4 to 5 percent. According to Douding.com, milk contains about 4 to 5 percent lactofructose, which is produced by the hydrolysis of lactose, with 4 to 5 grams of lactofructose per 100 milliliters of milk. Lactofructose is a naturally occurring sugar in dairy products that is produced by the breakdown of lactose by the enzyme lactase. The amount of lactofructose has an effect on the sweetness and taste of milk. Lactofructose not only provides energy for the body, but also helps to increase the growth of probiotics in the intestines, which is beneficial to the digestive and immune systems.