by Charlotte Dieroff
With interest growing in high-protein diets and on-the-go convenience, high-acid, protein-fortified, ready-to-drink (RTD) beverages are becoming more popular. Previously, this was a niche segment catering to supplemental nutrition and muscle-building drinks; but, today protein drinks are considered mainstream, with offerings targeting sports performance, satiety, muscle recovery and hydration. Clear, high-protein, high-acid beverages are also hot, as demonstrated by products such as Fonterra’s WH2OLE functional water and Gatorade’s Recover line. Protein fortification has never been so transparent; however, not all proteins are suitable for high-acid RTD applications. Traditionally, high-acid beverages have been fortified with whey proteins, but soy protein is also an option.
Traditionally, dairy proteins have dominated the high-acid RTD market with whey products being the best performers. Whey-protein concentrates (WPC) and whey-protein isolates (WPI) are soluble at low pH and are heat stable. Whey proteins are thus well suited for typical high-acid (pH 3 to 3.5), hot-fill processes. Furthermore, the clarity of whey protein increases as pH decreases, enabling the formulation of clear protein fortified beverages.
Not only is whey well suited for an acidic matrix, but it also offers premium nutrition. Whey proteins can have high protein levels with typical WPC at 30 percent to 80 percent protein and WPI at around 90 percent. Whey protein is a complete protein, containing all the essential amino acids the body needs for protein manufacture and metabolism. Important for building lean muscle mass, whey offers the highest level of branched-chain amino acids (BCAAs) (leucine, isoleucine and valine) of any food protein. BCAAs have the advantage of not needing to be metabolized by the liver first, and can thus quickly supply energy to muscles during exercise.
However, nutrition alone is not enough. RTD beverages need to be great tasting and shelf stable, which requires careful formulation. Whey-based RTD protein drinks can be difficult to formulate, but there are tricks to the trade. First off, adequate protein hydration directly relates to whey’s heat stability. Whey protein must be completely hydrated prior to acidification steps to ensure the protein is completely solubilized. If not, the proteins will aggregate during the beverage’s heat-processing step and produce an unstable beverage. Secondly, when acidifying the beverage, it’s necessary to quickly move through the protein’s isoelectric point, where the protein is the least soluble. At the protein’s isoelectric point, the protein has equal negative and positive charges, and thus, it tends to aggregate and come out of solution. Holding the protein base for too long at the proteins’ isoelectric point results in a denatured, chalky beverage.
Another technical hurdle when working with whey proteins is they tend to be astringent at lower pH. Thus, a mixture of differing acidulants such as phosphoric, citric and malic acid is often used when formulating these products to balance the flavor profile and reduce tartness. An industry response to this formulation challenge was the development of pre-acidified whey products. These proteins require less acidulant to achieve the beverage’s target pH, thus minimizing astringency.
With the surge for clear, protein-fortified beverages, whey suppliers and researchers are busy developing new specialty proteins to further improve its clarity. The department of food science and technology at the University of Tennessee is taking a unique approach trying to bolster whey’s clarity and heat stability by forming whey protein nanoparticles created by a unique microemulsion process.