Consumer focus on health and wellness is driving the growth in high-protein dairy beverages. The review discusses shelf-stable ready-to-drink beverages that are primarily dominated by sports nutrition and the "better for you" beverage categories. Both of these categories tend to have a "high in protein" claim. Because of their functionality, sensorial attributes, and protein quality, dairy protein ingredients are the ingredients of choice to meet protein claims. Due to the higher protein content of the beverages, the functionality of dairy protein ingredients plays a critical role in final product quality and stability. In the United States, Food and Drug Administration regulations classify shelf-stable foods into acid/acidified and low-acid foods. The differentiation is based on pH and water activity (a_w). In the context of shelf-stable high-protein dairy beverages, any beverage with a_w of >0.85 and with a finished equilibrium pH of >4.6 is classified as low acid. Beverages to which acids or acid foods are added and have a finished equilibrium pH of ≤4.6 and a_w >0.85 are classified as acidified food. Acid foods have a natural pH of ≤4.6. The final pH requirement of these shelf-stable products will affect the type of dairy protein used in these applications. In acidified dairy protein beverages, the go-to ingredient is whey protein. In low-acid beverages, the protein ingredients of choice are milk protein ingredients (with a casein-to-whey protein ratio of 80:20, as found in typical bovine milk) and casein-enriched ingredients. Rendering the product shelf-stable depends on whether the product is classified as acidified or low acid. Low-acid, shelf-stable beverages, in general, have 2 manufacturing options: retort and UHT processing, followed by hermetic sealing. Pasteurization is the standard processing choice for shelf-stable acidified beverages, followed by hot fill. Because of differences in pH and heat loads during the manufacture of high-protein dairy beverages, the functionality of protein ingredients will play an essential role in determining the final beverage quality. Two of the most important functional properties of dairy protein ingredients that have a role in producing these beverages are solubility and heat stability. This review elucidates the physicochemical properties of dairy protein ingredients for low- and high-acid shelf-stable dairy protein applications, analytical techniques to characterize protein ingredients, beverage processing conditions, and quality defects observed.

Reverse osmosis (RO) is known for the economic dewatering of dairy streams without any change in phase. At the household level, surplus milk is fermented and churned to obtain butter, which is subsequently heated to obtain clarified milk fat (ghee). The production of 1 kg ghee generates 15–20 kg sour buttermilk (SBM) as a by-product that is mostly drained. This causes a loss of milk solids and environmental pollution. The processing, preservation and valorization of SBM are quite challenging because of its low total solids (TS) and pH, poor heat stability and limited shelf life. This investigation aimed to transform SBM into a novel dried dairy ingredient. SBM was thermized, filtered, defatted and concentrated at 35 ± 1 °C, employing RO up to 3.62× (12.86%). The RO concentrate was subsequently converted into sour buttermilk powder (SBMP) by employing spray drying. SBMP was further characterized for its physicochemical, reconstitution and functional properties; rheological and morphological characteristics; and amino acid and fatty acid profiling, along with FTIR and XRD spectra. SBMP was “instant soluble-3 s” and exhibited excellent emulsion stability (80.70%), water binding capacity (4.34 g/g of protein), flowability (28.36°) and antioxidant properties. In nutshell, a process was developed for the valorization of sour buttermilk to a novel dairy ingredient by employing reverse osmosis and a spray-drying process.