Chemical Preservatives Flashcards
what are preservatives
chemicals that are added to foods that retard the growth of or kill microorganisms
T or F; most preservatives are added at levels that are bacteriostatic, or fungiostatic and do not actually kill the organism
True
Types of food preservatives
traditional and naturally occuring
3 characteristics of traditional food preservatives
- used for many years
- approved for use in many countries
- produced by synthetic processes
define naturally occuring preservatives
are when a specific food product naturally contains a compound that extends it’s shelf life
name the 7 traditional food preservatives
- organic acids
- dimethyl bicarbonate
- lactoferrin
- lysozyme
- nitrites
- para-hydroxybenzoic acid esters
- sulfites
weak organic acids are the most effective in their _____ & why?
undissociated states because they have no charge and are hydrophobic allowing them to diffuse easily through the cytoplasmic membrane and into the cell. once inside they dissociate and bacterial cells expend excessive energy trying to pump them out. no pumping = structural changes.
explain the reasoning behind the choice of acids used in food preservation
monoprotic acids (like acetic, benzoic, sorbic, propionic) because multiprotic acids are less effective. the pH is strongly related to the preservative effectiveness of the org acid. (undissociated)
org acid = must consider pH and pKa. ph of food = less than 5.5
organic acid with lowest pka =
lactic acid
explain the use of acetic acid as a food preservative
effective against yeast and bacteria than mold.
its used in condiments, bread dough and scald tanks
resistant bacteria = LAB and AAB.
benzoic acid is commonly used as
antifungals; good at reducing ecoli in cider and mold spoilage in grape juice
T or F: lactic acid reduce the aw of the food system further limiting microbial growth
T
explain the use of sorbic acid
inhibit both fungi, bacteria and most yeast. molds cant produce mycotoxins in the presence of sorbates. Used in bakery products for the inhibition of fungi and used in bev syrups, wine etc
Dimethyl dicarbonate
Dimethyl decarbonate (DMDC) is a colorless liquid that is only slightly soluble in water, and is very reactive with many substances (water, ethyl alcohol, aromatic amines, and sulfhydryl groups)
DMDC mainly targets yeasts, but is also bactericidal
The direct mechanism of action is unclear, but it likely leads to enzyme inactivation
DMDC is added to alcoholic beverages like apple cider or wine to inhibit the growth of spoilage yeast
Lactoferrin
iron chelating protein in milk. restricts microbial access to nutrients via the sequestration of iron, without access to iron bacterial cells cannot grow or divide.
Lysozyme
naturally occuring peptidoglycan hydrolase that occurs in avian eggs, mammalian milk, tears and other secretions.
- digest bonds in the cell wall peptidoglycan and result in cellular lysis in hypotonic systems.
- more active against gram + than gram neg. -reduce L monocytogenes.
- used in cheese
explain the use of nitrites in meat
nitrites have antimicrobial properties but are also used in cured meats for other purposes,
- nitrite reacts with the muscle protein myoglobin to form nitrosomyoglobin, which stabilizes the cured meat colour.
-Nitrites also contribute to that (yummy) cured meat taste
-The primary application of nitrite is for the inhibition of C. botulinum spore germination, growth, and toxin production in cured and fermented meats
-Nitrites work by inhibiting the ability of bacterial cells to generate ATP, and therefore depleting their energy stores
Meat products that contain nitrites include: bacon, corned beef, bologna, frankfurters, and other cold-meats such as cured hams, fermented sausages, shelf-stable canned/cured meats, and some perishable canned/ cured meat
___ are often added along with nitrites to accelerate the curing process by reducing nitrite, and this can also slow the formation of nitrosamines, which are carcinogens formed by the reaction of nitrite with secondary or tertiary amines
Ascorbates
para-hydroxybenzoic acid esters mode of action
generally more effective against fungi than bacteria, but gram positive bacteria are more sensitive to the effects of parabens than gram negative bacteria. They work by interferring with the cytoplasmic membrane likely through interferring with the electrochemical gradient.
what are sulfites and how are they used?
-Several different salts of Sulfur dioxide (SO2) are used as antimicrobials in the food industry:
Potassium sulfite (K2SO3), sodium sulfite (Na2SO3), potassium metabisulfite (K2S2O5), sodium bisulfite (Na2HSO3), and sodium metabisulfite (S2Na2O5)
-Sulfites are used mainly in fruit and vegetable products (fruits, juices, wines, sausages, fresh shrimp, and pickles to control the growth of fermentative fungi, AAB, and malolactic bacteria)
-They also have antioxidant properties that inhibit the enzymatic and non-enzymatic browning of foods
Name naturally occuring preservatives and state their sources
animal source; chitosan and lactoperoxidase
plant sources; spices and essential oils, allicin, hops and isothiocyanates
what are the issues with naturally occurring preservatives
- few exist at concentrations high enough to inhibit microbial growth without prior purification or refining.
- lack of economic feasibility
what is lactoperoxidase?
glycoprotein enzyme that occurs in raw milk, colostrum and other bio secretions. it oxidizes thiocyanate in the presence of available hydrogen peroxide from hypothiocyanate which is highly reactive oxidant and antimicrobial.
what is the limitation with lactoperoxidase
to be effective it needs hydrogen peroxide
what is chitosan?
- its a natural component in the fungal cell wall derived from chitin.
- can inhibit the growth of foodborne fungi and bacteria, especially when combined with other organic acids or antimicrobials.
- ability to chelate associated cations
top spices used for preservation include
Cinnamon and cloves contain eugenol and cinnamic aldehyde
Eugenol and cinnamic aldehyde appear to have antibacterial, fungal and yeast activity
what us allicin and how is it a food preservative?
compound found in onions and garlic. The growth and toxin production of severak microorganisms are inhibited by allicin. onions also produce chain phenolic compounds which may also contribute to the antimicrobial activity of onion essential oils and extracts.
how does allicin inhibit disulfide containing enzymes?
by oxidizing thios to disulfides
why is hops considered a natural preservative
About 3-12% of the resin from the hop vine is composed of bitter acids which have antibacterial activity against bacteria and fungi at reduced aw
The LAB that spoil beer appear to be resistant to the antimicrobial effects of these bitter acids, while other bacteria appear to be sensitive
what are isothiocyanates & why are they considered natural preservatives?
Isothiocyanates are derived from plants in the family Brassicaceae (cabbage, kohlrabi, Brussel sprouts, cauliflower, broccoli, kale, horseradish, mustard, turnip, and rutabaga)
Isothiocyanates are synthesized when the plant tissue is injured or mechanically disrupted
They are effective against fungi, yeast, and bacteria
The mechanism of action is not completely clear
what are the factors that affect activity of antimicrobials
- factors associated with the microorganism and factors associated with the physiochemistry of the preservative.
examples of factors associated with microorganism
Factors associated with the microorganism can be vegetative vs sporulated cells, interactions with other microbes, cellular structure, biofilm formation etc.
Factors associated with the preservative include
Factors associated with the preservatives could be physical barriers (membranes, shells, husks, hides), pH, buffering capacity, redox potential etc.
