IDM ¦ Technology/IT
ISI – Innovative Steam
Injection
Raw milk character is preserved
With the concept of ultra-high temperature
treated fresh milk, Dutch milk and food research
institute NIZO food research was ahead
of its time. The idea at that time was based
on the knowledge that milk only needed to be
heated to high temperatures only for a very short time to inactivate
harmful germs and their spores, but also heat-resistant enzymes.
The result is a milk that largely retains a character similar to raw
milk, but has a long shelf life.
Extremely gentle, but effective
Although the ISI (Innovative Steam Injection) concept is similar to
UHT treatment, it takes place in a completely different temperaturetime
window, explains Prof. Peter de Jong, Principal Scientist at NIZO.
Roughly described, milk is heated up to 60°C and then brought to
160°C in less than a second, before it is cooled back down to 60°C
in just 0.3 seconds. Such rapid temperature changes can only be
achieved by means of steam injection followed immediately by expansion
cooling. The steam used is extremely superheated at a pressure
of 18 bar to ensure high heat transfer. The process is so gentle
that 70% of the whey proteins retain their native form, according to
de Jong.
The starting point for the process development was a computer
model with which NIZO was able to determine the temperature-time
regime in advance on the basis of the expected chemical and biological
effects. Of course, extrapolation had to be carried out because
the individual inactivation kinetics were not always available in full.
However, the heating system constructed on the basis of NIZO calculations
and expert expectations worked better than the theoretical
predictions, according to de Jong.
"Despite its advantages, the ISI process was not able to establish itself
at the time," de Jong sums up. "The time was simply not yet
ripe for a longer shelf life of 60 days for fresh milk. In addition, the
process costs are around one cent per kilogram of milk, whereas conventional
pasteurisation only costs around 0.3 cent." Compared to
high-pressure pasteurisation, however, ISI appears to be absolutely
superior, both in terms of cost and homogeneity of heating. "ISI is a
reliable, fast and effective process that heats the product homogeneously
through," de Jong notes.
Prof. Peter de Jong, Principal Scientist at NIZO: the ISI
process heats milk to high temperature at very short time
(photo: NIZO)
Functionality is maintained
New findings on positive effects of raw milk consumption on human
health, such as signs of a strengthening of the immune system or
reduction of allergies, which researchers in Utrecht, Austria and the
USA are working on, are currently bringing ISI procedure back to the
fore. Scientists in Utrecht have discovered that β-lactoglobulin has
corresponding bioactive properties in its native structure. NIZO is also
involved in such a research project together with international dairies,
which is currently in the definition phase. Bioactivity of proteins
is increased and process performance of evaporators is increased due
to less fouling with milk preheated by ISI (as a result of lower viscosity).
With the focus on temperature effects, approaches are to be
developed to produce milk powder with even better suitability for use
in infant food. But ISI is also of interest on a smaller scale, namely in
the processing of goat's milk or a milk treatment directly on the farm.
44 · May/June 2021 ¦ international-dairy.com
/international-dairy.com
/international-dairy.com
