Biogenic amines play important roles in many human and
animal physiological functions such as regulation of body
temperature, stomach volume, stomach pH and brain activity (ten
Brink, 1990). Amines are low-molecular-weight organic bases
which can be formed and degraded during the normal metabolism
of animals, plants and microorganisms. They are essential for
cell growth, and it has been suggested that these molecules
promote the synthesis of DNA, RNA and protein, stabilization of
ribosomes and increased amino acid uptake by cells (Smith,
1990).
Biogenic amines are produced by degradation of the
corresponding free amino acid (see Table 1) precursor in foods.
This reaction is catalyzed by bacterial amino acid
decarboxylases. Prerequisites for a considerable amount of
biogenic amine formation are:
The availability of free amino acids;
The presence of decarboxylase-positive microorganisms;
and
Conditions that allow bacterial growth.
Determination of the exact threshold where these biogenic
amines become toxic is extremely difficult because it is
dependent on the detoxification efficiency of the individual.
Upper limits of 100 mg histamine/kg in foods; 2 mg
histamine/liter in beverages; and 100-800 mg/kg tyramine and 30
mg/kg phenylethylamine in foods have been suggested. Presently,
fishmeal is the only petfood ingredient that typically has a
biogenic amine limit specification, and this is for histamine
only.
The most well-known health impact of biogenic amines is
histamine poisoning, which occurs a few minutes to several
hours following the ingestion of foods containing high levels
of histamine. Primary symptoms in humans are skin rash, nausea,
vomiting, diarrhea, etc. The toxicity of histamine is
potentiated by other biogenic amines (agmatine, putrescine,
cadaverine, anserine, spermine and spermidine).
Humans may consume an occasional meal where biogenic amines
are elevated either due to poor handling or contamination with
a decarboxylating bacteria. Pets are more likely to encounter
biogenic amines in a prepared diet where the main protein
source is fish, chicken or a meat by-product. Healthy adult
cats and dogs may be able to detoxify biogenic amines present
in the diet; however, kittens and puppies, reproducing females
and ill animals could potentially be more prone to adverse
effects when consuming biogenic amines on a daily basis.
Histamine itself, along with other vasoactive biogenic
amines, is frequently present in petfoods, particularly those
foods containing fish products. Though the levels of these
substances in petfoods are not believed to be high enough to
induce a non-allergic reaction, feeding a petfood containing
these chemicals may predispose some dogs to developing allergic
food reactions by lowering the dog's tolerance threshold to
certain food allergens (Davol, 2001).
In studies involving companion animals, dogs did not show
adverse effects following oral administration of histamine
alone at doses of 20 mg/kg; however, the combination of
histamine with spoiled tuna did elicit emesis even at histamine
doses of 1-10 mg/kg. This shows that the presence of other
biogenic amines can inhibit intestinal histamine breakdown
(Taylor, 1986).
The presence of biogenic amines in petfood indicates that an
ingredient has undergone bacterial spoilage. The method of
handling of animal by-products prior to chilling, freezing,
extrusion, retorting or rendering may put these materials at
risk of biogenic amine formation. Proteolytic enzymes in these
materials from either viscera or bacteria can generate free
amino acids available for subsequent decarboxylation. Bacterial
contamination can occur in the conveyors, trucks, tanks and
other equipment that the by-products contact. Conditions are
thus ideal for biogenic amine formation to take place until the
ingredient makes its way into a high-temperature petfood
extrusion or retort process where the enzymatic process is
terminated.
Studies have demonstrated that biogenic amines can
accumulate to reach toxic levels even at low temperatures. This
is due to initial storage at higher temperatures (10-25ºC)
where the decarboxylase is generated and then continues to
produce biogenic amines when the temperature is reduced to 5ºC
or below (ten Brink, 1990; Klausen and Huss, 1987). Chicken,
meat or fish by-products that have experienced even a short
period of high-temperature abuse prior to chilling could
therefore generate significant biogenic amine levels before
processing. Biogenic amines are heat stable, and decarboxylases
may remain active even after pasteurization. Therefore, once
formed, the amount of amine formed will not be reduced during
processing and may even increase during storage (ten Brink,
1990).
Biogenic amine levels can be directly correlated with
bacterial counts and food freshness. Documenting
time/temperature profiles and the resulting biogenic amine
levels will establish sound quality assurance parameters for
classes of fresh and frozen ingredients such as:
Fresh chilled, collection and transit time prior to chilling
should be limited or eliminated to avoid mesophilic growth;
Frozena reduced microbial count due to freezing will not
reflect the decarboxylase and amines that may have developed in
abused material;
Hygieneorgan meats are sterile when harvested, and therefore
good hygiene of transfer and processing equipment will reduce
microbial growth; and
Freshness agents, when time, temperature and hygiene are not
ideal, classic food additives may be necessary in order to
retain freshness.
It has been proposed that the sum of histamine, tyramine,
cadaverine and putrescine can be used as a quality indexthe
Biogenic Amine Index (BAI), which has shown a correlation to
both time of storage and sensory assessment. The amounts of
histamine, putrescine and cadaverine usually increase during
spoilage of meat, whereas the amounts of spermine and
spermidine decrease during this process.
The Biogenic Amine Index (BAI) is defined as:
BAI = (histamine + putrescine + cadaverine)
/ (1 + spermine + spermidine)
Meat with a BAI value below 1 is considered to be top
quality, whereas BAI values above 10 indicate very poor
quality. Products in which lactic acid fermentation has taken
place may contain considerable amounts of putrescine,
cadaverine, histamine and tyramine. It is important to consider
the levels of tyramine, since high content of this amine are
related to toxicological problems (Veciana-Nogues, 1997).
BAI numbers show that the proposed quality index directly
correlates with the aerobic plate counts (see Table 2). A BAI
of 2 corresponds to an APC of 104-106 cfu/gram, while an 11 is
at 107 and the high BAI of 40 shows an elevated 108 cfu/gram
APC. The BAI calculations in Table 2, although not
comprehensive, suggest that the 300 mg/kg total biogenic amine
content may be a reasonable quality guideline for petfood
ingredients.
The total biogenic amine limit being considered in fish for
human consumption is 300 mg/kg, with histamine at a current 50
mg/kg action level. Literature does not define toxic levels of
biogenic amines for companion animals, but does establish the
potentiating effect of several in combination and also
documents their potential for reduced growth and physiological
impact in production animals.
Limiting biogenic amines in petfood ingredients would reduce
any unidentified adverse impact on the pet, regardless of
lifestage or disease state. Processing and handling measures
taken to reduce bacterial degradation, and thus biogenic amine
formation, would seem consistent with the industry's dedication
toward promoting the longevity and well being of companion
animals.