Hydrophilic lecithins protect milk proteins against heat-induced aggregation.

In the present study, the heat-induced interaction between whey proteins and casein micelles was studied. To that end, the particle size distribution of 5.5% (w/w) casein micellar dispersions was determined by photon correlation spectroscopy as a function of both the whey protein concentration and heating time at 80 degrees C. The results clearly indicated that heat-induced aggregation of the casein micelles only occurred in the presence of whey proteins. In an effort to overcome the heat-induced interactions between whey proteins and casein micelles, the influence of different soybean lecithins was investigated. Comparing native to hydrolysed, as well as hydroxylated soybean lecithin, it was observed that the heat-stabilising effect of the lecithins was directly related to their hydrophilicity: whereas native soybean lecithin had hardly any beneficial effect, highly hydrolysed as well as hydroxylated soybean lecithin largely prevented heat-induced casein micelle aggregation in the presence of whey proteins. From experimental observations on the heat-induced decrease of whey protein solubility both in the absence and presence of hydrolysed lecithin, it was deduced that the latter may stabilise the exposed hydrophobic surface sites of heat-denatured whey proteins. Dynamic surface tension measurements indicated that the heat-stabilising properties of lecithins were mainly determined by their critical aggregation concentration.