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FOREST SEED TECHNOLOGY

Forest Seed Technology 2009-TPFQ-18

Agenda Item: 8

FOREST SEED TECHNOLOGY

João Antonio Pereira Fowler^¹

Edson Tadeu Iede^²

SEED EXTRACTION

Definition: extraction denotes the procedure of physically releasing and separating the seeds from their enclosing fruit structure.

The extraction of seeds from the fruits have three main reasons: reduce bulk, easier handling and improve storage.

The extraction is usually undertaken prior to storage, but in some species it may delayed until just before sowing or omitted altogether: where storage of non-extracted seeds is considerably better than that of extracted seeds; where labor requirement for extraction is so high that its outweighs possible gain from extraction and where storage facilities, shipment, transport or other handling procedures do not make extraction mandatory.

Most fruit types can be classified as dry or fleshy. During extraction the former is dried to low moisture content , the latter extracted moist, often after initial soaking in water. A summary of extraction procedures is mentioned on table below.

Table 1. Extractions methods for various fruit types

FRUIT TYPE	EXTRACTION PROCEDURE
Dry dehiscent fruits: dehiscent pods, follicles, capsules and cones: Pines, Eucalypts and most Leguminosae	Drying→shaking/ tumbling
Dry indehiscent fruits: indehiscent pods of Acacia nilotica and Acacia siberiana	Drying→threshing
Serotinus fruits: cones, capsules plus some dry compounds fruits	Kiln heating→tumbling Scorching→tumbling
Fleshy fruits with very thin pulp: Vitex spp. and Ziziphus spp.	Drying Soaking→maceration→washing
Fleshy fruits with very soft pulp: Prunus, Olea and Ficus	Soaking→fermentation→washing Soaking→maceration→washing
Fleshy fruits with very soft, fibrous pulp: Gmelina	Soaking→maceration→washing→abrasion/polishing
Fleshy fruits with felty pulp: Tectona grandis, Sclerocarya spp.	Soaking→abrasion/polishing

Dry fruits

Morphologically, dry fruits are classified as dehiscent and indehiscent. Dehiscents fruits open at maturity to release their seeds; indehiscents remain closed at maturity. This classification is, however, more complex than that definition suggests since there is a gradual transition from indehiscense to dehiscence, which has practical implications for seed extraction. The extraction of seeds from dehiscent fruits is influenced by fruit type, stage of maturity at collection and external environment. Dry fruits are normally handled according to degree of dehiscense.

Dry fruits can be distributed in four groups:

dehiscent fruit that open upon drying;

serotinous cones and fruits;

indehiscent fruit where seeds are extracted

indehiscent fruit where seeds are not extracted.

Fleshy fruits

Fully mature fruits pulp of several drupes berries and other fleshy fruits often separates readily from the seeds. The pulp may be detached manually or by washing.

Other species like Azadirachta indica have relatively firm pulp that need softening to ease seed extraction.

Softening occurs during decomposition of the pulp, normally as a result of fermentation. Controlled fermentation can be used effectively as a pre-extraction procedure for several species. However, heat and possibly alcohol produced by the process sometimes have a negative effect on seed quality.

Soaking in water for one to several days often accelerates decomposition of the pulp, especially for fruit types with relatively dry pulp. Mechanical rupture of fruit skin prior to soaking often speeds up softening and decomposition.

If the fruit pulp has only been partly removed during field handling, the remainder having been dried, the seeds normally need to be soaked or wet again to remove the remaining pulp at the processing depot. During prolonged soaking of several days, water must be changed regularly once every twelve hours, or the container with fruit most be provided with a continuous water flow to prevent fermentation damage.

After soaking or decomposition the pulp and fruit skin are separated from the seed. Several methods, often used in combination, are applied. Selection of the most appropriate method depends on fruit type, quantity of fruits to be processed and equipment available:

Manual extraction

Manual extraction of seeds may be applicable to very small seed lots, seeds with extremely fragile seed coat, or large fruits where mechanical equipment cannot be efficiently used.

Washing in deep bowls or drums

This may be a continuation of soaking and applied if the pulp separates easily from the seeds. Mechanical stirring or using water stream while the fruits are submerged in water help to loosen the pulp. If pulp sticks to the seeds or stones, vigorous stirring or increase water pressure is necessary. Small seeds lots and small seeds may be extracted effectively by the aid of a blender used at low speed or an electric mixer. Separation of pulp and seeds is done by flotation in excess water: seeds remain at the bottom while pulp tend to ascend to the surface where they may be skimmed off.

Washing on wire mesh screens

Screens with mesh size that will retain the seeds while the pulp passes through are used. The pulp is released by manually rubbing the fruits against the grid and washing. High water pressure should be avoided because of the risk of washing away seeds. Fruit skin and firm fibers of the fruit flesh are normally retained with the seeds after rubbing and washing. They may be separated by flotation in excess water. The method is widely applicable to most fleshy fruits species , and the safest and most efficient procedure for extraction of very small seeds or seeds with fragile seed-coats. If high pressure water is available, a modification of this method is to place the fruits in wire meshbags with mesh size just below the seed size. The water pressure is then directly against the fruit, which may be cleaned completely by the water pressure.

Cement mixer with abranding material

The fruits are mixed with an abranding material like gravel plus excess water and rotated in the drum for various lengths of time, typically from 5 to 20 min. While the abranding material rubs against the fruits, the pulp is gradually torn off. The fruits are checked regularly in order to avoid unnecessary over treatment with possible damage the seed-coat. The method may be used as the only depulping method, not cleaning method.

Mechanical depulping

For large quantities of fruits or where the flesh tends to remains firm, mechanical depulping is applicable. The depulper mechanically abrands the fruits pulp by rupturing and squeezing against or between its mechanical parts. Because the risk of mechanical damage, the depulper is particularly applicable to fruits with relatively hard seed-coats.

Biological Extraction

Fleshy fruits and several indehiscent dry fruits are adapted to being ingested by animals. Seeds are often left cleaned and intact after ingestion althought in some species a relatively large amount of seeds may be digested. Accumulated manure in goat enclosure in areas with heavily fruiting often contains large amounts of seeds. Seeds can be extracted from manure by wet or dry extraction. During dry extraction the manure is initially dried and fractioned by gentle pounding in a mortar or the like, then cleaned by tumbling and sifting. During wet extraction the manure is soaked and washed in water. The seeds that gather at the bottom of the container are then separated by sifting under running water. A problem of collecting the seeds from manure is that the manure often contains a mixture of seeds from different species which can be difficult to separate.

EXTRACTION OF PINUS SEEDS

The exotic species cultivated in the Southern Brazil as: Pinus elliottii, Pinus pinaster and Pinus taeda, present fruition with a certain regularity. It is necessary to choose seed cones when the maturation process is very advanced to obtain seeds from these different species of the Pinus.

When the pine cones are harvested they still contain a high level of humidity. If they are immediately exposed to a heat source, probably they will dry only on the surface, while the inside remains green and wet. In this case, the cones will not open satisfactorily (Carneiro,1982).Then a previous drying is done on the shadow in sheds until the complete maturation for a variable period of time, depending on the environmental conditions. The sheds must be constructed in order to allow good ventilation.

In some occasions the pre-drying of Pinus elliottii and Pinus taeda cones is made on the sheds with zinc covering, provided with drawers with deep of screen. The cones remain on theses sheds during 30 to 120 days, when they gradually release the seeds, as they open. To speed up this operation the cones are daily scrambled. The seeds released the cones are retained on the screen.

During the drying, the scales that hold the seeds are separeted, causing the opening of the cones. However, the seeds are not totally released, being necessary the agitation of the cones for seeds release that still are imprisoned. This agitation can be made in revolving doughs mixer with screen walls. The seeds realised are retained in the scoop and the seeds fall through the screen on a tray. The most inconvenience of seeding are wings, therefore it is necessary to take off the wings before.

There are two methods to remove seed wings, although in some species like Pinus pinaster in proper of anatomical constitution, the wings can not be entirely removed.

Mechanical method to take off the seed wings– in this method there is a equipment that remove the wings, but not causes damages to the seeds. The principle of machine operation is: the seeds are deposited in a feed box of the equipment, under volume control. The seeds falling into a unit where there is a cylinder with brushes that turns, slightly compressing the seeds against a rubber cylindrical wall of this unit. Finally the seeds come into a compartment of aspiration, in which the air separates it from the wings, already removed.

Manual method – in this method the seeds are smashed with hands against the background of a sieve. After that they are launched to air and the detached wings are taken by the wind, while the seeds, heavier, fall back around the sieve.

EXTRACTION OF SEEDS OF EUCALIPTUS

The fruits are placed in treadmills, plies or trays and exposed to sun to release the seeds. Depending on the time of year and the weather conditions, it takes 3 to 10 days. As the fruits are collected in a certain state of maturation, they present radial cracks on top, forming shells. After the drying, the shells are opened, releasing the seeds that are inside the capsules. After the release of the seeds, the fruits are removed and the seeds are placed to dry in the sun or oven.

For the species cultivated in Brazil, normally are necessary 3 days of

exposure to the sun, or 24 to 36 of drying in oven at 45°C to dry the

capsules and to liberate the seeds.

References

ALBRECHT, J. 1993. Forest seed handling. In: Tropical Forestry Handbook. Pancel, J.ed., vol.1:381-457. Spring Verlag.

BONNER, F.T., VOZZO, J.A., ELAM, W.W., LAND,S.B. JR. 1994. Tree seed technology training course. Instructors Manual. Southern Forest Experimental Station.U.S. Dep. Agric.

GRAY, R. 1990. Professional seed collection. In: Sowing the seeds. Direct seeding and natural regeneration conference. Greening Australia. Proceedings pp 135-140.

WILLAN, R.L. 1985. A guide to forest seed handling:with special reference to the tropics. Roma:FAO.(FAO Forestry Paper 20/2) 379pp.

1Biologist, D.Sc.of EMBRAPA-National Forest of Research Center.

2Biologist, D.Sc.of EMBRAPA-National Forest of Research Center.

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