A natural additive obtained from the bark of certain varieties of acacia tree. Gum arabic is colorless, tasteless and odorless and is used in commercial food processing to thicken, emulsify and stabilize foods such as candy, ice cream and sweet syrups. Genetically modified (GM) foods are foods derived from genetically modified organisms. The DNA of genetically modified organisms has been modified through genetic engineering, unlike similar food organisms developed through the conventional genetic modification of selective breeding (plant breeding and animal breeding) or mutation breeding. GM foods were first put on the market in the early 1990s. Typically, genetically modified foods are transgenic plant products: soybean, corn, canola, and cotton seed oil, but animal products have been developed. For example, in 2006 a pig engineered to produce omega-3 fatty acids through the expression of a roundworm gene was controversially produced. Researchers have also developed a genetically-modified breed of pigs that are able to absorb plant phosphorus more efficiently, and as a consequence the phosphorus content of their manure is reduced by as much as 60%.  Critics have objected to GM foods on several grounds, including perceived safety issues, ecological concerns, and economic concerns raised by the fact that these organisms are subject to intellectual property law.