Effect of high hydrostatic pressure on the structural properties and bioactivity of immunoglobulins extracted from whey protein

High hydrostatic pressure was applied on immunoglobulin samples whose molecular, structural and glass transition properties were examined in comparison to thermal effects at atmospheric pressure. Immunoglobulins exhibit pressure stability throughout the experimental concentration range by conserving native conformation, which results in cohesive structure formation observed by small-deformation dynamic oscillation on shear, modulated differential scanning calorimetry and infrared spectroscopy. Application of the combined WLF/free volume theoretical framework demonstrates that pressurised immunoglobulin preparations are able to form glassy systems upon cooling at subzero temperatures. This has been attributed to a reduction in polymeric free volume under pressure and the development of an efficient friction coefficient amongst tightly packed particles that link to form a three-dimensional matrix. Pressure treated assemblies of condensed immunoglobulins demonstrate viscoelastic behaviour matching that of the thermally treated counterparts, but retain bioactivity, which is largely lost with thermal treatment.