Antimicrobial preservatives are used in food to prevent spoilage from microbes and increase shelf life. They include nitrites, sulfur dioxide, hydrogen peroxide, and organic acids which act on bacteria, molds, or yeasts through various mechanisms like disrupting cell membranes or inhibiting enzymes. An effective preservative is non-toxic, has a broad spectrum of activity, and does not affect the taste, odor or color of food.

2. Anti microbial preservative

3. Food and Dairy Microbiology

4. It is done for the following reasons:
 To preserve the natural characteristics of food.
 To preserve appearance of food.
 To increase shelf life of the food.
 To save the food from spoilage causing microbes.

5.  Definition:
 Chemicals used in food in relatively small
dose to kill undesirable microorganisms.
 Prevent decomposition of food by preventing
growth of bacteria or fungi.

6.  Differ greatly in ability
to act against different
microorganism.
 Some are Narrow
spectrum.
 Some are Broad
spectrum.
 Some act against
viruses,bacterial
spores,or fungi.

7.  Germicide
 Fungicide
 Bactericide
 Sporicide
 viricide
 Fungistatic
 bacteriostatic
Some have killing
effect
Some have static
effect

8.  Less toxic.
 Broader antimicrobial spectrum.
 Cidal effect.
 Not only effective against vegetative cells but also
against spores.
 Stable to heat and storage
 Chemically compatible.
 Reasonable cost.
 Acceptable taste,odour and color.

9.  Available in aqueous phase at effective level
concentration.
 Should be in unionized state to penetrate
bacteria.
 Must no bind to other components of
emulsion.

10.  There are some preservative chemicals that
have antimicrobial role in food:
Nitrites
Sulphur
dioxide
Hydrogen
peroxide
Epoxides
BHA,BHT,
TBHQ

11. EDTA Parabens Acids
Diacetyle Chitosan
Lysozyme Monolaurin
Wood
smoke
Antibiotics Spices

12. Acetic acid Disrupt cell membrane function(bacteria,yeast
and some molds)
Benzoic acid Disrupt cell membrane function/inhibit
enzyme(mold,yeast& some bacteria)
nitamycin Bind sterol group in fungal cell
membrane(mold & yeast)
nicin Disrupt cell membrane function(gram positive
bacteria& lactic acid producing bacteria)
Nitrates,nitrites Disrupt cell membrane function/inhibit
enzyme(bacteria primarily chlostridium
botulinum)
Propionic acid Disrupts cell membrane function(molds and
some yeast)
Sorbic acid Disrupt cell membrane,inhibit enzyme,disrupt
bacterial spore germination)
Suphites,sulphur
dioxide
Inhibit enzyme and form additional
compounds(bacteria,yeast and mold)

13.  Used in heat processed meat, poultry & fish
To control growth & toxin production by c.botulinum.
 Used in some cheeses
 to prevent gas production by c.butyricum &
c.tyrobutyricum.
 Inhibitory to Staphylococcus aureus, Escherichia,
Pseudomonas & Enterobacter.

14. Mode of action:
• React with enzymes in vegetative cells &
germinating spores, restriction of bacterial
use of iron and interference with membrane
permeability,thereby limiting transport.
Side effect :
Nitrite can lead to formation of carcinogenic
compounds,nitrosamines.So there is trend
to reduce nitrite or to use other
preservation.

15.  Used in soft fruits, fruit juices, lemon juices, beverages,
wines, sausages, pickles, and fresh shrimp.
Antimicrobial action:
 produced by undissociated sulfurous acid that
rapidly enters cell and reacts with thiol groups in
structural proteins, enzymes, and cofactors, as
well as with other cellular components.

16. Fungicidal: at low pH. & low Aw.
Bacteriostatic; at low concentration.
Bactericidal: at higher concentration.

17. Hydrogen
peroxide:  Germicidal
 Mode of action:In
secreted fluids, the
enzyme lactoperoxidase
(LP) catalyzes the
oxidation of thiocyanate
ion (SCN-) by hydrogen
peroxide (H2O2),
producing the weak
oxidizing agent
hypothiocyanite (OSCN-),
which has bacteriostatic
activity.
• Used in
 Cheese
production
&
 Liquid egg
for
destruction of
Salmonella.

18. Epoxides
Ethylene oxide & propylene oxide
Germicidal & fumigants
Mode of action:
act as alkylating agents and react with various
groups (e.g., –SH, –NH2, and –OH) in cellular
macromolecules, particularly structural proteins and
enzymes, adversely affecting their functions

19.  Indirect antimicrobials.
 BHA inhibits growth of many Gram-positive and
Gram-negative bacteria and also effectively prevent
growth and toxin production by molds and growth of
yeasts.
 The antimicrobial action is most likely produced by
their adverse effect on the cell membrane and enzymes.

20. Chitosan
Polycationic polymer,obtained by alkaline
hydrolysis of chitin from shell of crustaceae.
Effective against
bacteria,yeast &
molds.
Mode of action:
Causes destabilization
of cell wall and cell
membrane functions.

21. Ethylenediaminetetraacetate(EDTA)
Inhibitory for germination & outgrowth of
spores of c.botulinum.
Mode of action:
EDTA may not have much antimicrobial
effect, but because of its ability to chelate
divalent cations, it can destabilize the barrier
functions of the outer membrane of Gram-
negative bacteria and, to some extent, the
cell wall of Gram-positive bacteria.

22.  Present in large quantities in some foods such as egg
white and shellfish (oysters), as well as in small
amounts in milk and some plant tissues.
 Used in wine (sake) to prevent growth of undesirable
lactic acid bacteria.
 Mode of action: It hydrolyzes the mucopeptide layer
present in the cell wall of Gram-positive bacteria and
in the middle membrane of Gram-negative bacteria

23. Monolaurin(glycerol monolaurate)
 The ester of
lauric acid and
glycerol, is one
of the most
effective
bactericidal
agents.
 Its effectiveness in
deboned meat,
chicken sausages,
minced fish, and
other foods has been
observed against
undesirable bacteria,
particularly the
anaerobes.

24. It enhances the thermal inactivation of spores
of Bacillus spp.
In combination with monolaurin, the
fungistatic activity of several antifungal
compounds is enhanced
The antimicrobial activity of monolaurin
is produced through its ability to
destabilize the functions of the membrane.

25.  Stop or kills the microbes that cause spoilage of food.
 Used to preserve cheese.
 Used in feed given to food animals.
 Mostly following are used:
 Netamysin
 Tetracycline
 Tylosin

26. Tetracycline was
approved by FDA to
extend the refrigerated
shelf life of seafood and
poultry in the 1950s.
However, because of the
possible increase in
antibiotic-resistant
bacteria, use of these
antibiotics in food was
later banned.
Natamycin, a microlid
produced by
Streptomyces
natalensis, is an
antifungal agent. Its use
as a dip or spray to
prevent growth of molds
and formation of
mycotoxins on the
surface of some cheeses,
sausages, and in raw
peanuts.

27. Tylosin, a microlid that inhibits protein
synthesis, is a bactericidal antibiotic that
is more effective against Gram-positive
than Gram-negative bacteria and also
inhibits outgrowth of germinated
endospores.

28.  Contain chemicals that
deposited on food:
 formaldehyde
Phenols
Cresols
 Smoking can be
bactericidal,
bacteriostatic,
antifungal.Depending on
temperature,time, degree
of surface drying, &
concentration.

29.  It include cinnamic aldehyde in
cinnamon; eugenol (2-
methoxy-4-allyl phenol) in
cloves, and paramene and
thymol in oregano and thyme.
Their bacteriostatic and
fungistatic properties depend on
the active agent.
 Mode of action:Forms a layer
over a food product & hence it
forms a layer between air &
microbe and restrict them.

30. Benzoic acids
• Used in acidified food
• inhibit function of enzymes and membrane
protein ,destroy membrane potential.
Propionic acid
• Used in bread,bakery products etc..
• causes acidification of cytoplasm,
destabilization of membrane protein
Sorbic acid
• Effective against molds and yeasts.
• Interferes with synthesis of cell
wall,protien,RNA,DNA.Inhibit spore
germination.

31.  Broad spectrum
 Used in alcohlic beverages,jams, pickles, salad
dressing,mustards etc.
 Mode of action:
 inhibit function of enzymes.
 Interfere with transport of nutrients by binding with
lipids.
 Interfere with synthesis of proteins,RNA, DNA.
 Destroy membrane potential.

32.  Broad spectrum.
 Mostly used in dairy products.
 The antibacterial action is probably produced by
deactivating some important enzymes. The
dicarbonyl group (–CO–CO–) reacts with arginine in
the enzymes and modifies their catalytic sites.

34.  A number of chemical compounds are being used in
food preservation that kill or retard the
microbes.So,the food spoilage reduces due to the
presence of these compounds.The concentration of
these chemicals varies in different food
products.These chemicals are approved by regulatory
agencies.These chemicals must be harmless.