Caseins: utilizing molecular chaperone properties to control protein aggregation in foods

Denaturation and aggregation of proteins are reactions that are relevant to functional applications of proteins in foods. Depending on concentration, ionic strength, and pH, aggregation can result in turbidity, precipitation, or gelation. Aggregation may be desirable, as in the case of gelation, or undesirable, as in the case when it causes phase separation in beverages. One approach to improve the stability of globular proteins against heat stresses is through the addition of other compounds that alter aggregation. Numerous studies have shown the ability of molecular chaperones to assist proper folding/unfolding and assembly/disassembly of proteins, especially during stressed conditions. Recently, several papers have reported the molecular chaperone-like properties of caseins, especially using alpha(s)- and beta-caseins. Caseins appear to function like small heat shock proteins (sHSP). We have compared the results among investigations from the perspective of food processing conditions and related them to the mechanism for sHSP. Caseins possess three of the four common features among sHSP; lacking a similar sequence domain. Their function may be explained in part by having structures fitting the intrinsically unfolded class of proteins. With a few exceptions, most investigations were done at solution conditions that poorly represent foods; lacking investigations at pH < 4.5 and concentrations above 20 mg/mL. While it is clear that caseins can alter aggregation at neutral pH, their effectiveness at low pH, high protein concentration, and high thermal treatment (T >or= 100 degrees C) remains to be fully established.