An antioxidant donating an electron to a free radical and
thus stabilizing it.
Fat oxidation can lead to petfoods with objectionable odors
and flavors. That is, it leads to rancidity - production of
compounds such as hydrocarbons, aldehydes, ketones, alcohols
and organic acids. Antioxidants prevent fat oxidation and so
help avoid petfood rancidity.
A free radical is a molecule with a missing electron. When a
fat molecule loses an electron, it becomes a fat free radical.
An antioxidant donates one of its electrons to such a free
radical. This stops a free-radical chain reaction that can lead
to objectionable odors and flavors.
Selecting the appropriate antioxidant and dosage level can
be a complex decision that involves evaluating several
parameters, such as:
Natural vs. synthetic
Antioxidants are generally categorized into two classes:
primary and secondary. Primary antioxidants are capable of
interrupting and terminating the free radical propagation step.
The most common
primary antioxidants are butylated hydroxyanisole (BHA),
butylated hydroxytoluene (BHT), tert-butyl hydroquinone (TBHQ),
propyl gallate and ethoxyquin.
The most common
primary antioxidants are mixed-tocopherols and rosemary
extract. Mixed-tocopherols are composed of four homologs:
alpha-tocopherol (vitamin E), beta-tocopherol, gamma-tocopherol
and delta-tocopherol. It is well recognized that the order of
antioxidant activity is delta > gamma > beta > alpha.
In addition, delta-tocopherol also has superior process
stability and carry-through to gamma-tocopherol. In biological
), the alpha-tocopherol is most active.
Tocopherols have no legal limit, but can act as pro-oxidants
if added at excessive levels. Tocopherols are expensive
compared to synthetic antioxidants, and more importantly, they
have less antioxidant activity compared to synthetics. Petfoods
stabilized with tocopherols, as with all natural antioxidants,
have a reduced shelf life compared to those stabilized with
synthetic antioxidants. Other natural anioxidants are vitamin
C, carotenoids, flavenoids, sulfides and thiocyanates.
Secondary antioxidants are chemicals that can prevent free
radical formation. The main secondary antioxidants are metal
chelators (citrates and phosphates) and reducing agents
(ascorbates and sulfites).
Pros and cons
Vitamin C is one of several natural antioxidants
Following are commonly used antioxidants, along with some of
their pros and cons.
More effective than BHT, more heat stable than BHT and good oil
solubility. Solubility in propylene glycol allows it to be
mixed with high levels of propyl gallate and citric acid for
oils that are more unsaturated.
It is synthetic and it's susceptible to losses due to steam
Economical, good synergy with BHA and good oil solubility.
It is synthetic and less effective than BHA. It's susceptible
to losses due to steam distillation.
It is very effective in highly unsaturated fats such as fish
and vegetable oils and it has excellent process carry-through.
It is synthetic and lacks broad global regulatory approval.
Can't be used in combination with propyl gallate.
Good alternative in highly unsaturated fats where TBHQ is not a
desired or legal option. Good synergy with BHA and citric acid.
It is synthetic and can form colored complexes with copper and
iron ions. Poor process carry-through and poor oil
Very effective antioxidant. Regulations allow higher dosage
rates than other synthetics.
It is synthetic and has a negative consumer perception. In
1997, the FDA requested a voluntary reduction of ethoxyquin in
dog food from 150 ppm to 75 ppm. Usage has steadily decreased
since the mid-1990s, to the point it's scarcely used.
It is natural with good consumer acceptance. High heat
stability, good process carry-through, low volatility and
excellent solubility in fats.
Increased diet formulation costs and increased application rate
necessary. May require increased time to develop and maintain a
unique supply chain.
It is natural with good consumer appeal. Effective in
stabilizing unsaturated oils, such as fish and vegetable oils.
Poor carry-through in extrusion processing, only regulatory
approval is as a flavor or spice and there is a high level of
variability amongst suppliers. Increased diet formulation costs
and increased application rate necessary. May require increased
time to develop and maintain a unique supply chain.
Oxidation is irreversible
Increased usage of omega fatty acids has resulted in
products more difficult to stabilize. Another challenge is a
growing demand for natural products.
Oxidation is an irreversible process, so antioxidants should
be added as early in the process as possible. Development of a
quality supply chain and proper analytical testing procedures
can assist in ensuring that oxidation does not impact product
quality or performance.
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