IDM | Technology/IT
Milk protein fractionation
by means of microfiltration
Influence of preconcentration and diafiltration medium – part 1
16 · 8 2017 | international-dairy.com
Authors: Dipl.-Ing. (FH) Michael Reitmaier, Dipl.-Ing. Hans-Jürgen Heidebrecht,
Prof. Dr.-Ing. Ulrich Kulozik, Chair of Food and Bioprocess Engineering,
Weihenstephaner Berg 1, 85354 Freising, Germany
In three editions of IDM, future options and current issues concerning
the fractionation of milk proteins by means of microfiltration
(MF) will be addressed. The first article deals with the filtration efficiency
of ceramic membranes during the conduction of diafiltration
(DF) with different washing media. In part 2 a method to better
characterize polymeric membranes during the MF of milk will be presented.
The third article addresses the qualification of hollow fiber
membranes for this application and a new method for an in-situ detection
of the deposit layer.
Milk protein fractionation by MF:
Separation task
The prices for separated milk protein fractions differing in their
nutritional and technofunctional properties go far beyond the basic
value of milk and therefore offer a good option for diversification,
particularly in the case of fluctuating milk prices. The challenge
in the fractionation of milk proteins is to completely retain
the casein micelles with a diameter between 50-400 nm (d50.3=180
nm) while maximizing the transmission of the major whey proteins
with 2-4 nm (d50.3= 3 nm). Although pore sizes with 0.1-0.2 μm of
commonly applied MF-membranes are by far bigger than whey
proteins, the transmission is far below the expected 100%, normally
only around 50%. This is mainly due to the retention of casein
micelles, which form a deposit on the membrane surfaces, thus
acting as a secondary separation layer with a significant influence
on the filtration performance.
Purification by diafiltration: Improving
sustainability and product properties
In order to achieve a preferably high product purity and a high yield
a multi-step washout process called diafiltration (DF) is required.
This means that the medium, which permeates the MF membrane,
is replaced by a medium that does not contain whey proteins. Fig. 1
shows a DF process for the fractionation of milk proteins in which the
permeate is further processed by ultrafiltration. Depending on the intended
purity of the casein fraction, which can be achieved by a high
degree of removal of the whey proteins, a multiple of the retentate volume
must be replaced by a DF medium. Up to now, it is common to use
purified or fresh water. However, this leads to an increased water consumption
interrelated with an additional wastewater load, and may also
affect the properties of the obtained casein fraction. Moreover, in order
to save costs and increase the process sustainability, there is a great
interest in closed mass loops of processing side streams such as evaporation
condensates or reverse osmosis permeates by valorizing such
processing side streams and making use of them towards `zero-liquiddischarge’
de Boer 2014. Bringing these aims together, the objective of
this work is to investigate the effects of different potential DF media on
the filtration performance during the MF of skim milk and hence replace
fresh water as DF medium. In the dairy industry, also nanofiltration (NF)
Fig. 1 Scheme of a protein fractionation process by MF and UF
with potential DF media as a variable.