According to the US Department of Agriculture, tomatoes are
the second most popular vegetable crop behind potatoes, with an
annual average per capita consumption of 71 pounds going into
juice, sauce and paste. The backstory is that 10-30% of this is
seeds, skin and pulp, with no ready market in the human food
aisle. This translates into an estimated 750,000 metric tons of
dried tomato pomace potentially available to pet and livestock
feed markets.
Given that the US ranks about fifth in the world acreage of
tomatoes grown, tomato pomace could be a readily available
ingredient for petfood. To that end, we are seeing a growing
number of petfoods for which tomato pomace appears on the
ingredients list.
Is this growing popularity a function of cost and
availability, or does tomato pomace impart some nutritional
benefit to petfood? Yes and yes.
Tomato pomace is commonly traded on an air-dry basis
(approx. 5-10% moisture) at a composition of around 20%
protein, 13-15% fat, 3-5% ash and 25-35% crude fiber. The
Association of American Feed Control Officials defines it as
"the dried mixture of tomato skins, pulp and crushed
seeds."
Tomato pomace starts with the processing of whole tomatoes
into juice, sauce or paste. The tomatoes are pressed to expel
the juice, then separated from the seeds, skins and most of the
pulp. The resulting residue contains enough moisture (approx.
60-70%) that it must be dried to keep from spoiling.
Once dried, the residue is ground or pulverized into a
powder. Besides producing a consistent particle size, the
grinding also liberates the oils found in the seeds. These
tomato seed oils are substantial (about 35% of the seed) and
predominately unsaturated (approximately 82%; Giannelos
et al
., 2005) which makes them susceptible to oxidation. So after
grinding, an antioxidant preservative is often added for
long-term storage. The final product is an orange to pink,
finely ground, almost dusty, freely flowable tomato-smelling
powder.
One of the first research papers published evaluating tomato
pomace in pet diets reported that when dogs were fed a corn and
soybean meal diet supplemented with tomato pomace,
digestibility was comparable to those diets supplemented with
beet pulp or grape pomace (Allen
et al
., 1981). A few years later, Fahey et al. (1990) reported that
the total dietary fiber (a measure of nutritionally functional
fiber) found in tomato pomace was comparable to beet pulp and
wheat bran. When tomato pomace was included in dog diets at a
similar level to other fiber sources, the digestibility,
elimination frequency and fecal volume were similar.
Considering tomato pomace only for its fiber contribution may miss a big part of the story. - Greg AldrichMore recently, Swanson
et al.
(2001) reported that tomato pomace had a total dietary fiber
content of approximately 57% and a majority of this fiber was
insoluble (53% vs. 4% soluble). Following 24 hours of bench-top
(
in vitro
) fermentation, 35% of the tomato pomace was degraded.
Short-chain fatty acid production was moderate relative to
other fiber sources and resulted in high proportions of the
beneficial short-chain fatty acid butyrate. A major concern
with fiber sources is whether they lead to flatulence. These
researchers reported that gas production during the 24-hour
period was significantly less than from most other fiber
sources.
Tomato pomace is commonly incorporated in dry formulas at
3-7% of the ingredient mix and has little to no impact on food
processing.
Considering only this fiber contribution may miss a big part
of the storythe tomato's positive connection to human health.
Tomatoes and their content of the antioxidant carotenoid
lycopene have been linked to preventing numerous human
diseases, including some forms of cancer and coronary artery
disease, via a reduction in cholesterol.
Lycopene is the pigment responsible for tomatoes' red color,
and unlike many other vegetable carotenoids, it persists
through processing. For example, the content of lycopene in
tomato pomace has been reported at 281 mg/kg (Botsoglou
et al
., 2004).
While a link between tomato/lycopene and cancer prevention
or heart-health benefits has not been demonstrated for dogs and
cats, experiments with dogs have shown that following an oral
dose, lycopene is readily absorbed and distributed throughout
body tissues (Korytoko
et al
., 2003). Inclusion of tomato pomace at 1% of the diet, along
with other antioxidant fruits and vegetables, aided cognitive
function retention in older dogs (Milgram
et al
., 2005).
Tomato pomace has also been reported to contain relatively
large concentrations of vitamin E (224 ppm) and total mixed
tocopherols (2,059 ppm), along with other phytosterols such as
campesterol, stigmasterol and B-sitosterol (King and Zeidler,
2004).
While we know a fair amount about tomato pomace, we still
lack reports evaluating it in cat diets, and studies on the
differences among supply channels are conspicuously absent.
Some critics may suggest tomatoes are unsafe due to their
membership in the nightshade family or that tomato pomace is a
bio-accumulator of pesticides and herbicides. These suggestions
have no validity. Rather, tomato pomace appears to be safe and
effective, with a demonstrated record as a functional fiber and
viable source of bioactive antioxidant vitamins and
carotenoids.
Given that the US ranks about fifth in the world acreage of tomatoes grown, tomato pomace could be a readily available ingredient for petfood.As an ingredient in the formulator's toolbox, tomato pomace
is a cost-competitive, readily available ingredient that reads
well on the label and fits nicely in a petfood formula.