According to a food and health survey conducted by the International Food Information Council, protein is the most desired nutrient by consumers in the United States. This study also shows that consumers’ demand for protein is not only reflected in the purchase of traditional products, but they are also willing to accept milk protein as a high-quality source of protein. Milk proteins provide satiety, curb hunger and help the body retain muscle. Growth in the beverage market is gradually shifting towards products that offer consumers more complete nutrition and diverse benefits.

Protein drinks and shakes continue to attract new consumers, and non-traditional types of dairy beverages can also help consumers achieve their desire to get more protein.

Developing beverage products requires carefully selected ingredients. Because of their excellent nutritional properties, mild flavor, ease of digestion and unique functional properties in beverage systems, milk proteins are often the protein ingredients commonly used in beverage products.

Beverage Innovation Considerations

Various factors of a finished beverage product interact with each other. Regardless of the beverage type, the following factors must be identified and evaluated prior to formulation design and process development:

1) Determine packaging, transportation, and storage conditions, which will determine the appropriate production process, including heat treatment.
2) Describe the pH range of the product
3) Determine the approximate cost budget
4) Determine the nutritional composition of the product, which will be reflected in the nutritional labeling of the product, as well as meeting nutritional claims
5) Determine the required non-protein ingredients
6) Consider the compatibility of the above factors

The protein content of a beverage determines the processing and packaging format. Milk proteins can be soluble and stable over a relatively wide pH range, however their gelation properties due to temperature and concentration changes should also be considered, especially for whey proteins. Sugar and mineral ion concentrations in beverages also affect the stability of whey and milk proteins during processing and throughout shelf life. The interaction of the factors is formulation dependent, so small and pilot tests must be conducted before the formulation is finalized.

System environment selection

In general, the pH (acidity) of a product determines its processing in terms of safety and storage stability. With the exception of juice products, the U.S. Food and Drug Administration (FDA) does not specify heat treatment process conditions for acidic (pH < 4.6) products. Local government regulations should be consulted when formulating these products to ensure compliance with local regulations.

Shelf-stable beverage products can be broadly categorized into the following four basic types:

(1) Commercial aseptic beverages
(2) Commercial aseptic beverages with secondary autoclave sterilization
3) Tunnel pasteurized products
4) Hot-filled or pasteurized cold-filled products

Whey protein applied to neutral pH beverages

Commercial aseptic beverages processed using the heat treatments described above (types 1 and 2) are typically neutral pH and shaken beverages.

Their pH is usually between 4.6 and 7.5, depending on their flavor, such as strawberry (more sour) or chocolate (more neutral). These products must be aseptically heat-treated or secondary sterilized, or pasteurized and kept refrigerated. Whey proteins are also used in these products, but in general whey proteins are not the primary source of protein in these types of formulations.

The most commonly used proteins are those containing casein, such as milk protein concentrate or casein micelles. Typically neutral pH beverages, such as shaken products, are often secondary sterilized or UHT, a high temperature sterilization method.

Unmodified whey proteins are thermally unstable in amounts greater than 3% alone and will gel or precipitate under these conditions unless a stabilizing system is used. Using a combination of casein and whey proteins will provide some protection to whey proteins to maintain heat stability as the whey proteins will interact with the casein and remain soluble, preventing the formation of gels or precipitation due to the interaction of the whey proteins alone.

Milk proteins for neutral pH beverages

The proteins in milk protein concentrates, milk isolates and casein micelles are derived from milk and are well suited for use in low acidity beverages due to the inherent heat stability of casein.

Good hydration is the key to the ability of milk protein ingredients to function in low acidity beverages. There are several widely recognized methods to determine the degree of hydration.

First, the protein powder ingredients are dissolved in a high-speed blender, and it is important that the powdered ingredients have sufficient time to absorb the water so that the final beverage product remains thermally stable and soluble throughout its shelf life. Depending on the type of beverage desired to be obtained, hydration can be carried out using either milk or water, with both the temperature of the milk or water and the duration of hydration affecting the overall stability.

Published studies have confirmed that MPC ingredients perform poorly hydrated at protein contents of 70% and above. Hydration of MPC feedstocks can be improved by reducing the concentration of minerals, especially calcium.

Another functional property that needs to be measured to understand the functional performance of milk protein raw materials in beverages with low acidity is thermal stability. The thermal stability of a 5% solution of MPC85 was compared.

The results showed that MPC85 with reduced mineral content had better thermal stability after heating at 85°C (185°F) for 3 minutes compared to conventional MPC85. The samples were all stirred in room temperature distilled water for one hour for dissolution and hydration. Samples that hydrated more quickly typically exhibited better heat stability as more of the milk protein dissolved.

The storage environment and freshness of the MPC ingredients should also be considered when applying to beverages. Studies have shown that the solubility of MPC85 protein powders decreased after 60 days of storage at temperatures of 30°C (86°F) and above. When applied to beverages, insufficient hydration of milk protein ingredients results in poor solubility and heat stability.

The basic methods for improving protein stability in UHT sterilized, high protein, low acidity beverages are as follows:

1) Dissolve milk proteins in water at 50°C (122°F) with high speed agitation
2) Add other ingredients such as sweeteners, colors, stabilizers and flavors and mix at low speed and hydrate well for 1 hour
3) Add pH adjusting agent such as buffer to reach pH 7.0
4) Heat to 140°C (284°F) for 6 seconds
5) Homogenize at 2500 psi/700 psi
6) Cool to 24°C (74°F)

Whey protein applications for acidic beverages

Hot Filling or Pasteurization Cold Filling and Tunnel Pasteurization (Types 3 and 4) represent the processing of acidic whey protein beverages, which typically have a pH of 2.8-4.0. They are usually subjected to mild pasteurization, which results in a product that is stable at room temperature.

Beverages using whey protein isolate (WPI) as an ingredient in the pH range 2.8-3.5 have a high degree of clarity, or low turbidity, even at higher protein contents. The ability to create protein-fortified clarified beverages is a unique advantage of whey protein. The low fat and mineral content of whey protein isolate (WPI) results in products with high clarity and low turbidity.

Heat-treated acidic beverages can be hot-filled. Sterilization is also achieved in acidic environments by hot-fill product containers that have been pre-rinsed with ozonated water or other methods capable of killing oxygen-demanding contaminants. Hot-fill containers can be metal, glass, or specific plastic bottles that can withstand filling temperatures and the vacuum created when the product is cooled.

Cold filling is similar to hot filling in that the product is heat treated. Unlike hot filling, cold filled products are cooled to below 38°C (100°F) immediately before filling. Immediate cooling of the product helps prevent vitamin degradation and flavor changes that occur under hot filling conditions.

For acidic protein beverages, tunnel pasteurization of sealed metal cans or glass bottles is sufficient, and is the only practical way to make pasteurized carbonated beverages. Tunnel pasteurization is the traditional method for pasteurizing beer, but it is also practical for acidic protein drinks. However few producers have this type of pasteurization capability except for beer production.

Considerations for the application of milk proteins

The most important component in protein ready-to-drink beverages is the protein ingredient.

Protein sources can be milk protein concentrates (34%-89% protein), isolated milk proteins (90%-92% protein), or protein peptides that provide unique nutritional and functional benefits to the beverage. Sometimes milk proteins are also combined with other proteins, such as plant-based ingredients, to provide unique amino acid composition and textural properties to the product, but plant-sourced proteins can sometimes present flavor and texture challenges for formulators. These mixtures will be difficult to stabilize before or after heat treatment due to the reactions that can occur between the various ingredients. Different milk proteins have different isoelectric points and molecular sizes, and there are different molecular types of milk protein ingredients for commercial use.

There are two key factors to consider when selecting a milk protein: 1) the method of protein isolation, as this determines the composition of the WPC, WPI, MPC, MPI, or MCC; and 2) whether the milk protein has a stable source of raw materials and processing.

WPC80, MPC and MPI are obtained by separation by a physical process of membrane filtration. The fat and ash content may vary from supplier to supplier, as does the flavor, but the overall composition is basically the same.

There are two main processes for WPI: ion exchange (chemical treatment) and membrane filtration. The composition of the products obtained by these two methods varies in terms of mineral composition, carbohydrate content and glycopolypeptide (GMP) content, which in turn affects their application properties.

It is essential to maintain the stability of the raw material from batch to batch. Therefore, simple performance tests for the desired application are necessary, and this information is not reflected in standard specifications or test reports (COA). Simple performance tests are especially necessary when the end product or process is less resilient to change or when the protein content of the end product is close to conventional limits.