The objective of this work was to study the effects of high pressure jet (HPJ) processing on the foaming of whole milk at different temperatures. High pressure jet-treated whole milk (200 and 400 MPa) was foamed at 5, 20, 40, and 50 °C using a custom-made air injection device and the foam expansion and foam stability was compared to a non-HPJ-treated control. Aliquots of the foams (formed at 5 and 50 °C) were extracted for proximate analysis and visualization using confocal scanning laser microscopy (CSLM). The relative foam expansion values for the non-HPJ-treated sample at 5, 20, 40, and 50 °C were 45.5 ± 11.3%, 0 ± 0%, 79.6 ± 9.7%, and 88.2 ± 2.8%, respectively while the 400 MPa-treated sample foam expansion values were 36.4 ± 10.8%, 60.8 ± 5.7%, 50.0 ± 5.3%, and 71.7 ± 3.0%. Notably the HPJ-treated sample foamed at 20 °C while the control milk did not foam at all. Furthermore, the 400 MPa-treated foam was stable for >2 h at all foaming temperatures, unlike the non-HPJ-treated whole milk foam, which completely collapsed in 60 s and 1490 s after being foamed at 5 °C and 40 °C, respectively. CSLM and proximate analysis of the non-HPJ-treated sample revealed differences in foam composition based on foaming temperature with more fat present in the foam formed at 50 °C (3.2 ± 0.3%) than at 5 °C (2.5 ± 0.1%), likely due to the ability of liquid oil (at 50 °C) to migrate to the air-water interface during air incorporation. In contrast, there were no compositional differences in the foams from 400 MPa-treated milk based on foaming temperature, reflecting that there are structural differences, particularly in the fat, compared to the non-HPJ-treated foams. This was supported by evidence of fat-protein complexation and micron-size bubbles in CSLM images of the 400 MPa-treated foam.
All Science Journal Classification (ASJC) codes
- Food Science
- Chemical Engineering(all)