Citrus
juice upgrading
Often,
some orange and grapefruit juices form an undesired bitterness within
hours after extraction from the fruit. The compounds that cause the
bitterness are naringin and limonin. The organoleptic detection is at
approximately 5 ppm with limonin and 500 ppm for naringin. The bitter
content varies, depending upon the type of extractor and finisher as
well as of the ripeness of the fruits. Pulp wash usually contains up
to three to five times the limonin content in juice. These off tastes
can be removed with resin adsorption technique.
The FDA-approved
resins to be used do not influence the mineral and acid content of the
juice. For an optimised adsorption process, the juices should be filtered
prior to the adsorber plant with a cross-flow filtration system to clarify
the fruit juice to less than 0.1 per cent pulp particles. With a pulp-free
juice, the maximum resin efficiency and capacity can be used. Orange
and grapefruit juice has to be de-oiled to less than 0.01 per cent so
that there will be no fouling of the resins. Otherwise, this can lead
to more frequent regeneration and a higher consumption of chemical agents.
Also, fruit juice losses will be higher due to a more frequent sweetening
on and off of the plant. Additionally, cold adsorption brings a better
performance of the plant.
Process
description
Clarified
juice from an ultra-filtration system is processed through the adsorbent
resin in the column operation. By combining three columns in series,
a continuous and automated production is possible. One column is loaded,
one is on stand-by and the third is in regeneration. When the clarified
juice is debittered by the flow through column one, column two operates
as a police filter. As soon as the first column is saturated, the second
column is brought into operation for adsorption, while column three
acts as polishing unit and column one is regenerated.
Under normal
operating conditions, all of the limonin can be removed. Up to 40 per
cent or more of the naringin will be adsorbed by the resins. The high
chemical and physical stability of the resins allow the use of a wide
range of alkalines, acids and oxidants as regenerants. In combination
with an efficient regeneration regime, the resins can be used for several
years.
In a citrus
factory, the pulp wash stream is about 15 per cent of the total capacity.
This means that with the citrus pulp wash upgrading, the company will
have an increased benefit from this value-added by-product stream. Since
the pulp wash contains a very high level of limonin, it is necessary
that the clarification be done by an ultra-filtration system so that
the resins can operate at good conditions.
|
Unit
operation for fruit juice
|
Conventional
process
|
Ultra
- filtration process
|
| Suspended
solids removal |
Centrifugation |
None
|
| Pectin/starch
hydrolysis |
Enzyme
treatment |
Not
critical |
| Colloidal
and haze removal |
Fining
treatment |
Membrane |
| Fining
agent removal |
Diatomaceous earth filtration |
|
| Final
filtration |
Polishing
filtration |
|
| Clarified
juice yield |
80 per centto 95 per cent |
94
per cent to 99 per cent |
| Process
time |
12
to 36 hours |
2
to 4 hours |
