Acidification of high pressure treated milk: The role of whey protein denaturation

Whey protein denaturation, as measured by exposed hydrophobicity, was increased by pressure treatment between 200 and 400 MPa with further smaller increase at 600 MPa, similar to the hydrophobicity changes reported for milk. The role of denatured whey protein in particle aggregation in milk as pH decreased, was investigated by a light reflectance method. Aggregation began earlier with increasing pressure treatment and was rapid enough to prevent acid-induced casein dissociation. Comparison between pasteurized and UHT-milks showed that whey protein denaturation under pressure and micelle fragmentation interact to inhibit re-association of the casein micelle fragments on pressure release. This was essential for maximum enhancement of gel properties. Improvements to gel properties and to the apparent viscosities of stirred-style products prepared by disrupting the gels, were consistent with a fluid-filled open cellular foam structural model.