Phosphopeptides of casein and calcium uptake

Casein phosphopeptides (CPPs) originate from both in vitro and in vivo casein hydrolysis and are characterized by a sequence of five amino acids highly conserved, constituted by three phosphorylated serines and two glutamic acids and known as “acidic motif”. A role for this highly polar acidic domain has been attributed in stabilizing the colloidal calcium phosphate of casein micelles, and, in the case of casein phosphopeptides, in the ability to bind and solubilize calcium ions, thus preventing the formation of amorphous calcium phosphate. In milk, the physico-chemical form of calcium plays an important role in casein micelle stability, and contributes to high calcium availability. Also CPPs display the ability to form aggregates with calcium ions, and these aggregates have been demonstrated to represent the bioactive form of CPPs. Till their discovery, CPPs were hypothezed to act as promoters of calcium absorption by the human gut. Although experiments carried on in animals or in intestinal preparations were not conclusive, a CPP induced calcium uptake by the human intestinal tumour lines, HT-29 and Caco2, differentiated in vitro, was proved. This CPP bioactivity is correlated to the cell differentiation degree and to the presence of the “acidic motif”. The notion that the higher is the fraction of bioavailable calcium, the higher is the amount of the mineral for the specialized tissues, as bone and teeth, has attracted numerous researchers; indeed data available seem to confirm this possibility. Taken together and besides some controversial results, above all in humans, CPPs may be undoubtedly considered as potential nutraceutical and/or functional food. The potentiality of casein phosphopeptides could be of practical application for their presence in dairy products frequently consumed by the Western population. Moreover, their solubility in water allows to use these peptides as an easy to transfer ingredient in food.