Effect of high pressure and heat treatments on IgA immunoreactivity and lysozyme activity in human milk

Human milk from donor mothers is processed in human milk banks using low-temperature long-time pasteurization to ensure microbial safety. However, this treatment can degrade relevant bioactive components. High-pressure processing of food is a nonthermal treatment that exerts an antimicrobial effect maintaining the nutritional quality of foods. In this study, the effect of high pressure and heat treatments of human milk on denaturation of immunoglobulin A (IgA) and lysozyme activity was determined. Immunoreactive IgA was measured using a sandwich ELISA and lysozyme activity by a Micrococcus lysodeikticus turbidimetric assay. The retention kinetic of IgA in human milk treated by high pressure was studied. The experimental data obtained in the range of 350-650 MPa were well described by the Weibull model. The shape parameter (beta) was not affected by the pressure, whereas the scale parameter (alpha) was affected by the pressure and its behavior was described by an Eyring-type equation. The estimated activation volume (Delta V-a) was -25.67 +/- 5.32 ml mol(-1), and the constant reaction rate at the reference pressure (Kp) was 0.022 +/- 0.005 min(-1). Kinetic parameters obtained allow estimating the pressureinduced denaturation of IgA on the basis of pressure and holding times. A substantial activation of lysozyme activity was obtained after treatment at pressures of 400, 450 and 500 MPa for 30 min. Treatment of human milk at 65 degrees C for 30 min maintained 43 % of IgA immunoreactivity, whereas lysozyme activity was not affected.