Effect of high pressure processing on rheological and structural properties of milk–gelatin mixtures

• Treatment at 300 MPa caused a remarkable viscosity increase of milk–gelatin mixtures.
• Treatment at 600 MPa caused a decline in viscosity of milk–gelatin mixtures.
• Confocal microscopy revealed aggregation in pressure treated milk–gelatin mixtures.

There is an increasing demand to tailor the functional properties of mixed biopolymer systems that find application in dairy food products. The effect of static high pressure processing (HPP), up to 600 MPa for 15 min at room temperature, on milk–gelatin mixtures with different solid concentrations (5%, 10%, 15% and 20% w/w milk solid and 0.6% w/w gelatin) was investigated. The viscosity remarkably increased in mixtures prepared with high milk solid concentration (15% and 20% w/w) following HPP at 300 MPa, whereas HPP at 600 MPa caused a decline in viscosity. This was due to ruptured aggregates and phase separation as confirmed by confocal laser scanning microscopy. Molecular bonding of the milk–gelatin mixtures due to HPP was shown by Fourier-transform infrared spectra, particularly within the regions of 1610–1690 and 1480–1575 cm−1, which reflect the vibrational bands of amide I and amide II, respectively.