Thursday, May 14, 2009

Factoid: Tomato pomace

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.


  1. It has all those fatty acids and tocopherols if you're a cow or a bird and can digest the seed coats and the seeds inside. Dogs don't get any of it. I'm not even sure any available lycopene is left in commercial pomace which is mostly skins and seeds, once the juice and meat are removed to make paste and marketable juice. As far as dogs are concerned the pomace is almost wholly vegetable fiber, which they only need in very small quantity.

  2. The seeds are crushed so the fatty acids are bioavailable. Yes, there are flavonoids including lycopene in tomato pomace. I don't know what you mean by "very small quantity" but dogs do benefit from the right level and types of fiber in the diet, and this is a pretty good source of mixed fibers.

    Please sign your posts!

  3. I am a Fire Investigator and have had several fires involving spontaneous combustion in tomato pomace.The tomato pomace was stored outside in a covered commodity barn but open at both ends which would allow rain and moisture in. What chemical composition in the tomato pomace makes it suseptial to spontaneous heating? Marvin G. Casey

  4. Great question. I got an answer from a food company via people I think are their food scientists. They think it has to do with ingredients being not completely dry. When there is enough moisture for bacteria to proliferate and begin fermenting the sugars in the product, heat accumulates and the sugars can ignite. They say that this has been seen commmonly with soybean meal and corn meal as well. They recommend that the pomace not be allowed to get wet, and to store it only after
    it has been dried to at least to 10% moisture or less.

  5. And another scientist pointed out that tomato pomace also contains sufficient unsaturated fatty acids that they oxidize (become rancid) and can also spontaneously combust.

    He suggested that in addition to making sure the pomace is dry when stored, the stack should be turned regularly to cool or isolate hot-spots. If the seeds are well crushed, an antioxidant added to the product might also slow that oxidation.

  6. Does anyone buy into, Tomato pomace being laden with pesticides, and this combustible stuff ? Iget that organic grown is a iffy topic, but can we have some actual names dropped her so the average layman can make a decision as to WHO is saying these things, and what studies were done ?


  7. I'm sure there are pesticides in tomato pomace since we know they're used on the tomatoes and absorbed into the skin. I'd prefer not toTOTW feed pesticides to my pets but it's probably only a small amount since the pomace itself constitutes a small portion of the food. Unless you're storing large quantites of pomace, I don't think combustion is a concern but we are trusting the producers of our chosen pet foods to utilize products that are stored properly or that random testing will catch any bacterial or fungal blooms. ~Michelle