Short answer: Tomato pomace is the residual skins, seeds, and pulp left after tomato (Solanum lycopersicum) juice and paste production — a high-volume agricultural by-product that the global tomato processing industry generates at approximately 3–7 percent of fresh fruit input weight per Knoblich 2005 (J Sci Food Agric) tomato pomace composition review. Per AAFCO 2024 Official Publication, tomato pomace is an accepted pet food ingredient defined as "the dried mixture of skin, pulp, and crushed seeds of the tomato fruit." It is used in commercial pet food at modest inclusion (typically 1–5 percent) as a soluble fiber source plus modest contributions of lycopene (5–50 mg per 100g pomace dry matter), pectin, vitamin C, vitamin K1, and modest minerals. The principal canine safety concern that occasionally surfaces in consumer-facing content — solanine glycoalkaloid toxicity — refers to compounds concentrated in green (unripe) fruit, stems, and leaves, not in ripe-fruit pomace from juice production per ASPCA Animal Poison Control. Standard tomato pomace from ripe-fruit processing contains negligible solanine and is safely fed at typical pet food inclusion. The KibbleIQ rubric treats tomato pomace as a neutral fiber-source by-product: meaningful soluble pectin and lycopene contribution but modest absolute density at typical inclusion, and the by-product framing (residual processing fraction) is not penalized as a quality marker since the source is identified.

Source crop and pomace processing

Per USDA FoodData Central and Knoblich 2005 (J Sci Food Agric) tomato pomace composition review, Solanum lycopersicum is a herbaceous perennial plant in the Solanaceae family (which also includes potato, eggplant, pepper, and tobacco), native to western South America and now the world’s second-largest vegetable crop by production volume after potatoes. Modern commercial production is dominated by paste and juice processing for sauces, ketchup, and tomato-product manufacturing; fresh-market tomatoes are a separate cultivar segment.

Tomato pomace is generated as the residual skins, seeds, and pulp after juice extraction at processing facilities. Per Knoblich 2005, pomace constitutes approximately 3–7 percent of fresh fruit input weight, with the global tomato processing industry generating millions of tons annually. Pomace composition varies by extraction process: cold-break processing retains more pectin in pomace; hot-break processing transfers more pectin to juice. Pet food uses the dried pomace, typically dehydrated to ~10 percent moisture for storage stability. Per AAFCO 2024 Official Publication, tomato pomace is an accepted pet food ingredient under the broader vegetable-by-product category. The fiber-source by-product peer cluster overlaps with our beet pulp explainer and cellulose explainer.

Lycopene chemistry and antioxidant function

Per Knoblich 2005 (J Sci Food Agric) and Story 2010 (Annu Rev Food Sci Technol) lycopene review, tomato pomace contains 5–50 mg lycopene per 100g pomace dry matter, with substantial variation depending on cultivar, ripeness, and processing conditions. Lycopene is the dominant carotenoid responsible for the characteristic red color of ripe tomato; the molecule is an acyclic isomer of beta-carotene with 11 conjugated double bonds, conferring substantial in vitro antioxidant capacity. Unlike beta-carotene, lycopene does not have provitamin A activity — the cyclic ring structure required for retinol biosynthesis is absent.

Lycopene bioavailability is enhanced by heat processing, oil co-consumption, and lipid solvent matrix; tomato pomace as a dry kibble inclusion ingredient delivers lycopene in a thermally-processed and cell-wall-disrupted form supporting modest absorption. Companion-animal lycopene research is limited; the human evidence base for prostate cancer and cardiovascular disease prevention is mixed per Cochrane 2019 review (Ilic 2019). The peer carotenoid antioxidant framework overlaps with our beta-carotene explainer, lutein explainer, and zeaxanthin explainer.

Soluble pectin fiber and minerals

Per Knoblich 2005 (J Sci Food Agric) tomato pomace composition review, dried tomato pomace (100g dry matter) supplies approximately 350 kcal, 18–20g protein, 5–10g fat, 30–50g carbohydrate (~25–40g total dietary fiber), and substantial pectin content (~10–20g per 100g dry matter). The protein content from seed fraction is unexpectedly high relative to fresh tomato, with reasonable amino acid balance. The seed oil contributes modest polyunsaturated fatty acids including linoleic acid.

The dietary fiber is approximately 30–40 percent soluble (predominantly pectin from skin and pulp, supporting colonic short-chain fatty acid production per Holscher 2017 Adv Nutr) and 60–70 percent insoluble (predominantly cellulose and lignin from skin and seed coat, supporting fecal bulk and gut motility). Mineral content is modest with notable contribution of potassium (~2g per 100g), magnesium (~150 mg), iron (~10 mg), and zinc (~3 mg). Vitamin C and B-vitamin contributions are modest. The fiber framework overlaps with our pumpkin explainer, apples explainer, and best high-fiber dog food guide.

Solanine and the green-fruit caution context

Per ASPCA Animal Poison Control and Friedman 2006 (J Agric Food Chem) tomato glycoalkaloid review, the Solanaceae family (including tomato, potato, eggplant, and pepper) contains glycoalkaloid compounds — alpha-tomatine in tomato, alpha-solanine and alpha-chaconine in potato — that are concentrated in the green (unripe) fruit, stems, leaves, and sprouts as part of the plant’s defense against herbivory. These compounds inhibit acetylcholinesterase and disrupt cell membrane integrity; sufficient acute exposure in dogs can produce gastrointestinal signs (vomiting, diarrhea), neurological signs (lethargy, ataxia), and rarely severe systemic toxicity.

The critical disambiguation is that glycoalkaloid concentrations decline dramatically as fruit ripens: green tomato contains 9–25 mg alpha-tomatine per 100g; ripe red tomato contains less than 0.5 mg per 100g per Friedman 2006. Tomato pomace from juice and paste processing uses ripe red fruit almost exclusively, with green fruit excluded by harvest selection and quality grading. Pet food tomato pomace from reputable suppliers therefore contains negligible glycoalkaloid content and is safely fed at typical pet food inclusion. The toxicology peer cluster overlaps with our garlic explainer.

How KibbleIQ scores tomato pomace

The KibbleIQ Dry Kibble Rubric treats tomato pomace as a neutral fiber-source by-product at typical pet food levels (1–5 percent of formulation). Tomato pomace in the ingredient list does not earn meaningful positive rubric credit because the lycopene, pectin, and mineral contributions at typical inclusion are modest relative to dedicated functional ingredients. Tomato pomace also does not earn meaningful negative rubric credit at typical inclusion. The "by-product" framing is not penalized since the ingredient source is identified (tomato), distinguishing it from generic "vegetable by-products" or "animal by-products" without species or source identification.

Owners with concern about Solanaceae glycoalkaloid exposure should recognize that ripe-fruit tomato pomace contains negligible glycoalkaloid content per Friedman 2006 (J Agric Food Chem) and is safely fed at typical pet food inclusion; the green-fruit-and-stem caution does not apply to pet food formulations. To check whether your dog’s food contains tomato pomace or peer fiber-source by-products, paste the ingredient list into the KibbleIQ analyzer. For peer fiber context, see our beet pulp explainer, pumpkin explainer, apples explainer, and cellulose explainer. For methodology context, see our published methodology.