For ketchup I would like to talk about the acidity, the sugar content, and the science behind it's pseudoplastic viscosity.
This article talks about the rheological attributes of ketchup [1]
This article talks about the viscosity of ketchup [2]
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Composition
editHeinz tomato ketchup’s ingredients are: tomato concentrate from red ripe tomatoes, distilled vinegar, high fructose corn syrup, corn syrup, salt, spice, onion powder, and natural flavoring[3]. Tomato concentrate from red ripe tomatoes is the first ingredient on the list, which means it has the highest percentage of weight within the final product. Tomatoes have a complex composition of sugars, starch, pectin, ascorbic acids, organic acids, amino acids, steroids, carotenoids, lipids, free fatty acids, and volatiles.[4] The second ingredient listed is distilled vinegar, which is comprised of eighty percent pure water and twenty percent acetic acid.[5] Next is high fructose corn syrup, which is made up of 42% fructose, 53% glucose, and 5% other polysaccharides and sugars.[6] Corn syrup is 100% glucose[6]. Salt is the next ingredient listed and is composed of sodium and chloride ions. Spice, onion powder, and natural flavoring are the last ingredients on the list, meaning that they have the least percent weight. These three ingredients contribute to overall flavor of the product.
Separation
editKetchup is one of the many products that is leachable; meaning that the water within the product migrates together as the larger molecules within the product sediment, ultimately causing water to separate out. This forms a layer of water on top of the ketchup due to the molecular instability within the product.[5] This instability is caused by interactions between hydrophobic molecules and charged molecules within the ketchup suspension.
Pectin is a polysaccharide within tomatoes that has the ability to bind to itself and to other molecules, especially water, around it. This enables it to create a gel-like matrix, dependent on the amount within the solution. Water is a large part of ketchup, due to it being 80% of the composition of distilled vinegar. In order for the water within the ketchup to be at the lowest possible energy state, all of the hydrogen bonds that are able to be made within the matrix must be made.[7] The water bound to the polysaccharide moves more slowly within the matrix, which is unfavorable with respect to entropy.[5] The increased order within the polysaccharide-water complex gives rise to a high-energy state, in which the water will want to be relieved. This concept implies that water will more favorably bind with itself because of the increased disorder between water molecules. This is partially the cause for water leaching out of solution when left undisturbed for a short period of time.
Other interactions that induce leaching are electrostatic and ionic interactions. Electrostatic interactions occur between charged molecules, which have repulsive or attractive forces between each other. The pectin within ketchup will have negative and neutral charges along the molecule due to the hydroxyl groups and relative pH, which is 3.9 on average.[8] Pectin is most stable at a pH of 3.5, so the more basic pH within ketchup will protonate the hydroxyl side chains and therefore create a less viscous gel. Acetic acid within vinegar also has hydroxyl groups that will have a dispersed amount of negative and neutral charges along each molecule. The acetic acid and pectin will display repulsive interactions between the negatively charged oxygens on each molecule. The hydroxyls on each molecule will be able to form hydrogen bonds with the water in the product. The addition of salt will reduce the repulsive interactions between the negatively charged side chains of acetic acid and pectin within solution because they will create bonds with the dissociated sodium and chloride ions.[9] The hydrogen bonds and electrostatic interactions will encourage leaching because the formation of bonds associated with the need for molecules to be in the lowest energy state are not always bonds that happen between different molecules and instead are formed between like molecules, causing aggregation.
A way for ketchup manufacturing companies to avoid leaching of their products would be to add a hydrocolloid. Xanthan gum is able to stabilize ketchup by covalently binding to water. This strong bond keeps water from separating out of the ketchup and creating a layer at the surface.[5]
- ^ "The rheological properties of ketchup as a function of different hydrocollo...: Articles+". eds.b.ebscohost.com. Retrieved 2016-10-12.
- ^ Coussot, P.; Gaulard, F. "Gravity flow instability of viscoplastic materials: The ketchup drip". Physical Review E. 72 (3). doi:10.1103/physreve.72.031409.
- ^ "Ketchup – Tomato Ketchup | Heinz Ketchup". www.heinzketchup.com. Retrieved 2016-12-15.
- ^ Salunkhe, D.K., Jadhav, S.J., Yu M. H. Quality and Nutritional Composition of Tomato Fruit as Influenced by Certain Biochemical and Physiological Changes. Logan, Edmonton, & Washington. 1974.
- ^ a b c d Vilgis, T. 1893. Nineteen: Ketchup as Tasty Soft Matter. The Kitchen as Laboratory: Reflections on the Science of Food and Cooking. New York: Columbia University Press. 142-145
- ^ a b White, J. S., Straight talk about high-fructose corn syrup: what it is and what it ain’t. The American Journal of Clinical Nutrition. 2008.
- ^ Journel, A.G., Deutsch, C. V., Entropy and spatial disorder. Mathematical Geology. Volume 23, Is. 3. April 1993. 329-355.
- ^ Porretta, S., Analytical Profiling of Ketchup. Journal of the Science of Food and Agriculture. Volume 57. 2006. 293-301.
- ^ Schwarz, U. Theory of soft biomatter. June 2009. 19-65