The Effect of High-Pressure Treatment and Skimming on Caprine Milk Proteins

Abstract

Background: Proteins are susceptible to HP-treatment and there is a need to determine the applicability of HP-treatment in dairy production. The aim of this study was to determine the effect of HP-treatment at 200–500 MPa (tconst. = 10 min; Tconst. = 20 °C) and skimming of HP-treated milk on the content of nitrogen compounds and protein composition of caprine milk. Methods: The content of nitrogen (total, non-casein, non-protein) was determined using the Kjeldahl method. Casein fractions and whey proteins were separated using SDS-PAGE electrophoresis. Color parameters were measured in the CIELAB color space. Results: HP-treatment decreased (p < 0.05) the content of non-casein nitrogen and soluble whey proteins. Skimming decreased the content of nitrogen compounds, and the noted decrease was more pronounced in HP-treated milk. Pressure and skimming had no influence on the proportions of α-, β-, κ-casein, β-lactoglobulin and α-lactalbumin. Total color difference (ΔE) increased with a rise in pressure, particularly in skim milk. Conclusion: HP-treatment led to a loss of protein solubility at pH 4.6 in caprine milk. In HP-treated milk, skimming did not induce changes in protein composition, despite a decrease in the content of nitrogen compounds after the separation of the cream layer. Higher values of ΔE in skim milk than in whole milk point to changes in colloidal phase components.