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was obtained after treatment at pressures of 400, 450 and 500 MPa for 30 min. Treatment of human milk at 65 °C for 30 min maintained 43 % of IgA immunoreactivity, whereas lysozyme activity was not affected.

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Lactoferrin and lactoperoxidase are whey proteins with biological properties that may provide health benefits to consumers. These properties are vulnerable to potentially denaturing conditions during processing. High-pressure treatment is an appealing alternative to the traditional heat processing of foods because it exerts an antimicrobial effect without changing the sensory and nutritional quality of foods. In this work, the effect of high-pressure treatment on the denaturation of lactoferrin and lactoperoxidase present in skim milk and whey, and as isolated proteins in buffer, was studied over a pressure range of 450 to 700 MPa at 20°C. Denaturation of lactoferrin was measured by the loss of reactivity with their specific antibodies using a sandwich ELISA. Denaturation of lactoperoxidase was determined by measuring the loss of enzymatic activity using a spectrophotometric technique. No substantial inactivation of lactoperoxidase was observed in any treatment assayed. The concentration of the residual immunoreactive lactoferrin after each pressure treatment was determined, and the data were subjected to kinetic analysis to obtain D and Z values. Denaturation of lactoferrin increased with pressure and holding time, and D values were lower when lactoferrin was treated in whey than in milk, and lower in both whey and milk than in phosphate buffer. Thus, protein is denatured more slowly in buffer and in milk than in whey. Denaturation of lactoferrin in the 3 media was found to follow a reaction order of n=1.5. Volumes of activation of about -34.77, -24.35, and -24.09 mL/mol were obtained for lactoferrin treated in skim milk, whey, and buffer, respectively, indicating a decrease in protein volume under pressure.

The effect of high-pressure treatment on denaturation of b-lactoglobulin and a-lactalbumin in skimmed milk, whey, and phosphate buffer was studied over a pressure range of 450-700 MPa at 20°C. The degree of protein denaturation was measured by the loss of reactivity with their specific antibodies using radial immunodiffusion. The denaturation of b-lactoglobulin increased with the increase of pressure and holding time. Denaturation rate constants of b-lactoglobulin were higher when the protein was treated in skimmed milk than in whey, and in both media higher than in buffer, indicating that the stability of the protein depends on the treatment media. a-Lactalbumin is much more baroresistant than b-lactoglobulin as a low level of denaturation was obtained at all treatments assayed. Denaturation of b-lactoglobulin in the three media was found to follow a reaction order of n = 1.5. A linear relationship was obtained between the logarithm of the rate constants and pressure over the pressure range studied. Activation volumes obtained for the protein treated in milk, whey, and buffer were -17.7 ± 0.5, -24.8 ± 0.4, and -18.9 ± 0.8 mL/mol, respectively, which indicate that under pressure, reactions of volume decrease of b-lactoglobulin are favoured. Kinetic parameters obtained in this work allow calculating the pressure-induced denaturation of b-lactoglobulin on the basis of pressure and holding times applied.

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