Just a small sampling of examples follows.
One long-used protein-hydrocolloid ingredient interaction is that between the dairy protein casein and carrageenan. The exterior of casein micelles — spherical aggregates of casein molecules dispersed in an aqueous solution such as milk — have a positive electrostatic charge in typical food systems. Carrageenan, which normally gels in water, possesses negatively charged sulfate groups. Like magnets, "opposites attract," and the two molecules form links to produce a gel structure that is much stronger than what the carrageenan would form by itself.
The classic use of this is in chocolate milk where a weak gel structure is formed that can suspend cocoa. The gel is thixotropic in nature, meaning it becomes less viscous when disturbed, such as when milk is poured into a glass. It then returns to a more viscous state when the milk is put back in the refrigerator and sets undisturbed.
Interactions between proteins and flavoring compounds are complicated and result in created, reduced and altered flavorings.
For instance, proteins are known to bind to flavorings. This is undesirable when binding decreases the perception of a wanted aromatic (flavor) molecule or alters the ratio of various aromatics to change the overall flavor profile. Examples include the general tendency for dairy proteins to reduce the intensity of vanillin such as occurs with vanilla in dairy products, or when a "fish flavor" is used to enhance the tuna aroma in a textured vegetable protein-based food. However, the ability to bind unwanted flavors can be an advantage if the flavor is reduced (e.g., as in flavor masking).
Much research is geared toward better understanding the types of bonds that occur, a major factor in the results of an interaction. For instance, one study investigated how the binding of various flavor chemicals by whey protein isolates (WPI) was impacted by heat and high pressure denaturation of the protein. (Kühn J, et al. 2008. Binding of flavor compounds and whey protein isolate as affected by heat and high pressure treatments. J Agric Food Chem. 56(21):10218-24.) Results showed that the interaction depended on the structure of the flavor molecule. The effect of the processing ranged from decreased WPI binding of one flavor component (2-nonanone) to increased binding of another (trans-2-nonenal). The authors concluded that "hydrophobic interactions are weakened upon heat or high pressure denaturation, whereas covalent interactions are enhanced."
Just as the individual whey fractions have differences in functionality, they have also been shown to bind differently with flavors. Other research studied the binding capacities of various whey proteins for 2-nonanone, an aroma reported to be strongly present in UHT milk as well as naturally occurring in blue and cheddar cheese, fish and coconut. The whey fraction bovine serum albumin was found to have the greatest binding capacity followed by beta-lactoglobulin, then alpha-lactalbumin, alpha s1-casein and the least binding was shown by beta-casein. They also found that WPI bound more strongly to 2-nonanone than did sodium caseinate. (Janina, K, et. al. 2007. Binding of 2-Nonanone and Milk Proteins in Aqueous Model Systems. J Agric Food Chem. 55(9):3599-604.)
Maillard reactions occur between a reducing sugar (e.g., glucose, fructose, maltose and lactose) and amino acids. It results in flavor compounds and browning. Different amino acids produce different amounts of browning. All other things being equal, a protein with high levels of proline and particularly lysine, which pea protein has, will tend to create a browner product upon heating than one with lower levels. This can be potentially useful in products where achieving a desirable brown shade is a challenge, such as gluten free baked goods.
Proteins are both complex and intriguing. The evolving understanding of protein functionality and increasing market availability of novel protein ingredients means they will continue to provide both challenges and answers to creative development of new foods and beverages.
This article originally appeared in the February 2013 issue of Food Processing Magazine.