Membrane and Desalination Technologies - TCE Moodle Website

Treatment of Food Industry Foods and Wastes by Membrane Filtration 255
membranes. The RO plant processes more than 250 tons/h (during the season) of 4.5 degree
Brix juice to 8 degree Brix. It should be noted that the usual concentration of natural tomato
juice is 4.5–5.0 degree Brix. Commercial tomato sauces are 8–12 degree Brix, and tomato
pastes are 28–29 degree Brix. Retention of organic acids (citric and L-malic), sugars (glucose,
fructose), mineral ions (K, Mg, Na, F, Cl), and free amino acids is excellent. The color of the
tomato juice product is very good and shows none of the browning normally associated with
evaporation. This color quality is retained when evaporated further to 28–30 degree Brix
paste because of the reduced time in the evaporator.
When the membrane technology is applied to the production of concentrated fruit and
tomato juices, the following considerations should be taken into account, according to Dr. A.
Sabater de Sabates, Chief of the Food Processing Unit, UNIDO (8):
1. The main advantage of the membrane process system lies in the lower energy consumption. Total
liquid volume remains the same. The influent feed stream is equal to the permeate stream plus the
retentate stream. The economic advantages depend on energy costs, membrane replacement costs,
as well as the duration of the campaign.
2. As the citrus fruit juices are also non-Newtonian, there are flow problems as well as the classical
fouling problems. This may increase investment and running costs.
3. For the time being, the membrane process system cannot produce orange juice concentrated up to
65 degree Brix, which is standard. This step, from 55 to 65 degrees, is done by vacuum
evaporation.
4. The juice obtained by the membrane process system has fewer microparticles and therefore is
more transparent. When consumer preference goes to a more cloudy juice, the juice fibers can be
blended.
5. As the rheological behavior of tomato juice is irreversibly shear dependent, the apparent viscosity
of the final product is therefore lower than with the conventional process. In any case, tomato juice
has to be quickly heated to inactivate pectinase, but it is a fact that the color is better with the
membrane technology.
6. As the membrane process system has inherent advantages in energy savings and low temperature
processing, some comparative analysis of investment and running vs. the conventional vacuum
evaporation methods, would be of great interest.
5.3. Removal of Salts from Food Processing Water Streams Using NF
The single most important food manufacturing application of NF membranes is desalting
of whey permeate (Fig. 6.15) or other food processing water streams (32). Salty cheese whey,
for instance, poses a serious waste disposal problem in the food industry. The salt content,
whey solids content and biochemical oxygen demand of the salty cheese whey are about 4–6,
6% and 45,000 mg/L, respectively. Accordingly, the salty cheese whey can neither be
discharged directly into a POTW system, nor mixed with normal cheese whey because of
its extremely high salt content (33).
Figure 6.15 shows how a major waste disposal problem is solved by desalting of cheese
whey permeate using NF membranes. The NF system effectively removes sodium chloride as
permeate, which is recycled or discharged. The retentate that is desalted whey is added back
to the normal whey. This is a typical example of cleaner production as well as a cost-saving
process.