Functional beverages are vitamin-enhanced waters that are popular with consumers because of convenience, perceived health benefits, and improved flavor over tap water. These beverages, enriched with vitamin C, B-complex vitamins, and vitamins A and E, are promoted as offering the benefits of increased energy from B vitamins and antioxidant value from vitamins A, C, and E. Sales of these beverages are expected to increase to 4.4 billion liters per year by 2011.1
Explore this issueJune/July 2010
Because the U.S. Food and Drug Administration (FDA) regulates how the nutritional content is listed on these beverages, vitamin assay methods are needed to support product labeling.2 Determination of vitamins in foods is inherently difficult, and deviation of the determined amounts from the labeled values has been observed.3 Analysis of these waters is challenging due to the presence of both water- and fat-soluble vitamins. Proprietary formulations of vitamins that remain soluble and shelf-stable are used to enrich these beverages. Additionally, gums, preservatives, and other additives are used to emulsify and stabilize the drink.
Traditional determinations require that multiple methods be used to quantify the various vitamins added to the beverage. Water-soluble vitamins are often determined with reversed phase-high performance liquid chromatography (HPLC) using an aqueous mobile phase, while the fat-soluble vitamins use organic solvent mobile phases in both reversed- and normal-phase HPLC methods.4 Simultaneous determination of both types of vitamins poses a challenge due to the difference in solubility limits of the two classes of vitamins and the many different biologically equivalent compounds that can be added but are listed as a single vitamin. For example, niacin is available as nicotinic acid and nicotinamide, both of which are biologically active and referred to as niacin in product labeling.
The simultaneous determination of a wide range of vitamins increases the complexity of an analytical method. Their structures range from small unconjugated organic acids that are minimally ultraviolet (UV) active, such as pantothenic acid (vitamin B5), to large complexes that absorb at different wavelengths, such as cyanocobalamine (vitamin B12). Due to the chemical diversity of vitamins, multiple detection wavelengths are needed to optimize the method sensitivity.
Described below is a single method with simple sample preparation that can determine many common vitamins added to functional waters.5 By using a silica-based polar-embedded column compatible with 100% aqueous mobile phases over a wide pH range (1.5-10), a single gradient method can be used to quantify both water- and fat-soluble vitamins with stable retention times, excellent peak shapes, and high efficiencies for basic and acidic compounds.