|
Cross-flow
membrane filtration
Hollow-fibre
cross-flow membrane systems are considered state-of-the-art products
in many industries. In food applications, these membranes are being
used in protein and milk concentrations, fruit juice clarifications
and for producing filtered wine or vinegar for many years. The new tubular
membrane product is developed specifically for the citrus industry,
using components approved by FDA and USDA, providing a sanitary design
and high-density configuration.
The configuration
of the membranes used most often in fruit juice clarification is tubular
or hollow fibre. Tubular membranes are used for handling the high pulp
content of many juices. Hollow-fibre membranes are between 1 and 1.5
millimetres in diameter, while tubular are 7 millimetres to 25 millimetres
in diameter.
Specialised
polymeric adsorption process
Features
of citrus upgrading by adsorption resin process
- Bitterness
reduction
- Colour
improvement
- Ratio
adjustment
- Hesperin
reduction (clarified concentrate)
Advantages
- FDA-approved
resins.
- Complete
adsorption of bitter components, thereby eliminating the need for sugar
or taste-maskers.
- Life of
the adsorbent resins is over three years.
These
resins are special sorbents, highly and rigidly cross-linked in the
swollen state, and thus characterised by very high internal surface
areas, approaching those of activated carbons. As a result of their
unique manufacturing technology unlike the conventional polymeric sorbents,
they will retain their swollen state porosity, and hence show little
or no change in swelling with change of permeating liquid. The performance
in some specialised applications can be further enhanced by using macronet
types with the increased hydrophilicity obtained by the presence on
the sorbent's internal surface of a minor amount of ion-exchange or
other polar functional groups.
This adsorbent
resin is based on polystyrene with a weak base-anion functionality in
the form of spherical beads. It has a distinct macro and micro-porous
structure with a large specific surface area. It is normally supplied
in water-swollen form. It has a high intrinsic hydrophilicity, and,
as a result, retains its moisture quite well even in the presence of
organic solvents.
Due to
its extraordinary pore structure and its hydrophilicity, the resin is
especially suitable for citrus debittering, cephalospor in isolation
and many other applications.
Limitations
- It needs
higher initial capital investment.
- The frequency
of choking of membranes is on the higher side since fruit juices contain
higher solids and this results in need to clean the membranes often
than usual water applications.
Other
membrane applications
Tomato
juice concentration
Tomato
juice has high pulp concentration and high viscosity. It behaves as
a non-Newtonian fluid. The concentration of tomato juice is normally
4.5 to 5 brix. Membrane processes like UF followed by reverse osmosis
clarify the juice and concentrate to eight to 12 brix at a cost significantly
lower than evaporation. The tomato paste final product will contain
28 brix to 29 brix, which is done by evaporation. The lesser time that
the juice spends in the evaporator means that the colour quality is
very good, showing a little browning usually associated with the evaporation
alone.
Similarly,
juices from carrots and celery, and cucumber juices, are processed with
UF/RO combination for concentration.
Apple
juice clarification
One of
the biggest applications of membranes in fruit juice production has
been the clarification of apple juice by ultra-filtration. Ultra-filtration
performance on apple juice depends upon the variety and processing method,
95 to 98 per cent of the juice is recovered as clarified juice. With
25,000 molecular weight cut-off membrane, the tannins remain in the
clarified juice imparting a brownish colour and a sharp flavour. With
a smaller MWCO membrane, the tannins are removed and the clarified juice
has a light golden colour. The colour and clarity is much better than
those produced from a rotary vacuum filter.
Juice
ultra-filtration process generates savings in cost and manpower due
to:
- Reduction
in the quantity of enzymes required to depectinise the juice
- Reduction
in filter aids, bentonite, kieselguhr usage and final filtration steps
- Improved
overall extraction efficiency, typically 95 to 97 per cent against 90
to 93 per cent in traditional processes.
- The plants
are compact and simple to operate.
- The technology
is no more complicated than ordinary filtration and maintenance needs
are usually lower.
-
The writer is vice-president - corporate marketing, Ion Exchange, Mumbai.
This article is a presentation made at Brewtech/bevtech 2002
|
