by Donna O’Connor
Whey protein is a high-quality dairy protein derived from nature’s purest source—milk. It is a “complete” and rich protein containing all the essential amino acids the body requires for protein synthesis and metabolism. Whey proteins may be concentrated in protein content from 12 percent in sweet whey solids to between 34 percent and 80 percent for whey protein concentrates (WPCs) to 90 percent as whey protein isolates (WPIs). Varying protein contents provide degrees of functional performance and nutritional compatibility. As a rule of thumb, 80 percent to 90 percent whey proteins are used primarily for protein fortification in liquid and dry beverage systems. Various combinations of WPCs and WPIs blends are popular for various functionalities, desired aesthetics and costs.
Many variables and ingredient interactions when formulating with whey proteins affect their functional properties including viscosity, emulsification, gelation, film formation and hydration. They also improve mouthfeel, have rich-bodied texture and can complement the sweetness, flavor, color and appearance (opacity) of the beverage system. These attributes vary in beverages based on the whey protein type, amino acid composition, conformational structure, protein fractions and form.
Whey proteins are soluble over a wide pH range (pH 2 to 10), which is suitable for beverages. Their susceptibility to heat denaturation calls for some caution and careful design in usage. Some whey proteins are not heat-stable due to their globular conformational structure; stabilizers can correct this.
Even though heat denaturation is a concern, that very attribute can be harnessed for maximum beverage stability. The denaturization leaves intact the peptide bonds of the amino acid chains, but changes the globular protein structure. These structural changes affect the protein’s solubility and ionic charge. Whey proteins lose solubility near their isoelectric point (IEP), the exact pH in which the protein has no net charge. With no charge repelling each other, the proteins aggregate, gel, flocculate and/or precipitate out of solution. Whey proteins have an IEP of about 3.8 to 5.5, dependent on the whey fractions. Formulators should develop beverages below the pH of 3.8 for the high-acid ready-to-drink beverages (RTDs) or above pH 5.5 close to neutral pH for “creamy” RTDs.
