SUMMARY. Differential scanning calorimetry (DSC) was used to study thermal transitions of the following whey proteins and enzymes in milk ultrafiltrate solution: /Mactoglobulin, a-lactalbumin, serum albumin, y-globulin, apo-and Fe-lactoferrin, lysozyme, ribonuclease, a-chymotrypsin and xanthine oxidase. Denaturation enthalpies (A-Ho), denaturation temperatures (T D ) and the half width of the denaturation peaks in DSC thermograms (A? 1 !)) were determined and the degree of renaturation was estimated by rescanning previously denatured samples. A fair correlation between the results obtained by DSC and other more classical methods was found in general. However, for some proteins (a-lactalbumin, lysozyme, ribonuclease and xanthine oxidase), which have so far been considered relatively thermostable, calorimetry reveals conformational changes starting at temperatures as low as about 45 °C. In these cases thermostability observed after heat treatment of milk should be interpreted in terms of renaturation and not of high temperatures of denaturation.Calorimetric techniques have been found useful for studying the effect of heat on proteins in aqueous solutions (Privalov, 1974; Sturtevant, 1974). The published calorimetric investigations of protein denaturation, however, either do not include milk proteins or were not carried out in solutions resembling the natural milk medium. It was thus considered useful to examine the thermal transitions of milk proteins in milk ultrafiltrate by differential scanning calorimetry (DSC). This should give some insight into the structure and stability of proteins in milk as well as the changes in the properties of milk and milk products during heat treatment.The present communication summarizes the results of a calorimetric investigation of the heat-induced transitions and reactions observed in milk ultrafiltrate of the following proteins: /

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0 3Effect of calcium on the hydration of casein. I. Water vapour sorption and fine structure of calcium caseinates compared with sodium caseinates in the pH range 4-6-80 SUMMARY. Hydration of Ca and Na caseinates which were prepared from whole casein at different pH levels (range 4-7-8-0) was determined by means of water vapour sorption measurements in the water activity (a w ) range O58-O95. Water uptake of Ca caseinates was systematically lower than that of Na caseinates prepared at equal pH, the differences increasing with increasing pH and a w . Plots of the water content v. the amount of added hydroxide at constant a w revealed a linear relationship between water uptake and cation content, suggesting that the increase in water uptake is mainly determined by the amount and type of cations associated with the caseins.In the a w range tested, Ca 2+ adsorbed about 2-7 and Na + 3-18 mol water/mol of cation. This implies that replacement of one mol of casein-bound Na + by Ca 2+ is accompanied by a displacement of 1-11 mol water at a w 0-58-0-95. The loss of water is a consequence of conformational changes induced by the chelating and cross-linking effects of Ca 2+ , which also lead to micelle formation.

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