Soy Protein in Beverage Formulation

Most American consumers, 89 percent, feel that nutrition is an important factor when selecting food items, and 74 percent of consumers consider soy or soy-products to be healthy. The same study indicates that one-third of consumers say they seek out products specifically because they contain soy and soymilk is the most readily recognized soy product with 38 percent consumer awareness . A greater consumer interest in a healthful diet has prompted manufacturers to embrace soy's popularity and develop new products, including beverages, that feature soy protein.

Soy proteins and protein isolates have received increased attention since the FDA approved the soy protein/heart health claim in October 1999. Many beverages containing soy isolates with vanilla, chocolate and juice flavors are gaining popularity with mainstream consumers, as well as health-food consumers. Soy based beverages increased more than 200 percent in 2002. There are several factors driving the success of soy beverages, including: the soy protein health claim, more baby-boomers seeking longevity and good health, a rise in lactose-intolerant minorities, as well as technological improvements in processing and flavoring these products.

When the FDA approved the soy protein health claim and allowed manufacturers to emphasize soy protein's health benefits on packaging, a new market emerged. However, adding 6.25 grams protein per serving needed for the claim presents some major challenges for the beverage industry. One of the challenges is to keep soy protein in suspension while achieving a smooth mouthfeel. In order to satisfy consumer tastes, it is important to reduce the gritty or chalky feel in the mouth. Stabilizer blends help reduce the amount of sediments in beverages by protecting the soy protein during heat processing and pasteurization. The sedimentation reduction provides a smoother mouthfeel to the beverage - a major factor in the acceptance of soy beverages. Another challenge commonly faced when working with soy-based beverages is achieving a consumer-friendly flavor. Masking systems specifically designed to reduce soy's off-notes have proven extremely effective. These flavors mask the beany flavor associated with soy without imparting a characteristic flavor. Other flavors, such as vanilla or strawberry, then can be added to work synergistically with the masking flavor system.

Some of the questions that need to be answered prior to developing a soy beverage are2: What is the age of the product's target audience? What are the nutritional expectations of the target audience? Is the beverage going to be "lite" – have reduced sugar and calories? What finished product characteristics, such as clarity or pH, will influence the type of stabilizer needed? What type of processing, packaging and distribution is the product expected to undergo? What is the target price of the product?

In general, solubility, viscosity, flavor and fortification of soy beverages are the major challenges facing food industries.

Solubility:
Simply adding soy ingredients, such as soy protein isolates to a beverage will not increase sales unless the product tastes good. Beverage processing became increasingly sophisticated during the 20th century, allowing food processors to successfully add nutrients, minerals and herbs without compromising the product's flavor, appearance or texture. The advent of the 21st century spawned the development of a wide variety of drinks to appeal a wide variety of consumer tastes, from "natural" products to beverages with unique colors and textures never found in nature. As a result, beverage formulators are now faced with the increasingly difficult challenge of developing new or reformulating old products to suit the latest consumer trends. To accomplish this goal, the selection of appropriate and economical beverage stabilization systems becomes a crucial part of the formulation process. Stabilizers largely depend on the type of beverage formulated, the ingredients used and the desired end product.

Similar to whey proteins, processes such as agglomeration, lecithination and changes in the protein solubility will improve soy protein's dispersibility in a dry-mix application. Specifically, lower solubility will improve the dispersibility of the protein. In a liquid beverage, it is essential that the soy protein be properly hydrated in order to achieve the desired results3. Agglomeration makes soy protein highly soluble and also makes it possible to develop a new generation of soy-based ingredients. Soyfood companies have developed an agglomerated product that combines isolated soy protein, a soluble fiber and lecithin. The fiber helps mask any off-flavor from the soy by forming a complex with the protein that prevents the tongue from detecting off-notes, while the lecithin aids dispersion. These agglomerated soy ingredients can be used at the level of 10-20 grams per serving in both powdered and ready-to-drink soy beverages. Soluble fiber can also reduce the amount of stabilizer in the beverage. In some cases, it may also reduce flavor masking as well, making it easier to achieve a delicately flavored beverage such as vanilla or strawberry4. Homogenization is critical to maintain protein solubility in ready to drink beverages.

Viscosity:
One might call hydrocolloids and gums the silent partners in soy beverage formulation because neither will be tasted or smelled when formulated correctly, yet they can provide many useful functions. Added food gums provide protein stabilization and viscosity in liquid applications. Carrageenen, xanthan, locust bean, guar and cellulose gums work well in neutral pH drinks. Pectins, xanthan and guar are designed for acid beverages. Gums and hydrocolloids can provide pleasant mouthfeel, good suspension and produce a desirable level of cloud in the proper proportions4. Carrageenan and lecithin help build body in the beverage, improve mouthfeel and suspend solids.

Low levels of soy protein will produce a slightly cloudy drink. A high-viscosity isolate will provide a soy shake with a smoothie-like consistency, while a low-viscosity isolate will result in a protein drink with milk-like consistency5, 6. A low level of hydrolysis in a soy protein isolate will yield a low-viscosity product with good emulsification properties.

As soy protein use increases, especially in beverages that serve as quick, high protein meals, the challenge has been to mimic the consistency of a milkshake or fresh blended smoothie. One solution is to enhance the viscosity contributed by soy protein with combinations of other stabilizers, emulsifiers and proteins to make the soy more palatable. These applications require a highly dispersible and soluble soy protein isolate that offers very low viscosity7. Numerous isolated proteins from various soy companies with a wide range of viscosity profiles can help provide the desired consistency in finished beverages. Juice based soy beverages require special stabilization, the preferred stabilizer being pectin. Homogenization also is critical in this process.

To-date, there are no soy proteins that will produce a clear-based liquid beverage. Companies can produce a beverage that is slightly cloudy with a low level of soy protein. Clear beverages would require highly hydrolyzed protein products (currently there are no such commercial products) and there is no evidence to support the heart health benefits with a highly hydrolyzed soy protein product. Soy beverage developers of calcium rich products should bear in mind that soy proteins coagulate and aggregate in the presence of free calcium ions8.

There is confusion between solubility and dispersibility. These terms, are often used interchangeably, however, this should not be the case. In general, soy proteins with high solubility have poor dispersibility. To improve the latter, processors may lower the pH of the finished protein products or apply lecithin to the finished powder. Agglomeration of the protein powder is another, more costly dispersion aiding option8.

Flavor:
A new generation of soymilk beverages has entered the marketplace with the introduction of soymilk/juice-blended beverages. Although finding flavors that complement the soy/juice base can take several trials, keeping the two liquids blended together presents a challenge9. Taste is one of the most difficult challenges faced in developing soy beverages. Manufacturers are aware that most consumers may be unwilling to purchase a product a second time if they did not like the taste of it initially.

To date, most soy proteins continue to contribute notes to the finished product. The flavor industry recently developed several very good masking flavors for soy proteins that can be used in beverage manufacturing. Soy processing technologies have made strides in improving soy protein flavors through processes such as alcohol washing. This can simplify the formulation of high protein soy drinks for beverage manufacturers. When formulating with hydrocollides and fiber, keep in mind that they can flatten flavor notes at high concentration. Therefore, flavor testing should be conducted before and after formulating with mouthfeel modifiers and fiber sources.

Fortification:
In addition to interesting flavor combinations, one of the biggest trends in the beverage industry today is the advent of drinks with health and nutritional benefits. Recommended daily intakes of vitamins and minerals now can be ingested through a glass or two of fortified beverages10.

Soy beverages can be fortified with calcium, vitamin D, riboflavin and vitamin A. If a consumer is looking for soy, they may be looking for the nutritional claims associated with soy proteins. The amino acid profile of soy ingredients makes it a high-quality source of protein, and soy's high lysine content makes it unique among vegetable proteins. Despite a small deficiency of the sulfur-containing amino acids methionine and cystine, the quality of soy proteins as measured by Protein Digestibility Corrected Amino Acid Score (PDCAAS) compare favorably to beef, egg white and casein.

Tips for processing soy beverages11:

• Numerous soy protein isolates (SPI) are available in the market for beverages. It is important to start with an SPI that has the appropriate functional characteristics for the particular beverage application.
• Soy proteins for powdered applications rarely are appropriate for liquid applications, and vice versa. Discussing the project objectives with a supplier will help identify the proper soy protein ingredients.
• Special processing conditions and stabilization are required for high acid (low pH) protein beverages.
• Soy protein must be hydrated to obtain the desired results for liquid beverages. Soy protein will foam, so air incorporation needs to be minimized during the mixing process.
• On average, shelf life of soy protein products is one year under ideal storage conditions (> 75 F, > 60% relative humidity). Soy proteins stored above this range will have limited shelf life. Because of the solubility issue, shelf life of soy proteins for liquid beverages is very important as compared to powdered beverages.
• A variety of masking flavors are available for soy beverages. A soy protein manufacturer should provide guidelines about which masking product will work best with its soy protein.
• There are always some unforeseen interactions that take place when we move a formula from bench-top to pilot plant.
• Making a prototype beverage in the laboratory is different than mixing ingredients for a commercial batch. Consequently, testing should be done on every stage.
• Pilot runs and tests should be conducted when research, development and marketing staff are present in the plant.
• Given the rapidly shifting demographics of the United States, manufacturers should look for more innovations in beverages to suit the aging population. Improvements in formulating fiber and vitamins into soy beverages will be satisfying to the mature palate, and will fulfill minimum daily nutritional requirements.

References:
1. National Report on Consumer Attitudes About Nutrition 2003-2004, United Soybean Board

2. Beverage stabilizers. Paula Gerlat, Food Product Design, Oct. 2000

3. High powered protein drinks. Kimberly Burrington, Food Product Design, Oct. 2001

4. Formulating function into beverage. Cindy Hazen, Food Product Design, Jan. 2003

5. Beverage Creation. Lucy Saunders, Food Product Design, April 1994.

6. Soyfoods soar on health and taste. Linda Ohr, Prepared Foods, April 2001

7. Beverage viscosity, Any way you like it. Suanne Klahorst, Food Product Design, Jan. 2002

8. Putting proteins to work. Kimberly Decker, Food Product Design, June 2001

9. Flavoring alternative beverage, Laura A Brandt. Prepared Foods, Sep. 2000.

10. Beverage for bounty. Dan Turner, Food Product Design, July 2001.

11. Soy: The beneficial bean. Scott Hegenbart, Food Product Design, Jan. 2002.

Fact sheet written by Mian N. Riaz, Ph.D., Head of the Extrusion Technology Program and Associate Research Scientist at the Food Protein Research and Development Center at Texas A&M University in College Station Texas.