Transcript Control Of Microorganisms In Foods

Introduction
The objective of controlling microorganisms in foods
is to minimize their numbers or completely eliminate
them from food. Several methods are used to achieve
this objective by:
* controlling access of the microorganisms in foods.
* Physically removing the microorganisms present
in foods
* Preventing or reducing the growth of
microorganisms and germination of spores present In
foods
* Killing microbial cells and spores present in foods
Irrespective of the methods used, It is important to
recognize that a control method is more effective
when a food has fewer microbial cells and when
the cells are in the exponential growth phase and
are injured.
Spores are more resistant than vegetative cells,
and Gram-negative cells are generally more
susceptible than Gram-positive cells to many
control methods.
Bacteria, yeasts, molds, and viruses differ in
sensitivity to the methods used to control them.
Control Methods
* Control of Access
* Control by physical removal
* Control by heat
* Control by low temperature
* Control by reduced Aw
* Control by low pH and organic acids
* Control by reducing Oxidation- reduction
potential
* Control by antimicrobial preservatives
* Control by irradiation
Control By Antimicrobial Preservatives
Many chemical compounds, either present naturally,
formed during processing, or legally added as
ingredients, can kill microorganisms or control their
growth in foods.
They are, as a group designated as antimicrobial
inhibitors or preservatives.
Some of the naturally occurring preservatives can be
present in sufficient amounts in foods to produce
antimicrobial action, such as lysozyme in egg white and
organic acids in citrus fruits.
Similarly, some of the antimicrobials can be formed in
enough quantities during food processing to control
undesirable microbial growth, such as lactic acid in
yogurt fermentation.
Others can be naturally present or formed in small
quantities and do not produce antimicrobial action
in foods, e.g., lysozyme in milk and diacetyl in some
fermented dairy products.
Some additives such as sodium nitrite(NaNO2) is
used in cured meat to control spore germination
Especially of C. botulinum, whereas others are
added to improve the functional properties of a
food such as butylhydroxyanisol(BHA), it has both
antioxidant and antimicrobial properties.
Some preservatives had been used since long
time, e.g., salting of fish and meat, burning sulfur
to generate SO2 to sanitize the environment and
equipment used for baking and brewing; smoking
fish and meats, and adding spices, herbs, acids
and alcohol to foods.
Different preservatives and additives may have
harmful effect on human health.
Many health authorities are interested in foods
that do not contain any preservatives, especially
those not normally found in foods.
These authorities are looking for preservatives
that are either naturally present in the food of
plant and animal origin or produced by safe foodgrade microorganisms used to produce
fermented foods. They are designated as
biopreservatives. Examples are lactic, acetic, and
propionic acids.
Antimicrobial chemicals differ in their ability to
act against different microorganisms:
Broad spectrum: effective against many
microorganisms.
Narrow spectrum: effective against molds and
yeasts or only bacteria(Gram-positive or Gramnegative).
Germicides: Kill all types. Fungistatic: inhibit or
Fungicides: kill fungi.
Retard fungal growth
Bactericides: Kill bacteria. Bacteriostatic: inhibit
Sporicides: Kill spores.
Or retard bacterial
Viricides: Kill viruses.
Growth.
Influencing Factors
Several factors need to be considered in evaluating
the suitability of an antimicrobial agent as a food
preservative:
A compound that kills(-cidal) in stead of
controlling growth(-static) is preferred.
A compound with a broader antimicrobial
spectrum is more suitable for application in foods
as compared with one that has a narrow spectrum.
A compound effective against vegetative cells and
spores is preferred.
A compound that not allows development of
resistant strains is preferred.
Most compounds do not meet all these
requirements.
More than one compound is used frequently to
increase the inhibitory spectrum.
In addition to antimicrobial activity, a compound
should not affect the normal quality of
food(texture, flavor or color). It should not interact
with food constituents and becomes inactive.
It should have a high antimicrobial activity at the
pH,Aw, EH, and storage temperature of a food.
It should be economical and readily available.
The Regulatory Requirements
The regulatory requirements include the
expected effectiveness of an antimicrobial agent
In a food system.
It should be effective in small concentrations.
It should not hide any fault of a food(e.g.,
conceal poor quality and spoilage).
It should be safe for human consumption.
It should be listed in the label, indicating its
purpose in the food.
Some Antimicrobial Chemical
Preservatives Used In Foods
*Acetaldehyde
*Acetic acid
*Ascorbic acid
*Bacteriocins
*Benzoic acid
*Betapropiolactum
*Butylhydroxyanisol
*Boric acid
*Caprylic acid
*Chitosan
*Citric acid
*CO2
*Dehydroacetate
*Diacetate
*Diacetyl
*Diethyl dicarbonate
*Diphenyl
*Ethyl alcohol
*Ethyl formate
*EDTA
*Ethylene oxide
*H2O2
*Lactic acid
*Lauric acid
*Lysozyme
*Malic acid
*Methyl bromide
*Monolaurin
*Natamycin
*Nitrite and nitrate
*Parabens
*Peracetate
*Polyphosphates
*Propionic acid
*Propylene glycol
*Propylene oxide
*Propyl gallate
*Smoke
*Sodium chloride
*Sorbic acid
*spices
*Succinic acid
*Sucrose
*Sulfites and SO2
*Tetracyclines
*Thiabendazole
*Tylosin
Nitrite (NaNO2 and KNO2)
Curing agents that contain nitrite, and together wit
NaCl, sugar, spices, ascorbate, and erythorbate, are
permitted for use in heat-processed meat, poultry,
and fish products to control growth and toxin
production by C.botulinum. Nitrate and nitrite are
also used in some cheeses to prevent gas blowing by
C. butyricum and C. tyrobutyricum.
Nitrite react with some enzymes in vegetative cells
and germinating spores, restriction of the bacterial
use of iron, and interference with membrane
permeability thus inhibits bacterial growth.
Nitrite is inhibitory to some extent, to S. aureus,
E. coli, Pseudomonas and Enterobacter spp. A t 200
ppm. Lactobacillus and Salmonella serovars seem to
be resistant to this concentration of NO2.
The antibacterial effect of NO2 is enhanced at low pH,
in the presence of reducing agents e.g.,ascorbate,
erythorbate, and cysteine and with sorbate.
In cured meat , NO2 reacts with myoglobin to form a
stable pink color of nitrosyl hemochrome during
heating. In bacon, nitrite can lead to the formation of
carcinogenic compounds,nitrosoamines. There is a
trend to use other preservatives instead of nitrites.