The United States Reference Daily Intake (RDI) lists 20 different vitamins and minerals. While not all may be added to a specific product, unless only a single nutrient is added, a blend makes sense from several standpoints. -- Quality. When a nutritional premix is manufactured, stringent quality control measures provide assurance that the product delivers the required dosage. Premix manufacturers must provide a certificate of analysis specifying the level of each nutrient. The end user can be confident that the finished product meets requirements and that none of the critical nutrients have been left out. -- Convenience. Instead of multiple ingredients for processing, inventory and scaling, a premix provides a single ingredient. Only one product comes in to test. -- Handling. The chances of error during scaling and mixing decreases significantly. A premix supplies a larger matrix to ensure even distribution of microingredients. -- Technical service. Along with ingredients, companies experienced in the handling and use of nutrients can assist with technical issues -- such as appropriate ingredient forms, interactions, label claims and shelf-life concerns. What goes in In terms of supplementation, all vitamins in commercial use are synthetically produced, says Sam Sylvetsky, director of sales for Fortitech, Inc., Schenectady, NY. "They may be naturally derived using food products as a starting material," he explains, "but even 'natural' vitamin E has gone through several reactions and purification steps. There's really no definition for the term natural." Synthetic vitamins used for supplementation are largely considered superior -- low cost, purity, less calibration and analysis required. ("Natural" vitamins isolated for supplementation are not to be confused with those occurring and consumed naturally in foods.) Minerals for premix blends are also mostly synthetic. Typically, they take the form of mono- and divalent-metal ions. Their function is controlled, mainly by chelating, which makes them soluble, so they can be readily absorbed by the human body. Different mineral compounds can be used to provide the same nutrient. The choice depends on the food system. For example, Michael Weibel, Ph.D., vice president, research and development, Watson Foods, Co., Inc., West Haven, CT, recommends that when working with a product containing high levels of unsaturated fat, elemental iron in colloidal form should be used rather than ferrous sulfate, as it will be less reactive. In addition to the vitamin and mineral supplements, other ingredients can make up a blend. Carriers. In most situations a carrier will be required. The ingredient chosen primarily depends on its compatibility to the product. The most common carriers include maltodextrin and dicalcium phosphate; for oil, soluble vitamins, vegetable oil. Other ingredients used include starch, salts and sugars -- especially sucrose. Properties, such as solubility, flavor contribution, cost and physical properties are also taken into account. Insoluble dicalcium phosphate would not be used for a beverage system. According to James Watson, executive vice president, Watson Foods, the carrier provides two main functions: Because nutrients are generally present in small quantities, the carrier will spread them throughout a larger mass and aid in uniform dispersion. Allowing the premix manufacturer to add "overages." This refers to extra amounts added during manufacturing to compensate for nutrient loss through storage, processing and product shelf life.