FIG. 1. Schematic representation of a common UHPH device
HOW DOEs UHpH WORK?
UHPH has some of the same action mechanisms as High Hydrostatic Pressure (HHP)—although it is important to keep in mind
that these are two completely different technologies. HHP is
a batch system in which the applied pressure is evenly distributed throughout the sample. UHPH is a continuous process that
combines pressure with homogenization forces, which produces
effects that are different from those caused by HHP.
UHPH is based on the same principles as conventional
homogenization. The process forces a liquid product through a
narrow gap (e.g. nozzle or valve) at high pressure. This sudden
restriction of flow under high pressure subjects the liquid to very
high sheer stress, which causes the formation of very fine emulsion droplets (Fig. 1). In conventional homogenization, the maximum pressure rarely exceeds 50 MPa, while special designs and
pressure-resistant materials enable UHPH to apply pressures of
up to 400 MPa (Alvarez-Sabatel, 2016). Although the energy produced during the process is partially dissipated as thermal energy,
UHPH is considered a non-thermal technology (Zamora and
During depressurization, different types of homogenization
forces (shear, impact, cavitation, and turbulence, and so on) are
used to reduce particle size and increase process efficiency. The
magnitude of these forces depends on several processing parameters, including equipment design (impact to valve walls and collision with other fluids, for example), the applied pressure, and the
temperature of the incoming fluid. Other properties of an incoming fluid, such as its viscosity and the nature of its ingredients and
their concentrations, can also affect process efficiency and the
properties of the outgoing fluid.
The high pressures (up to 400 MPa) and homogenization
forces that are applied during UHPH not only reduce particle size
and change fluid properties, but also inactivate microorganisms,
opening the door for pasteurization and homogenization of food
liquids in a unique phase (Diels and Michiels, 2006).
UHpH’s ROlE IN stRUctURINg
UHPH technology can significantly reduce both oil droplet diameter and size distribution polydispersity which, in turn, increases
the droplet packing density and emulsion stability (Fig. 2, page
16). This was observed in stability tests comparing reduced-fat
mayonnaise (down to 35 wt% oil content) that had been structured with and without UHPH. Samples that were structured
without UHPH creamed during the first month of storage, while
those that were structured using UHPH remained stable during
the entire length of the six-month experiment (Alvarez-Sabatel,
Also, the rheological properties of the UHPH-structured samples changed appreciably due to the increased droplet packing.
The UHPH reduced-fat mayonnaises exhibited textural properties
similar to those of traditional full-fat mayonnaises, while the non-UHPH processed samples behaved like liquids. Processing at various UHPH pressures between 100–300 MPa resulted in stable,
low-fat mayonnaises (down to 35 wt% oil content) with rheologically different and interesting properties, indicating that UHPH
could be used to modulate the final textural properties in a fixed
emulsion recipe. On the other hand, using UHPH to produce
mayonnaise with a fat content lower than 35 wt% resulted in
non-acceptable rheological properties regardless of the pressure that was applied. However, this limitation could be overcome
by using the technology in combination with fat substitutes, and
these two fat-reduction approaches could even produce a synergistic effect.
UHPH is able to change the technological functionality of
some thickening agents that are extensively used as fat substitutes. For example, UHPH improves the gelling properties of
inulin, a low-caloric ( 1. 5 Kcal/g) fructoligosaccharide with fiber-like properties (Alvarez-Sabatel, Martínez de Marañón, and
Arboleya, 2015). Using inulin, it is possible to produce reduced-fat
mayonnaise with as little as 1. 5 wt% oil, with long-term stability
and relatively adequate texture, but with a poor sensory profile.
Applying UHPH (from 100 MPa) could allow the inulin concentration to be decreased by more than the 50%, while maintaining the desirable properties and reducing the described negative
sensory profile associated with high inulin concentration (
Independent of the presence of fat substitutes, increasing
pressure results in mayonnaises with higher viscoelastic properties. However, above a critical threshold pressure, over-process-ing phenomena—lower vicoelasticities, creaming, sedimentation,
or the immediate separation of the oil and water phases, occur.
This critical pressure value varies based on the specific emulsion