John Lucey, PhD, associate professor at the University of Wisconsin-Madison and researcher with Wisconsin Center for Dairy Research, has explored this mechanism further. High-heat treatment of 90° to 95°C for 5 to 10 minutes denatures the majority of whey proteins. At the recent 2005 International Whey Conference in Chicago, Lucey explained that some denatured whey proteins (DWP) remain in the serum and will be "soluble." The majority of DWP become attached or "bound" to the casein micelle. It is necessary to have some of the bound DWP attached to the micelle surface during heating to reinforce the gel matrix and increase viscosity in the finished yogurt.

Processing parameters, such as pH at heating, salts and subsequent pH adjustment, all affect the amount of DWP that are bound to the casein micelle. Lucey found that when the milk is heated at pH 6.5, most denatured whey proteins are associated with micelles. He also found that lowering the incubation temperature helps improve texture and reduce whey separation, thus reducing syneresis. For fortification of the milk solids content of the yogurt mix along with some skim milk powder, Lucey recommends using around 2% WPC34 (whey protein concentrate with 34% protein) or 0.4 - 0.75% WPC80/WPI (whey protein isolate). Higher levels of whey protein can lead to graininess, lumpiness and a short, brittle texture, depending upon the yogurt processing conditions.

Whey proteins also can be used to fortify protein levels in yogurt or smoothies. Because smoothies are thick and shake-like, processors can fortify these products with high levels of whey protein. For example, Unilever's Slim-Fast™ uses whey protein isolate to make the protein content of its Optima™ Smoothies 12 grams per 10.5-fl oz serving. Whey protein isolate works well in this application because of its superior heat and acid stability. General Mills' Yoplait Nouriche® Light Breakfast Smoothies offer 10 grams of protein per 11-oz serving, thanks to the whey protein concentrate in the formulation.

Processors who produce both cottage cheese and yogurt in the same facility can incorporate fresh cottage cheese whey (CCW) directly from a production line into their yogurt products with favorable results. Research by Rajiv Dave, PhD, at South Dakota State University, explored the texture and taste of yogurt mixes prepared with CCW as well as dried acid whey powder (AWP). Sensory evaluations showed that a consumer panel rated samples made with 5.5% CCW comparable to the commercialized yogurt control. Panelists gave the yogurt sample made with 1.9% CCW higher marks for body and texture than other samples.

There are nutritional benefits beyond protein to this type of fortification as well. Addition of 3.8% AWP, for instance, will increase the calcium content by 29%. The acid whey also increased the growth rate of probiotic L. acidophilus and helped maintain those higher levels over the storage life of the yogurt. In a consumer test, panelists rated strawberry-flavored yogurt with 1.9% AWP to be as good as a control yogurt.

For more information on how to incorporate whey into your next yogurt or smoothie formula, call the DMI Dairy Technical Support Hotline at 800/248-8829 or visit www.innovatewithdairy.com. Dairy Management Inc. is the domestic and international planning and management organization that builds demand for U.S.-produced dairy products on behalf of America's dairy farmers.