meats such as cured hams, fermented sausages, shelf-stable canned/cured meats, and some perishable canned-cured meat
what is the significance of ascorbates?
added along with nitrites to accelerate the curing process by reducing nitrite, and this can also be slow the formation of nitrosamines.
what are nitrosamines?
carcinogens that are formed by the reaction of nitrite with secondary or tertiary amines
what are para-hydroxybenzoic acid esters?
otherwise known as parabens, which are effective compounds against fungal growth, more than bacterial growth
what mechanism of parabens results in no fungal growth?
paraben-directed interference with the cytoplasmic membrane , likely through interfering with the electrochemical gradient
what beverages are parabens in?
beers, non-carbonated soft drinks, and fruit based beverages
what other foods are parabens used in?
baked goods, fruit products, preserves, fermented foods, syrups, dressings, wines, and pie fillings
what is the significance of sulfites?
used as antimicrobials in the food industry
what products are sulfites mainly used in?
fruits and vegetable products to control the growth of fermentative fungi, AAB, and malolactic bacteria
what do sulfites’ antioxidant properties result in?
the inhibition of enzymatic and non-enzymatic browning of foods
what do aqueous solutions of sulfur dioxide theoretically yield?
sulfurous acid (H2SO3)
what are naturally occurring preservatives from animals?
lactoperoxidase and chitosan
what are naturally occurring preservatives from plant sources?
spices and essential oils, allicin (garlic and onions), hops, isothiocyanates (eliminate of carcinogens)
what is lactoperoxidase?
a glycoprotein enzyme that occurs naturally in raw milk, colostrum, saliva, and other biological secretions
lactoperoxidase oxidizes ____ in the presence of available hydrogen peroxide, forming ___ which is a highly reactive oxidant and therefore antimicrobial
thiocyanate
hypothiocyanate
what must you add to effectively use a lactoperoxidase system?
hydrogen peroxide - required for oxidation of thiocyanate
what is chitosan?
a natural component of the fungal cell wall that can be derived from chitin, a by-product of shellfish processing
what is the significance of chitosan?
inhibits the growth of foodborne fungi and bacteria, especially when combined with other organic acids or antimicrobials
what is chitosan added to for inhibition of microbial growth?
edible films
What are spices?
roots, bark, seeds, buds, leaves, or fruit that are added to foods as flavoring agents
what is the significance of spices?
have antimicrobial activity and have been used as preservatives since 1550 bce when ancient egyptians used spices for food preservation and embalming the dead
what spices possess the greatest antimicrobial activity?
cloves, cinnamon, oregano, thyme, and to a lesser extent sage and rosemary
what important compound do cinnamon and cloves contain?
contain eugenol and cinnamic aldehyde
what is the significance of eugenol and cinnamic aldehyde?
have antibacterial, fungal and yeast activity
what antimicrobial compounds do herbs contain?
Oregano - carvacol Thyme - thymol Sage - thujone rosemary - bornel, pinene, camphene, and camphor basil - linalool and methyl chaviol
where is allicin found?
onions and garlic
what does allicin inhibit?
growth and toxin production of several microorganisms (including C. botulinum)
what are the chain phenolic compounds that onions produce?
catechol - may also contribute to antimicrobial activity of onion essential oils and extracts
what proteins does allicin inactivate?
disulfide-containing enzymes
what is the significance of hops?
resin from the hop vine has antibacterial activity against bacteria and fungi at reduced water activity
what bacteria are resistant to hops antibacterial activity?
LAB - little information about the mechanism of action
where are isothiocyanates derived from?
plants in the family brassicaceae (cabbage, kohlrabi, brussel sprouts, cauliflower, broccoli, kale, horseradish, mustard, shrimp, turnip, and rutabaga)
when are isothiocyanates synthesized?
when the plant tissue is injured or mechanically disrupted
what are isothiocyanates effective against?
fungi, yeast, and bacteria - mechanism of action not clearly understood
factors are known to affect the activity of antimicrobials?
- factors associated with the microorganism
- factors associated with the physiochemistry of the preservative
activity against antimicrobials, factors assoc. with the microorganism could be:
vegetative vs sporulated cells, interactions with other microbes, cellular structure, biofilm formation, etc.
factors against antimicrobial activity associated with the preservatives could be:
physcial barriers, pH, buffering capacity, redox potential etc.
