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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.

 

-Citrus Fruit Processing

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