Citrus Processing with Pectinase
Pectinase use in the peeling of citrus fruits
and its highly efficient and cost effective enzyme can facilitate the rapid and
semi-automated peeling of oranges and other citrus varieties, such as
grapefruit. The use of enzyme in citrus fruit processing allows bulk production
of individual citrus segments to be carried out with a much lower reliance on
manual labour. Pectinase is the principal enzymes of choice in this area. In the
process, the inner peel of the orange (or other fruit) is softened and
subsequent manual or mechanical removal of the skin is made much easier. Enzyme
methods are ideal for use in the production of segments.
Prior to immersion in an enzyme bath, the fruit needs to be treated thus
allowing access of the enzyme through the otherwise waxy impervious waxy
exterior to the pith. This can be done either with a knife manually, or by means
of one of a number of mechanical methods. An example may be by using two rollers
fitted with embedded blades and spaced by an adjustable system which allows
sufficient pressure to ensure scoring of the fruit skins, but not too much so as
to crush or squash the fruit. Recent developments indicate that multiple needle
entries into the skin, over the whole of the fruit surface, can speed up the
processing.
There is no one optimum system for orange peeling and there are many different
pieces of process plant that can be used. Due to these multiple process options
there is no one enzyme that is optimum for every plant.
|
-Typical Peeling Protocol (using Pectinase) |
The conditions under which the Pectinase enzyme
offers optimal performance have been extensively studied and are well
understood. An enzyme bath needs to be prepared and the temperature and pH
(preferably) set at the optimum conditions for the enzyme.The scored or pricked
fruit is normally placed in a wire basket and lifted into the enzyme bath.
Previous citrus fruit residence times in the bath were typically 40 to 50
minutes, but this can be reduced to 10 minutes or less in processing systems
which utilise devices such as a vacuum hood over the enzyme bath. The vacuum
method helps the enzyme penetrate the fruit by sucking out the air from within
the pithy layer, prior to the enzyme solution taking its place.
|
1 |
Option: Wash the (chilled
for storage) fruit. |
|
2 |
Option: Warm outer fruit
layers to 30 to 45°C, usually in a water bath. |
|
3 |
Apply mechanical scoring
by cutting or needle type entry (pricking) methods. |
|
4 |
Immerse the fruit into
the Pectinase bath and apply the vacuum cycle for approximately 3 to 5
minutes. This time will be optimised by the operator through experience. |
|
5 |
Inspect the fruit for
ease of peel removal. Re-apply vacuum cycle as necessary. |
|
6 |
Transfer the fruit to
mechanical peel removers (a variety of design options exist), or pass to
line for rapid removal of peel by hand. Final product finishing is usually
still by hand, even with almost complete automation elsewhere in the
process. |
|
7 |
Wash the peeled fruit in a 1 to 3% by weight
citric acid bath, to “freshen” the fruit, reduce microbial contamination and
de-activate the enzyme (this is sometimes done prior to segmentation). |
|
8 |
Bath maintenance: Top up
the enzyme bath and adjust the enzyme concentration, pH and temperature
prior to the next batch of fruit. To comply with Good Manufacturing
Practice, the enzyme bath should only be used for a maximum of 24 hours or
applicable number of batches, before being discarded and replaced.
Experience will determine the optimisation of bath usage. The pH and
temperature should be monitored, but care should be taken not to apply heat
directly to the pectinase solution, as this may de-activate the enzyme.
It is recommended that the same citrus fruit type be used in any one batch,
as varying types and qualities of fruit will give different results in the
same bath. For example, thinner skinned fruit is likely to require a shorter
immersion time. |
Common Problems encountered in Citrus Processing
|
Problem |
Enzyme Solution |
|
Peel not easily removed |
Insufficient pricking/scoring of skin thus reducing exposure of albedo to
enzyme |
|
Current blend not working due to peel being too hard |
Cellulase content may be too low, use a pectinase modified type |
|
Process taking longer than predicted |
|
1. |
Ensure fruit is warm so that temperature
of bath does not drop thus reducing enzyme efficiency. |
|
2. |
Ensure vacuum is adequate |
|
|
Enzyme not working |
Ensure no direct heat is de-naturing enzyme solution and rendering it
ineffective |
|
Flow diagram for citrus
fruit processing |
|
Wash the fruit |
|
 |
|
Warm outer fruit layers
to eg 30-45°c,
usually in a water bath |
|
 |
|
Apply mechanical scoring
by cutting or pricking methods |
|
 |
|
Immerse the fruit into
the Pectinase bath
and apply vacuum cycle for approx 3-5 minutes |
|
 |
|
Inspect fruit for ease of
peel removal.
re-apply vacuum cycle as necessary |
|
 |
|
Pass fruit to mechanical
peel removers
or for hand finishing |
|
 |
|
Wash peeled fruit in a
2%W/V citric acid bath,
to freshen the fruit, reduce microbial
contamination and inactivate enzyme |
