The leftovers from production of tomato juice, sauce and paste include seeds, skin and pulp – about 750,000 metric tons yearly. Since humans don’t eat tomato pomace, where does it go? That’s right – the pet food market, like beet pulp, grape pomace and other by-products of processing for human food.
Dried tomato pomace has a nutritional profile of about 20% protein, 13-15% fat, 3-5% fat, and 25-57% crude fiber. The fiber includes 4% soluble fibers- the stuff that primarily supports probiotic populations in the gut. The other fiber can also be fermented by bacteria as well, and as with many foods, there is a concern that a high fiber content can lead to flatulence. As it turns out, testing shows that tomato pomace produces less gas on fermentation than most other fiber sources.
Tomato pomace contains approximately 50% linoleic acid, followed by oleic (20%) and palmitic (15%) acids. Other FAs present in lower concentrations are myristic, stearic, arachidic, linolenic, behenic, erucic, and lignoceric acids. Because of this high fat content, tomato pomace usually has a preservative added by the manufacturer (which, you will recall, means that this preservative is not listed in the final ingredient list on a pet food bag). The pomace is included in pet foods at about 3-7% of the total mix.
Other nutrients contained in tomato pomace include lycopene, Vitamin E and other tocopherols and phytosterols, giving it antioxidant potential. The nutrient composition might be expected to differ between lots of this product however, depending on the types of tomatoes used and how they are raised. One study found differences in the contents of minerals like cesium, iron, potassion, molybdenum, and sodium between tomato seeds from conventional or organic systems.
Some people have voiced concern about the connection of nightshade products to arthritis and other problems. Vegetables in the nightshade family – potato, tomato, eggplants and peppers – contain much lower levels of the offending alkaloids than do the poisonous plants in this family. They do contain traces of alkaloids such as solanine, chaconine, nicotine, and tomatine, but the connection with arthritis remains unclear if it exists. On the other hand, some of these alkaloids seem to prevent cancer, at least in test tubes.
My conclusion remains the same – feed your pets a variety of different brands and flavors, and if some of them contain tomato pomace, that’s ok.
Aldrich G. Functional Fiber with Color. Pet Food Industry, April 2009, p. 42-43
Cámara, M., Del Valle, M., Torija, M.E. and Castilho, C. 2001. Fatty acid composition of tomato pomace. Acta Hort. (ISHS) 542:175-180
A. A. Ferrari, E. A. De Nadai Fernandes, F. S. Tagliaferro, M. A. Bacchi and T. C. G. Martins. Chemical composition of tomato seeds affected by conventional and organic production systems. Journal of Radioanalytical and Nuclear Chemistry. Volume 278, Number 2 / November, 2008.